Degradation or humification: rethinking strategies to attenuate organic pollutants

Effect of environmental factors on laccase-mediated 17β-estradiol coupling reaction

Hazardous 17β-estradiol (E2) with a higher estrogen effect, has attracted the attention of many scholars. How to transform and remove E2 in the environment becomes a research hotspot. This paper systematically explores the impacts of environmental elements like temperature, pH value, laccase concentration, humic acid concentration, and the type and concentration of metal ions on the laccase-catalyzed oxidation process of E2. The results show that the optimal environmental conditions for laccase-catalyzed oxidation of E2 are temperatures of 25 °C to 30 °C, pH values of 4 to 5, laccase concentration of 30 unit·L-1, no addition of humic acid, and the addition of Cu2+ at a density of 1 mmol·L-1. The conversion rate of E2 by laccase remained above 70%. The coupling products were formed through covalent coupling mechanisms mediated by functional groups such as C-C and C-O-C, with the main product being E2 dimers. E2 underwent chain extension polymerization during the reaction. Laccase has the potential to remediate E2 contaminated environment in a green and efficient manner.

Electroactive bacteria-established long-distance electron transfer to oxygen facilitates bio-transformation of dissolved organic matter for sediment remediation

Electroactive bacteria (EAB) in sediment commonly establish long-distance electron transfer (LDET) to access O2, facilitating the degradation of organic contaminants, which we hypothesize is mediated by the bio-transformation of dissolved organic matter (DOM). This study confirmed that EAB-established LDET to O2 via a microbial electrochemical snorkel raised the electric potential of sediment by increasing HCl-extracted Fe(III) and NO3- concentrations while reducing DOM concentrations, which further modified microbial diversity and composition, notably reduced the relative abundance of fermentative bacteria. As a result, DOM showed the highest SUVA254 value (3.88) and SUVA280 value (1.61), preliminarily suggesting their enhanced aromaticity, humification and average molecular weight. Additionally, these DOM exhibited the highest electron transfer capacity (174.14±3.62 μmol e- /g C) and redox current. Based on these findings, we propose four possible avenues through which EAB-established LDET to O2 facilitates sediment remediation, mainly including DOM involved affinity, direct and indirect electron transfer, and induced photochemical reaction in degradation or humification process of organic contaminants. Although these proposed avenues require further verification, this work sheds light on deciphering the mechanisms underlying the augmented degradation of organic contaminants facilitated by EAB-established LDET to O2, offering fresh insights into sediment remediation.

Insights into hydrothermal deconstruction and humification of vegetable waste by non-catalytic steam explosion

Source minimization and valorization of vegetable waste has attracted considerable interests recently, but has been limited by its distinctive features of high humidity and perishability. To mitigate these challenges and draw upon its features, this study provides a novel non-catalytic hydrothermal process for rapid humification of broccoli waste by steam explosion (SE). The highest humic substance, fulvic acid (FA) and humic acid yields of 23.48 wt%, 18.70 wt% and 6.07 wt% were obtained within 30 min. Thermal-acidic condition and instantaneous decompression action proved to be favorable for substrate deconstruction, precursor production and humus formation. Potential pathways of hydrothermal humification of vegetable waste were revealed after clarifying the molecular level structure of FA by EA, FTIR, XPS, 2D-NMR and Py-GCMS. This work fills the knowledge gap in the mechanism of hydrothermal humification of vegetable waste and provides technical support for enhancing its agronomic value and efficient cycle in clean production.

Unveiling electron transfer and radical transformation pathways in coupled electrocatalysis and persulfate oxidation reactions for complex pollutant removal

