Prospective usage of magnesium potassium phosphate cement combined with Bougainvillea alba derived biochar to reduce Pb bioavailability in soil and its uptake by Spinacia oleracea L

Advancements in Biochar for Soil Remediation of Heavy Metals and/or Organic Pollutants

The rapid industrialization and economic growth have exacerbated the contamination of soils with both heavy metals and organic pollutants. These persistent contaminants pose substantial threats to ecosystem integrity and human health due to their long-term environmental persistence and potential for bioaccumulation. Biochar, with its high specific surface area, well-developed pore structure, and abundant surface functional groups, has emerged as a promising material for remediating soils contaminated by heavy metals and organic pollutants. While some research has explored the role of biochar in soil remediation, several aspects remain under investigation. Fully harnessing the potential of biochar for soil contamination remediation is of critical importance. This review provides an overview of the preparation methods and physicochemical properties of biochar, discusses its application in soils contaminated by organic compounds and/or heavy metals, and examines the mechanisms underlying its interaction with pollutants. Additionally, it summarizes the toxicity assessments of biochar during soil remediation and outlines future research directions, offering scientific insights and references for the practical deployment of biochar in soil pollution remediation.

Zea mays cultivation, biochar, and arbuscular mycorrhizal fungal inoculation influenced lead immobilization

Plant cultivation can influence the immobilization of heavy metals in soil. However, the roles of soil amendments and microorganisms in crop-based phytoremediation require further exploration. In this study, we evaluated the impact of Zea mays L. cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation on soil lead (Pb) immobilization. Our results indicated that biochar addition resulted in a significant, 42.00%, reduction in AMF colonization. Plant cultivation, AMF inoculation, and biochar addition all contributed to enhanced Pb immobilization, as evidenced by decreased levels of diethylenetriaminepentaacetic acid- and CaCl2-extractable Pb in the soil. Furthermore, soil subjected to plant cultivation with AMF and biochar displayed reduced concentrations of bioavailable Pb. Biochar addition altered the distribution of Pb fractions in the soil, transforming the acid-soluble form into the relatively inert reducible and oxidizable forms. Additionally, biochar, AMF, and their combined use promoted maize growth parameters, including height, stem diameter, shoot and root biomass, and phosphorus uptake, while simultaneously reducing the shoot Pb concentration. These findings suggest a synergistic effect in Pb phytostabilization. In summary, despite the adverse impact of biochar on mycorrhizal growth, cultivating maize with the concurrent use of biochar and AMF emerges as a recommended and effective strategy for Pb phytoremediation.IMPORTANCEHeavy metal contamination in soil is a pressing environmental issue, and phytoremediation has emerged as a sustainable approach for mitigating this problem. This study sheds light on the potential of maize cultivation, biochar application, and arbuscular mycorrhizal fungi (AMF) inoculation to enhance the immobilization of Pb in contaminated soil. The findings demonstrate that the combined use of biochar and AMF during maize cultivation can significantly improve Pb immobilization and simultaneously enhance maize growth, offering a promising strategy for sustainable and effective Pb phytoremediation practices. This research contributes valuable insights into the field of phytoremediation and its potential to address heavy metal pollution in agricultural soils.

Industrial by-products-derived binders for in-situ remediation of high Pb content pyrite ash: Synergistic use of ground granulated blast furnace slag and steel slag to achieve efficient Pb retention and CO2 mitigation

Ordinary Portland cement (OPC) is a cost-effective and conventional binder that is widely adopted in brownfield site remediation and redevelopment. However, the substantial carbon dioxide emission during OPC production and the concerns about its undesirable retention capacity for potentially toxic elements strain this strategy. To tackle this objective, we herein tailored four alternative binders (calcium aluminate cement, OPC-activated ground-granulated blast-furnace slag (GGBFS), white-steel-slag activated GGBFS, and alkaline-activated GGBFS) for facilitating immobilization of high Pb content pyrite ash, with the perspectives of enhancing Pb retention and mitigating anthropogenic carbon dioxide emissions. The characterizations revealed that the incorporation of white steel slag efficiently benefits the activity of GGBFS, herein facilitating the hydration products (mainly ettringite and calcium silicate hydrates) precipitation and Pb immobilization. Further, we quantified the cradle-to-gate carbon footprint and cost analysis attributed to each binder-Pb contaminants system, finding that the application of these alternative binders could be pivotal in the envisaged carbon-neutral world if the growth of the OPC-free roadmap continues. The findings suggest that the synergistic use of recycled white steel slag and GGBFS can be proposed as a profitable and sustainable OPC-free candidate to facilitate the management of lead-contaminated brownfield sites. The overall results underscore the potential immobilization mechanisms of Pb in multiple OPC-free/substitution binder systems and highlight the urgent need to bridge the zero-emission insights to sustainable in-situ solidification/stabilization technologies.

Influence of Organic and Inorganic Fertilizers on Tea Growth and Quality and Soil Properties of Tea Orchards' Top Rhizosphere Soil

Organic-based fertilizers have been ratified to be effective in ameliorating tea growth and the fertility of soil. However, the effect of integrated fertilization on tea growth and quality and the chemical properties of the soil in tea gardens are unclear. To address this, from 2020 to 2021, five different treatments were carried out in the greenhouse of the Tea Research Institute, Hangzhou, CAAS, including CK (control), NPK (chemical fertilizers), RC (rapeseed cake), NPK+B (chemical fertilizer + biochar), and NPK+RC, to investigate the effects of different fertilizations on soil chemistry and tea growth and quality. The results indicated that NPK+B and NPK+RC significantly improved the different amino acid and catechin concentrations in the young shoots, stems, and roots of the tea compared to the CK. The plant growth parameters, e.g., the plant height, no. of leaves, mid-stem girth, and fresh weights of stems and leaves, were significantly increased with integrated fertilization (NPK+B and NPK+RC) compared to the CK and solo organic and inorganic fertilizers. The chlorophyll contents (Chl a, Chl b, and Chl a+b) were generally higher with NPK+RC than with the CK (37%, 35%, and 36%), RC (14%, 26%, and 18%), and NPK (9%, 13%, and 11%) treatments. Integrated fertilization buffered the acidic soil of the tea garden and decreased the soil C:N ratio. NPK+RC also significantly increased the soil's total C (31% and 16%), N (43% and 31%), P (65% and 40%), available P (31% and 58%), K (70% and 25%), nitrate (504% and 188%), and ammonium (267% and 146%) concentrations compared to the CK and RC. The soil macro- (Mg and Ca) and micronutrients (Mn, Fe, Zn, and Cu) were significantly improved by the RC (100% and 72%) (49%, 161%, 112%, and 40%) and NPK+RC (88% and 48%) (47%, 75%, 45%, and 14%) compared to the CK. The chlorophyll contents and soil macro- and micronutrients were all significantly positively correlated with tea quality (amino acids and catechin contents) and growth. These results indicated that integrated fertilization improved the soil nutrient status, which is associated with the improvement of tea growth and quality. Thus, integrated nutrient management is a feasible tool for improving tea growth, quality, and low nutrient levels in the soil.

Combined contribution of biochar and introduced AM fungi on lead stability and microbial community in polluted agricultural soil

Introduction

Lead (Pb) pollution in agricultural soil has been accelerated by industrial development and human activities, and poses a major threat to agricultural ecosystems. Both biochar and arbuscular mycorrhiza (AM) fungi are considered to play an important role in remediation of Pb contaminated soil.

Methods

The combined remediation effects of introduced AM fungi and biochar on soil properties, Pb availability, microbial community and functional profiles were systematically investigated in unsterilized Pb-polluted agricultural soil.

Results

Results indicated that soil nutrients were significantly improved through the combined application of biochar and introduced AM fungi. The introduced AM fungi combined with biochar prepared at 400°C and 500°C promoted the transformation of Pb to a more stable state with low bioavailability. Moreover, the addition of AM fungi and biochar affected the relative abundances of dominant bacteria and fungi at the phylum and genus levels. Biochar mainly affected soil bacterial community and obviously increased the relative abundance of Actinobacteria and Blastococcus. The interactions between biochar and introduced AM fungi mainly affected fungal community, and increased the abundance of Ascomycota and Botryotrichum. Further, PICRUSt analysis indicated biochar amendment supported stronger bacterial metabolic functional potentials.

Discussion

Therefore, the combined application of biochar and Therefore, the combined application of biochar and introduced AM fungi could improve soil nutrients, reduce Pb introduced AM fungi could improve soil nutrients, reduce Pb availability, availability, and show and show a positive effect on a positive effect on indigenous microbial communities and indigenous microbial communities and metabolic functions in metabolic functions in farmland soil.

