Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge

Impacts of conventional and biodegradable microplastics in maize-soil ecosystems: Above and below ground

The increasing accumulation of microplastics (MPs) in agroecosystems has raised significant environmental and public health concerns, facilitating the application of biodegradable plastics. However, the comparative effects of conventional and biodegradable MPs in agroecosystem are still far from fully understood. Here we developed microcosm experiments to reveal the ecological effects of conventional (polyethylene [PE] and polypropylene [PP]) and biodegradable (polyadipate/butylene terephthalate [PBAT] and polycaprolactone [PCL]) MPs (0, 1%, 5%; w/w) in the maize-soil ecosystem. We found that PCL MPs reduced plant production by 73.6-75.2%, while PE, PP and PBAT MPs elicited almost negligible change. The addition of PCL MPs decreased specific enzyme activities critical for soil nutrients cycling by 71.5-95.3%. Biodegradable MPs tended to reduce bacterial α-diversity. The 1% treatments of PE and PBAT, and PCL enhanced bacterial networks complexity, whereas 5% of PE and PBAT, and PP had adverse effect. Moreover, biodegradable MPs appeared to reduce the α-diversity and networks complexity of fungal community. Overall, PCL reduced the ecosystem multifunctionality, mainly by inhibiting the microbial metabolic activity. This study offers evidence that biodegradable MPs can impair agroecosystem multifunctionality, and highlights the potential risks to replace the conventional plastics by biodegradable ones in agricultural practices.

Straw degradation enhanced in Thermomyces lanuginosus by transferring AgCMCase from Aspergillus glaucus

Fungi play a crucial role in straw composting due to the synergistic degradation effects of their secreted lignocellulose hydrolases. An efficient straw-composting system relies on thermophilic fungi and their lignocellulose hydrolases. Thermomyces lanuginosus, a typical thermophilic fungus in compost, lacks cellulase genes. A versatile Thermomyces strain capable of degrading cellulose, T. lanuginosus M85, which grows at 67 °C, was developed and transformed using the AgCMCase of Aspergillus glaucus. The R6 transformant exhibited high-level expression of the AgCMCase. Significant quantities of active cellulase produced by R6 were detected in the cellulose fermentation broth, peaking within 6-8 days. Compost analysis indicated that R6 increased the internal compost temperatures and prolonged high-temperature durations. Correspondingly, more reducing sugars and humus were released, which could promote plants growth. In summary, a cellulase-producing strain of T. lanuginosus capable of efficiently converting straws into organic fertilizers was engineered. This innovation holds considerable promise for sustainable and circular agricultural practices.

Inoculation of Saccharomyces cerevisiae for facilitating aerobic composting of acidified food waste

In aerobic composting of food waste, acidification of the material (acidified food waste, AFW) often occurs and consequently leads to failure of fermentation initiation. In this study, we solved this problem by adding Saccharomyces cerevisiae inoculants. The results showed that the inoculation with S. cerevisiae effectively promoted the composting process. In 2 kg composting, inoculation with S. cerevisiae significantly elevated the pile temperatures by 4 ~ 14 °C, accompanied by a rapid increase in pH from 4.5 to 6.0. In 15 kg composting, total acid decreased faster and the thermophilic stage above 50 °C was prolonged by 3 days longer than in the control. The residual oxygen content in the reactor indicated that S. cerevisiae, which proliferated during composting, increased microbial activity and reduced ammonia emission during the thermophilic phase. Cell density analysis showed that compost inoculated with S. cerevisiae promoted thermophilic bacterial propagation. Metagenomic analysis showed that the dominant bacteria in the AFW compost were Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria, and the relative abundance of Bacillus, Thermobacillus, and Thermobifida increased when inoculated with S. cerevisiae. These results indicate that the inoculation of S. cerevisiae is an effective strategy to improve the aerobic composting process of AFW by accelerating the initial phase and altering microbial community structure in the thermophilic phase. Our findings suggest that S. cerevisiae can be applied to aerobic composting of organic wastes to effectively address the problem of acidification.