The degradation of multiple organic pollutants in wastewater via advanced oxidation processes might involve different radicals, of which the types and concentrations vary upon interacting with different pollutants. In this study, electrochemical activation of peroxymonosulfate (E/PMS) using advanced activated carbon cloth (ACC) as electrode was applied for simultaneous degradation of mixed pollutants, e.g., metronidazole (MNZ) and p-chloroaniline (PCA). 92.5 % of MNZ and 91.4 % of PCA can be degraded at the cathode and anode at a low current density and PMS concentration, respectively. The rate constants for the simultaneous removal of MNZ and PCA in the E/PMS/MNZ(PCA) system were 118 times and 6 times higher than those in the sole PMS system, and 2.5 times and 1.6 times higher than those in the E/Na2SO4/MNZ(PCA) system, respectively. Different electrochemical characteristics, EPR spectra and radical quenching tests verified that the degradation of MNZ and PCA in the optimal system proceeded primarily through non-radical-dominated oxidation, involving electron transfer and 1O2 effect. The system also exhibited low energy consumption (0.215 kWh/m-3·order-1), broad operational pH range, excellent removal efficiency for water matrix, and low by-products toxicity, indicating its strong potential for practical applications. The ACC, with its super stable, low cost, and electrochemical activity, make it as a promising materials applicable in the E/PMS system for degradation of multiple pollutants. The study further elucidated the mechanism of pollutant interaction with electrode materials in terms of radical and non-radical transformation, providing fundamental insight into the application of this system for treatment of complex wastewater.

Application of catalytic technology based on the piezoelectric effect in wastewater purification

The demands of human life and industrial activities result in a significant influx of toxic contaminants into aquatic ecosystems. In particular, organic pollutants such as antibiotics and dye molecules, bacteria, and heavy metal ions are represented, posing a severe risk to the health and continued existence of living organisms. The method of removing pollutants from water bodies by utilizing the principle of the piezoelectric effect in combination with chemical catalytic processes is superior to other wastewater purification technologies because it can collect water energy, mechanical energy, etc. to achieve cleanliness and high removal efficiency. Herein, we briefly introduced the piezoelectric mechanisms and then reviewed the latest advances in the design and synthesis of piezoelectric materials, followed by a summary of applications based on the principle of piezoelectric effect to degrade pollutants in water for wastewater purification. Moreover, water purification technologies incorporating the piezoelectric effect, including piezoelectric effect-assisted membrane filtration, activation of persulfate, and battery electrocatalysis are elaborated. Finally, future challenges and research directions for the piezoelectric effect are proposed.

Response of humification process to fungal inoculant in corn straw composting with two different kinds of nitrogen sources

Inoculation is widely used in composting to improve the mineralization process, however, the link of fungal inoculant to humification is rarely proposed. The objective of this study was to investigate the effect of compound fungal inoculation on humification process and fungal community dynamics in corn straw composting with two different kinds of nitrogen sources [pig manure (PM) and urea (UR)]. Structural equation modeling and random forest analysis were conducted to identify key fungi and explore the fungi-mediated humification mechanism. Results showed that fungal inoculation increased the content of humic acids in PM and UR by 71.76 % and 53.01 % compared to control, respectively. High-throughput sequencing indicated that there were more key fungal genera for lignin degradation in PM especially in the later stage of composting, but a more complex fungal (genera) connections with lower humification degree was found in UR. Network analysis and random forest suggested that inoculation promoted dominant genus such as Coprinus, affecting lignocellulose degradation. Structural equation modeling indicated that fungal inoculation could promote humification by direct pathway based on lignin degradation and indirect pathway based on stimulating the indigenous microbes such as Scedosporiu and Coprinus for the accumulation of carboxyl and polyphenol hydroxyl groups. In summary, fungal inoculation is suitable to be used combining with complex nitrogen source such as pig manure in straw composting.

Contribution of complexed Fe(Ⅱ) oxygenation to norfloxacin humification and stabilization: Producing and trapping of more humified products

Organic pollutants polymerization in advanced oxidation processes or environmental matrices has attracted increasing attention, but little is known about stabilization of the polymerization products. The results in this work revealed the contribution of Fe(Ⅱ) oxygenation to stabilization of the products from norfloxacin (NOR) humification. It was found that upon oxygenation of Fe(Ⅱ) complexed by catechol (CT), NOR polymerized into the products with larger molecular weight through nucleophilic addition. Around 83.9-89.7 % organic carbon (OC) can be retained in the reaction solution and the precipitates at different Fe(II)/CT molar ratio. In this system with humification potential, the produced hydroxyl radical (HO•) dominantly modified, instead of decomposed, the structure of transformation products (TPs). TPs with diversified side chains were formed through hydroxylation and ring-opening, leading to the more humified products. In the subsequent Fe(Ⅱ) oxidative precipitation, Fe-TPs composites were formed as spherical particle clusters, which could steadily incorporate OC species with molecular fractionation. Specifically, lignin-like, tannins-like, condensed aromatic and high-molecular-weight TPs were preferentially preserved in the precipitates, while the recalcitrant aliphatic products mainly retained in the solution. These findings shed light on the role of Fe(Ⅱ) oxygenation in stabilizing the products from pollutants humification, which could strengthen both decontamination and organics sequestration.

