Occurrence and dissipation mechanism of organic pollutants during the composting of sewage sludge: A critical review

Evaluation of the potential horizontal gene transfer ability during chicken manure and pig manure composting

Resistance genes have been identified as emerging pollutants due to their ability to rapidly spread in the environment through horizontal gene transfer (HGT). Microbial community serves as the pivotal factor influencing the frequency of HGT during manure composting. However, the characteristics of HGT in microbial community from different types of manure were unclear. Therefore, this study aimed to evaluate the potential risk of HGT in bacterial community through the co-composting of chicken manure and pig manure in different proportions. The experimental results showed that the abundance of sulfonamide antibiotic resistance genes and integrase genes was higher during pig manure composting than those during chicken manure composting. In addition, the addition of pig manure also increased resistance genes abundance during chicken manure composting. These results suggested that the potential HGT risk was greater during pig manure composting. Furthermore, microbial analysis of co-composting suggested that bacterial community of pig manure was more competitive and adaptable than that of chicken manure. Ultimately, statistical analysis indicated that compared to chicken manure composting, the potential ability of HGT was greater during pig manure composting. This study provided the vital theoretical support and scientific guidance for mitigating the HGT risk during manure composting.

Temporal trends of polycyclic aromatic hydrocarbons in soils amended with sludge, compost, and manure in a Scotland pasture: An 8-year field experiment

To optimize the effective utilization of organic waste in agricultural practices, a comprehensive assessment of associated risks and benefits is crucial. This study investigated the impact of three types of organic wastes (sludge, compost, and manure) on polycyclic aromatic hydrocarbons (PAHs) in contaminated soil in a Scottish pasture. The experimental setup comprised 16 plots with four treatments (compost, manure, sludge, and inorganic fertilizer) and four replicates. After eight years of this study, notable disparities in ΣPAH16 concentrations were observed among the different treatments, with compost-amended soil at 378 μg kg-1, sludge-amended soil at 331 μg kg-1, and manure-amended soil at 223 μg kg-1. The concentrations of ΣPAH16 in soil amended with compost and sludge exhibited a linear increase with extended sampling time. Significant changes in ΣPAH16 concentration were evident in the compost treatment plot, with an increase of 20% in the first year and 82% in the eighth year. Risk assessment suggested a low level of health risk from exposure to PAHs at the measured concentrations in the three organic wastes. In conclusion, this study highlights the importance of considering the effects of organic waste amendments on soil PAH levels to make informed decisions in sustainable agricultural practices. It also underscores the need for ongoing research to fully understand the implications of different organic waste applications on soil health and environmental quality.

Revealing the interplay of dissolved organic matters variation with microbial symbiotic network in lime-treated sludge landscaping

Lime pretreatment is commonly used for sludge hygienization. Appropriate lime dosage is crucial for achieving both sludge stabilization (lime dosage >0.2 g/g-TS) and promoting plant and soil health during subsequent landscaping (lime dosage <0.8 g/g-TS). While much research has been conducted on sludge lime treatment, few studies have examined the effects of lime dosing on integrating sludge stabilization and plant growth promotion during landscaping. In this study, we investigated microbial dynamics and dissolved organic matter (DOM) transformation during sludge landscaping with five lime dosage gradients (0, 0.2, 0.4, 0.6, 0.8 g lime/g-TS) over 90 days. Our results showed that a lime dosage of 0.4 g/g-TS is the lower threshold for achieving waste activated sludge (WAS) stabilization during landscaping, leading to maximum humic substance formation and minimal phytotoxicity. Specifically, at 0.4 g/g-TS lime dosage, protein degradation and decarboxylation-induced humification were significantly enhanced. The predominant microbial genera shifted from Aromatoleum to Exiguobacterium and Romboutsia (both affiliated with the phylum Firmicutes). Reactomics analysis further indicated that a 0.4 g/g-TS lime dosage promoted the hydrolysis of proteins (lyase reactions on C-C, C-O, and C-N bonds), amino acid metabolism, and decarboxylation-induced humification (e.g., C1H2O2, C2H4O2, C5H4O2, C6H4O2). The co-occurrence network analysis suggested that the phyla Firmicutes, Proteobacteria, and Bacteroidetes were key players in DOM transformation. This study provides an in-depth understanding of microbe-mediated DOM transformation during sludge landscaping and identifies the optimal lime dosage for improving sludge landscaping efficiency.

Tracing contaminants of emerging concern and their transformations in the whole treatment process of a municipal wastewater treatment plant using nontarget screening and molecular networking strategies

This study employed nontarget screening with high-resolution mass spectrometry and molecular network strategy to characterize the occurrence and tranformation of contaminants of emerging concern (CECs) through a wastewater treatment plant in Guangzhou. We detected 70,631 compounds in positive mode and 14,423 in negative mode in influent, from which 94.5 % of these compounds were successfully eliminated after treatment. Among them, 510 chemicals were identified, with pharmaceuticals being the largest category excluding natural products, accounting for 146 compounds. And 29 CECs were semiquantified with concentrations ranging from 2.80 ng/L (Fluconazole) to 10,351 ng/L (Nicotine). The removal efficiency varied: 60 compounds were easily removable (>90 % removal), 17 were partially removable (40-90 % removal), and 44 were non-degradable (<40 % removal). Additionally, we tentatively identified transformation products (TPs) of CECs using a molecular network analysis, revealing over 20,000 compound pairs sharing common fragments, with 191 compounds potentially linked to 47 level 1 compounds, suggesting their role as TPs of CECs. These findings illuminated the actual treatment efficiency of wastewater treatment plants for CECs and the potential TPs, offering valuable insights for future improvements in wastewater management practices.

Enhancing biodegradation efficiency of PLA/PBAT-ST20 bioplastic using thermophilic bacteria co-culture system: New insight from structural characterization, enzyme activity, and metabolic pathways

The rising utilization of PLA/PBAT-ST20 presents potential ecological risks stemming from its casual disposal and incomplete degradation. To solve this problem, this study investigated the degradation capabilities of PLA/PBAT-ST20 by a co-culture system comprising two thermophilic bacteria, Pseudomonas G1 and Kocuria G2, selected and identified from the thermophilic phase of compost. Structural characterization results revealed that the strains colonized the PLA/PBAT-ST20's surface, causing holes and cracks, with an increase in the carbonyl index (CI) and polydispersity index (PDI), indicating oxidative degradation. Enzyme activity results demonstrated that the co-culture system significantly enhanced the secretion and activity of proteases and lipases, promoting the breakdown of ester bonds. LC-QTOF-MS results showed that various intermediate products were obtained after degradation, ultimately participating in the TCA cycle (ko00020), further completely mineralized. Additionally, after 15-day compost, the co-culture system achieved a degradation rate of 72.14 ± 2.1 wt% for PBAT/PLA-ST20 films, with a decrease in the abundance of plastic fragments of all sizes, demonstrating efficient degradation of PLA/PBAT-ST20 films. This study highlights the potential of thermophilic bacteria to address plastic pollution through biodegradation and emphasizes that the co-culture system could serve as an ideal solution for the remediation of PLA/PBAT plastics.