Research on compound pollution characteristics and health risk evaluation of particulate matter and heavy metals in waste glass recycling process

Owing to the large amount of waste glass generated, the waste glass recycling base is an indispensable municipal supporting facility of a sustainable city. However, waste glass recycling is a complex process involving stages such as multiple-stage crushing and material sorting. Consequently, waste glass recycling base has a considerable impact on the surrounding environment, such as health risk of particulate matter on workers. In this study, we aimed to perform a comprehensive investigation and analysis of compound pollution characteristics and health risk evaluation of particulate matter and heavy metals generated from waste glass recycling process. Soil, particulate fallout, and glass samples were collected from inside and outside a recycling plant in eastern China. Our findings showed that the waste glass treatment process produces a large amount of air particulate matter, and the PM2.5 and PM10 concentrations can reach 3725 and 4055 μg/m3, respectively, in the production workshop during working hours. Meanwhile, the monitoring results show that the concentration of heavy metals on fine particles is higher compared to coarse particles. The high Zn and Pb concentrations detected in the soil and dustfall were proved to be derived from the glass raw materials. However, health risk assessment and particle deposition modeling in the human respiratory system revealed that heavy metals from the air particulate matter have no significant carcinogenicity or non-carcinogenic risk. The Gaussian dispersion model showed that the impact of particulate matter on the surrounding environment and health of the surrounding residents is minimal. Furthermore, transportation is the major emission link according to the particulate emission calculation, indicating that it is imperative to upgrade and reform the existing processes of waste glass recycling. Taken together, this study provides a scientific basis for the green development of waste glass recycling process and further environmental information regarding waste glass recycling plants.

Hormones and the antioxidant transduction pathway and gene expression, mediated by Serratia marcescens DB1, lessen the lethality of heavy metals (As, Ni, and Cr) in Oryza sativa L

Microorganisms have recently gained recognition as efficient biological tool for reducing heavy metal toxicity in crops. In this experiment, we isolated a potent heavy metal (As, Ni, and Cr) resistant rhizobacterium Serratia marcescens DB1 and detected its plant growth promoting traits such as phosphate solubilization, gibberellin synthesis, organic acid production and amino acid regulation. Based on these findings, DB1 was further investigated for application in a rice var. Hwayeongbyeo subjected to 1 mM As, 4 mM Ni, and 4 mM Cr stress. The rice plants treated with Cr and Ni appeared healthy but were lethal, indicating unfitness for consumption due to toxic metal deposition, whereas the plants treated with > 1 mM As instantaneously died. Our results showed that DB1 inoculation significantly decreased metal accumulation in the rice shoots. Particularly, Cr uptake dropped by 16.55% and 22.12% in (Cr + DB1) and (Cr + As + Ni + DB1), respectively, As dropped by 48.90% and 35.82% in (As + DB1) and (Cr + As + Ni + DB1), respectively, and Ni dropped by 7.95% and 19.56% in (Ni + DB1) and (Cr + As + Ni + DB1), respectively. These findings were further validated by gene expression analysis results, which showed that DB1 inoculation significantly decreased the expression of OsPCS1 (a phytochelatin synthase gene), OsMTP1 (a metal transporting gene), and OsMTP5 (a gene for the expulsion of excess metal). Moreover, DB1 inoculation considerably enhanced the morphological growth of rice through modulation of endogenous phytohormones (abscisic acid, salicylic acid, and jasmonic acid) and uptake of essential elements such as K and P. These findings indicate that DB1 is an effective biofertilizer that can mitigate heavy metal toxicity in rice crops.

Multi-scenario simulation of China's dynamic relationship between water-land resources allocation and cultivated land use based on shared socioeconomic pathways

Rapid urban expansion, population growth, and limited cultivated land in China necessitate rethinking the path to sustainable management of cultivated land. Understanding the long-term dynamic relationship between water-land resource endowment and cultivated land use contributes to effective management and use of cultivated land. However, few studies have systematically documented this relationship, especially for future trends. Accordingly, we modified water-land resource matching (WLRM) using a more refined grid-scale and assessed cultivated land use efficiency (CLUE), then deployed spatial panel regression models to quantify historical changes. We subsequently simulated future trends under three Shared Socioeconomic Pathways scenarios. The results showed that the relationship assumed an N-shaped curve in nation, while the curve followed a down-up-down pattern in economically less developed regions, largely because of structural transformations of production factors. Under three development scenarios, the stage-specific characteristics of production factors were pronounced, and the dynamic relationship varied across regions.

Soil Amendments and Foliar Melatonin Reduced Pb Uptake, and Oxidative Stress, and Improved Spinach Quality in Pb-Contaminated Soil

Amending Pb-affected soil with biochar (BH) and magnesium potassium phosphate cement (MKC) reduces Pb uptake in plants. Moreover, foliar applications of melatonin and proline are also known to reduce plant oxidative stress and Pb uptake. However, little is known about combining both techniques, i.e., adding a combo immobilizing dose (CIA = mixture of BH and MKC at 50:50 ratio) in Pb-polluted soil and foliar application of proline and melatonin for reducing Pb uptake and oxidative stress in spinach. Control, proline, melatonin, CIA, CIA+proline, and CIA+melatonin were the treatments utilized in this pot study to see their effects on reducing plant oxidative stress, Pb uptake, and improving spinach quality in Pb-polluted soil. Moreover, Pb bioavailability, enzymatic activities, and numbers of bacteria, fungi, and actinomycetes in the soil were also evaluated. The effect of CIA on reducing Pb in the soil-plant system and improving soil enzymes and microbial numbers was more pronounced than melatonin alone. The most effective treatment was CIA+melatonin reducing Pb availability in soil (77%), shoots (95%), and roots (84%), alleviating oxidative stress, and improving plant biomass (98%) and nutrients. Soil enzymatic activities and the number of microorganisms in the rhizosphere were also highest with CIA+melatonin. Results highlight the significance of CIA+melatonin, as an inexpensive approach, in remediating Pb-polluted soil and improving spinach quality. However, further research is needed to understand the significance of CIA+melatonin on different crops and various soil Pb concentrations before employing this technique commercially in agriculture and environment sectors.

Biorefining of rapeseed meal: A new and sustainable strategy for improving Cr(VI) biosorption on residual wastes from agricultural byproducts after phenolic extraction

Phenolic recovery from agricultural byproducts has been highlighted due to their health-promoting bioactivities. However, uncontrolled discard of residues after extraction process would induce environmental pollution and bioresource waste. In this study, biorefining of phenolic-rich rapeseed meal (RSM) and its defatted sample (dRSM) was attempted by holistic utilization of phenolic extract and residue separately. Phenolic removal could significantly improve residues' Cr(VI) adsorption capacities by about 21%, which presented extended physical surface and more released functional groups. Moreover, simulating raw material by remixing 3% separated phenolic extracts or main component sinapic acid therein with corresponding residues further improved about 12% adsorption efficiencies. These indicated that the different present forms of phenolics had opposite effects on Cr(VI) removal. While natural conjugational form inhibited hosts' biosorption, free form had enhanced functions for either extract or residue. Four optimal adsorption parameters (pH, adsorbent dosage, contact time and initial Cr(VI) concentration), three kinetic (pseudo-first order, pseudo-second order and intra-particle diffusion) models and two isotherms (Langmuir and Freundlich) were used to reveal the adsorption process. The maximum Cr(VI) adsorption capacity on residues could reach about 100 mg/g, which was superior to that of most biosorbents derived from agricultural byproducts, even some biochar. Together with the residues' advantages with everlasting capacity after 3 adsorption-desorption cycles and excellent abilities for adsorbing multiple co-existed metal ions (Cr(VI), Cd(II), Cu(II), Pb(II), Ni(II) and Zn(II)), phenolic recovery was first proved to be a new and sustainable strategy for modifying biosorbents from agricultural byproducts with zero waste.

First-principle study on the stability of Cd passivates in soil

The stable existence of heavy metals in soil under natural conditions is the core issue in heavy metal pollution solidification and remediation technology. However, the existing research is limited to soil passivation tests of different materials or biochar adsorption tests and cannot reveal the internal mechanism of functional groups of different compounds in soil passivation. This paper takes the common heavy metal ion Cd2+ as an example to analyze the stability of the combination of heavy metal ions and common ion groups in soil. The stability and existing form of Cd are analyzed by using first-principle calculations, and the free energy, band structure, and partial density of states of CdCO3, CdSO4, CdCl2, and CdSiO3 are computed. The stability of Cd binding to common anions in soil is determined. Results show the descending order of structural stability of cadmium compounds is CdSiO3, CdSO4, CdCO3, and CdCl2. SO42- and SiO32- can be used as preferred functional groups for cadmium pollution passivation. Anhydrous sodium sulfate and sodium silicate are promising passivators.

Long-term cattle manure addition enhances soil-available phosphorus fractions in subtropical open-field rotated vegetable systems

INTRODUCTION

Evaluation of the changes in phosphorus (P) fractions (various P forms) and their availability at different soil layers is critical for enhancing P resource use efficiency, mitigating subsequent environmental pollution, and establishing a suitable manure application strategy. However, changes in P fractions at different soil layers in response to cattle manure (M), as well as a combined cattle manure and chemical fertilizer application (M+F), remain unclear in open-field vegetable systems. If the amount of annual P input remains the same, identifying which treatment would cause a higher phosphate fertilizer use efficiency (PUE) and vegetable yield while simultaneously reducing the P surplus is especially warranted.