Differential responses of the electron transfer capacities of soil humic acid and fulvic acid to long-term wastewater irrigation

Wastewater irrigation is used to supplement agricultural irrigation because of its benefits and freshwater resource scarcity. However, whether wastewater irrigation for many years affects the electron transfer capacity (ETC) of natural organic matter in soil remains unclear, and organic matter could influence the decomposition and mineralization of substances with redox characteristics in soil through electron transfer, ultimately affecting the soil environment. The composition of soil humic substances (HS) is highly complex, and the effects of soil humic acid (HA) and fulvic acid (FA) on ETC is poorly understood. In this study, we separately evaluated the responses of the electron-accepting capacity (EAC) and electron-donating capacity (EDC) of soil HA and FA in agricultural fields to various durations of wastewater irrigation. Results showed that the EAC of HA and FA increased significantly with increasing the duration of wastewater irrigation. When wastewater irrigation lasted for 56 years, the EAC of HA showed a higher increment (590 %) than that of FA (223 %). The EDC of soil HA and FA, conversely, decreased compared to the control, with the highest reduction of 35.6 % for HA and 65.9 % for FA. Specifically, the EDC of HA gradually decreased starting from 29 years of wastewater irrigation, whereas the decrease in the EDC of FA exhibited no clear pattern in relation to the duration of wastewater irrigation. Increased soil organic matter and total nitrogen content under long-term wastewater irrigation led to an increase in sucrase and phosphatase activities, along with an increase in EAC and a decrease in EDC of HS. This suggests that soil enzyme activities may ultimately lead to changes in ETC. The results of this research provide practical insights into the redox system in soil and its driving role in soil organic matter transformation and nutrient cycling under wastewater irrigation.

Natural flocculant chitosan inhibits short-chain fatty acid production in anaerobic fermentation of waste activated sludge

Chitosan (CTS) serves as an excellent natural flocculant in wastewater purification and sludge conditioning, but its potential impact on anaerobic fermentation of waste-activated sludge is unclear. The current study investigated the role of CTS in short-chain fatty acids (SCFAs) generation via sludge alkaline anaerobic fermentation. The results showed a drastic reduction in SCFA production with CTS, showing a maximum inhibition of 33 % at 6 mg/g of total suspended solids. CTS hindered sludge solubilization through flocculation, and acted as a humus precursor, promoting humus formation, and consequently reduced the amount of available substrates. Further, CTS promoted free ammonia production, posing a challenge to enzymes and cell viability. Additionally, CTS increased the population of Rikenellaceae sp. and weakened the dominance of hydrolyzing and acidifying bacteria. This study deepens the understanding of the potential impact of CTS on anaerobic fermentation and provides a theoretical basis for reducing the risk of polymeric flocculants.

Degradation and humification of steroidal estrogens in the soil environment: A review

Emerging pollutants are toxic and harmful chemical substances characterized by environmental persistence, bioaccumulation and biotoxicity, which can harm the ecological environment and even threaten human health. There are four categories of emerging pollutants that are causing widespread concern, namely, persistent organic pollutants, endocrine disruptors, antibiotics, and microplastics. The distribution of emerging pollutants has spatial and temporal heterogeneity, which is influenced by factors such as geographical location, climatic conditions, population density, emission amount, etc. Steroidal estrogens (SEs) discussed in this paper belong to the category of endocrine disruptors. There are generally three types of fate for SEs in the soil environment: sorption, degradation and humification. Humification is a promising pathway for the removal of SEs, especially for those that are difficult to degrade. Through humification, these difficult-to-degrade SEs can be effectively transferred or fixed, thus reducing their impact on the environment and organisms. Contrary to the well-studied process of sorption and degradation, the role and promise of the humification process for the removal of SEs has been underestimated. Based on the existing research, this paper reviews the sources, classification, properties, hazards and environmental behaviors of SEs in soil, and focuses on the degradation and humification processes of SEs and the environmental factors affecting their processes, such as temperature, pH, etc. It aims to provide references for the follow-up research of SEs, and advocates further research on the humification of organic pollutants in future studies.