Characteristics of humification, functional enzymes and bacterial community metabolism during manganese dioxide-added composting of municipal sludge

The aim of this study was to assess effects of MnO2 addition (CK-0%, T1-2% and T2-5%) on humification and bacterial community during municipal sludge (MS) composting. The results suggested that MnO2 addition inhibited the growth of Nitrospira but stimulated Nonomuraea, Actinomadura, Streptomyces and Thermopolyspora, facilitating the lignocellulose degradation and humification with the increase in organic matter degradation by 13.8%-19.2% and humic acid content by 10.9%-20.6%. Compared to CK, the abundances of exoglucanase (EC:3.2.1.91), endo-1,4-beta-xylanase (EC:3.2.1.136) and endomannanase (EC:3.2.1.78) increased by 88-99, 52-66 and 4-15 folds, respectively. However, 5%-MnO2 induced the enrichment of Mizugakiibacter that harms the environment of agricultural production. The addition of 2%-MnO2 was recommended for MS composting. Furthermore, metabolic function analysis indicated that MnO2 addition altered amino acid and carbohydrate metabolism, especially enhancing propanoate metabolism and butanoate metabolism but inhibiting citrate cycle. Structural equation modeling revealed that Nonomuraea and Actinomadura were the main drivers for lignocellulose degradation. This study provided theoretical guidance in regulating humification via MnO2 for MS composting.

Terrestrial bioassays for assessing the biochemical and toxicological impact of biosolids application derived from wastewater treatment plants

Wastewater treatment plants (WWTP) are facilities where municipal wastewater undergoes treatment so that its organic load and its pathogenic potential are minimized. Sewage sludge is a by-product of this process and when properly treated is preferentially called "biosolids". These treatments may include some or most of the following: thickening, dewatering, drying, digestion, composting, liming. Nowadays it is almost impossible to landfill biosolids, which however can well be used as crop fertilizers. Continuous or superfluous biosolids fertilization may negatively affect non-target organisms such as soil macro-organisms or even plants. These effects can be depicted through bioassays on terrestrial animals and plants. It has been shown that earthworms have been affected to various degrees on the following endpoints: pollutants' bioaccumulation, viability, reproduction, avoidance behavior, burrowing behavior. Collembola have been affected on viability, reproduction, avoidance behavior. Other terrestrial organisms such as nematodes and diplopods have also shown adverse health effects. Phytotoxicity have been caused by some biosolids regimes as measured through the following endpoints: seed germination, root length, shoot length, shoot biomass, root biomass, chlorophyll content, antioxidant enzyme activity. Very limited statistical correlations between pollutant concentrations and toxicity endpoints have been established such as between juvenile mortality (earthworms) and As or Ba concentration in the biosolids, between juvenile mortality (collembola) and Cd or S concentration in the biosolids, or between phytotoxicity and some extractable metals in leachates or aquatic extracts from the biosolids; more correlations between physicochemical characteristics and toxicity endpoints have been found such as between phytotoxicity and ammonium N in biosolids or their liquid extracts, or between phytotoxicity and salinity. An inverse correlation between earthworm/collembola mortality and stable organic matter has also been found. Basing the appropriateness of biosolids only on chemical analyses for pollutants is not cost-effective. To enable risk characterization and subsequent risk mitigation it is important to apply a battery of bioassays on soil macro-organisms and on plants, utilizing a combination of endpoints and established protocols. Through combined analytical quantification and toxicity testing, safe use of biosolids in agriculture can be achieved.

Response of phosphorus fractions transformation and microbial community to carbon-to-phosphorus ratios during sludge composting

Phosphorus (P) is one of the essential nutrient elements for plant growth and development. Sludge compost products can be used as an important source of soil P to solve the shortage of soil P. The difference in the initial carbon-to-phosphorus ratio (C/P) will lead to difference in the bacterial community, which would affect the biological pathway of P conversion in composting. However, few studies have been reported on adjusting the initial C/P of composting to explore P conversion. Therefore, this study investigated the response of P component transformations, bacterial community and P availability to C/P during sludge composting by adjusting initial C/P. The results showed that increasing C/P promoted the mineralization of organic P and significantly increased the content of the labile P. High C/P also increased the relative content of available P, especially when the C/P was at 45 and 60, it reached 60.51% and 60.47%. High C/P caused differences in the community structure, and improved the binding ability of microbial network modules and the competitiveness of microbial communities. Additionally, high C/P strengthened the effect of microbial communities on the transformation of P components. Finally, the study showed that C/P was the main contributor to P content variation (64.7%) and indirectly affected P component conversion by affecting the microbial community. Therefore, adjusting the C/P is crucial to improve the P utilization rate of composting products.

Modifying humus-phosphorus-arsenic interactions in sludge composting: The strengthening of phosphorus availability and arsenic efflux detoxification mechanisms

Arsenic (As) in sewage sludge poses a significant threat to environmental and human health, which has attracted widespread attention. This study investigated the value of adding sodium percarbonate (SP) on phosphorus (P) availability and As efflux detoxification through HS-P-As interactions. Due to the unique structure of humus (HS) and the similar chemical properties of P and As, the conditions for HS-P-As interaction are provided. This study discussed the content, morphology and microbial communities of HS, P and As by using metagenomic and correlation analysis. The results showed that the humification index in the experiment group (SPC) was 2.34 times higher than that in the control group (CK). The available phosphorus (AP) content of SPC increased from 71.09 mg/kg to 126.14 mg/kg, and SPC was 1.11 times that of CK. The relative abundance of ACR3/ArsB increased. Pst, Actinomyces and Bacillus commonly participated in P and As conversion. The correlation analysis revealed that the humification process was enhanced, the AP was strengthened, and the As was efflux detoxified after SP amendment. All in all, this study elucidated the key mechanism of HS-P-As interaction and put forward a new strategy for sewage sludge resource utilization and detoxification.