METHODS

Based on a long-term manure experiment that started in 2008, we used a modified P fractionation scheme to analyze P fractions at two soil layers for three treatments (M, M+F, and control without fertilizer application) in an open-field cabbage (Brassica oleracea) and lettuce (Lactuca sativa) system, and assessed the PUE and accumulated P surplus.

RESULTS

The concentrations of the soil P fractions were higher in the 0-20-cm soil layer compared to the 20-40-cm layer, except for organic P (Po) and residual-P. M application significantly increased the inorganic P (Pi) (by 8.92%-72.26%) and the Po content (by 5.01%-61.23%) at the two soil layers. Compared with the control and M+F treatments, M significantly increased residual-P, Resin-P, and NaHCO3-Pi at both soil layers (by 31.9%-32.95%, 68.40%-72.60%, and 48.22%-61.04%), whereas NaOH-Pi and HCl-Pi at 0-20 cm were positively correlated with available P. Soil moderately labile-P was the predominant P component in the two soil layers (accounting for 59%-70%). With the same annual P input amount, M+CF created the highest vegetable yield (117.86 t ha-1), and PUE (37.88%) and M created the highest accumulated P surplus (128.80 kg ha^-1yr^-1).

DISCUSSION

Collectively, a combined manure-chemical fertilizer application has great potential to yield a long-term positive outcome both in terms of vegetable productivity and environmental health in open-field vegetable systems. This highlights the methods' benefits as a sustainable practice in subtropical vegetable systems. Specific attention should be given to a P balance to avoid excessive P input if a rational strategy for manure application is to be attained. This is especially the case for stem vegetables that require manure application and decreases the environmental risk of P loss in vegetable systems.

Solidification/stabilization of lead-contaminated soils by phosphogypsum slag-based cementitious materials

In the present study, phosphogypsum slag-based cementitious material (PS) was designed, and the potential use for solidifying/stabilizing lead-contaminated soils was investigated. The physicochemical properties, performance, and mechanisms of its stabilization of lead in soil were studied by the methods of toxic leaching test, compressive strength, XRD, TGA, FTIR and XPS. The compressive strength of the PS solidified body was from 0.52 to 6.66 MPa when he concentration of lead ions in contaminated soil was set as 6000 mg/kg (0.6 %), 10,000 mg/kg (1.0 %) and 15,000 mg/kg (1.5 %) and the dosage of curing agent is 10 %, 20 % and 30 %., which is acceptable for backfill treatments or roadbed materials. Under the conditions, Pb leaching concentrations ranged from 40.98 to 355.21 μg·L-1, which was within the safety limit specified in Chinese standard (GB5085.3-2007). There is the potential for safe disposal and reuse of PS stabilized soil. TGA and XRD showed that the main components of PS-solidified soil were ettringite (AFt), calcium silicate hydrate (C-S-H), and lead phosphate. FTIR, XPS, and SEM-EDS analysis demonstrated the lead was successfully incorporated into AFt and C-S-H. Pb forms bonds with lead oxide and aluminum oxide tetrahedra and replaces part of the adsorbed Ca ions in AFt and C-S-H. In addition, the resulting phosphate precipitates were also encapsulated in the C-S-H phase, together with the stabilization of lead in the soil.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.

Co-application of biochar and nitrogen fertilizer promotes rice performance, decreases cadmium availability, and shapes rhizosphere bacterial community in paddy soil

Cadmium (Cd) contamination in soil has posed a great threat to crop safety and yield as well as soil quality. Biochar blended with nitrogen fertilizer have been reported to be effective in remediating Cd-contaminated soil. However, the influence of co-application of biochar and nitrogen fertilizer on the Cd bioavailability, rice yield and soil microbiome remains unclear. In this study, eight different treatments including control (CK), 5% biochar (B), 2.6, 3.5, 4.4 g/pot nitrogen fertilizers (N1, N2 and N3), and co-application of biochar and nitrogen fertilizers (BN1, BN2, BN3) were performed in a pot experiment with paddy soil for observations in an entire rice cycle growth period. Results showed single N increased soil available Cd content and Cd uptake in edible part of rice, while the soil available Cd content significantly decreased by 14.8% and 7.4%-11.1% under the B, BN treatments, and the Cd content in edible part of rice was significantly reduced by 35.1% and 18.5%-26.5%, respectively. Besides, B, N and BN treatments significantly increased the yield of rice by 14.3%-86.6% compared with CK, and the highest yield was gained under BN3 treatment. Soil bacterial diversity indices (Shannon, Chao1, observed species and PD whole tree index) under N2, N3 were generally improved. Cluster analysis indicated that bacterial community structures under BN treatments differed from those of CK and single N treatments. BN treatments enhanced the abundances of key bacterial phylum such as Acidobacteria, positively associated with yield, and increased the abundance of Spirochaetes, negatively correlated to soil available Cd and Cd uptake of rice. Furthermore, the regression path analysis (RPA) revealed that pH, organic matter (OM), alkaline hydrolysis of nitrogen (AHN) and available Cd were the major properties influencing Cd content in edible part of rice. Redundancy analysis (RDA) revealed that pH and available Cd played key role in shaping soil bacterial community. Thus, BN is a feasible practice for the improvements of rice growth and remediation of Cd-polluted soil.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Use of Eggshell-Catalyzed Biochar Adsorbents for Pb Removal from Aqueous Solution

Eggshell is a cheap and environmentally friendly calcium source. In this study, Ca-modified biochar adsorbents (CEA) were prepared by 1:10, 1:2, and 1:1 mass ratio of the eggshell and Eupatorium adenophorum. The CEA-2 sample prepared with a 1:2 mass ratio showed a maximum Pb adsorption capacity (97.74 mg·g^-1) at the conditions of an initial pH of 7.0, an adsorbent dosage of 0.5 g·L^-1, and a contact time of 8.0 h. The kinetic and isotherm studies indicated that the adsorption process of the CEA-2 sample had monolayer adsorption characteristics, which was controlled together by intraparticle and interface diffusion. Thermodynamic studies indicated that the adsorption process of CEA-2 was spontaneous (ΔG ⁰ <0) and endothermic (ΔH ⁰ > 0). X-ray diffraction and scanning electron microscopy analyses showed a uniform distribution of Ca-Pb precipitation on the CEA-2 surface, which proved that chemical precipitation was the main adsorption mechanism. Fourier transform infrared spectra found that CEA-2 had abundant active groups, especially nitrogen-containing functional groups, which could adsorb Pb through a surface complexation reaction. The Brunauer-Emmett-Teller surface area of CEA-2 was found to be 621 m²·g^-1, and such developed pores could ensure the smooth diffusion of Pb. Finally, the effect of coexisting cation and anion experiment and the cyclic regeneration experiment indicated that CEA-2 had prominent stability and reusability for Pb adsorption.

A review of pristine and modified biochar immobilizing typical heavy metals in soil: Applications and challenges

In recent years, the application of biochar in the remediation of heavy metals (HMs) contaminated soil has received tremendous attention globally. We reviewed the latest research on the immobilization of soil HMs by biochar almost in the last 5 years (until 2021). The methods, effects and mechanisms of biochar and modified biochar on the immobilization of typical HMs in soil have been systematically summarized. In general, the HMs contaminating the soil can be categorized into two groups, the oxy-anionic HMs (As and Cr) and the cationic HMs (Pb, Cd, etc.). Reduction and precipitation of oxy-anionic HMs by biochar/modified biochar are the dominant mechanism for reducing HMs toxicity. Pristine biochar can effectively immobilize cationic HMs. The commonly applied modification method is to add substances that can precipitate HMs to the biochar. In addition, we assessed the risks of biochar applications. For instance, biochar may cause the leaching of certain HMs; biochar aging; co-transportation of biochar nanoparticles with HMs. Future work should focus on the artificial/intelligent design of biochar to make it suitable for remediation of multiple HMs contaminated soil.

Adsorption and immobilization of soil lead by two phosphate-based biochars and phosphorus release risk assessment

Phosphorus-based biochar can effectively immobilize lead (Pb) in soils, but the effects of soluble and insoluble phosphate on the remediation efficiency of Pb and phosphorus (P) release risks remain largely unknown. In this study, three biochars were produced from reed (Phragmites australis L.) straw, potassium dihydrogen phosphate (PDP, soluble) and hydroxyapatite (HAP, insoluble) modified reed straws and marked as BC, BCP, and BCH, respectively. Pb adsorptions and immobilizations by the three biochars and their P release risks were investigated. The P release kinetics of the three biochars were all fitted with the pseudo-second-order kinetic model and the P-release capacity followed the order of BCP > BCH > BC. The sorption isotherms of Pb²⁺ by three biochars were better described using the Langmuir model and the maximum adsorption capacities of BCP (59.3 mg/g) and BCH (58.8 mg/g) were higher than that of BC (48.1 mg/g). However, the P concentrations remained in BCP treated solution were significantly higher than those in BCH and BC under initial Pb²⁺ concentrations in the ranges of 5-25 mg/L. Soil pH and available P were increased with the increasing dosage of BCP and BCH, decreasing CaCl₂-extractable Pb concentrations. BCH was more effective to decrease the exchangeable Pb and transform it into iron/manganese oxides and residual fractions. Compared to BC, BCH applications in the range of 2-5% can significantly increase labile P by 15.2-17.7%, but 21.0-33.6% for BCP, indicating BCP had a higher P release risk. The major implication is that HAP-modified biochar can effectively immobilize Pb and decrease P release risks compared to soluble P-modified biochar.