Novel insights into the mechanism of laccase-driven rhizosphere humification for alleviating wheat 17β-estradiol contamination

Global-scale crop contamination with environmental estrogens has posed a huge risk to agri-food safety and human health. Laccase is regarded as an unexceptionable biocatalyst for regulating pollution and expediting humification, but the knowledge of estrogen bioremediation and C storage strengthened by laccase-driven rhizosphere humification (LDRH) remains largely unknown. Herein, a greenhouse microcosm was performed to explore the migration and fate of 17β-estradiol (E2) in water-wheat (Triticum aestivum L.) matrices by LDRH. Compared to the non-added laccase, the pseudo-first-order decay rate constants of E2 in the rhizosphere solution after 10 and 50 μM exposures by LDRH increased from 0.03 and 0.02 h-1 to 0.36 and 0.09 h-1, respectively. Furthermore, LDRH conferred higher yield, polymerizability, O-containing groups, and functional-C signals in the humified precipitates, because it accelerated the formation of highly complex precipitates by radical-controlled continuous polymerization. In particular, not only did LDRH mitigate the phytotoxicity of E2, but it also diminished the metabolic load of E2 in wheat tissues. This was attributed to the rapid attenuation of E2 in the rhizosphere solution during LDRH, which limited E2 uptake and accumulation in each subcellular fraction of the wheat roots and shoots. Although several typical intermediate products such as estrone, estriol, and E2 oligomers were detected in roots, only small-molecule species were found in shoots, evidencing that the polymeric products of E2 were unable to be translocated acropetally due to the vast hydrophobicity and biounavailability. For the first time, our study highlights a novel, eco-friendly, and sustainable candidate for increasing the low-C treatment of organics in rhizosphere microenvironments and alleviating the potential risks of estrogenic contaminants in agroenvironments.

Humification levels of dissolved organic matter in the eastern plain lakes of China based on long-term satellite observations

Under the influence of intensive human activities and global climate change, the sources and compositions of dissolved organic matter (DOM) in the eastern plain lake (EPL) region in China have fluctuated sharply. It has been successfully proven that the humification index (HIX), which can be derived from three-dimensional excitation-emission matrix fluorescence spectroscopy, can be an effective proxy for the sources and compositions of DOM. Therefore, combined with remote sensing technology, the sources and compositions of DOM can be tracked on a large scale by associating the HIX with optically active components. Here, we proposed a novel HIX remote sensing retrieval (IRHIX) model suitable for Landsat series sensors based on the comprehensive analysis of the covariation mechanism between HIX and optically active components in different water types. The validation results showed that the model runs well on the independent validation dataset and the satellite-ground synchronous sampling dataset, with an uncertainty ranging from 30.85 % to 36.92 % (average ± standard deviation = 33.6 % ± 3.07 %). The image-derived HIX revealed substantial spatiotemporal variations in the sources and compositions of DOM in 474 lakes in the EPL during 1986-2021. Subsequently, we obtained three long-term change modes of the HIX trend, namely, significant decline, gentle change, and significant rise, accounting for 74.68 %, 17.09 %, and 8.23 % of the lake number, respectively. The driving factor analysis showed that human activities had the most extensive influence on the DOM humification level. In addition, we also found that the HIX increased slightly with increasing lake area (R2 = 0.07, P < 0.05) or significantly with decreasing trophic state (R2 = 0.83, P < 0.05). Our results provide a new exploration for the effective acquisition of long-term dynamic information about the sources and compositions of DOM in inland lakes and provide important support for lake water quality management and restoration.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Waste milk humification product can be used as a slow release nano-fertilizer

The demand for milk has increased globally, accompanied by an increase in waste milk. Here, we provide an artificial humification technology to recycle waste milk into an agricultural nano-fertilizer. We use KOH-activated persulfate to convert waste milk into fulvic-like acid and humic-like acid. We mix the product with attapulgite to obtain a slow-release nano fulvic-like acid fertilizer. We apply this nano-fertilizer to chickweeds growing in pots, resulting in improved yield and root elongation. These results indicate that waste milk could be recycled for agricultural purposes, however, this nano-fertilizer needs to be tested further in field experiments.