Sustainable management of tea wastes: resource recovery and conversion techniques

As the demand for tea (Camellia sinensis) has grown across the world, the amount of biomass waste that has been produced during the harvesting process has also increased. Tea consumption was estimated at about 6.3 million tonnes in 2020 and is anticipated to reach 7.4 million tonnes by 2025. The generation of tea waste (TW) after use has also increased concurrently with rising tea consumption. TW includes clipped stems, wasted tea leaves, and buds. Many TW-derived products have proven benefits in various applications, including energy generation, energy storage, wastewater treatment, and pharmaceuticals. TW is widely used in environmental and energy-related applications. Energy recovery from low- and medium-calorific value fuels may be accomplished in a highly efficient manner using pyrolysis, anaerobic digestion, and gasification. TW-made biochar and activated carbon are also promising adsorbents for use in environmental applications. Another area where TW shows promise is in the synthesis of phytochemicals. This review offers an overview of the conversion procedures for TW into value-added products. Further, the improvements in their applications for energy generation, energy storage, removal of different contaminants, and extraction of phytochemicals have been reviewed. A comprehensive assessment of the sustainable use of TWs as environmentally acceptable renewable resources is compiled in this review.

The high dose of biochar reduces polycyclic aromatic hydrocarbons losses during co-composting of sewage sludge and wheat straw

The aim of the study was to investigate the effect of the biochar (BC) dose on solvent extractable (Ctot) and freely dissolved (Cfree) polycyclic aromatic hydrocarbons (PAHs) content during co-composting. A significantly better reduction of Σ16 Ctot PAHs after 98 days occurred during composting with BC (for 1% of BC - 44% and for 5% of BC - 23%) than in the control (15%). Despite the relatively high reduction of Ctot PAHs in the experiment with 5% BC rate, the content of the PAHs was still the highest compared to other variants. Regarding Cfree PAHs, 5% rate of BC resulted in the best reduction of PAHs, while the 1% BC dose resulted in a lower reduction of Cfree than the control. For 1% BC, PAHs losses was more effective, and sequestration processes played a less significant role than in the experiment with 5% dose of BC. The total and dissolved organic carbon, and ash were predominantly responsible for Ctot and Cfree losses, and additionally pH for Cfree. The results of the experiment indicate that BC performs a crucial role in composting, affecting the Ctot and Cfree PAHs in the compost but the final effect strictly depends on the BC dose.

Pollution Status and Associated Risk Assessment of Heavy Metals in Sewage Sludge in the Yangtze River Delta, China

The risk assessment of heavy metals (HMs) in sewage sludge (SS) is essential before land application. Six HMs in nineteen SS collected in the Yangtze River Delta were analyzed to assess risks to environment, ecosystem, and human health. HMs concentrations were ranked in the order of Zn > Cu > Cr > Ni > Pb > Cd, with Cu, Zn, and Ni in a total of 16% of samples exceeding the legal standard. Zn showed greatest extractability according to EDTA-extractable concentrations. HMs in 16% of SS samples posed heavy contamination to the environment with Zn as the major pollutant. HMs in 26% of samples posed ecological risk to the ecosystem and Cd was the highest risky HM. The probabilistic health risk assessment revealed that HMs posed carcinogenic risks to all populations, but non-carcinogenic risks only to children. This work will provide fundamental information for land application of SS in this area.

Degradation mechanism of microplastics and potential risks during sewage sludge co-composting: A comprehensive review

Microplastics (MPs) as a kind of emerging contaminants, widely exists in various kinds of medium, sewage sludge (SS) is no exception. In the sewage treatment process, a large number of microplastics will be deposited in SS. More seriously, microplastics in sewage sludge can migrate to other environmental media and threaten human health. Therefore, it is necessary to remove MPs from SS. Among the various restorations, aerobic composting is emerging as a green microplastic removal method. There are more and more reports of using aerobic compost to degrade microplastics. However, there are few reports on the degradation mechanism of MPs in aerobic composting, hindering the innovation of aerobic composting methods. Therefore, in this paper, the degradation mechanism of MPs in SS is discussed based on the environmental factors such as physical, chemical and biological factors in the composting process. In addition, this paper expounds the MPs in potential hazards, and combined with the problems in the present study were studied the outlook.

Identification of key degraders for controlling toxicity risks of disguised toxic pollutants with division of labor mechanisms in activated sludge microbiomes: Using nonylphenol ethoxylate as an example

Efficient management of disguised toxic pollutants (DTPs), which can undergo microbial degradation and convert into more toxic substances, necessitates the collaboration of diverse microbial populations in wastewater treatment plants. However, the identification of key bacterial degraders capable of controlling the toxicity risks of DTPs through division of labor mechanisms in activated sludge microbiomes has received limited attention. In this study, we investigated the key degraders capable of controlling the risk of estrogenicity associated with nonylphenol ethoxylate (NPEO), a representative DTP, in textile activated sludge microbiomes. The results of our batch experiments revealed that the transformation of NPEO into NP and subsequent NP degradation were the rate-limiting processes for controlling the risk of estrogenicity, resulting in an inverted V-shaped curve of estrogenicity in water samples during the biodegradation of NPEO by textile activated sludge. By utilizing enrichment sludge microbiomes treated with NPEO or NP as the sole carbon and energy source, a total of 15 bacterial degraders, including Sphingbium, Pseudomonas, Dokdonella, Comamonas, and Hyphomicrobium, were identified as capable of participating in these processes, Among them, Sphingobium and Pseudomonas were the two key degraders that could cooperatively interact in the degradation of NPEO with division of labor mechanisms. Co-culturing Sphingobium and Pseudomonas isolates exhibited a synergistic effect in degrading NPEO and reducing estrogenicity. Our study underscores the potential of the identified functional bacteria for controlling estrogenicity associated with NPEO and provides a methodological framework for identifying key cooperators engaged in labor division, contributing to the management of risks associated with DTPs by leveraging intrinsic microbial metabolic interactions.