Inoculation with the pH Lowering Plant Growth Promoting Bacterium Bacillus sp. ZV6 Enhances Ni Phytoextraction by Salix alba from a Ni-Polluted Soil Receiving Effluents from Ni Electroplating Industry

Soil contamination with Ni poses serious ecological risks to the environment. Several members of the Salix genus have the ability to accumulate high concentrations of Ni in their aerial parts, and thus can be used for the remediation of Ni-contaminated soils. Interestingly, the efficacy of Ni phytoextraction by Salix may be improved by the acidification of rhizosphere with rhizosphere acidifying bacterial strains. Therefore, the aim of this study was to assess the efficacy of bacterial strain Bacillus sp. ZV6 in the presence of animal manure (AM) and leaf manure (LM) for enhancing the bioavailability of Ni in the rhizosphere of Salix alba via reducing the pH of rhizosphere and resultantly, enhanced phytoextraction of Ni. Inoculation of Ni-contaminated soil with strain ZV6 significantly increased plant growth as well as Ni uptake by alba. It was found that the addition of AM and LM resulted into a significant increase in plant growth and Ni uptake by alba in Ni-contaminated soil inoculated with ZV6 stain. However, the highest improvements in diethylene triamine penta-acetic acid (DTPA) extractable Ni (10%), Ni removal from soil (54%), Ni bioconcentration factor (26%) and Ni translocation factor (13%) were detected in the soil inoculated with ZV6 along with the addition of LM, compared to control. Similarly, the enhancements in microbial biomass (92%), bacterial count (348%), organic carbon (organic C) (57%) and various enzymatic activities such as urease (56%), dehydrogenase (32%), β-glucosidase (53%), peroxidase (26%) and acid phosphatase (38%) were also significantly higher in the soil inoculated with ZV6 along with the addition of LM. The findings of this study suggest that the inoculation of Ni-contaminated soils with rhizosphere acidifying bacteria can effectively improve Ni phytoextraction and, in parallel, enhance soil health.

Biochar impacts on the soil environment of soybean root systems

Biochar has been widely studied as a soil amendment, but little is known about the "biochar-freeze-thaw soil-crop root system" interface in seasonally frozen soil areas. In the second year after the application of biochar, we conducted research on the morphological characteristic indicators of the soybean root system and the nutrient migration of the soil in the root zone under different biochar application periods (spring and autumn mixed, autumn, and spring biochar application) and different biochar application rates (3 kg·m-2, 6 kg·m-2, 9 kg·m-2, and 12 kg·m-2). The effects of different biochar treatments on the growth and development of soybean roots were examined. The soil organic carbon, ammonium nitrogen and nitrate nitrogen contents of the soil were measured at different locations in the root zone, and the migration processes of these nutrients in the soil were explored. The conclusions drawn from the experiments are as follows. (i) The biochar application rate and application method together determine the root morphological characteristic indicators of soybean plants. During long freeze-thaw periods, the freeze-thaw cycles change the internal environment of the biochar-freeze-thaw soil complex. (ii) Biochar tends to move towards the root system, which can increase soil organic carbon content, but the effect of biochar on root characteristics is not caused by the change in soil organic carbon content. (iii) Biochar promotes nitrogen cycling in the soil and the migration of soil nitrogen to the root sheath, increasing the number of nitrogen compounds that can be directly absorbed and utilized by crops. (iv) From a comparison of the effects of various biochar treatments on crop roots and farmland soils, we suggest that the 9 kg·m-2 biochar application rate under spring and autumn mixed biochar application is the optimal treatment.

Variability in Soil Parent Materials at Different Development Stages Controlled Phosphorus Fractions and Its Uptake by Maize Crop

An adequate phosphorus (P) supply in the rhizosphere is essential for proper P uptake through plant roots. Distributions of P varies depending on the soil structure, formation, and the parent material from which it originates. More research is needed to determine whether soil depth and parent materials have an impact on P distribution. It was hypothesized that the type of soil formed by different parent materials is related to P uptake and soil P fractions. Soil samples were taken from different profiles at various stages of development in loess, alluvium, shale, and sandstone parent materials. The samples were analyzed for P fractions using the Jiang and Gu fractionation scheme. In the present study, the P fractions were controlled according to the quantity and the components, such as organic matter, clay minerals, carbonates, iron, and aluminum oxides. Studying the phosphatase enzyme activity related to P fractions, the soil parent material, and their development was highly beneficial in defining which P pools are more accessible to plants, as well as the effect of phosphatase in limiting P availability. Among all the tested parent materials, the total P in soils derived from the loess parent material was higher (792 mg kg−1) than in soils derived from alluvium, shale, and sandstone, respectively. The amount of apatite P in alluvium parent material was higher, accounting for 51–56% of total P. Other P forms varied significantly in parent materials in the following order loess > alluvium > shale >> sandstone. Phosphatase enzyme was found to be an indicator of P availability by limiting its uptake by plants.

Integrating Tank Model and adsorption/desorption characteristics of filter media to simulate outflow water quantity and quality of a bioretention basin: A case study of biochar-based bioretention basin

Reliable approaches for accurately assessing the performance of stormwater treatment systems is essential for their effective design, including filter media selection which can be a significant constituent in stormwater treatment systems. This study presents an innovative modelling approach integrating the Tank Model with the adsorption-desorption characteristics of the filter media. The resulting modelling approach was applied to simulate a field-scale bioretention basin where biochar was used as filter media with over ten years of rainfall records. The resulting outflow and overflow volumes were compared with observed data for calibration. The Stormwater Treatment Tank Model (STTM) was validated using the Leave-One-Out-Cross-Validation (LOOCV) method. The simulation outcomes include water outflow and overflow (quantity) from the bioretention basin as well as outflow water quality represented by three heavy metals (Pb, Cu, and Zn). The modelling approach developed was found to be capable of accurately simulating outflow and overflow volumes, with outlet water quantity being significantly influenced by the total rainfall depth. The modeling results also suggested that a sole treatment system would not be adequate, particularly for large rainfall events (>100 mm) and a treatment train would be more effective. Simulating long-term (over ten years) pollutant removal performance in the bioretention basin indicated that heavy metals outflow event mean concentration (EMCs) values calculated using simulated results of 30% biochar application rate generated the best pollutant removal with consistent values (2.7 μg/L, 3.0 μg/L, 17.2 μg/L for Pb, Cu, and Zn, respectively). These results confirm that the modelling approach is reliable for assessing long-term treatment performance, as well as a robust tool able to contribute to more effective treatment system design, particularly filter media selection and evaluation.

Effects of white-rot fungal pretreatment of corn straw return on greenhouse gas emissions from the North China Plain soil

Straw-return with fungal treatment is a potential method for reducing soil greenhouse gas emissions through carbon (C) sequestration and N₂O mitigation. However, there is little information on the effects of different fungal treatments of crop straw return on soil CO₂ and N₂O emissions. To explore to what extent decomposed corn straw and its components controls soil CO₂ and N₂O emissions, we set up three sequential incubation experiments using soil collected from the North China Plain, an intensive agricultural area. Interactions between the different C contents of corn straw (CS), CS pretreated with Irpex lacteus (ICS), CS pretreated with Phanerochaete chrysosporium (PCS) and different NO₃^--N concentrations on the effect of soil CO₂ and N₂O emissions were conducted, and the kinetics of CO₂ and N₂O as influenced by changes in soil biochemical factors were analyzed. The effects of different lignocellulose components (lignin, cellulose, and xylan) on soil CO₂ and N₂O emissions were further studied. The results showed that straw pretreatment did not affect CO₂ emissions. Both CO₂ and N₂O emissions increased when the C and N contents increased. However, applying PCS to 70% water-filled pore space soil effectively decreased the soil N₂O emissions, by 41.8%-76.3% compared with adding the same level of CS. Moreover, extracellular enzyme activities related to C and N cycling were triggered, and the nosZI and nosZII abundances were significantly stimulated by the PCS application. These effects are closely related to the initial soluble C content of this treatment. Furthermore, adding xylan can significantly reduce N₂O emissions. Overall, our data suggest that the environmentally beneficial effects of returning straw can be greatly enhanced by applying the straw-degrading white-rot fungi of P. chrysosporium in the North China Plain soil. Future studies are needed in the field to upscale this technology.