Integrated nutrient recycling: Ammonia recovery from thermophilic composting of shrimp aquaculture sludge via self-heated bench-scale reactor and mango plant growth enhancement by the compost

Due to the rapid growth of the aquaculture industry, large amounts of organic waste are released into nature and polluted the environment. Traditional organic waste treatment such as composting is a time-consuming process that retains the ammonia (NH3) in the compost, and the compost produced has little economic value as organic fertilizer. Illegal direct discharge into the environment is therefore widespread. This study investigates the recovery of NH3 through thermophilic composting of shrimp aquaculture sludge (SAS) and its application as a soil conditioner for the growth of mango plants. A maximum composting temperature of 57.10 °C was achieved through self-heating in a 200 L bench-scale reactor, resulting in NH3 recovery of 224.04 mol/ton-ds after 14 days. The addition of calcium hydroxide and increased aeration have been shown to increase NH3 volatilization. The recovered NH3 up to 3 kg-N can be used as a source of clean nitrogen for high-value microalgae cultivation, with a theoretical yield of up to 34.85 kg-algae of microalgae biomass from 1 ton-ds of SAS composting. Despite the high salinity, SAS compost improved mango plant growth and disease resistance. These results highlight the potential of SAS compost as a sustainable source of clean nitrogen for microalgae cultivation and soil conditioner, contributing to a waste-free circular economy through nutrient recycling and sustainable agriculture.

Phage lysate can regulate the humification process of composting

Phages play a crucial role in orchestrating top-down control within microbial communities, influencing the dynamics of the composting process. Despite this, the impact of phage-induced thermophilic bacterial lysis on humification remains ambiguous. This study investigates the effects of phage lysate, derived explicitly from Geobacillus subterraneus, on simulated composting, employing ultrahigh-resolution mass spectrometry and 16S rRNA sequencing techniques. The results show the significant role of phage lysate in expediting humus formation over 40 days. Notably, the rapid transformation of protein-like precursors released from phage-induced lysis of the host bacterium resulted in a 14.8 % increase in the proportion of lignins/CRAM-like molecules. Furthermore, the phage lysate orchestrated a succession in bacterial communities, leading to the enrichment of core microbes, exemplified by the prevalence of Geobacillus. Through network analysis, it was revealed that these enriched microbes exhibit a capacity to convert protein and lignin into essential building blocks such as amino acids and phenols. Subsequently, these components were polymerized into humus, aligning with the phenol-protein theory. These findings enhance our understanding of the intricate microbial interactions during composting and provide a scientific foundation for developing engineering-ready composting humification regulation technologies.

Persistence and potential risks of tetracyclines and their transformation products in two typical different animal manure composting treatments

Abundant residues of tetracyclines in animal manures and manure-derived organic fertilizers can pose a substantial risk to environments. However, our knowledge on the residual levels and potential risk of tetracyclines and their transformation products (TPs) in manure and manure-derived organic fertilizers produced by different composting treatments is still limited. Herein, the occurrence and distribution of four veterinary tetracyclines (tetracycline, oxytetracycline, chlortetracycline, and doxycycline) and ten of their TPs were investigated in paired samples of fresh manure and manure-derived organic fertilizers. Tetracyclines and TPs were frequently detected in manure and manure-derived organic fertilizer samples in ranging from 130 to 118,137 μg·kg-1 and 54.6 to 104,891 μg·kg-1, respectively. Notably, the TPs concentrations of tetracycline and chlortetracycline were comparable to those of the parent compounds, with 4-epimers being always dominant and retained antibacterial potency. Based on paired-sampling strategy, the removal efficiency of tetracyclines and TPs in thermophilic composting was higher than that in manure storage. Toxicological data in the soil environment and the data derived from equilibrium partitioning method, indicated that tetracyclines and some TPs like 4-epitetracycline, 4-epichlortetracycline and isochlortetracycline could pose median to high ecological risk to terrestrial organisms. Total concentrations of TPs in manure-derived organic fertilizers were significantly correlated with the absolute abundance of tet(X) family genes, which provide evidence to evaluate the effects of TPs on the levels of antibiotic resistance in the environment. Among them, the 4-epitetracycline could pose ecological risk and retain antibacterial potency. Our findings emphasize the importance of monitoring and controlling the prevalence of tetracyclines and their TPs in livestock-related environments.

