Effects of biochar on bacterial communities in a newly established landfill cover topsoil

Biochar pH reduction using elemental sulfur and biological activation using compost or vermicompost

This study aimed to improve biochar's quality for arid land applications by using elemental sulfur as a pH reducer agent co-applied with compost or vermicompost as biological activators. Biochar pH was decreased by the addition of elemental sulfur, with the highest reduction from 8.1 to 7.2 occurring when co-amended with vermicompost. Elemental sulfur increased the water-soluble concentrations of calcium, magnesium, and many other elements, and stimulated substrate-induced respiration, especially when co-amended with vermicompost. The bacterial diversity community structure were significantly affected by all treatments. The Shannon index significantly increased in response to compost and sulfur treatments, while the vermicompost treatments showed higher microbial evenness and equitability diversity indices. Multivariate analyses indicated that elemental sulfur oxidation was associated with specific sulfur-oxidizing bacterial clusters. Integrating biochar with sulfur and (vermi)compost was found to be a promising sustainable technology for managing excessive biochar alkalinity, increasing its fertility and potential for application in aridlands.

Differential response of biochar in mitigating salinity stress in periwinkle (Catharanthus roseus L.) as an ornamental-medicinal plant species

To investigate the effect of various levels of salinity and biochar on the growth and biochemical traits of Catharanthus roseus L., a medicinal plant, a factorial experiment with three levels of biochar (0, 2, and 4%) and four levels of salinity (0, 1,000, 2,000, and 3,000 mg/kg soil) was conducted in pots under greenhouse conditions, in three replications, 36 pots, and 6 plants/plot. Salinity reduced the vegetative and reproductive growth and Ca and K uptake, and chlorophyll content of the plants, and increased the Na+, Cl-, electrolyte leakage, and antioxidant enzyme (SOD, CAT, GPX) activities. Biochar improved all the vegetative and reproductive growth and biochemical traits of Catharanthus roseus L. and enhanced soil fertility. The application of biochar at the rate of 2% at all four levels of NaCl reduced the activity of antioxidants and decreased electrolyte leakage, reflecting the alleviation of salinity effects and the retention of cell health for survival. The application of biochar 2% was more effective than biochar 4% in alleviating salinity stress. Therefore, by using 2% biochar, it is possible to improve saline soils (soils containing 1,000 or 2,000 mg/kg NaCl) and grow periwinkle ornamental-medicinal plant in it. The plants showed acceptable performance at salinity levels of 1,000 or 2,000 mg/kg with biochar 2%.

" Assessing the impact of biochar on microbes in acidic soils: Alleviating the toxicity of aluminum and acidity"

In arable soils, anthropogenic activities such as fertilizer applications have intensified soil acidification in recent years. This has resulted in frequent environmental problems such as aluminum (Al) and H+ stress, which negatively impact crop yields and quality in acidic soils. Biochar, as a promising soil conditioner, has attracted much attention globally. The present study was conducted in a greenhouse by setting up 2% biochar rate to investigate how biochar relieves Al3+ hazards in acidic soil by affecting soil quality, soil environment, and soil microbiomes. The addition of biochar significantly improved soil fertility and enzyme activities, which were attributed to its ability to enhance the utilization of soil carbon sources by influencing the activity of soil microorganisms. Moreover, the Al3+ contents were significantly decreased by 66.61-88.83% compared to the C0 level (without biochar treatment). In particular, the results of the 27Al NMR suggested that forms of AlVI (Al(OH)2+, Al(OH)+ 2, and Al3+) were increased by 88.69-100.44% on the surface of biochar, reducing the Al3+ stress on soil health. The combination of biochar and nitrogen (N) fertilizer contributed to the augmentation of bacterial diversity. The application of biochar and N fertilizer increased the relative abundance of the majority of bacterial species. Additionally, the application of biochar and N fertilizer had a significant impact on soil microbial metabolism, specifically in the biosynthesis of secondary metabolites (lipids and organic acids) and carbon metabolic ability. In conclusion, biochar can enhance soil microbial activity and improve the overall health of acidic soil by driving microbial metabolism. This study offers both theoretical and technical guidance for enhancing biochar in acidified soil and promoting sustainable development in farmland production.