Lignin precursors enhance exolaccase-started humification of bisphenol A to form functional polymers

Humification plays a significant role in converting phenolic pollutants and forming heterogeneous polymers, but few studies have been performed to investigate exolaccase-started humification (ESH). Herein, the influences of lignin precursors (LPs) on exolaccase-induced bisphenol A (BPA) removal and humification were explored. In particular, the architectural features and botanical effects of the formed humification products were also tested. ESH was extremely beneficial in boosting BPA removal in the presence of LPs. Compared with LP-free (58.49%), 100% of BPA was eliminated after the reaction with ESH for 72 h. Such a process was controlled by an exolaccase-caused random assembly of radicals, which generated a large number of hydrophobic polymers through nonspecific covalent binding of C-C and/or C-O. These humified polymers were extremely stable at pH 2.0-10.0 and -20 °C to 80 °C and displayed unique functions, i.e., scavenged 2,2-diphenyl-1-picrylhydrazyl/2,2'-azino-bis3-ethylbenzothiazoline-6-sulphonic acid radicals and exerted antioxidant capacities. More importantly, the functional polymers could act as auxin analogs to increase the germination index (>100%), plant biomass, and salt tolerance of radish seedlings. Our findings disclosed that ESH could not only be optimized to mitigate the ecological risks of phenolic pollutants and sequester organic carbon in environmental bioremediation, but the resulting abundant auxin analogs also contributed to agricultural productivity.

Humic acid-dependent respiratory growth of Methanosarcina acetivorans involves pyrroloquinoline quinone

Although microbial humus respiration plays a critical role in organic matter decomposition and biogeochemical cycling of elements in diverse anoxic environments, the role of methane-producing species (methanogens) is not well defined. Here we report that a major fraction of humus, humic acid reduction enhanced the growth of Methanosarcina acetivorans above that attributed to methanogenesis when utilizing the energy sources methanol or acetate, results which showed both respiratory and fermentative modes of energy conservation. Growth characteristics with methanol were the same for an identically cultured mutant deleted for the gene encoding a multi-heme cytochrome c (MmcA), results indicating MmcA is not essential for respiratory electron transport to humic acid. Transcriptomic analyses revealed that growth with humic acid promoted the upregulation of genes annotated as cell surface pyrroloquinoline quinone (PQQ)-binding proteins. Furthermore, PQQ isolated from the membrane fraction was more abundant in humic acid-respiring cells, and the addition of PQQ improved efficiency of the extracellular electron transport. Given that the PQQ-binding proteins are widely distributed in methanogens, the findings extend current understanding of microbial humus respiration in the context of global methane dynamics.

Remote sensing identification of urban water pollution source types using hyperspectral data

Owing to accelerated urbanisation, increased pollutants have degraded urban water quality. Timely identification and control of pollution sources enable relevant departments to effectively perform water treatment and restoration. To achieve this goal, a remote sensing identification method for urban water pollution sources applicable to unmanned aerial vehicle (UAV) hyperspectral images was established. First, seven fluorescent components were obtained through three-dimensional excitation-emission matrix fluorescence spectroscopy of dissolved organic matter (DOM) combined with parallel factor analysis. Based on the hierarchical cluster analysis of the seven fluorescence components and three spectral indices, four pollution source (PS) types were determined, namely, domestic sewage, terrestrial input, agricultural and algal, and industrial wastewater sources. Second, several water colour and optical parameters, including the absorption coefficient of chromophoric DOM at 254 nm, humification index, chlorophyll-a concentration, and hue angle, were utilised to develop an identification method with a recognition accuracy exceeding 70% for the four PSs that is suitable for UAV hyperspectral data. This study demonstrated the potential of identifying PSs by combining the fluorescence characteristics of DOM with the optical properties of water, thus expanding the application of remote sensing technologies and providing more comprehensive and reliable information for urban water quality management.