Pharmaceutical active compounds in sewage sludge: Degradation improvement and conversion into an organic amendment by bioaugmentation-composting processes

Around 143,000 chemicals find their fate in wastewater treatment plants in the European Union. Low efficiency on their removal at lab-based studies and even poorer performance at large scale experiments have been reported. Here, a coupled biological technology (bioaugmentation and composting) is proposed and proved for pharmaceutical active compounds degradation and toxicity reduction. The optimization was conducted through in situ inoculation of Penicillium oxalicum XD 3.1 and an enriched consortium (obtained from non-digested sewage sludge), into pilot scale piles of sewage sludge under real conditions. This bioaugmentation-composting system allowed a better performance of micropollutants degradation (21 % from the total pharmaceuticals detected at the beginning of the experiment) than a traditional composting process. Particularly, inoculation with P. oxalicum allowed the degradation of some recalcitrant compounds like carbamazepine, cotinine and methadone, and also produced better stabilization features in the mature compost (significant passivation of copper and zinc, higher macronutrients value, adequate physicochemical conditions for soil direct application and less toxic effect on germination) compared to the control and the enriched culture. These findings provide a feasible, alternative strategy to obtain a safer mature compost and a better removal of micropollutants performance at large scale.

Di-n-butyl phthalate stress hampers compost multifunctionality by reducing microbial biomass, diversity and network complexity

Phthalates are common pollutants in agriculture. Here, the influence of di-n-butyl phthalate (DBP) on multifunctionality of composting was assessed. Results indicated that DBP stress (100 mg/kg) hampered multifunctionality from the thermophilic phase onwards and resulted in a 6.5 % reduction of all assessed functions. DBP stress also significantly reduced microbial biomass (P < 0.05), altered microbial composition (P < 0.05), and decreased network complexity (P < 0.01). Multifunctionality was found to be strongly correlated (P < 0.001) with microbial biomass, diversity, and network complexity. In addition, keystone taxa responsive to DBP were identified as Streptomyces, Thermoactinomyces, Mycothermus, and Lutispora. These taxa were significantly (P < 0.001) affected by DBP stress, and a correlation between them and multifunctionality was shown. This study contributes to a better understanding of the negative implications of phthalates during composting processes, which is of great significance to the development of new treatment strategies for agricultural waste.

Production of compost from logging residues

The implementation of forest management generates logging residue which can be used in several ways. One of the option is to use of logging residue in the composting process. Therefore, this study determined the possibility of producing compost based on logging residue and the produced fertilizer used to fertilize forest nurseries. Pine chips and sewage sludge were used for carrying out the study. The compost, as well as the leachate produced during composting, were characterized by high NPK content. The leachate collected at the end of the experiment was characterized by nitrogen content of approximately 6500 mg‧dm^-3, phosphorus of approximately 450 mg‧dm^-3, and potassium of approximately 500-700 mg‧dm^-3. In contrast, the compost produced contained approximately 0.57 g‧kg^-1 nitrogen, approximately 0.39 g‧kg^-1 phosphorus, and approximately 0.24 g‧kg^-1 potassium. The disadvantage in terms of the usefulness of the resulting fertilizer in forest nurseries is its pH, which exceeded 9.0.

Potassium-rich mining waste addition can shorten the composting period by increasing the abundance of thermophilic bacteria during high-temperature periods

Conventional compost sludge has a long fermentation period and is not nutrient rich. Potassium-rich mining waste was used as an additive for aerobic composting of activated sludge to make a new sludge product. The effects of different feeding ratios of potassium-rich mining waste and activated sludge on the physicochemical properties and thermophilic bacterial community structure during aerobic composting were investigated. The results showed that potassium-rich waste minerals contribute to the increase in mineral element contents; although the addition of potassium-rich waste minerals affected the peak temperature and duration of composting, the more sufficient oxygen content promoted the growth of thermophilic bacteria and thus shortened the overall composting period. Considering the requirements of composting temperature, it is recommended that the addition of potassium-rich waste minerals is less than or equal to 20%.

Di-n-butyl phthalate stress induces changes in the core bacterial community associated with nitrogen conversion during agricultural waste composting

Nitrogen (N) loss during composting reduces the quality of compost products and causes secondary environmental pollution. Phthalate esters (PAEs) are common pollutants in agricultural wastes. However, little information is currently available on how PAEs affect N conversion during agricultural waste composting. This research systematically analyzed the impact of di-n-butyl phthalate (DBP) pollution on the N conversion and its related microbial community during composting. Our results indicated that DBP stress results in a shorter thermophilic phase, and then slower compost maturation during composting. Notably, DBP stress inhibited the conversion of ammonia to nitrate, but increased the release of NH₃ and N₂O leading to an increased N loss and an elevated greenhouse effect. Furthermore, DBP exposure led to a reduction of bacteria related to NH₄⁺ and NO₃^- conversion and altered the network complexity of the bacterial community involved in N conversion. It also reduced the abundance of a major nitrification gene (amoA) (P < 0.01) and increased the abundance of denitrification genes (nirK and norB) (P < 0.05). Moreover, DBP affected the overall microbial community composition at all tested concentrations. These findings provide theoretical and methodological basis for improving the quality of PAE-contaminated agricultural waste compost products and reducing secondary environmental pollution.

Microplastics as an underestimated emerging contaminant in solid organic waste and their biological products: Occurrence, fate and ecological risks

Microplastics (MPs), as an emerging pollutant, have been widely detected in aquatic, terrestrial, and atmospheric ecosystems. Recently, more researchers indicated that solid organic waste is also a crucial repository of MPs and has become a vital pollution source in ecosystems. Although the occurrence and fate of MPs in solid organic waste and the interaction between MPs and biological treatments have been explored, there still needs to be comprehensive summaries. Hence, this study reviewed the occurrence and characteristics of MPs in solid organic waste and organic fertilizers. Meanwhile, this study summarized the influence of MPs on biological treatments (composting and anaerobic digestion) and their degradation characteristics. MPs are abundant in solid organic waste (0-220 ×10³ particles/kg) and organic fertilizer (0-30 ×10³ particles/kg), PP and PE are the prominent MPs, and fibers and fragments are the main shapes. MPs can affect the carbon and nitrogen conversion during biological treatments and interfere with microbial communities. The MP's characteristics changed after biological treatments, which should further consider their potential ecological risks. This review points out the existing problems of MPs in organic waste recycling and provides directions for their treatment in the future.

Impact of different structures of biochar on decreasing methane emissions from sewage sludge composting

Methane (CH₄) emissions from sewage sludge composting can be reduced by using biochar more effectively. This study investigates the impact of different structure of biochar on CH₄ emissions during sewage sludge composting. Corncob biochar (CB, pore size = 35.3990 nm), rice husk biochar (RB, pore size = 3.4242 nm) and wood biochar (WB, pore size = 1.6691 nm) were applied to the composting. The results showed that biochar decreased CH₄ emissions, mainly through the indirect effect of improving the pile environment. Compared with the control group (CK), the biochars with smaller pore structures, WB and RB, reduced CH₄ emissions by 41.83% and 33.59%, respectively, compared to only 8.20% for CB, which has a larger pore structure. In addition, RB and WB increased the free air space (FAS) by more than 10% and CB improved the microbial diversity. Methanothermobacter was reported in WB and RB, with an abundance of 45.45% in WB. Redundancy analysis (RDA) showed that pore size was positively correlated with the CH₄ emission rate. The results of this study can provide a theoretical reference for CH₄ reduction from biochar co-composting of sewage sludge.