Meta-Analysis of the Effects of Biochar Application on the Diversity of Soil Bacteria and Fungi

Biochar is increasingly being used for soil improvement, but the effects on microbial diversity in soil are still ambiguous due to contrasting results reported in the literature. We conducted a meta-analysis to clarify the effect of biochar addition on soil bacterial and fungal diversity with an increase in Shannon or Chao1 index as the outcome. Different experimental setups, quantitative levels of biochar addition, various biochar source materials and preparation temperatures, and the effect of natural precipitation in field experiments were the investigated variables. From a total of 95 publications identified for analysis, 384 datasets for Shannon index and 277 datasets for Chao1 index were extracted that described the bacterial diversity in the soils, of which field experiments and locations in China dominated. The application of biochar in soil significantly increased the diversity of soil bacteria but it had no significant effect on the diversity of fungi. Of the different experimental setups, the largest increase in bacterial diversity was seen for field experiments, followed by pot experiments, but laboratory and greenhouse settings did not report a significant increase. In field experiments, natural precipitation had a strong effect, and biochar increased bacterial diversity most in humid conditions (mean annual precipitation, MAP > 800 mm), followed by semi-arid conditions (MAP 200–400 mm). Biochar prepared from herbaceous materials was more effective to increase bacterial diversity than other raw materials and the optimal pyrolysis temperature was 350–550 °C. Addition of biochar at various levels produced inconclusive data for Chao1 and Shannon indices, and its effect was less strong than that of the other assessed variables.

Investigating soil properties and vegetation parameters in different biochar-amended vegetated soil at large suction for application in bioengineered structures

Bioengineered structures, such as landfill cover, vegetated slopes or embankments, green roof and turf are comprised of soil and vegetation where vegetation imparts stability and protection through root reinforcement and hydrologic action. Soil in bioengineered structures often compacted and subjected to prolong drying due to irregular irrigation which necessitates the investigation of soil properties and vegetation growth in biochar-amended soil (BAS) under large suction range and it is scarce in the literature. In the present study, the effect of different biochar types on soil properties, and the vegetation growth in compacted soil and under large suction range was investigated for application in bioengineered structures. The results revealed that the biochar amendment decreased the dry density (5-32%) and increased the water retention capacity (θ_s by 15-104%, θ₁₅₀₀ by 82-445% and plant available water content (PAWC) by 22-55%), pH (28-77%) and cation exchange capacity (CEC, 16-723%) of the soil. Further, the vegetation growth i.e., vegetation density, dry root mass and shoot mass increased by 8-13%, 33-108% and 4-157% respectively after biochar amendment. The vegetation wilting was started at a higher suction (~ 900 kPa) relative to bare soil (800 kPa), the permanent wilting point (PWP) increased (by 3-35%) and the complete photosynthetic activity remained unchanged at a higher suction (1600 kPa) relative to bare soil (1050 kPa) after biochar amendment. Among the biochar types i.e., Sugarcane Bagasse biochar (SBB), Mesquite biochar (MB) and Water Hyacinth biochar (WHB) tested, the MB showed the best performance i.e., the suitable vegetation growth and health status. The improved water retention due to increased porosity, specific surface area (SSA) and presence of hydrophilic functional groups, and the higher pH, CEC and lower dry density in BAS attributed to the higher vegetation growth. The findings of the present study suggest the application of BAS in bioengineered structures.

Estimating the methane emissions and energy potential from Trichy and Thanjavur dumpsite by LandGEM model

One major factor, contributing to the emission of greenhouse gas in the environment, is generation of hazardous gases in municipal landfills. Due to these potential negative impacts, it is obligatory to estimate the amount and type of landfill gasses to design and build a gas collecting system. Landfill gas emissions are governed by the type of waste, its biodegradability, its methane emission potential, the degree of separation, and other miscellaneous factors. LandGEM model was used to predict the amount of gases produced in the landfills of Trichy (Ariyamangalam) and Thanjavur (Srinivasapuram). According to the results, the largest amount of landfill gas emissions would be in 1993 for Trichy (Ariyamangalam) landfill and in 2027 for Thanjavur (Srinivasapuram) landfill. The total amount of produced gas, methane, and carbon dioxide would be 16.2E + 10, 8.2E + 10, and 16.2 + 10 cubic meters per year in 1993 for Trichy and 13E + 6, 5E + 6 and 13E + 6 cubic meters per year in 2027 for Thanjavur.