Purification mechanism of microbial metabolism in kitchen-oil wastewater enhanced by cationic vacancies on γ-Al2O3

The use of catalyst materials to mediate the enhancement of microbial degradation in wastewater is a new economic and energy saving breakthrough in water treatment technology. In this study, γ-Al2O3, which is commonly used as catalyst/carrier, is used as biological filler to treat kitchen-oil wastewater with low biodegradability, and the COD removal rate is about 50 %. It is found that the complexation of cationic vacancies on Al2O3 surface with extracellular polymeric substance (EPS) secreted by microorganisms in wastewater lead to the polarization of electron distribution on biofilm. The efficient degrading bacteria are enriched on reaction interface and obtain electrons to maintain electron dynamic balance by enhancing the transmembrane metabolism of pollutants. The aluminum vacancies on Al2O3 surface accelerate the microbial degradation of pollutants. The cationic vacancies in the structure of catalyst accelerate the acquisition of exogenous electrons by microorganisms without the addition of external energy, which provides a new idea for catalytic fillers to enhance wastewater degradation.

Efficient nitrogen removal and robustness enhancement of a two-stage partial nitrification-anammox (PN/A) process with low sludge concentration for mature landfill leachate

The biological treatment system for high-strength wastewater, particularly landfill leachate, typically requires high sludge concentration to maintain nitrogen removal performance. However, it frequently causes an excessive accumulation of toxins in microbial metabolism, resulting in unstable performance during long-term operation. An efficient two-stage partial nitrification/anammox (PN/A) mature landfill leachate process with low sludge concentration was constructed by settling time reduction and Ca2+ addition. The ammonia removal rate reached 46.7 mg N/(L·h) in PN-SBR. Nitrosomonas (2.0%) was the sole genus responsible for partial nitrification. The influent NO2--N/NH4+-N of A-SBR was kept at 1.39, leading to a dynamic equilibrium of anammox and denitrification. Ca. Brocadia recovered fastest (0.32% → 1.8%) among the detected AnAOB genera. The process achieved NRE of 95.0% with effluent TIN of 37.6 mg/L (<40 mg/L). This research offered recommendations for the favorable operation of the two-stage PN/A mature landfill leachate treatment system with low sludge concentration.

The effect of calcium hydroxide addition on enhancing ammonia recovery during thermophilic composting in a self-heated pilot-scale reactor

A modified outdoor large-scale nutrient recycling system was developed to compost organic sludge and aimed to recover clean nitrogen for the cultivation of high-value-added microalgae. This study investigated the effect of calcium hydroxide addition on enhancing NH₃ recovery in a pilot-scale reactor self-heated by metabolic heat of microorganisms during thermophilic composting of dewatered cow dung. 350 kg-ww of compost was prepared at the ratio of 5: 14: 1 (dewatered cowdung: rice husk: compost-seed) in a 4 m³ cylindrical rotary drum composting reactor for 14 days of aerated composting. High compost temperature up to 67 °C was observed from day 1 of composting, proving that thermophilic composting was achieved through the self-heating process. The temperature of compost increases as microbial activity increases and temperature decreases as organic matter decreases. The high CO₂ evolution rate on day 0-2 (0.02-0.08 mol/min) indicated that microorganisms are most active in degrading organic matter. The increasing conversion of carbon demonstrated that organic carbon was degraded by microbial activity and emitted as CO₂. The nitrogen mass balance revealed that adding calcium hydroxide to the compost and increasing the aeration rate on day 3 volatilized 9.83 % of the remaining ammonium ions in the compost, thereby improving the ammonia recovery. Moreover, Geobacillus was found to be the most dominant bacteria under elevated temperature that functions in the hydrolysis of non-dissolved nitrogen for better NH₃ recovery. The presented results show that by thermophilic composting 1 ton-ds of dewatered cowdung for NH₃ recovery, up to 11.54 kg-ds of microalgae can be produced.