Recent Research on Municipal Sludge as Soil Fertilizer in China: a Review

Due to the annual increase in wastewater treatment in most Chinese cities, a major environmental issue has arisen: safe treatment, disposal, and recycling of municipal sludge. Municipal sludge has a high content of carbon and essential nutrients for plant growth; hence, it has gained interest among researchers as a soil fertilizer. This study discusses the potential usage of municipal sludge as soil fertilizer (indicators include nitrogen (N), phosphorus (P), and trace elements) along with its shortcomings and drawbacks (potentially toxic elements (PTEs), organic matter (OM), pathogens, etc.) as well as reviews the latest reports on the role of municipal sludge in land use. The use of municipal sludge as a soil fertilizer is a sustainable management practice and a single application of sludge does not harm the environment. However, repeated use of sludge may result in the accumulation of harmful chemicals and pathogens that can enter the food chain and endanger human health. Therefore, long-term field studies are needed to develop ways to eliminate these adverse effects and make municipal sludge available for agricultural use.

Characteristics of Solidified Carbon Dioxide and Perspectives for Its Sustainable Application in Sewage Sludge Management

Appropriate management is necessary to mitigate the environmental impacts of wastewater sludge. One lesser-known technology concerns the use of solidified CO₂ for dewatering, sanitization, and digestion improvement. Solidified CO₂ is a normal byproduct of natural gas treatment processes and can also be produced by dedicated biogas upgrading technologies. The way solidified CO₂ is sourced is fully in line with the principles of the circular economy and carbon dioxide mitigation. The aim of this review is to summarize the current state of knowledge on the production and application of solid CO₂ in the pretreatment and management of sewage sludge. Using solidified CO₂ for sludge conditioning causes effective lysis of microbial cells, which destroys activated sludge flocs, promotes biomass fragmentation, facilitates efficient dispersion of molecular associations, modifies cell morphology, and denatures macromolecules. Solidified CO₂ can be used as an attractive tool to sanitize and dewater sludge and as a pretreatment technology to improve methane digestion and fermentative hydrogen production. Furthermore, it can also be incorporated into a closed CO₂ cycle of biogas production-biogas upgrading-solidified CO₂ production-sludge disintegration-digestion-biogas production. This feature not only bolsters the technology's capacity to improve the performance and cost-effectiveness of digestion processes, but can also help reduce atmospheric CO₂ emissions, a crucial advantage in terms of environment protection. This new approach to solidified CO₂ generation and application largely counteracts previous limitations, which are mainly related to the low cost-effectiveness of the production process.

Effects of biochar on the degradation of organophosphate esters in sewage sludge aerobic composting

In this study, the impact of biochar on the degradation of organophosphate esters (OPEs) during the aerobic composting of sewage sludge was investigated. Three treatments were conducted with different percentages of biochar in the compost, including 5 %, 10 %, and 20 %. The treatment with 10 % of biochar showed the longest thermophilic phase compared to that of 5 % and 20 % of biochar, which greatly promoted the decomposition of organic matter. In addition, the degradation rate of the hard-to-degrade chlorinated-OPEs was significantly increased by 10 % biochar, reaching to 57.2 %. Correspondingly, approximately 43.6 % of the total concentration of OPEs (Σ₆OPEs) was eliminated in the presence of 10 % of biochar, which was higher than the treatments with 5 % and 20 % of biochar. Biochar significantly influenced the microbial community structure of compost, but the previously reported organophosphorus-degrading bacteria did not play a major role in the degradation of OPEs. The redox ability of the increased oxygen-containing functional groups such as quinone on the surface of biochar and the biochar-mediated electron transfer ability may play an essential role in the degradation of OPEs during the composting process.

Influence of waste brake oil on the rheological properties of coal-sludge water slurry

In this work, the effect of waste brake oil (WBO) on the dispersion property of coal-sludge oil slurry (CSOS) was investigated and comprehensively analyzed. Apparent viscosity of CSOS decreases from 997 to 276 mPa.s with the increasing of SS content from 0 to 12% under the calorific value (CV) of 17.70 MJ/kg and oil/sludge ratio (O/S) of 2.0. The combination of sewage sludge (SS) and WBO could decrease the apparent viscosity of CSOS, and SS content and O/S are two important parameters to affect the apparent viscosity. WBO mainly contains the hydrocarbon compound and a lot of oxygenated functional groups according to its GC/MS results. WBO could cover on the surface of SS and coal particle, and reduce their hydrophobic character and the adsorbance amount of dispersant based on the FTIR, XPS and adsorption performance results. In addition, the mechanism of WBO on slurry characteristics of CSOS was investigated. With the low content of WBO, the liquid bridges from WBO force the solid particles to adhere together and form a stable network structure, thus reducing the flow ability of the suspension. With the increasing of WBO, the network structures could be broken into cells, resulting in a dramatic decrease in viscosity. This research provides a potential way to dispose the SS and waste industry oil.

Composting of Organic Solid Waste of Municipal Origin: The Role of Research in Enhancing Its Sustainability

The organic solid waste of municipal origin stands as one of the residual streams of greatest concern: the great amounts continuously produced over time as well as its biochemical and physical characteristics require its proper handling via biological processes, pursuing the recovery of material and/or the generation of energy. At the European level, most of the industrial plants treating the organic fraction of municipal solid waste (OFMSW) rely on composting, which is a well-established and reliable process that is easy to operate in different socio-economic contexts. Nevertheless, when regarded in a life cycle perspective as well as in the view of the principles of circular economy underlying waste management, several issues (e.g., the presence of toxic substances in compost) can be recognized as technical challenges, requiring further studies to identify possible sustainable solutions. This work aims at discussing these challenges and figuring out the state of the art of composting in a circular perspective. Firstly, the main mentioned issues affecting compost quality and process sustainability are briefly reviewed. Next, to promote the effective use of composting in light of the circular economy principles, research experiences are critically presented to highlight the current technical challenges concerning the environmental and health impact reduction and possible scientific perspectives to overcome issues affecting the compost quality. Based on the critical analysis of reviewed studies, it emerged that further research should be aimed at unveiling the hazard potential of emerging contaminants as well as to address the understanding of the mechanisms underlying their potential removal during composting. Moreover, the adoption of a multidisciplinary perspective in the design of research studies may play a key role towards the definition of cost-effective and environmentally friendly strategies to overcome the technical issues affecting the process.