Effects of biochar on shear strength of completely decomposed granite

Biochar has a great potential to sustainably improve the performance of bio-engineered slope due to its ability to retain water and to supply nutrients. Existing studies mainly focus on hydrological properties of biochar-amended soil. However, the effects of biochar on shear strength of soil are not well studied. This study aims to assess the shearing behaviour of biochar-amended completely decomposed granite (CDG). Soil specimens were prepared by mixing CDG with two types of biochar at a mass ratio of 5% and compacted at 95% of the maximum dry density. Although the peak shear strength of biochar-amended CDG is reduced by up to 20% because of lower initial dry density of the soil and crushing of biochar particles during shearing, both types of biochar have negligible effects on the ultimate shear strength, which is governed by friction between soil particles. This highlights that the ultimate friction angle can be adopted for designing bio-engineered slopes using biochar-amended soils.

Biochar produced from the straw of common crops simultaneously stabilizes soil organic matter and heavy metals

The simultaneous stabilization of heavy metals and organic matter in polluted soil has received little research attention. In this study, we studied the immobilization of Cu and Cd and the mineralization of organic matter in the acidic soil amended with biochar produced from rice, wheat, corn, and rape straws through incubation experiments. Compared with that in the control treatment, the availability of Cu and Cd in the biochar amended soils decreased by 17-31% and 3-17%, respectively. The cumulative amount of CO₂ released from each treatment in 60 days of incubation followed the order: control treatment (399 mg CO₂-C kg^-1) > rape straw biochar treatment (388 mg CO₂-C kg^-1) > rice straw biochar treatment (374 mg CO₂-C kg^-1) > corn straw biochar treatment (355 mg CO₂-C kg^-1) > wheat straw biochar treatment (288 mg CO₂-C kg^-1). The information implied that biochar produced from the straw of common crops can simultaneously stabilize both heavy metals and organic matter in the acidic soil. The transformation of Cu and Cd from acid soluble fraction to residual fraction was the potential mechanism of biochar in facilitating soil heavy metal immobilization. The significant decrease in soil β-glucosidase activity, which controlled the degradation of soil organic matter, was an important potential pathway of biochar in decreasing soil organic matter mineralization. A significant decrease in the content and a substantial increase in the structural complexity of soil dissolved organic matter could further the decrease of wheat straw biochar in soil organic matter mineralization. Thus, biochar produced from the straw of common crops is a promising amendment for simultaneously stabilizing both heavy metals and organic matter in the acidic soil.

Methane Emission Reduction and Biological Characteristics of Landfill Cover Soil Amended With Hydrophobic Biochar

Biochar-amended landfill cover soil (BLCS) can promote CH₄ and O₂ diffusion, but it increases rainwater entry in the rainy season, which is not conducive to CH₄ emission reduction. Hydrophobic biochar–amended landfill cover soil (HLCS) was prepared to investigate the changes in CH₄ emission reduction and biological characteristics, and BLCS was prepared as control. Results showed that rainwater retention time in HLCS was reduced by half. HLCS had a higher CH₄ reduction potential, achieving 100% CH₄ removal at 25% CH₄ content of landfill gas, and its main contributors to CH₄ reduction were found to be at depths of 10–30 cm (upper layer) and 50–60 cm (lower layer). The relative abundances of methane-oxidizing bacteria (MOB) in the upper and lower layers of HLCS were 55.93% and 46.93%, respectively, higher than those of BLCS (50.80% and 31.40%, respectively). Hydrophobic biochar amended to the landfill cover soil can realize waterproofing, ventilation, MOB growth promotion, and efficient CH₄ reduction.