Enhanced degradation of microplastics during sludge composting via microbially-driven Fenton reaction

It has been increasingly documented that the hydroxyl radical (•OH) can promote the transformation of organic contaminants such as microplastics (MPs) in various environments. However, few studies have sought to identify an ideal strategy for accelerating in situ MPs degradation through boosting the process of •OH production in practical applications. In this work, iron-mineral-supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing in situ degradation of sludge-based MPs through strengthening •OH generation. The results show that the reduction efficiency of sludge-based MPs abundance was about 35.93% in imTC after treatment for 36 days, which was 38.99% higher than that of ordinary thermophilic composting (oTC). Further investigation on polyethylene-microplastics (PE-MPs) suggested that higher abundance of •OH (the maximum value was 408.1 μmol·kg^-1) could be detected on the MPs isolated from imTC through microbially-mediated redox transformation of iron oxides, as compared to oTC. Analyses of the physicochemical properties of the composted PE-MPs indicated that increased •OH generation could largely accelerate the oxidative degradation of MPs. This work, for the first time, proposes a feasible strategy to enhance the reduction efficiency of MPs abundance during composting through the regulation of •OH production.

Insights into solid phase denitrification in wastewater tertiary treatment: the role of solid carbon source in carbon biodegradation and heterotrophic denitrification

The practical application of solid phase denitrification (SPD) was hindered by either poor water quality from natural plant-like materials or high cost of pure synthetic biodegradable polymers. In this study, by combining polycaprolactone (PCL) with new natural materials (peanut shell, sugarcane bagasse), two novel economical solid carbon sources (SCSs) named as PCL/PS and PCL/SB were developed. Pure PCL and PCL/TPS (PCL with thermal plastic starch) were supplied as controls. During the 162-day operation, especially in the shortest HRT (2 h), higher NO₃^--N removal was achieved by PCL/PS (87.60%±0.06%) and PCL/SB (87.93%±0.05%) compared to PCL (83.28%±0.07%) and PCL/TPS (81.83%±0.05%). The predicted abundance of functional enzymes revealed the potential metabolism pathways of major components of SCSs. The natural components entered the glycolytic cycle by enzymatical generation of intermediates, while biopolymers being converted into small molecule products under specific enzyme activities (i.e., carboxylesterase, aldehyde dehydrogenase), together providing electrons and energy for denitrification.

Evaluation of sludge anaerobic fermentation driving partial denitrification capability: In view of kinetics and metagenomic mechanisms

Partial denitrification (PD) provides a promising approach of efficient and stable nitrite (NO₂^--N) generation for annamox. In this study, the feasibility of short-term sludge anaerobic fermentation driving PD was evaluated. It was found that a higher NO₂^--N accumulation in nitrate (NO₃^--N) reduction was obtained with the 5-days fermented sludge compared to 8 and 15-days fermentation. Moreover, compared to acetate as carbon source, sludge fermentation products (SFPs) induced the higher NO₂^--N production with nitrate-to-nitrite transformation ratio (NTR) nearly 100 %. Denitrification activity of fermented sludge were obviously improved with SFPs as electron donor. Metagenomic analysis revealed that Thauera was the dominant bacteria, which was assumed to be the key contributor to PD performance by harboring the highest narGHI and napAB but much lower nirS and nirK. Under the conditions of SFPs and fermented sludge, Thauera was speculated to have higher resistance than other denitrifiers attributed to versatile carbon metabolic capabilities utilizing SFPs with the significantly improved genes for metabolism of complex organic carbon via glycolysis after anaerobic fermentation. A novel integration of sludge fermentation driving PD and anammox for mainstream wastewater treatment and sidestream polishing was proposed to offer a promising application with reduced commercial carbon source consumption and waste sludge reduction.

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.