Reciprocal Interactions of Abiotic and Biotic Dechlorination of Chloroethenes in Soil

Chloroethenes (CEs) as common organic pollutants in soil could be attenuated via abiotic and biotic dechlorination. Nonetheless, information on the key catalyzing matter and their reciprocal interactions remains scarce. In this study, FeS was identified as a major catalyzing matter in soil for the abiotic dechlorination of CEs, and acetylene could be employed as an indicator of the FeS-mediated abiotic CE-dechlorination. Organohalide-respiring bacteria (OHRB)-mediated dechlorination enhanced abiotic CEs-to-acetylene potential by providing dichloroethenes (DCEs) and trichloroethene (TCE) since chlorination extent determined CEs-to-acetylene potential with an order of trans-DCE > cis-DCE > TCE > tetrachloroethene/PCE. In contrast, FeS was shown to inhibit OHRB-mediated dechlorination, inhibition of which could be alleviated by the addition of soil humic substances. Moreover, sulfate-reducing bacteria and fermenting microorganisms affected FeS-mediated abiotic dechlorination by re-generation of FeS and providing short chain fatty acids, respectively. A new scenario was proposed to elucidate major abiotic and biotic processes and their reciprocal interactions in determining the fate of CEs in soil. Our results may guide the sustainable management of CE-contaminated sites by providing insights into interactions of the abiotic and biotic dechlorination in soil.

Exolaccase Propels Humification to Decontaminate Bisphenol A and Create Humic-like Biostimulants

Exolaccase-propelled humification (E-PH) helps eliminate phenolic pollutants and produce macromolecular precipitates. Herein, we investigated the influencing mechanism of 12 humic precursors (HPs) on exolaccase-enabled bisphenol A (BPA) decontamination and humification. Catechol, vanillic acid, caffeic acid, and gentian acid not only expedited BPA removal but also created large amounts of copolymeric precipitates. These precipitates had rich functional groups similar to natural humic substances, which presented great aromatic and acidic characteristics. The releasing amounts of BPA monomer from four precipitates were 0.08-12.87% at pH 2.0-11.0, suggesting that BPA-HP copolymers had pH stability. More excitingly, certain copolymeric precipitates could stimulate the growth and development of radish seedlings. The radish growth-promotion mechanisms of copolymers were involved in two aspects: (1) Copolymers interacted with root exudates to accelerate nutrient uptake; (2) Copolymers released auxins to provoke radish growth. These results may provide an innovative strategy for decontaminating phenolic pollutants and yielding humic-like biostimulants in E-PH.

Bioremediation of polycyclic aromatic hydrocarbons: An updated microbiological review

A class of organic priority pollutants known as PAHs is of critical public health and environmental concern due to its carcinogenic properties as well as its genotoxic, mutagenic, and cytotoxic properties. Research to eliminate PAHs from the environment has increased significantly due to awareness about their negative effects on the environment and human health. Various environmental factors, including nutrients, microorganisms present and their abundance, and the nature and chemical properties of the PAH affect the biodegradation of PAHs. A large spectrum of bacteria, fungi, and algae have ability to degrade PAHs with the biodegradation capacity of bacteria and fungi receiving the most attention. A considerable amount of research has been conducted in the last few decades on analyzing microbial communities for their genomic organization, enzymatic and biochemical properties capable of degrading PAH. While it is true that PAH degrading microorganisms offer potential for recovering damaged ecosystems in a cost-efficient way, new advances are needed to make these microbes more robust and successful at eliminating toxic chemicals. By optimizing some factors like adsorption, bioavailability and mass transfer of PAHs, microorganisms in their natural habitat could be greatly improved to biodegrade PAHs. This review aims to comprehensively discuss the latest findings and address the current wealth of knowledge in the microbial bioremediation of PAHs. Additionally, recent breakthroughs in PAH degradation are discussed in order to facilitate a broader understanding of the bioremediation of PAHs in the environment.

Artificial neural network implementation for dissolved organic carbon quantification using fluorescence intensity as a predictor in wastewater treatment plants