Four-year biochar study: Positive response of acidic soil microenvironment and citrus growth to biochar under potassium deficiency conditions

Biochar has direct or indirect effects on soil microorganisms, but the changes in soil metabolism are rarely monitored and analyzed. In addition, the potassium (K) effect of biochar has not attracted much attention. This study set up a four-year experiment with acid soil and citrus as the test soil and plants, respectively. The long-term effects of biochar on the acid soil microenvironment and citrus growth were explored from soil properties (nutrient contents, microbial communities, and metabolites) and citrus growth (nutrient contents, reactive oxygen species (ROS), and root endophytes). The results showed that the four-year amendment of biochar in acid soil was very significant, in which the soil pH was increased by 1 unit, organic matter and cation exchange capacity (CEC) increased by 120.77% and 16.21%, respectively. Biochar improved the K availability of soil by increasing the number and metabolic activity of Azotobacter and Pseudomonas, and finally effectively alleviated the K deficiency of citrus. From the perspective of available K content, 2% biochar reduced the 20% conventional K application rate. The pH, organic matter, and cation exchange capacity (CEC) were the most important factors affecting the bacterial community structure, while the fungal community was more sensitive to the change in the nutrient environment. Biochar mainly stimulated the progress of soil metabolism by affecting the metabolic activity of bacterial communities. Biochar application increased some of the beneficial bacteria in the soil, i.e., the relative abundance of Pseudarthrobacter increased by 700 times. However, biochar and exogenous K did not significantly affect arbuscular mycorrhizal fungi (AMF) and endophytic bacteria in citrus roots. In general, biochar has a long-term and positive response to the acidic soil microenvironment and citrus growth, as well as promotion value in the agricultural field.

An urgent call to think globally and act locally on landfill disposable plastics under and after covid-19 pandemic: Pollution prevention and technological (Bio) remediation solutions

Landfilling and illegal waste disposal have risen to deal with the COVID-19 potentially infectious waste, particularly in developing countries, which aggravates plastic pollution and inherent environmental threats to human and animal health. It is estimated that 3.5 million metric tonnes of masks (equivalent to 601 TIR containers) have been landfilled worldwide in the first year, with the potential to increase global plastic municipal solid waste by 3.5%, alter biogas composition, and release 2.3 × 10²¹ microplastics to leachates or adjacent environments, in the coming years. This paper reviews the challenges raised in the pandemic scenario on landfills and discusses the potential environmental and health implications that might drive us apart from the 2030 U.N. sustainable goals. Also, it highlights some innovative technologies to improve waste management (from collection to disposal, waste reduction, sterilization) and mitigates plastic leakage (emission control approaches, application of biotechnological and monitoring/computational tools) that can pave the way to environmental recovery. COVID-19 will eventually subside, but if no action is taken in the short-term towards effective plastic policies, replacement of plastics for sustainable alternatives (e.g., biobased plastics), improvement of waste management streams (prioritising flexible and decentralized approaches), and a greater awareness and responsibility of the general public, stakeholders, industries; we will soon reach a tipping-point in natural environments worldwide.

The Use of Biochar for Plant Pathogen Control

To support the search for alternative, nonchemical plant disease control strategies, we present a review of the pathogen-suppressive effects of biochar, a product derived from agricultural and other organic wastes, used as a soil amendment. A wide range of biochar effects contribute to the control of root or foliar fungal pathogens through modification of root exudates, soil properties, and nutrient availability, which influence the growth of antagonist microorganisms. The induction of systemic plant defenses by biochar in the roots to reduce foliar pathogenic fungi, the activation of stress-hormone responses, as well as changes in active oxygen species are indicative of a coordinated hormonal signaling within the plant. Although scarce data are available for oomycetes and bacterial pathogens, reports indicate that biochar promotes changes in the soil microbiota influencing pathogen motility and colonization, and the induction of plant systemic defenses, both contributing to disease suppression. Biochar also suppresses nematode and insect pests. For plant-parasitic nematodes, the primary modes of action are changes in soil microbial community diversity, the release of nematicidal compounds, and the induction of plant defenses. Use of biochar-based soil amendments is a promising strategy compatible with a circular economy, based on zero waste, as part of integrated pathogen and pest management. Since biochars exert complex and distinct modes of action for the control of plant pathogens, its nature and application regimes should be designed for particular pathogens and its effects studied locally.