Identification of microbial consortia for sustainable disposal of constructed wetland reed litter wastes

Reed is a typical emerged plant in constructed wetlands (CWs). Its litters were used as raw materials for preparing Fe-C ceramic-filler (Fe-C-CF). The physical and chemical properties of Fe-C-CF were studied under different conditions, including the mass ration of Fe to carbon (Fe/C ratio), sintering temperature, and time, to determine the optimum preparing conditions. Meanwhile, the denitrification performance and CO₂ emission flux of the surface flow constructed wetland (SFCW) systems were investigated when using Fe-C-CF as the matrix. The optimum preparing conditions for Fe-C-CF were Fe/C ratio of 1:1, sintering temperature and time of 500 °C and 20 min, respectively. The SFCW system with Fe-C-CF obtained a higher total nitrogen (TN), nitrate nitrogen (NO₃^--N), and ammonia nitrogen (NH₃-N) removal efficiencies than the control SFCW system without Fe-C-CF. Compared with the heterotrophic denitrification process, the SFCW system with Fe-C-CF decreased CO₂ emission by 67.9 g m^-2 per year. The results of microbial community analysis indicated that addition of Fe-C-CF increased the diversity and abundance of microbial communities in the SFCW systems. The dominant genus of the SFCW system with Fe-C-CF was Bacillus, while Uliginosibacterium was the dominant genus in the system without the filler.

Denitrification efficiency, microbial communities and metabolic mechanisms of corn cob hydrolysate as denitrifying carbon source

In this study, the denitrification efficacy of corn cob hydrolysate (CCH) was compared and analyzed with that of glucose and acetate to determine its feasibility as an additional carbon source, and its metabolic mechanism as a denitrification carbon source was investigated in depth. By constructing a denitrification reactor, it was found that the TN removal rate exceeded 97% and the effluent COD remained below 70 mg/L during the stable operation with CCH as the carbon source, and the denitrification effect was comparable to that of the glucose stage (GS) and the acetate stage (AS). The analysis of the microbial community showed that the dominant phylum was Proteobacteria and Bacteroidota, where the abundance of Bacteroidota in the hydrolysate stage (HS) (24.37%) was significantly higher than that of GS (4.89%) and AS (11.93%). And the analysis at the genus level showed the presence of a large number of genera of organic matter hydrolysis and acid production in HS that were almost absent in other stages, such as Paludibacter (12.83%), Gracilibacteria (4.27%), f__Prolixibacteraceae_Unclassified (2.94%). In addition, the higher fatty acid metabolism and lower sugar metabolism of HS during carbon metabolism were similar to the ratio of AS, suggesting that CCH was mainly fermented to acids and then involved in the tricarboxylic acid (TCA) cycle. During nitrogen metabolism, the high relative abundance of narG, nirS, and nosZ ensured the denitrification process. The results of this study were expected to provide a theoretical basis and data support for promoting denitrification from novel carbon sources.

Improved Denitrification Performance of Polybutylene Succinate/Corncob Composite Carbon Source by Proper Pretreatment: Performance, Functional Genes and Microbial Community Structure

Blending biodegradable polymers with plant materials is an effective method to improve the biodegradability of solid carbon sources and save denitrification costs, but the recalcitrant lignin in plant materials hinders the microbial decomposition of available carbon sources. In the present study, corncob pretreated by different methods was used to prepare polybutylene succinate/corncob (PBS/corncob) composites for biological denitrification. The PBS/corncob composite with alkaline pretreatment achieved the optimal NO₃^--N removal rate (0.13 kg NO₃^--N m^-3 day^-1) with less adverse effects. The pretreatment degree, temperature, and their interaction distinctly impacted the nitrogen removal performance and dissolved organic carbon (DOC) release, while the N₂O emission was mainly affected by the temperature and the interaction of temperature and pretreatment degree. Microbial community analysis showed that the bacterial community was responsible for both denitrification and lignocellulose degradation, while the fungal community was primarily in charge of lignocellulose degradation. The outcomes of this study provide an effective strategy for improving the denitrification performance of composite carbon sources.