A critical review on utilization of sewage sludge as environmental functional materials

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

Feasibility of Biochar Derived from Sewage Sludge to Promote Sustainable Agriculture and Mitigate GHG Emissions-A Review

Sewage sludge (SS) has been connected to a variety of global environmental problems. Assessing the risk of various disposal techniques can be quite useful in recommending appropriate management. The preparation of sewage sludge biochar (SSB) and its impacts on soil characteristics, plant health, nutrient leaching, and greenhouse gas emissions (GHGs) are critically reviewed in this study. Comparing the features of SSB obtained at various pyrolysis temperatures revealed changes in its elemental content. Lower hydrogen/carbon ratios in SSB generated at higher pyrolysis temperatures point to the existence of more aromatic carbon molecules. Additionally, the preparation of SSB has an increased ash content, a lower yield, and a higher surface area as a result of the rise in pyrolysis temperature. The worldwide potential of SS output and CO₂-equivalent emissions in 2050 were predicted as factors of global population and common disposal management in order to create a futuristic strategy and cope with the quantity of abundant global SS. According to estimations, the worldwide SS output and associated CO₂-eq emissions were around 115 million tons dry solid (Mt DS) and 14,139 teragrams (Tg), respectively, in 2020. This quantity will rise to about 138 Mt DS sewage sludge and 16985 Tg CO₂-eq emissions in 2050, a 20% increase. In this regard, developing and populous countries may support economic growth by utilizing low-cost methods for producing biochar and employing it in local agriculture. To completely comprehend the benefits and drawbacks of SSB as a soil supplement, further study on long-term field applications of SSB is required.

Effect of calcium peroxide dosage on organic matter degradation, humification during sewage sludge composting and application as amendment for Cu (II)-polluted soils

In this research, it was the first time to investigate the effect of two dosages (5% (T1) and 10% (T2), w/w) of calcium peroxide (CP) on organic matter degradation, humification during sewage sludge composting. Additionally, the complexation of Cu to humic substance (HS) derived from CP-compost compared to no CP addition-compost (CK) was also studied. Results showed that compared to CK, T1 and T2 significantly enhanced organic matter degradation and promoted the formation of HS. Two-dimensional correlation Fourier transform infrared spectroscopy (2D-FTIR-COS) and Parallel factor (PARAFAC) analysis revealed that the addition of CP accelerated the synthesis of HS with high aromatization degree and molecular weight than those in CK, owing to the oxidation of small molecules to form carboxyl. The stability constant (log K_M) of Cu with CP-derived HS (log K_M = 4.22-5.13) indicated a greater complexation ability than CK-derived HS (log K_M = 4.05-4.45), due to the faster response of polysaccharides binding to Cu (II) and the higher humification degree of CP-derived HS. This study revealed the potential mechanisms of CP addition on the synthesis of HS and utilization of CP-compost product might provide an effective way to remedy Cu (II)-contaminated soils.

Effects of di-n-butyl phthalate on aerobic composting process of agricultural waste: Mainly based on bacterial biomass and community dynamics analysis

Phthalic acid esters (PAEs) pollution has become a major environmental problem in agricultural waste composting. However, little information was available about the how the PAEs alter microbial processes during composting. This study investigated the effects of di-n-butyl phthalate (DBP) on bacterial biomass and community dynamics during composting. The results showed that a decreasing of DBP was observed from thermophilic phase and 43.26% of DBP was degraded after composting. The bacterial biomass and diversity during composting were reduced under DBP stress, so delaying the decomposition of organic matter. Moreover, the changes in bacterial community were observed since the thermophilic phase of DBP-contaminated composting. KEGG pathway analysis indicated that DBP stress decreased the relative abundance of the main metabolic pathways and inhibited compost maturation. Moreover, DBP stress had more significant correlation with the dominant bacteria. This work will expand the understanding of PAEs-contaminated organic waste composting and further control of PAEs pollutants.

Di-n-butyl phthalate negatively affects humic acid conversion and microbial enzymatic dynamics during composting

To understand the effects of phthalic acid esters (PAEs) on humic acid (HA) conversion, enzymatic and specific metabolic dynamics during composting under di-n-butyl phthalate (DBP) stress were evaluated for the first time. The results indicated that HA conversion was mainly related to bacteria rather than fungi, with positive associations with Actinobacteria, Chloroflexi, and Gemmatimonadota (all P < 0.05), and negative associations with Proteobacteria and Bacteroidota (all P < 0.05), while DBP stress retarded HA formation by altering the core microbes related to HA formation and their metabolic functions. Moreover, typical hydrolase and oxidoreductase activities were altered under DBP stress, proteases and cellulases were hindered, and peroxidases as well as polyphenol oxidases were promoted during composting. Overall, our data shows that DBP stress can retard HA formation and compost maturation by interfering with microbial activity. This study provides potentially useful information for the degradation and reuse of PAE-contaminated waste.

Sewage sludge treatment methods and P-recovery possibilities: Current state-of-the-art

With the growing emphasis on environmental protection, the ways of sewage sludge treatment are changing. In this review, we analyse different methods of sewage sludge treatment in terms of potential environmental risk and raw materials recovery. The review begins with a comparison and assessment of existing reviews on this topic. Then, it focuses on the properties and current utilisation of sewage sludge in agriculture and a brief description of sludge thermal treatment methods (mono- and co-incineration, pyrolysis, and gasification). The final part of the review is devoted to technologies for treating sludge ash from mono-incinerators to recover phosphorus, a substance listed as a critical raw material by the EU. Our results show that direct use of sewage sludge likewise composts containing sewage sludge should no longer be considered as a direct source of nutrients and organic matter in agriculture, because of its pollutant content. Co-incineration and landfilling represent a dead-end in sludge treatment due to the loss of raw materials, whereas pyrolysis is sustainable for remote locations with low heavy metal content sludge. Heavy metals also pose a problem for the direct use of sludge ash and must be therefore removed. There are already sludge ash processing technologies that are capable of processing ash to form a variety of raw materials such as phosphorus. These regeneration approaches are currently in their infancy, but are gradually being introduced. The sewage sludge treatment industry is rapidly evolving, and we have attempted to summarise and discuss the current state of knowledge in this review, which will provide a baseline towards the future of sewage sludge suitable treatment.