Bacterial Diversity and Community Structure of a Municipal Solid Waste Landfill: A Source of Lignocellulolytic Potential

Omics have given rise to research on sparsely studied microbial communities such as the landfill, lignocellulolytic microorganisms and enzymes. The bacterial diversity of Municipal Solid Waste sediments was determined using the illumina MiSeq system after DNA extraction and Polymerase chain reactions. Data analysis was used to determine the community's richness, diversity, and correlation with environmental factors. Physicochemical studies revealed sites with mesophilic and thermophilic temperature ranges and a mixture of acidic and alkaline pH values. Temperature and moisture content showed the highest correlation with the bacteria community. The bacterial analysis of the community DNA revealed 357,030 effective sequences and 1891 operational taxonomic units (OTUs) assigned. Forty phyla were found, with the dominant phyla Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidota, while Aerococcus, Stenotrophomonas, and Sporosarcina were the dominant species. PICRUSt provided insight on community's metabolic function, which was narrowed down to search for lignocellulolytic enzymes' function. Cellulase, xylanase, esterase, and peroxidase were gene functions inferred from the data. This article reports on the first phylogenetic analysis of the Pulau Burung landfill bacterial community. These results will help to improve the understanding of organisms dominant in the landfill and the corresponding enzymes that contribute to lignocellulose breakdown.

Composition and diversity of bacterial communities in the rhizosphere of the Chinese medicinal herb Dendrobium

BACKGROUND

Dendrobium is a precious herbal that belongs to Orchidaceae and is widely used as health care traditional Chinese medicine in Asia. Although orchids are mycorrhizal plants, most research still focuses on endophytes, and there is still large amount unknown about rhizosphere microorganisms. To investigate the rhizosphere microbial community of different Dendrobium species during the maturity stage, we used high-throughput sequencing to analyze microbial community in rhizosphere soil during the maturity stage of three kinds of Dendrobium species.

RESULTS

In our study, a total of 240,320 sequences and 11,179 OTUs were obtained from these three Dendrobium species. According to the analysis of OTU annotation results, different Dendrobium rhizosphere soil bacteria include 2 kingdoms, 63 phyla, 72 classes, 159 orders, 309 families, 850 genera and 663 species. Among all sequences, the dominant bacterial phyla (relative abundance > 1%) were Proteobacteria, Actinobacteria, Bacteroidetes, Acidobacteria, Firmicutes, Verrucomicrobia, Planctomycetes, Chloroflexi, and Gemmatimonadetes. And through WGCNA analysis, we found the hub flora was also belong to Acidobacteria, Actinobacteria and Proteobacteria.

CONCLUSIONS

We found that the rhizosphere bacterial communities of the three kinds of Dendrobium have significant differences, and that the main species of rhizosphere microorganisms of Dendrobium are concentrated in the Proteobacteria, Actinobacteria, and Bacteroidetes. Moreover, the smaller the bacterial level, the greater the difference among Dendrobium species. These results fill knowledge gaps in the rhizosphere microbial community of Dendrobium and provide a theoretical basis for the subsequent mining of microbial functions and the study of biological fertilizers.

Microbial structure and diversity in non-sanitary landfills and association with physicochemical parameters

This study assessed the bacterial populations in a non-sanitary landfill around Guarani Aquifer recharge zone in Brazil. Samples from two different positions (sites 1 and 2) at three different depths were evaluated, totaling six solid waste samples; two samples from an impacted stream were also collected. 16S rRNA sequencing was performed using the Ion S5TM XL platform; 3113 operational taxonomic units (OTUs) and 52 phyla were identified. Proteobacteria (37%) and Firmicutes (28%) were the most abundant phyla in the landfill, whereas Proteobacteria (~ 50%) and Bacteroidetes (~ 10%) were more profuse in surface water samples. Canonical correlation analysis (CCA) enabled us to clearly separate the samples according to their spatial location (site 1 or 2) or environmental matrix (surface water or solid waste samples), showing that microbiological populations are strongly associated with site-specific conditions and the kind of environmental matrix they come from. Environmental factors that mostly influenced the microbial communities were organic matter, oxidation-reduction potential, moisture, alkalinity, nitrogen (TKN), sodium, potassium, and zinc. Exiguobacterium (phylum Firmicutes) was overwhelmingly dominant at site 1 and was associated with higher concentrations of organic matter and potassium. Differently, site 2 did not present such dominant genera and was more diverse having lower concentrations of organic matter and nutrients. Distinct environments co-exist inside the same waste deposit, including zones which are representative of active and closed landfills and the occurrence of considerable physicochemical and microbiological shifts within short distances. Those shifts indicate that microbial populations are well adapted to the heterogeneity typical of urban solid waste, which is possibly beneficial to contaminant degradation. Graphical abstract.