Effect of Turning Frequency on the Survival of Fecal Indicator Microorganisms during Aerobic Composting of Fecal Sludge with Sawdust

The study investigated the effect of turning frequency on survival of fecal indicator pathogens (E. coli, Enterococcus spp., Salmonella spp. and helminth eggs) during fecal sludge (FS) co-composting with sawdust. Dewatered FS was mixed with sawdust and composted on a pilot scale using different turning frequencies-i.e., 3 days (3TF), 7 days (7TF), and 14 days (14TF). Composting piles were monitored weekly for survival of fecal indicator microorganisms and evolution of selected physical and chemical characteristics for 14 weeks. Our results show that turning frequency has a statistically significant (p < 0.05) effect on pathogen inactivation in FS compost. The 3TF piles exhibited shorter pathogen inactivation periods (8 weeks) than 7TF and 14TF piles (10 weeks). Temperature-time was found to be the major factor responsible for the survival of pathogens in FS composting piles, followed by indigenous microbial activities and toxic by-products (monitored as NH4+-N). Our study findings suggest that even at low composting temperatures, the high turning frequency can enhance pathogen inactivation. This is a significant finding for composting activities in some rural areas where suitable organic solid waste for co-composting with FS to attain the recommended high thermophilic conditions could be greatly lacking.

Estimation of sulfur fate and contribution to VSC emissions from lakes during algae decay

Algae decay is an important process influencing environmental variables and emissions of volatile sulfur compounds (VSCs) in eutrophic lakes. However, effects of algae decay on VSC emissions from eutrophic lakes as well as fate of algae-derived sulfur remain poorly understood. In this study, simulated algae-sediment systems were used to explore the flow and distribution of sulfur during algae decay. VSCs including hydrogen sulfide (H₂S), methanethiol (CH₃SH), carbon disulfide (CS₂) and dimethyl sulfide ((CH₃)₂S) were detected during algae decay, which increased with algae biomass and eutrophic levels in lakes. During algae decay, the highest H₂S, CH₃SH and (CH₃)₂S emission rates of 10.45, 21.82 and 43.26 μg d^-1 occurred in the first 1-2 days, respectively, while the highest CS₂ emission rates were observed between days 8 and 11. The maximum emissions of H₂S and CS₂ from algae decay were estimated at 0.51 and 0.35 mg m^-2 d^-1 in Lake Taihu, accounting for 1.57% and 0.69% of the total H₂S and CS₂ emissions of in situ, respectively. Algae decay could significantly increase the contents of total sulfur and total carbon in sediments by 2.90%-21.11% and 4.23%-45.05%, respectively. The VSC emissions during algae decay could be predicted using the multiple regression models with the contents of total carbon, total nitrogen and sulfur-containing compounds in sediments. Partial least squares path modelling demonstrated that algae decay had a low direct effect on VSC emissions with a strength of 0.06, while it had a significant influence on environmental variables with a strength of 0.63, which could affect VSC emissions with a strength of 0.85, indicating VSC emissions from eutrophic lakes were affected by the environmental variables rather than the direct influence of algae decay. These findings illustrated the mechanisms of VSC emissions during algae decay and provided insights into VSC control and mitigation for eutrophic lakes.

Degradation of poly(butylene adipate-co-terephthalate) films by Thermobifida fusca FXJ-1 isolated from compost

In recent years, Poly(butylene adipate-co-terephthalate) (PBAT) films were wildly used due to its biodegradable properties. However, there are few reports of strains that can high efficiently degrade PBAT. Thermobifida fusca FXJ-1, a thermophilic actinomycete, was screened and identified from compost. FXJ-1 can efficiently degrade PBAT at 55 °C in MSM medium. The degradation rates of the pure PBAT film (PF), PBAT film used for mulching on agricultural fields (PAF), and PBAT-PLA-ST film (PPSF) were 82.87 ± 1.01%, 87.83 ± 2.00% and 52.53 ± 0.54%, respectively, after nine days of incubation in MSM medium. Cracking areas were monitored uniformly distributed on the surfaces of three kinds of PBAT-based films after treatment with FXJ-1 using scanning electron microscopy. The LC-MS results showed that PBAT might be degraded into adipic acid, terephthalic acid, butylene adipate, butylene terephthalate and butylene adipate-co-terephthalate, and these products are involved in the cleavage of ester bonds. We also found that amylase produced by FXJ-1 played an important role in the degradation of PPSF. FXJ-1 also showed an efficient PBAT-based films degradation ability in simulating compost environment, which implied its potential application in PBAT and starch-based film degradation by industrial composting.