Although spectroscopic methods provide a fast and cost-effective means of monitoring dissolved organic carbon (DOC) in natural and engineered water systems, the prediction accuracy of these methods is limited by the complex relationship between optical properties and DOC concentration. In this study, we developed DOC prediction models using multiple linear/log-linear regression and feedforward artificial neural network (ANN) and investigated the effectiveness of spectroscopic properties, such as fluorescence intensity and UV absorption at 254 nm (UV₂₅₄), as predictors. Optimum predictors were identified based on correlation analysis to construct models using single and multiple predictors. We compared the peak-picking and parallel factor analysis (PARAFAC) methods for selecting appropriate fluorescence wavelengths. Both methods had similar prediction capability (p-values >0.05), suggesting PARAFAC was not necessary for choosing fluorescence predictors. Fluorescence peak T was identified as a more accurate predictor than UV₂₅₄. Combining UV₂₅₄ and multiple fluorescence peak intensities as predictors further improved the prediction capability of the models. The ANN models outperformed the linear/log-linear regression models with multiple predictors, achieving higher prediction accuracy (peak-picking: R² = 0.8978, RMSE = 0.3105 mg/L; PARAFAC: R² = 0.9079, RMSE = 0.2989 mg/L). These findings suggest the potential to develop a real-time DOC concentration sensor based on optical properties using an ANN for signal processing.

Insight into the fate of metal ions in response to the refined classification and transformation order of dissolved organic matter components during municipal solid waste composting

The refined classification and subtle transformation order of dissolved organic matter (DOM) components may govern the fate of metal ions (MIs) during composting. However, the classification of DOM components is still rough and the fate of MIs in response to the refined transformation order of DOM during municipal solid waste composting (MSWC) has not been studied. Here, the refined classification and evolution order of DOM components were redefined by two-dimensional correlation spectroscopy (2DCOS) analysis. Eight DOM components were redefined and their evolution order was: tyrosine-like (peak B)>humic acid-like (peak C1>peak C2)>terrestrial humic-like with small molecular size (peak A)>UVA humic-like with medium molecular size (peak D2)>UVC humic-like with medium molecular size (peak D1)>UVA humic-like with large molecular size (peak E2)>UVC humic-like with large molecular size (peak E1). Na and As were releasing in the whole process of DOM transformation. Cu and Al showed strong affinity with humic-like fraction, the anabolism of which leading to storage of Cu and Al in compost. Si, Fe, Mn, Co, Zn, Ni, Sr, Mg and Cr tend to combine with humic-like fraction with small molecular size. These responses were influenced by synergistic effect of key microorganisms (two bacterial groups and three fungal groups), in which the contribution of bacteria was greater than fungus. Finally, partial least-square path models of "environmental factors-key microorganisms-transformation order of DOM-MIs" were constructed. The combination of humic-like fractions continuously produced during MSWC and MIs made compost product with potential environmental risks. It is of great significance to develop abiotic factors regulation approach based on refined classification and transformation of organic components for reducing environmental risks of compost product.

Anthropogenic, Carbon-Reinforced Soil as a Living Engineered Material

In recent years, the simple synthesis of artificial humic substances (A-HS) by alkaline hydrothermal processing of waste biomass was described. This A-HS was shown to support water and mineral binding, to change soil structure, to avoid fertilizer mineralization, and to support plant growth. Many of the observed macroscopic effects could, however, not be directly related to the minute amounts of A-HS which have been added, and an A-HS stimulated microbiome was found to be the key for understanding. In this review, we describe such anthropogenic soil in the language of the modern concept of living engineered materials and identify natural and artificial HS as the enabler to set up the interactive microbial system along the interfaces of the mineral grains. In that, old chemical concepts as surface activity, redox mediation, and pH buffering are the base of the system structure build-up and the complex self-adaptability of biological systems. The resulting chemical/biological hybrid system has the potential to address world problems as soil fertility, nutrition of a growing world population, and climate change.

Total petroleum hydrocarbons and influencing factors in co-composting of rural sewage sludge and organic solid wastes

Co-composting is an efficient strategy for collaborative disposal of multiple organic wastes in rural areas. In this study, we explored the co-composting of rural sewage sludge and other organic solid wastes (corn stalks and kitchen waste), with a focus on the variation of total petroleum hydrocarbons (TPH) during this process. 12% corn-derived biochar was applied in the composting (BC), with no additives applied as the control treatment (CK). The TPH contents of piles after composting ranged from 0.70 to 0.74 mg/g, with overall removal efficiencies of 35.6% and 61.1% for CK and BC, respectively. The results indicate that the addition of 12% biochar increased the rate of TPH degradation and accelerated the degradation process. 16s rDNA high-throughput sequencing was applied to investigate the biodiversity and bacterial community succession during the composting process. Diverse bacterial communities with TPH degradation functions were observed in the composting process, including Acinetobacter, Flavobacterium, Paenibacillus, Pseudomonas, and Bacillus spp. These functional bacteria synergistically degraded TPH, with cooperative behavior dominating during composting. Biochar amendment enhanced the microbial activity and effectively promoted the biodegradation of TPH. The physicochemical properties of the compost piles, including environmental factors (pH and temperature), nutrients (nitrogen, phosphorus, potassium), and humic substances produced in composting (humic acids and fulvic acids), directly and indirectly affected the variation in TPH contents. In conclusion, this work illustrates the variation in TPH content and associated influencing factors during co-composting of rural organic solid wastes, providing valuable guidance toward the further optimization of rural organic waste management.