Short- and Long-Term Biochar Cadmium and Lead Immobilization Mechanisms

The mechanisms of soil Cd and Pb alterations and distribution following biochar (BC; 0 to 40 t ha−1) amendments applied (in either 2009 [long-term] or in 2016 [short-term]) to a contaminated rice paddy soil, and subsequent plant Cd and Pb tissue distribution over time was investigated. Water-soluble Cd and Pb concentrations decreased by 6.7–76.0% (short-term) and 10.3–88.1% (long-term) with biochar application compared to the control. The soil exchangeable metal fractions (i.e., considered more available) decreased, and the residual metal fractions (i.e., considered less available) increased with short- and long-term biochar amendments, the latter likely a function of biochar increasing pH and forcing Cd and Pb to form crystal mineral lattice associations. Biochar application reduced Cd (16.1–84.1%) and Pb (4.1–40.0%) transfer from root to rice grain, with rice Cd and Pb concentrations lowered to nearly Chinese national food safety standards. Concomitantly, soil organic matter (SOM), pH and soil water content increased by 3.9–49.3%, 0.05–0.35 pH units, and 3.8–77.4%, respectively, with increasing biochar application rate. Following biochar applications, soil microbial diversity (Shannon index) also increased (0.8–46.2%) and soil enzymatic activities were enhanced. Biochar appears to play a pivotal role in forcing Cd and Pb sequestration in contaminated paddy soils, reducing heavy metal transfer to rice grain, and potentially leading to reduced heavy metal consumption by humans.

Effects of biochar on soil microbial community and functional genes of a landfill cover three years after ecological restoration

Landfills, as the most common approach to disposing of municipal solid waste worldwide, disturb native ecosystems and create a need for ecological restoration. The restoration of landfill cover with biochar has shown immediate potential to improve soil microbial functions within one year. However, such characteristics could change after a longer period of time. Here, soil properties, microbial communities, and microbial functional genes related to nutrient cycling were investigated three years after the biochar amendment of the topsoil of a subtropical landfill cover. The results showed that the levels of soil organic matter, water content, total carbon (C), total nitrogen (N) and total phosphorus (P) of biochar-amended soils were higher than those of control soil. Different soil microbial community structures were observed in the biochar-amended and control soils. Nine phyla, including Proteobacteria and Acidobacteria, but not Actinobacteria or Chloroflexi, were enriched in the biochar-amended soil. Although the impact of biochar on shaping microbial communities increased after a longer period of restoration, no differences were observed in soils that were amended using different biochar:soil ratios. The abundances of functional genes related to C and N cycling decreased, whereas those of genes related to P cycling were higher in soils that received biochar amendment. This finding suggests that compared with the control soil, biochar-amended soils were less active in processes involved in C and N cycling but enhanced in processes related to P cycling. This study can serve as a reference for future ecological restoration of degraded lands using biochar.

Two-year evaluation of hydraulic properties of biochar-amended vegetated soil for application in landfill cover system

Landfill cover should ideally have a medium with high water retention ability and low hydraulic conductivity to prevent rainfall infiltrating into the hazardous waste layer. Even though biochar amended soil (BAS) is advocated as cover medium, the interactions between biochar and plant, as well as the effects of biochar aging and plant growth on soil hydraulic properties are still not clear. This study aims to investigate the effects of grass (Cynodon dactylon) growth in BAS on soil water retention and saturated hydraulic conductivity (k_s) over a two-year period. Four ground conditions were tested, namely bare silty sand with and without biochar, vegetated silty sand with and without biochar. The biochar content was kept at 10% (v/v). During the first 6 months, soil water content corresponding to field capacity (FC) and permanent wilting point (PWP) in grassed soil increased by 17% and 27%, respectively. With biochar inclusion, 43% and 57% additional increases in FC and PWP respectively were observed. Moreover, k_s in biochar-amended grassed soil decreased by 50%. Furthermore, grass growth from 6 to 24 months reduced FC by 32%, PWP by 40% but caused 20 times increase in k_s of grassed soil. With the presence of biochar, FC and PWP decreased by only 6% and 8%, respectively, and k_s increased by 200% due to the enhanced plant growth (specifically root growth) by biochar. After two years, k_s of grassed soil with biochar was 16 times smaller than that without biochar. This study demonstrated the effectiveness of biochar in maintaining the enhanced soil water retention ability and reduced k_s in vegetated soil over a two-year study period.