Persistent organic pollutants in water resources: Fate, occurrence, characterization and risk analysis

Persistent organic pollutants (POPs) are organic chemicals that can persist in the environment for a longer period due to their non-biodegradability. The pervasive and bio-accumulative behavior of POPs makes them highly toxic to the environmental species including plants, animals, and humans. The present review specifies the POP along with their fate, persistence, occurrence, and risk analysis towards humans. The different biological POPs degradation methods, especially the microbial degradation using bacteria, fungi, algae, and actinomycetes, and their mechanisms were described. Moreover, the source, transport of POPs to the environmental sources, and the toxic nature of POPs were discussed in detail. Agricultural and industrial activities are distinguished as the primary source of these toxic compounds, which are delivered to air, soil, and water, affecting on the social and economic advancement of society at a worldwide scale. This review also demonstrated the microbial degradation of POPs and outlines the potential for an eco-accommodating and cost-effective approach for the biological remediation of POPs using microbes. The direction for future research in eliminating POPs from the environmental sources through various microbial processes was emphasized.

Feasibility of sewage sludge and food waste aerobic co-composting: Physicochemical properties, microbial community structures, and contradiction between microbial metabolic activity and safety risks

Co-composting of sludge and food waste eliminates the disadvantages of composting these waste products separately. Specifically, co-composing neutralizes the pollutants and improves the organic matter that occur in sewage sludge, and solves the problem of the low pH values and high moisture content of food waste. However, little is known about the functional microorganisms, microbial metabolic capacity, and biosecurity risks involved in sewage sludge and food waste co-composting. Therefore, this study established four lab-scale composting reactors [T1 (separate composting of food waste), T2 (separate composting of sewage sludge), T3 (sewage sludge and food waste co-composting at a C/N ratio of 25), and T4 (equal proportions composting of sewage sludge and food waste)] to assess the feasibility of sewage sludge and food waste aerobic co-composting. Our findings indicated that polysaccharides and proteins in T3 could be effectively degraded, and the total nutrient levels in T3 were higher than those in the other groups. After composting, the microbial diversity and richness of T3 were higher than that of T1. In later composting stages, the functional microorganisms in T1 maintained higher metabolic activity, however, it also had a higher biosecurity risk than T3 due to the presence of pathogenic bacteria such as Enterococcus_faecalis and Bacillus_circulan. Although the product of T3 could not be used as a microbial fertilizer, its biosecurity risk was lower than that of T1 and could therefore be used as an organic fertilizer. Redundancy analysis (RDA) results indicated that changing the microbial community structure by adjusting key environmental factors could improve composting quality and reduce microbial safety risks. Collectively, our results provide a theoretical basis for the development of co-composting strategies for the biodegradation of perishable solid organic waste, in addition to proposing the risk of pathogenic bacteria exposure that could endanger human and animal health.

Free radicals accelerate in situ ageing of microplastics during sludge composting

Composting is the last "barrier" for microplastics (MPs) in the entry of organic solid wastes into the environment. The transformation of MPs is thought to be mainly driven by microorganisms during composting, whereas the contribution of abiotic processes that involve free radicals is often overlooked. Herein, we provide initial evidence for the generation of free radicals during sludge composting, including environmental persistent free radicals and reactive oxygen species, which accelerate the oxidative degradation of MPs. The ·OH yield of composting fluctuated greatly from 23.03 to 277.18 μmol/kg during composting, which was closely related to the dynamic changes in Fe(II) (R² = 0.926). Analyses of the composted MPs physicochemical properties indicated that MPs were aged gradually with molecular weights decrease from 18% to 27% and carbonyl index value increase from 0.23 to 0.52. Further investigation suggested that the microbially-mediated redox transformation of iron oxides could occur on the MPs surface accompanied by the production of abundant free radicals, thereby leading to the damage of MPs during composting. These results reveal the critical role of free radicals in MPs ageing under oxic/anoxic alternation conditions of composting and provide new insights into the bio-chemical mechanism of contaminant removal or transformation during sludge composting.

Critical review on negative emerging contaminant removal efficiency of wastewater treatment systems: Concept, consistency and consequences

Emerging contaminants (ECs) are not completely removed by wastewater treatment owing to their capabilities of making complexes, toxic derivatives, byproduct formation, and dynamic partitioning. Negative contaminant removal i.e., higher concentrations (up to 5731%) of these ECs in the effluent with respect to the influent sampled on the same occasions, is globally prevalent in almost all types of treatment systems. Conventional WWTPs showed the highest negative removal (NR) for Carbamazepine, and Carbadox. Conjugation-deconjugation, types of WWTPs, transformations, leaching, operational parameters, sampling schemes, and nature of substance governs the NR efficiencies. Among the various categories of micropollutants, pesticides and beta-blockers are reported to exhibit the maximum percentage of NR, posing threat to human and the environment. With > 200% of NR for beta-blockers, low blood-pressure related symptoms may likely to get more prevalent in the near future. Study red-flags this phenomenon of negative removal that needs urgent attention.

Organic Waste Generation and Its Valorization Potential through Composting in Shashemene, Southern Ethiopia

Composting organic waste and human excreta could significantly reduce the amount of waste dumped and increase soil fertility and agricultural yields. However, studies focusing on the replacement of mineral fertilizer with compost from these resources are rare. The presented study quantifies the potential of human excreta and other organic waste for compost production. During wet and dry seasons, the generation and composition of household solid waste (HSW) was measured from three wealth categories: poor, medium, and rich, as well as the organic waste generated from 20 commercial facilities. Furthermore, the amount of human excreta, when converting unimproved into ecological sanitation facilities, was assessed. The HSW generation was significantly higher in the wet (0.77 ± 0.07 kg fresh weight (FW) cap−1 day−1) compared to the dry season (0.54 ± 0.04 kg FW cap−1 day−1). Organic waste was the main component of HSW in the dry and wet seasons, accounting for 84% and 76% of the total HSW, respectively. Annually, about 6824 Mg of organic dry matter could be collected from households, 212 Mg from commercial units, and 12,472 Mg from ecological sanitation. With these resources, 11,732 Mg of compost could be produced annually and used for fertilizing 470 ha of farmland, completely replacing mineral fertilizer.