Piezocatalytic Techniques in Environmental Remediation

As a consequence of rapid industrialization throughout the world, various environmental pollutants have begun to accumulate in water, air, and soil. This endangers the ecological environment of the earth, and environmental remediation has become an immediate priority. Among various environmental remediation techniques, piezocatalytic techniques, which uniquely take advantage of the piezoelectric effect, have attracted much attention. Piezoelectric effects allow pollutant degradation directly, while also enhancing photocatalysis by reducing the recombination of photogenerated carriers. In this Review, we provide a comprehensive summary of recent developments in piezocatalytic techniques for environmental remediation. The origin of the piezoelectric effect as well as classification of piezoelectric materials and their application in environmental remediation are systematically summarized. We also analyze the potential underlying mechanisms. Finally, urgent problems and the future development of piezocatalytic techniques are discussed.

Effects of microplastic sorption on microbial degradation of halogenated polycyclic aromatic hydrocarbons in water

Halogenated PAHs (HPAHs) are ubiquitous in the environment and have a toxicity similar to that of dioxin. Microplastics exist widely in the environment, and their sorption allows them to act as carriers of HPAHs, potentially changing the bioavailability of HPAHs. However, to the best of our knowledge related studies are limited. In this study, degrading bacteria of five HPAHs were cultivated from mangrove sediments. Among them, the Hyphomicrobium genus has good degradation ability on 9-BrAnt, 2-BrPhe and 2-ClPhe. The degradation process is in line with the first-order degradation kinetic characteristics. The kinetic equations of five kinds of HPAHs showed that the degradation half-lives are 0.65 days (2-BrFle), 0.79 days (9-ClPhe), 1.50 days (2-ClAnt), 5.94 days (9-BrPhe) and 14.1 days (9-BrAnt). The greater the number of benzene rings and the heavier the halogen substituents, the slower the degradation of HPAHs. The sorption of microplastics inhibited the biodegradation of HPAHs, and the degradation half-life of HPAHs will be extended from 0.65 to 14.1 days (the average is 4.59 days) to 1.71-9.93 days (average 5.40 days) for PA, 0.70-35.2 days (average 12.8 days) for PE, 6.02-28.2 (average 15.7 days) days for POM, and 4.60-24.0 (average 19.2 days) days for PP, which is mainly related to the partition coefficient between microplastics and water. This study provides a reference for reducing the uncertainty of the ecological risk assessment of HOCs in the aquatic environment.

Exolaccase-boosted humification for agricultural applications

Globally, phenolic contaminants have posed a considerable threat to agro-ecosystems. Exolaccase-boosted humification may be an admirable strategy for phenolic detoxification by creating multifunctional humic-like products (H-LPs). Nonetheless, the potential applicability of the formed H-LPs in agricultural production is still overlooked. This review describes immobilized exolaccase-enabled humification in eliminating phenolic pollutants and producing artificial H-LPs. The similarities and differences between artificial H-LPs and natural humic substances (HSs) in chemical properties are compared. In particular, the agronomic effects of these reproducible artificial H-LPs are highlighted. On the basis of the above summary, the granulation process is employed to prepare granular humic-like organic fertilizers, which can be applied to field crops by mechanical side-deep fertilization. Finally, the challenges and perspectives of exolaccase-boosted humification for practical applications are also discussed. This review is a first step toward a more profound understanding of phenolic detoxification, soil improvement, and agricultural production by exolaccase-boosted humification.

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Exolaccase-initiated humification is conductive to phenolic detoxification

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Multiple humic-like products are created in exolaccase-boosted humification

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Similarities and differences between artificial and natural humus are disclosed

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Humic-like products can be used to sustain soil health and increase crop yield