Gibberellic acid and urease inhibitor optimize nitrogen uptake and yield of maize at varying nitrogen levels under changing climate

Worldwide, nitrogen (N) deficiency is the main yield limiting factor owing to its losses via leaching and volatilization. Urease inhibitors slow down urea hydrolysis in soil by inhibiting urease enzyme activities whereas gibberellic acid is growth regulator. That is why, we evaluated the role of urease inhibitor [N-(n-butyl)thiophosphorictriamide (NBPT)] and gibberellic acid (GA₃) in improving nitrogen uptake and yield of maize under different N levels (120 and 150 kg ha^-1) along with control. Both N levels alone and in combination with GA₃ and NBPT significantly increased yield and yield components of maize over control. In addition, 150 kg N ha^-1 + NBPT + GA₃ produced highest biological, grain, and stover yields, 1000 grain weight, plant height, and N uptake exhibiting 33.15%, 56.46%, 27.56%, 19.56%, 23.24%, and 78% increase over 150 kg N ha^-1, respectively. The sole use of gibberellic acid or NBPT with each level of N also improved the yield and yield components of maize compared to sole N application and control. Furthermore, application of 120 kg N ha^-1 along with NBPT and GA₃ performed at par to 150 kg N ha^-1 + NBPT + GA₃ but it was superior than sole applied 150 kg N ha^-1 for all the studied traits. These results imply that application of GA₃ and/or NBPT can reduce dependence on urea and improve the yield and N uptake in maize by slowing urea hydrolysis in calcareous soils and shall be practiced.

A 3-year field study on lead immobilisation in paddy soil by a novel active silicate amendment

Lead (Pb) is a toxic metal in industrial production, which can seriously threat to human health and food safety. Thus, it is particularly crucial to reduce the content of Pb in the environment. In this study, raw fly ash (FA) was used to synthesise a new active silicate materials (IM) employing the low-temperature-assisted alkali (NaOH) roasting approach. The IM was further synthesised to form zeolite-A (ZA) using the hydrothermal method. The physicochemical characteristics of IM and ZA amendments before and after Pb²⁺ adsorption were analysed using the Scanning electron microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) apparatuses. The results revealed the considerably change in the microstructure and functional groups of IM and ZA amendments, conducive to Pb²⁺ removal. Moreover, a 3-year field experiment revealed that the IM and ZA significantly improved the growth of rice and reduced available Pb by 21%-26.8% and 9.7%-16.9%, respectively. After 3 years of remediation, the Pb concentration of the rice grain reached the national edible standard (≤0.2 mg kg^-1) of 0.171 mg kg^-1 and 0.179 mg kg^-1, respectively. Meanwhile, the concentration of acid-exchangeable Pb reduced, while those of reducible and residual fractions of Pb increased. There was no significant difference between the IM and ZA treatments. The potential mechanisms of remediation by the amendments were ion-exchange, complexation, precipitation, and electrostatic attraction. Overall, the results indicate that IM is suitable for the remediation of contaminated soil and promotes safe food production, and develops an environmentally friendly and cost-effective amendment for the remediation of polluted soil.

Environmental fate of Bt proteins in soil: Transport, adsorption/desorption and degradation

During the production and application of Bacillus thuringiensis (Bt) transgenic crops, large doses of insecticidal Bt toxic proteins are expressed continuously. The multi-interfacial behaviors of Bt proteins entering the environment in multi-media affects their states of existence transformation, transport and fate as well as biological and ecological impacts. Because both soil matrix and organisms will be exposed to Bt proteins to a certain extent, knowledge of the multi-interfacial behaviors and affecting factors of Bt proteins are vital not only for understanding the source-sink distribution mechanisms, predicting their bio-availability, but also for exploring the soil safety and environmental problems caused by the interaction between Bt proteins and soil matrix. This review summarized and analyzed various internal and external factors that affect the adsorption/ desorption and degradation of Bt proteins in the environment, so as to understand the multi-interfacial behaviors of Bt proteins. In addition, the reasons of concentration changes of Bt proteins in soil are discussed. This review will also discuss the existing knowledge of the combined effects of Bt proteins and other pollutants in environment. Finally, discussing the factors that should be considered when assessing the environmental risk of Bt proteins, thus to further improve the understanding of the environmental fate of Bt proteins.

Effects of iron-modified biochar with S-rich and Si-rich feedstocks on Cd immobilization in the soil-rice system

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Effect of fertilization on nitrogen losses through surface runoffs in Chinese farmlands: A meta-analysis

Surface runoff is the main cause of farmland nitrogen (N) losses in plain areas, which adversely affect water quality. The impact of fertilization on N runoff loss often varies. A meta-analysis was performed using 245 observations from 31 studies in China, to estimate the response of N loss in both paddy and upland fields subjected to different fertilization strategies, and investigate the link between N runoffs, soil properties, as well as precipitation in the planting season. The results showed that compared to the control (without fertilization), N losses subjected to fertilization increased from 3.31 kg/ha to 10.03 kg/ha and from 3.00 kg/ha to 11.24 kg/ha in paddy and upland fields respectively. Importantly, paddy N loss was significantly correlated with fertilizer type and N application rate (predictors); in upland fields N application rate and seasonal precipitation were the main driving factors. For the N application rate, N loss increased with increase in rates for both paddies and upland fields. Moreover, the N loss from upland fields increased with the precipitation during planting season. Between the three fertilizers used in paddies, the increase in loss of CRF (controlled release fertilizer) or OF (organic fertilizer) was lower than that of CF (inorganic chemical fertilizer) with the lowest value in CRF. Subset analysis showed that the effect of CRF and OF in paddies was not affected by the predictors, revealing the steadily controlling property of CRF and OF in paddies. Also, all the predictors had an insignificant impact to N loss risk in paddies during the high application rate. Overall, the results confirm the importance of N dosage in N runoff loss from farmland. Fertilizer type is a key consideration for N loss control in paddies, while the seasonal precipitation should not be ignored in upland fields.

Solid state anaerobic digestion of food waste and sewage sludge: Impact of mixing ratios and temperature on microbial diversity, reactor stability and methane yield

Food waste (FW) and sewage sludge (SS) were anaerobically co digested under solid state conditions (Total solids >15%) and observed that mixing ratio of 3:1 and 2:1 is optimum for mesophilic and thermophilic conditions respectively. The VS reduction and methane yield at optimized ratio was 76% and 0.35 L CH₄/(g VS reduced) respectively at mesophilic temperature whereas it was 88% and 0.42 L CH₄/(g VS reduced) at thermophilic temperature. The metagenomic analysis for these cases were done and high throughput DNA sequencing revealed that diversified bacterial groups that participate in the different metabolisms (hydrolysis, acidogenesis and acetogenesis) were mainly dominated by the phylum Firmicutes and Bacteriodetes. Genus Methanothrix is found to be dominant which is capable of generating methane by any methanogenic pathway among all the archaeal communities in the reactors followed by Methanolinea and Methanoculleus. However, it was understood through metagenomic studies that acetotrophic pathway is observed to be the major metabolic pathway in the reactors.

Redesign of urban biowaste sustainable management system based on industrial ecology concept: A case study in China

Urban biowaste, which refers to the organic fraction of municipal solid waste (MSW), is a predominant type of waste in low- and middle-income countries. Therefore, the sustainable management of urban biowaste is a key problem in solid waste management (SWM). However, treatment technologies usually come with secondary pollution and by-products that need further treatment, which would limit the economic and environmental benefits of the waste management system. The concept of industrial ecology has the potential to be introduced into the waste management field to solve this problem. Based on a practical case study of a city in eastern China, this paper conducted a complete urban biowaste treatment system planning exercise using concepts in industrial ecology. The establishment of the new system has significant economic, environmental and social benefits. The total output value of the project would reach 342 million yuan in 2025, corresponding to 945,000 tons of solid wastes consumed every year, which would significantly reduce the environmental pollution caused by solid waste. More than 700 jobs could also be created. In addition, the establishment of an urban biowaste sustainable management system requires the joint effort of enterprise, government and the public, which in turn requires innovation in business models and management policies. Therefore, a special management committee should be established to promote collaboration among stakeholders, and an online platform that enables end-to-end process supervision covering the entire system, including emergency management mechanisms, needs to be established to ensure the long-term stable operation of various treatment facilities. The results of this paper show that synergies among technologies should be promoted to provide systemic benefit, and that the infrastructure for pollution control should be shared to ensure high utilization.