Assessment of the occurrence of 455 pharmaceutical compounds in sludge according to their physical and chemical properties: A review

Sludge agronomical reuse is of major interest due to the beneficial contribution of nutrients. However, it implies the introduction of unregulated pharmaceuticals into amended-soils and creates a controversial issue about sludge management. To limit their dissemination, it is essential to identify the compounds of interest and understand their attenuation mechanisms through the sludge processes. This paper summarizes the knowledge on 455 investigated pharmaceuticals among 32 therapeutical categories in amendable sludge matrices. It contributes to enlarging the list of commonly quantified compounds to 305 residues including 84 additional compounds compared to previous reviews. It highlights that sorption appears as the main mechanism controlling the occurrence of pharmaceuticals in sludge matrices and shows the considerable residual levels of pharmaceuticals reaching several mg/kg in dry weight. Antibiotics, stimulants, and antidepressants show the highest concentrations up to 232 mg/kg, while diuretics, anti-anxieties or anticoagulants present the lowest concentrations reaching up to 686 µg/kg. Collected data show the increase in investigated compounds as antifungals or antihistamines, and underline emerging categories like antidiabetics, antivirals, or antiarrhythmics. The in-depth analysis of the substantial database guides onto the pharmaceuticals that are the most likely to occur in these amendable matrices to assist future research.

Plant-scale hyperthermophilic composting of sewage sludge shifts bacterial community and promotes the removal of organic pollutants

The dissipation of toxic organic pollutants during plant-scale hyperthermophilic composting and the influence of microbial community remain unclear. The results of plant-scale hyperthermophilic composting of municipal sludge with green waste showed that the residual concentrations of polyaromatic hydrocarbons, phthalates, polybrominated diphenyl ethers were <5 mg/kg and decreased over time, with the removal percentages from 12.1% to 51.2% during seven days of composting. High-throughput sequencingreveals that hyperthermophilic composting significantly reduced the diversity (e.g., observed species, chao1 and Shannon index) of bacterial community, shifting their structure and functions. The relative abundances of dominant phyla Proteobacteria and Firmicutes declined significantly, while those of extremophilic and heat-resisting phyla Deinococcus-Thermus and Chloroflexi increased dramatically. Some genera capable of degrading organic pollutants presented stably in sludge composts. Moreover, hyperthermophilic composting enriched the bacterial functions related to degradation and metabolism of cellulose and xenobiotics pollutants, which promoted the dissipation of organic pollutants and humification.

Insight into the evolution of antibiotic resistance genes and microbial community during spiramycin fermentation residue composting process after thermally activated peroxydisulfate pretreatment

Previous research has been demonstrated that the residual unextracted antibiotics in spiramycin fermentation residue (SFR) could be efficiently removed by thermally activated peroxodisulfate (TAP) pretreatment, indicating the improvement of biodegradability. This study aimed to investigate the effect of TAP pretreatment on the succession of bacterial community and fate of antibiotic resistance genes (ARGs) during SFR composting. Results indicated that TAP pretreatment increased the composting temperature and promoted the decomposition of organic matters. Furthermore, TAP pretreatment could increase bacterial alpha diversity and significantly reduce the relative abundance of ARGs (1.13-1.75 times) and mobile genetic elements (MGEs) (1.13-1.32 times) after composting. The compost of pretreated SFR by TAP could reduce the enrichment of ARGs and MGEs in the bacterial community, especially the rRNA methylase genes of ermB (4-142-folds). Redundancy analysis showed that Actinobacteria, Bacteroidetes, Proteobacteria and horizontal gene transfer mediated by MGEs (intI1) was positively related to the changes in ARGs (accounted for 97.4%). Network analysis showed that Firmicutes was the main bacterial hosts of ARGs and MGEs. These findings demonstrated that TAP pretreatment combined composting was a promising strategy for SFR safe treatment and disposal that could reduce the proliferation and transfer of ARGs.

Impact of microbial inoculants combined with humic acid on the fate of estrogens during pig manure composting under low-temperature conditions

To investigate the efficiency of psychrotrophic cellulose-degrading fungal strains (PCDFSs) and estrogen-degrading bacteria (EDBs) combined with humic acid (HA) on estrone (E1) and 17-β-estradiol (E2) degradation, five compost groups (T, HA, EDB, PCDFS, and CK) were prepared and composted for 32 days at 11-14°C. The results indicated that inoculation increased the temperature to 62.2°C and promoted E1 degradation to the lowest level of 100.1 ng/kg, while E2 was undetected from day 16. Metagenomic analysis revealed that inoculation altered the microbial community structure by increasing the abundance of cellulose-degrading fungi, especially Meyerozyma (16.7%) (among PCDFSs), and of estrogen-degrading bacteria, particularly Microbacterium (13.4%) (involved in EDBs). Moreover, inoculation increased the levels (>0.500%) of Gene Ontology (GO) associated with estrogen degradation, like 3-β-hydroxy-delta 5-steroid dehydrogenase and monooxygenase. Redundancy analysis demonstrated that temperature and Microbacterium were positively correlated with estrogen degradation. Structural equation model indicated that temperature and estrogen-degrading bacterial genera exhibited positive, significant (p < 0.001) and direct impacts on estrogen degradation. This is the first study to suggest that applying microbial inoculants and HA could accelerate estrogen degradation during composting in cold regions. The research outcomes offer a practical reference for managing compost safety, thereby decreasing its potential environmental and human health impacts.

Valorization of hydrothermal carbonization products by anaerobic digestion: Inhibitor identification, biomethanization potential and process intensification

Integrating hydrothermal carbonization (HTC) and anaerobic digestion for biorefinery-oriented full utilization of wet organic wastes is a promising emerging technology. The objectives of this study were to identify the potential inhibitory substances, evaluate the biomethane potential of mixed and aqueous products and explore process intensifying strategies. The results indicated that the high HTC temperature of 240 °C resulted in a significantly low methane yield of 60 ± 5 mL/g COD and a high Short chain fatty acid (SCFAs) accumulation of 4174 ± 76 mg/L. GC-MS analysis showed that the contents of inhibitory pyrazines, pyridines and ketones in aqueous fraction at 240 °C substantially increased from 13.14%, 0.4%, 0.55% at 180 °C to 23.34%, 2.89%, 5.13%, respectively. When the aqueous products obtained from 240 °C-HTC was supplemented or pretreated by carbonaceous material, the methane yields were greatly improved and increased to 1.3-fold and 1.8-fold, respectively. These finding could provide some valuable technical information for HTC based biorefinery of organic waste.