The importance of rest phase and pollutant removal mechanism of tidal flow constructed wetlands (TFCW) in rural grey water treatment

This paper explored the effects of the rest phase of tidal flow constructed wetlands (TFCW) on pollutant removal and microbial communities, and further analyzed the mechanism of TFCW removal of pollutants from grey water. The results showed that the removal rate of organic matter was 69.91 ± 2.44% in the control group (NR-TFCW) without the rest phase, 94.95 ± 1.17% in the experimental group (TFCW), and 96.95 ± 2.43% in the control group (P-TFCW) with the ventilation pipe enhanced rest phase. Limiting and enhancing the oxygen supply in the emptying stage of TFCW will enhance the overlap rate of microorganisms in the upper, middle and lower layers of the reactor. Enhancing the rest phase of TFCW leaded to better aerobic removal of organic matter in the microbial community, while limiting the rest phase of TFCW results in the opposite. In addition, the species overlap rate of the top, middle and bottom layers of NR-TFCW (69.98%) and P-TFCW (54.29%) was higher than that of TFCW (11.34%). The removal of organic matter by TFCW mainly relied on the adsorption of biochar in the flood phase, and the microorganisms aerobic degraded the organic matter adsorbed on the biochar in the rest phase. And thus form a continuous cycle of adsorption and biological regeneration. The microbial community in TFCW did not have the ability to nitrify, but had the ability to remove phosphorus. Ammonia nitrogen in the influent was adsorbed by biochar or converted into cytoplasm. While the phosphorus in the influent was adsorbed by the biochar, it was also being biologically removed.

Large Semi-Membrane Covered Composting System Improves the Spatial Homogeneity and Efficiency of Fermentation

Homogenous spatial distribution of fermentation characteristics, local anaerobic conditions, and large amounts of greenhouse gas (GHGs) emissions are common problems in large-scale aerobic composting systems. The aim of this study was to examine the effects of a semi-membrane covering on the spatial homogeneity and efficiency of fermentation in aerobic composting systems. In the covered group, the pile was covered with a semi-membrane, while in the non-covered group (control group), the pile was uncovered. The covered group entered the high-temperature period earlier and the spatial gradient difference in the group was smaller compared with the non-covered group. The moisture content loss ratio (5.91%) in the covered group was slower than that in the non-covered group (10.78%), and the covered group had a more homogeneous spatial distribution of water. The degradation rate of organic matter in the non-covered group (11.39%) was faster than that in the covered group (10.21%). The final germination index in the covered group (85.82%) was higher than that of the non-covered group (82.79%) and the spatial gradient difference in the covered group was smaller. Compared with the non-covered group, the oxygen consumption rate in the covered group was higher. The GHG emissions (by 30.36%) and power consumption in the covered group were reduced more significantly. The spatial microbial diversity of the non-covered group was greater compared with the covered group. This work shows that aerobic compost covered with a semi-membrane can improve the space homogeneity and efficiency of fermentation.

Effects of oxygen supply rate on organic matter decomposition and microbial communities during composting in a controlled lab-scale composting system

The study aimed to elucidate the effect of oxygen supply rate (OSR) on the composting of model organic waste independently from other factors by using a controlled laboratory-scale reactor system. Four OSRs, 96.2, 24.2, 13.7, and 3.45 mL-O₂/min/kg-WS (wet solid), were tested. The delay of organic matter degradation was observed temporarily in the early stage of composting with 13.7 mL-O₂/min/kg-WS and severe oxygen deficiency was observed in lower OSR, indicating that the critical OSR existed around this value. Composting with 3.45 mL-O₂/min/kg-WS resulted in constantly low CO₂ evolution rate and remarkably low degree of organic matter degradation. Under deficient oxygen, all enzymes measured, such as phosphatases, esterases, lipases, proteases, and sugar degrading enzymes, showed lower activities. High-throughput sequencing revealed Caldibacillus and Ureibacillus became dominant in the later stages of the oxygen deficiency composting, while Geobacillus was the most dominant microorganism throughout composting with OSR higher than 13.7 mL-O₂/min/kg-WS.