Biogas feedstock potentials and related water footprints from residues in China and the European Union

China encounters heavy air pollution caused by coal consumption. China and the EU aim to decrease greenhouse gas emissions. Shifting to biogas from residues contributes to solving both problems. This study assesses China's biogas potentials and related water footprints (WFs) and compares results with potentials and WFs for the EU. Starting from a literature review on EU biogas potentials, it analyzes information resulting in a calculation methodology, its validation and application to China. Finally, it estimates WFs and makes a comparative assessment of biogas potentials of the EU and China. In the EU, biogas from agricultural, forestry and other residues might contribute 8% (5300 PJ) to primary energy consumption, in China 10% (13,275 PJ.) In the EU, agriculture contributes 41%, forestry 26%, other residues 23%, and manure 10%. The corresponding results for China are agriculture (67%), forestry (23%), manure (7%) and other residues (3%). In the EU, biogas might contribute 45% to total gas demand; in China more biogas can be produced than consumed in 2018 (185% of demand). The EU results fall in the range of residue potentials from earlier studies. Maize, wheat, barley and rapeseed contribute 78% to the EU agricultural biogas potential. In China, dominant crops are maize (49%), rice (18%), wheat (12%) and seed cotton (6%). For water, there are large differences among WFs of specific crop residues, but also between WFs for EU and Chinese crop residues. Most Chinese crop residues have larger WFs than the EU residues. Biogas from sugar beet residues has the smallest WFs, biogas from tobacco residues the largest. Although using residues for energy does not change total national WFs, it reallocates WFs over main products and residues. The comparative assessment supports better use of biogas potentials from residues with lower WFs and is also applicable for other regions and countries.

Rhizosphere dissolved organic matter and iron plaque modified by organic amendments and its relations to cadmium bioavailability and accumulation in rice

Organic amendments can modify rhizosphere dissolved organic matter (DOM) properties and Fe-plaque quantity, thereby affecting cadmium (Cd) bioavailability and uptake by rice. Pot experiments were conducted to investigate effects of biochar (BC) and vermicompost (VC) at different rates (0, 1%, and 5%) on rhizosphere DOM characteristics and Fe-plaque quantity, and their impacts on Cd bioavailability and accumulation in high and low Cd-accumulation rice cultivars (HAC and LAC). Soil DOM was characterized by ultraviolet-visible (UV-Vis) and fluorescence excitation-emission matrix (EEM) spectrum analyses. Hydroponic experiments were conducted to investigate effects of BC- or VC-derived DOM combined Fe-plaque on Cd uptake by rice. Results showed that increasing rates of organic amendments increased DOM concentration while decreased Cd availability in rhizosphere and bulk soils and Cd contents in rice tissues. The Cd reduction in LAC grains (31.9%-72.7%) was better than that in HAC grains (6.3%-25.4%) after organic amendment addition. Soil DOM properties were modified by organic amendments towards higher aromaticity, molecular weight, and stability. VC resulted in a greater increase of humic-like fractions but reduced protein-like proportions in rhizosphere DOM over BC. Negative correlations were observed between humic-like fractions and available Cd in the rhizosphere. Likewise, VC (especially 5%VC) promoted the formation of Fe-plaque and limited Cd soil-to-root transport, while BC groups showed a reverse trend. The results of hydroponic experiments confirmed BC- and VC-derived DOM and Fe-plaque further inhibited Cd uptake by rice via the complexation with Cd and the sequestration of Cd, respectively. Hence, VC application combined with low Cd-accumulation rice could be an effective strategy for the safe utilization of Cd-contamination soils.

A novel glucose-based highly selective phosphate adsorbent

Industrial wastewater discharge leads to serious eutrophication of water bodies, but most of the adsorbents are difficult to selectively remove phosphorus and are difficult to use multiple times, therefore, developing an efficient and reusable material for removal phosphate is extremely necessary. In this work, a kind of highly selective phosphate adsorbent, microporous carbon material (MCM), based on glucose was synthesized by hydrothermal and activation method. The MCM were characterized by SEM, XPS, BET, element analysis, et al. The phosphate adsorption mechanism of MCM were investigated by batch adsorption experiment and model calculation. Results showed that MCM had a high adsorption capacity for phosphate in a wide range of pH (1.5-10). Langmuir model and pseudo-second-order kinetic revealed that the process was endothermic and involved both physical and chemical adsorption. The main phosphate adsorption mechanisms of MCM are electrostatic attraction, ion complexation, hydrogen bonding, and physical adsorption. The ions competition simulation experiment indicated that the MCM was highly selective for phosphate removal. Furthermore, the phosphate adsorption tests were carried out on five kinds of water, and the removal rates were all above 99.98%. The 20 regenerative cycles experiment revealed that the MCM had high reusability. Therefore, this kind of novel glucose-based highly selective phosphate adsorbent with multi-cycle phosphorus removal performance can improve the eutrophication of water. This study provides a new idea for phosphate removal and expands the application range of glucose-based carbon materials.

Heavy metals concentrations and naturally occurring radionuclides in soils affected by and around a solid waste dumpsite in Osogbo metropolis, Nigeria

The presence of heavy metals and naturally occurring radioactive materials (NORMs) in high concentrations in soils can be hazardous to exposed humans. This study is aimed at measuring the concentrations of heavy metals (Cu, Pb, Ni, Zn, Cd, Co, and Cr) and activity concentration of ²³²Th, ²³⁸U, and ⁴⁰K in soils affected by and around a solid waste dumpsite in Osogbo metropolis, Nigeria. Atomic absorption spectrometry and gamma-ray spectrometric techniques were used to determine the concentrations of metals and NORMs, respectively. Possible environmental impact of the heavy metal content and the probable radiological hazard by the NORMs to the general public were assessed. The calculated pollution indices reported in this work for Co, Cr, Pb, and Ni show low pollution status. Geoaccumulation indices for Cu, Zn, and Cd indicated that the area under study is strongly contaminated by these metals. Evaluated ecological risk index narrowed down Cd as the poisonous metal with high concentration. The measured radionuclides' mean activity concentrations and the evaluated mean of radium equivalent and absorbed dose rate values are higher than the recommended safe limit, an indication of possible radiological hazard. The principal factor analysis results explained 76% of the collection of data and described chips of galvanized/chrome metals, scrap metals, waste from electronics, Cr, and Cd-containing waste as sources of the heavy metals. The practice of land cultivation around the dumpsite should be deterred to prevent the transportation of these vicious heavy metals into the food chain.

Response surface optimization, combustion characteristics and kinetic analysis of mixed fuels of Fenton/CaO conditioned municipal sewage sludge and rice husk

The co-combustion characteristics and kinetics of Fenton/CaO conditioned MSS, and biomass rice husk (RH) are studied by thermogravimetry, and the condition optimization was carried out by response surface methodology (RSM). The results show that the mixed fuel with RH is helpful to decrease T_i and T_b values and increase combustion characteristic index (CCI). The CCI of MSS after conditioning is 0.59-0.88 times lower than that of the pure MSS. In addition, the total E_m of S2, MSS/RH mixed combustion after Fenton/CaO conditioning is lower, the combustion reactivity is stronger. According to RSM, the optimum conditions are considered to be: RH mixing ratio 56%, Fenton/CaO conditioner dosage 147 mg g^-1 dry solids, heating rate 30 K min^-1, the maximum CCI 25.3305 × 10^-7%² °C^-3 min^-2, and the minimum E_m 10.6403 kJ min^-1. This study supplies new insights into combustion technology of sludge.

Evaluating scenarios for carbon reduction using different tableware in China

Global consumption of disposable plastic tableware (DPT) is massive because it is durable, light and inexpensive. Using the life cycle assessment method, we found that DPT for per person per meal emitted 597 g of CO₂ and was far more than that of reusable plastic tableware (RPT, 7.00 g), ceramic tableware (9.55 g) and straw tableware (14.6 g). If the demand growth for DPT continues, 416 MT of CO₂ will be emitted due to DPT consumption by 2050 globally. We further explored strategies to reduce CO₂ emissions by examining the life cycles of four types of tableware according to sensitivity analysis. According to our results, if the recycling rate of DPT reaches 60% at the end-of-life stage, 50% of CO₂ emissions can be cut; if dishwashing instead of hand washing is used to clean RPT, ceramic, and straw tableware, approximately 64%, 71%, and 23% of CO₂ emissions can be reduced, respectively. If 60% of DPT is replaced by RPT, this plastic tableware will halve carbon emissions. If the rate reaches 100%, carbon emissions will be reduced by 92%. Although the CO₂ emissions of the three types of tableware other than DPT are relatively small, RPT will bring other environmental burdens and human health risks, ceramic tableware is bulky and its additives are toxic. Straw tableware combines practical and safety performance. The results show that the choice of straw tableware plays a significant role in curbing the greenhouse effect without compromising consumer safety.

Estimation of the biogeochemical reactivities of dissolved organic matter from modified biochars using color

Modified biochar is widely used as a soil amendment in agricultural systems to improve crop yields and remove environmental pollutants. The water-soluble fraction of biochar, called biochar-derived dissolved organic matter (DOM_BC), is the most active biochar component. However, the correlation between the optical properties of DOM_BC and its biogeochemical activity remain unclear. In this study, one biochar and six modified derivatives were used to extract DOM_BC and characterize its optical properties. The biogeochemical reactivities of DOM_BC were determined using biodegradation, photodegradation, and electron-donating capacity assays. The results show that modification changes the biochar characteristics, leading to a variety of DOM_BC properties. The DOM_BC from modified biochars degrades more rapidly than the original biochar. On the other hand, modification reduces the redox functional groups in DOM_BC, resulting in a lower electron-donating capacity of DOM samples. However, the modifications did not seem to affect photodegradation. Not all spectral parameters provide information about the correlations between the DOM_BC properties and biogeochemical reactivity. However, two fundamental properties, that is, the specific UV absorbance at 254 nm (SUVA₂₅₄, showing aromaticity) and spectral slopes over the ranges of 275-295 nm of the UV absorbance (S_275-295, showing molecular weight), are the dominant factors affecting the biodegradation and electron-donating capacities of DOM_BC. In this study, a rapid and straightforward method is presented, which can be used to characterize DOM_BC and predict the reactivity of biochar that is used as an environmental amendment to minimize toxic organic compounds.