The role of biochar in organic waste composting and soil improvement: A review

Large amounts of organic wastes, which pose a severe threat to the environment, can be thermally pyrolyzed to produce biochar. Biochar has many potential uses owing to its unique physicochemical properties and attracts increasing attentions. Therefore, this review focuses on the agronomic functions of biochar used as compost additives and soil amendments. As a compost additive, biochar provides multiple benefits including improving composting performance and humification process, enhancing microbial activities, reducing greenhouse gas and NH₄ emissions, immobilizing heavy metals and organic pollutants. As a soil amendment, biochar shows a good performance in improving soil properties and plant growth, alleviating drought and salinity stresses, interacting with heavy metals and organic pollutants and changing their fate of being uptaken from soils to plants. Furthermore, combined application of biochar and compost shows a good performance and a high agricultural value when applied to soils. Objectively and undeniably, there are still negative or ineffective cases of biochar amendment on crop yield and heavy metal immobilization, which is worthy of further attention. The medium-long term field monitoring of biochar-specific agricultural functions, as well as the exploration of wider sources for biochar feedstocks, are still needed.

Methane Emission Reduction Enhanced by Hydrophobic Biochar-Modified Soil Cover

The microbial oxidation of CH4 in biochar-modified soil cover is considered a potent option for the mitigation of emissions from old landfills or sites containing wastes full of low CH4 generation rates. The mechanism of methane oxidizing bacteria (MOB) can be enhanced by amending the landfill cover soil with biochar, which is recalcitrant to biological degradation and can adsorb CH4 while facilitating the growth and activity of MOB within its porous structure. However, the increase in the permeability coefficient and water content of the cover due to the addition of biochar also affects the methane removal efficiency. A hydrophobic biochar modified by KH-570 was employed to reduce the water content and to promote the diffusion and oxidation of CH4 in the cover. Several series of small-scale column tests were conducted to quantify the CH4 oxidation properties of the landfill cover soil amended with biochar and hydrophobic biochar under different levels of exposed CH4 concentrations (5% and 15%), heights (10–66 cm), and temperatures (15–40 °C). After 30 days of domestication, the removal rate of the hydrophobic biochar-modified soil cover reached 98.8%. The water holding capacity of the cover and the CH4 oxidation efficiency under different moisture contents were investigated in different columns. The hydrophobic biochar-modified soil cover has a weak water holding capacity, low saturated water content, and optimal CH4 oxidation efficiency at this time.

Enhancement of COD removal in constructed wetlands treating saline wastewater: Intertidal wetland sediment as a novel inoculation

This study investigated intertidal wetland sediment (IWS) as a novel inoculation source for saline wastewater treatment in constructed wetlands (CWs). Samples of IWS (5-20 cm subsurface sediment), which are highly productive and rich in halophilic and anaerobic bacteria, were collected from a high-salinity natural wetland and added to CW matrix. IWS-supplemented CW microcosms that are planted and unplanted Phragmites australis were investigated under salty (150 mM NaCl: PA+(S) and CT+(S)) and non-salty (0 mM NaCl: PA+ and CT+) conditions. The chemical oxygen demand (COD) removal potential of IWS-supplemented CWs was compared with that of conventional CWs without IWS (PA(S) and CT(S), PA, and CT). Results showed that the COD removal rate was higher in PA+(S) (51.80% ± 3.03%) and CT+(S) (29.20% ± 1.26%) than in PA(S) (27.40% ± 3.09%) and CT(S) (27.20% ± 3.06%) at 150 mM NaCl. The plants' chlorophyll content and antioxidant enzyme activity indicated that the addition of IWS enhanced the resistance of plants to salt. Microbial community analysis showed that the dominant microorganisms in PA+(S) and CT+(S), namely, Anaerolineae, Desulfobacterales, and Desulfuromonadales, enhanced the organic removal rates via anaerobic degradation. IWS-induced Dehalococcoides, which is a key participant in ethylene formation, improved the plants' stress tolerance. Several halophilic/tolerant microorganisms were also detected in the CW system with IWS. Thus, IWS is a promising inoculation source for CWs that treat saline wastewater.