Basic physiology and biochemistry in environmental/experimental plant studies: How to quantify and interpret metabolites correctly

As a reviewer of ca. 50 manuscripts per year submitted to various journals, I often come across questionable metabolic data (both over- or under-estimated) mainly in the journals from the section of Environmental Sciences of Web of Science. Though the trends of visibly incorrect metabolite values may be informative (changes in response to applied treatments or environmental factors), absolute values must be precise enough to allow inter-specific comparison and eventual subsequent calculations. Technical correctness of quantification and calculation of such data is therefore often questionable. One problem arises when calculating metabolites concentration (often nmol or μmol/g of biomass) and another problem is the impact of altered water content on metabolite level (then trend per gram of fresh or dry biomass will differ). Recent discrepancies I found when searching for the literature prompted me to write this technical note aimed at focusing attention of researchers on these problems. I exclude any conflict of interest when discussing the quoted published studies. I strongly urge interested researchers to verify the correctness of metabolite quantification (extraction, dilution/calculation and alternative methods) and also to study similar literature for comparison in order to prevent the spread of incorrect data in the scientific literature.

Development of an acidized biochar-supported hydrated Fe(III) oxides for highly efficient cadmium and copper sequestration from water

Biochar-supported metallic oxides are attractive adsorbents for heavy metal cleanup, but the adsorption performance is still unsatisfactory as a result of the self-aggregation of the incorporated metallic oxides. A new hybrid nano-material was prepared through impregnating hydrated ferric oxide (HFO) nanoparticles within biochar bearing high-density charged oxygen-containing groups (e.g., carboxyl and hydroxyl groups) (ABC) derived from HNO₃ treatment. The as-made adsorbent, denoted as HFO-ABC, possesses highly dispersed HFO nanoparticles with typical size lower than 20 nm, and exhibits greater sorption capacity for Cd(II) and Cu(II) than the pristine biochar-supported HFO. It also shows great sorption preference toward Cd(II) and Cu(II) in co-presence of high levels of Ca²⁺, Mg²⁺ and humic acid (HA). Such prominent performance is put down to the high-density charged functional groups on the host ABC, which not only promote the dispersion of the immobilized HFO nanoparticles but also generate the potential Donnan membrane effect, i.e., the pre-concentration and permeation of target metals prior to their preferable adsorption by nano-HFO. The predicted effective coefficients of intra-particle diffusion for Cu(II) and Cd(II) are 3.83 × 10^-9 and 4.33 × 10^-9 cm²/s, respectively. HFO-ABC exhibits excellent performance for fixed-bed column application, and yields 513 and 990 BV effluents for Cd(II) and Cu(II) to achieve their discharge standards, respectively. The spent HFO-ABC could be in situ regenerated using binary HCl-CaCl₂ solution with desorption efficiency higher than 95%. All results manifest that increasing charged functional groups via HNO₃ treatment is an effective measure for boosting sorption performance of biochar-based nanocomposites.

New perception of Zn(II) and Mn(II) removal mechanism on sustainable sunflower biochar from alkaline batteries contaminated water

The combination of several methods (X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy) was applied to study the changes that have occurred during the adsorption of Zn(II) and Mn(II) ions on a carbonized sunflower sample for understanding a mechanism of heavy metals adsorption. Sunflower biochar was obtained from the stem and inflorescences sunflower wastes through pyrolysis at 600 °C for 30 min. According to the infrared spectroscopy and Boehm titration data, this carbonized material has acidic and basic functional groups on its surface, but they do not participate in the metal ions adsorption. However, the synthesized carbon proved to be a sustainable high-effective adsorbent for zinc(II) and manganese(II) ions removal with adsorption capacity 138.3 mg g^-1 of Zn²⁺ and 45.4 mg g^-1 for Mn²⁺. Surface analysis of the carbonized material by energy dispersive X-ray analysis, X-ray diffraction, and X-ray photoelectron spectroscopy indicated the presence of soluble and insoluble inorganic salts, such as KCl, NaCl, NaHCO₃, KHCO₃, CaCO₃, MgCO₃. It was established, that during the adsorption process, soluble salts are washed away, and new insoluble ones are formed assisting by Zn(II) and Mn(II) ions. It has been revealed that the adsorptive removal of Zn²⁺ and Mn²⁺ is caused by the precipitation mechanism. The efficiency of removing Zn(II) and Mn(II) ions from water contaminated with battery waste by the same mechanism is shown.

After-effects of straw and straw-derived biochar application on crop growth, yield, and soil properties in wheat (Triticum aestivum L.) -maize (Zea mays L.) rotations: A four-year field experiment

Research on the after-effects of straw and straw-derived biochar applications on crop growth, yield, and retention of carbon (C) and nitrogen (N) in soil in wheat-maize rotation systems is limited, and has presented inconsistent conclusions. The purpose of this research was to compare the after-effects of straw and straw-derived biochar on wheat (Triticum aestivum L.) and maize (Zea mays L.) growth and yield, and on soil properties. A field experiment was conducted in four consecutive wheat-maize rotation cycles in the Loess Plateau of China under five treatments: CK (control without nitrogen and phosphate fertilizer, straw, or biochar); NP (conventional single application of nitrogen and phosphate chemical fertilizers); SNP (8 t ha^-1 wheat straw returned to the field plus fertilizer); B1NP (8 t ha^-1 straw-derived biochar plus fertilizer); B2NP (16 t ha^-1 straw-derived biochar plus fertilizer). The highest plant height and aboveground biomass for both wheat and maize always occurred with the B2NP treatment for the four study years. Grains per spike/ear and 1000-grain weight for both wheat and maize in B2NP and B1NP were significantly higher than observed for the other treatments. The four-year average wheat yields for NP, SNP, B1NP, and B2NP were 50.5%, 63.1%, 66.3%, and 81.7% greater than for CK, respectively, and the four-year average maize yields were 45.0%, 49.8%, 65.4%, and 72.1% greater than for CK, respectively. The application of straw-derived biochar significantly increased soil organic carbon, total nitrogen, microbial biomass carbon, and nitrogen in the soil surface layer compared with returning straw to the field. Both straw and straw-derived biochar reduced nitrate N leaching. Therefore, using straw-derived biochar to amend soil could be an appropriate practice for sustaining soil fertility and crop yield in wheat-maize rotation systems in the Loess Plateau of China.

Combined effects of biochar and chicken manure on maize (Zea mays L.) growth, lead uptake and soil enzyme activities under lead stress

The goal of the present work was to evaluate the additive effects of biochar and chicken manure on maize growth in Pb-contaminated soils. In this study, we conducted a pot experiment to investigate how biochar in soil (20, 40 g·kg^-1), chicken manure in soil (20, 40 g·kg^-1), or a combination of biochar and chicken manure in soil (each at 20 g·kg^-1) effect maize growth, Pb uptake, leaves' antioxidant enzymatic activities, and soil enzyme activities under artificial conditions to simulate moderate soil pollution (800 Pb mg·kg^-1). The results showed that all biochar and/or chicken manure treatments significantly (P < 0.05) increased maize plant height, biomass, and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity but decreased the malondialdehyde (MDA) content. These results indicated that amending the soil with biochar and/or chicken manure could alleviate Pb's phytotoxicity. The biochar and/or chicken manure treatments remarkably decreased the Pb concentration in maize roots, stems, leaves, bioconcentration factor (BCF), translocation factor (TF), and available Pb concentration in the soil. Amending the soil with chicken manure alone was more effective at increasing maize growth and antioxidant enzymatic activity; the biochar treatment alone was more effective at inducing soil alkalinization and contributing to Pb immobilization. The combined use of biochar and chicken manure had an additive effect and produced the largest increases in maize growth, leaves' antioxidant enzymatic activity, and soil enzyme activity. Their combined use also led to the most significant decreases in maize tissues Pb and soil available Pb. These results suggest that a combination of biochar and chicken manure was more effective at reducing soil Pb bioavailability and uptake by maize tissues, and increasing maize growth. This combination increased plant height by 43.23% and dry weight by 69.63% compared to the control.

Assessing the effect of treated erythromycin fermentation residue on antibiotic resistome in soybean planting soil: In situ field study

As a by-product in the pharmaceutical industry, antibiotic fermentation residue is expected to be able to be utilized after effectively removing the antibiotics. However, evaluation of the effect of fermentation residue application on soil, especially the in situ environmental consequences considering not only the antibiotic resistance gene (ARG) abundance but also the resistome risk, has still not been sufficiently evaluated. Herein, the impact of treated erythromycin fermentation residue (EFR) on the resistome and risk score in soybean planting soil was investigated. Treated EFR application with dosages of 3750 kg (EFR250) and 7500 kg (EFR500) per hm2 soil did not increase the diversity (Shannon index, 2.84-3.38) or relative abundance (0.086-0.142 copies/16S rRNA gene) of the soil resistome compared with the Control (CK: 2.92-3.2, 0.088-0.096 copies/16S rRNA gene). Soil resistome risk scores calculated by metagenomic assembly, showing the dissemination potential of ARGs, ranged from 22.9 to 25.0, and were also not significantly different between treated EFR amended soil and the Control. Notably, the diversity of the resistome increased at the sprout stage (Mann-Whitney U test, P < 0.05) and the abundance of some ARG types (macrolide-lincosamide-streptogramin, aminoglycoside and tetracycline, etc.) shifted along the course of soybean growth (Kruskal-Wallis test, P < 0.05). Structural equation model analysis showed that the soybean growth period affected the composition of ARGs by affecting the microbial community, which was further supported by Procrustes analysis (P < 0.05) and metagenomic binning. Our findings emphasized that soil ARG abundance and resistome risk did not increase during one-time field application of treated EFR at the studied dosage. Comprehensive consideration including resistome risk and multiple influencing factors also should be given for further assessment of fermentation residue application.

Miscanthus biochar value chain - A review

To complete a loop of the Miscanthus value chain including production, phytomanagement, conversion to energy, and bioproducts, the wastes accumulated from these processes have to be returned to the production cycle to provide sustainable use of the feedstock, to reduce costs, and to ensure a zero-waste approach. This can be achieved by converting Miscanthus feedstock into biogas and biochar using pyrolysis and then returning biochar to the production cycle of Miscanthus crop applications in the phytotechnology of trace elements (TEs)-contaminated/marginal lands. These processes are subjects of the current review, which focused on the peculiarities of biochar received from Miscanthus by pyrolysis, its properties, the impact on soil characteristics, the phytoremediation process, biomass yield, and the abundance of soil biodiversity. Results from the literature indicated that the pH, surface area, and porosity of Miscanthus biochar are important in determining its impact on soil characteristics. It was inferred that the most effective Miscanthus biochar was produced with a pyrolysis temperature of about 600 °C with a residence time from about 30 min to an hour. Another important factor that determined the impact of Miscanthus biochar on soil health is the application rate: with its increase, the effect became more essential, and the recommended rate is between 5% and 10%. The influence of Miscanthus biochar on the TEs phytoremediation parameters is less studied, generally Miscanthus biochar produced at higher temperatures and added with higher application rates is more likely to restrict the mobility and availability of TEs by different plants. However, some published results are contradictory to these conclusions and showed absence of significant difference in TEs reduction during application of different Miscanthus biochar doses. The future experimental studies have to focus on determining the impact of a technological pyrolysis regime on Miscanthus biochar properties on TEs-contaminated or marginal land when biochar will be obtained from contaminated rhizomes and waste after the application of phytotechnology. In addition, studies must explore the influence of this biochar on TEs phytoparameters, enhancements in biomass yield, improvements in soil parameters, and the abundance of soil diversity.

Enhanced ammonium removal on biochar from a new forestry waste by ultrasonic activation: Characteristics, mechanisms and evaluation

The adsorption treatment of ammonium-containing wastewater has attracted significant global attention. Most enhanced adsorption methods employ chemical modification, and there are few reports on physical activation. We present a physical activation to explore whether physical ultrasound may enhance the adsorption performance and comprehensive utilisation of a new forestry waste, Caragana korshinskii was used as a feedstock to prepare activated biochar (ACB) by controlling the pyrolysis temperatures and ultrasound parameters. The optimal parameters were determined via batch adsorption of NH₄⁺, and the adsorption characteristics were assessed by 8 kinds of models and influence experiments. Moreover, the physicochemical properties of ACB during the pyrolysis process were investigated, and the ultrasonic activation and adsorption mechanisms were discussed using multiple characterisation techniques. Additionally, the cost analysis, the safety of the ultrasonic process and disposal method also were evaluated. The results showed that the ultrasonic activation significantly enhanced the NH₄⁺ adsorption efficiency of biochar by approximately 5 times. ACB exhibited the best performance at 500 °C with an ultrasonic activation time of 480 min, frequency of 45 kHz, and power of 700 W. The ultrasonic activation reduced the biochar ash and induced pore formation, which increased the specific surface area through cavitation corrosion and micro-acoustic flow mechanism. The NH₄⁺ adsorption mechanisms comprised physicochemical processes, of which physical adsorption was dominant. The preparation cost of 1 kg ACB was about 0.42 US dollar, and no secondary pollution occurred in the activation process. The findings prove that ultrasonic technology is efficient and convenient for enhancing biochar adsorption performance, and thus is suitable for industrial applications and promotion.

Utilization of modified copper slag activated by Na2SO4 and CaO for unclassified lead/zinc mine tailings based cemented paste backfill

Serious heavy metals pollution was characterized in the lead/zinc mine tailings dam and surrounding soils, as well as copper slag disposal sites. This study investigates the efficacy of modified granulated copper slag (MGCS) as a partial replacement of ordinary Portland cement (OPC) for lead/zinc mine tailings-based cemented paste backfill (CPB) application using Na₂SO₄ (CSN) and CaO (CSC) as alkali-activated materials. The effect of different scenarios was ascertained by unconfined compressive strength (UCS). Also, the correlated microstructural evolution and mineralogical phase generation were obtained by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD). The main findings proved that CSN was more effective in improving mechanical performance. Na₂SO₄ was found associated with C-S-H gel formation accompanied by a compact microstructure and better pore distribution with lower porosity. However, deposition of chloride compound was found in the surface layer of CSN samples, which could bring deterioration to the mechanical properties. Results above extend the knowledge of reusing MGCS as supplementary material to CPB, promoting the concept of a circular economy demand for both lead/zinc mine extraction and copper industries.

The application of urban anthropogenic background to pollution evaluation and source identification of soil contaminants in Macau, China

The anthropogenic background characterized by the accumulation characteristics of contaminants is recognized as an important evidence in pollution assessment and source identification in urban soil due to its less arbitrariness compared with the existing quality standards and the guidelines. A credible approach for pollution index calculation referring to anthropogenic background values (ABVs) combined with entropy weight method was developed. By the approach, the soil pollution degrees in Macau, China (one of the most densely populated region worldwide) were assessed based on the database of the heavy metals, Cd, Cu, Hg, Pb, and Zn, and high molecular weight polycyclic aromatic hydrocarbons (HMW PAHs) from 31 sites spatially distributed all over Macau. It was revealed that approximately half of the sites had no specific point source pollution. Mercury, benzo(a)anthracene (BaA), fluoranthene (FLT), and benzo(b)fluorantene (BbF), which had the highest weights were considered as the main contaminants. Macau Peninsula was identified as the critical polluted area. Then, the positive matrix factorization (PMF) coupled with ABVs as one of the data uncertainty inputs was used to identify the anthropogenic pollution sources of the contaminants. Three main anthropogenic sources with their contributions, including vehicle emissions (51.3%), use of hazard material (24.8%), and municipal or domestic waste (23.9%), could be well identified and quantified in the study area. The error estimation of the results showed that the variation of the contaminants in the derived factors were stable. The approaches which were in conformity with ABVs of soil contaminants are proved applicable in soil pollution assessment and source identification.

Effect of carbon-enriched digestate on the microbial soil activity

OBJECTIVES

As a liquid organic fertilizer used in agriculture, digestate is rich in many nutrients (i.e. nitrogen, phosphorus, sulfur, calcium, potassium); their utilization may be however less efficient in soils poor in organic carbon (due to low carbon:nitrogen ratio). In order to solve the disadvantages, digestate enrichment with carbon-rich amendments biochar or humic acids (Humac) was tested.

METHODS

Soil variants amended with enriched digestate: digestate + biochar, digestate + Humac, and digestate + combined biochar and humic acids-were compared to control with untreated digestate in their effect on total soil carbon and nitrogen, microbial biomass carbon, soil respiration and soil enzymatic activities in a pot experiment. Yield of the test crop lettuce was also determined for all variants.

RESULTS

Soil respiration was the most significantly increased property, positively affected by digestate + Humac. Both digestate + biochar and digestate + Humac significantly increased microbial biomass carbon. Significant negative effect of digestate + biochar (compared to the control digestate) on particular enzyme activities was alleviated by the addition of humic acids. No significant differences among the tested variants were found in the above-ground and root plant biomass.

CONCLUSIONS

The tested organic supplements improved the digestate effect on some determined soil properties. We deduced from the results (carbon:nitrogen ratio, microbial biomass and activity) that the assimilation of nutrients by plants increased; however, the most desired positive effect on the yield of crop biomass was not demonstrated. We assume that the digestate enrichment with organic amendments may be more beneficial in a long time-scaled trial.