Ex-situ biogas upgrading in thermophilic trickle bed reactors packed with micro-porous packing materials

Two thermophilic trickle bed reactors (TBRs) were packed with different packing densities with polyurethane foam (PUF) and their performance under different retention times were evaluated during ex-situ biogas upgrading process. The results showed that the TBR more tightly packed i.e. containing more layers of PUF achieved higher H₂ utilization efficiency (>99%) and thus, higher methane content (>95%) in the output gas. The tightly packed micro-porous PUF enhanced biofilm immobilization, gas-liquid mass transfer and biomethanation efficiency. Moreover, applying a continuous high-rate nutrient trickling could lead to liquid overflow resulting in formation of non-homogenous biofilm and severe deduction of biomethanation efficiency. High-throughput 16S rRNA gene sequencing revealed that the liquid media were predominated by hydrogenotrophic methanogens. Moreover, members of Peptococcaceae family and uncultured members of Clostridia class were identified as the most abundant species in the biofilm. The proliferation of hydrogenotrophic methanogens together with syntrophic bacteria showed that H₂ addition resulted in altering the microbial community in biogas upgrading process.

Bacterial Community Structure and Predicted Metabolic Function of Landfilled Municipal Solid Waste in China

The biodegradation behavior of municipal solid waste (MSW) depends on the diversity and metabolic function of bacterial communities, which are affected by environmental factors. However, the diversity of the bacterial communities and metabolic functions in MSW, as well as their influencing factors, remain unclear. In deep-aged MSW, the abovementioned deficiencies are more significant, and will effectively hamper landfill disposal. In this study, high-throughput sequencing was performed to examine the bacterial community structure and metabolic function from depths of 10 m to 40 m, of two large MSW landfills on the southeast coast of China. Thermotogota (1.6–32.0%), Firmicutes (44.2–77.1%), and Bacteroidota (4.0–34.3%) were the three dominant phyla among the 39 bacterial phyla identified in aged MSW samples. Bacterial genera associated with the degradation of many macromolecules, e.g., Defluviitoga, Hydrogenispora, and Lentimicrobium were abundantly detected in MSW samples, even in aged MSW. Redundancy analysis (RDA) showed that bacterial diversity in the landfills was most strongly correlated with electrical conductivity, age, and moisture content of the MSW. Tax4fun2 analysis predicted that there were abundant metabolism functions in aged MSW, especially functional enzymes (e.g., glycine dehydrogenase and cellulase) related to amino acids and cellulose degradation. This study increases our understanding of the bacterial diversity and functional characteristics in landfilled MSW.

Effect of enzymatic pre-treatment on thermophilic composting of shrimp pond sludge to improve ammonia recovery

In recent years, attempts have been made to develop a thermophilic composting process for organic sludge to produce ammonia gas for high value-added algal production. However, the hydrolysis of non-dissolved organic nitrogen in sludge is a bottleneck for ammonia conversion. The aim of this study was to identify enzymes that enhance sludge hydrolysis in a thermophilic composting system for ammonia recovery from shrimp pond sludge. This was achieved by screening useful enzymes to degrade non-dissolved nitrogen and subsequently investigating their effectiveness in lab-scale composting systems. Among the four hydrolytic enzyme classes assessed (lysozyme, protease, phospholipase, and collagenase), proteases from Streptomyces griseus were the most effective at hydrolysing non-dissolved nitrogen in the sludge. After composting sludge pre-treated with proteases, the final amount of non-dissolved nitrogen was 46.2% of the total N in the control sample and 22.3% of the total N in the protease sample, thus increasing the ammonia (gaseous and in-compost) conversion efficiency from 41.5% to 56.4% of the total N. The decrease in non-dissolved nitrogen was greater in the protease sample than in the control sample during the pre-treatment period, and no difference was observed during the subsequent composting period. These results suggest that Streptomyces proteases hydrolyse the organic nitrogen fraction, which cannot be degraded by the bacterial community in the compost. Functional potential analysis of the bacterial community using PICRUSt2 suggested that 4 (EC:3.4.21.80, EC:3.4.21.81, EC:3.4.21.82, and EC:3.4.24.77) out of 13 endopeptidase genes in S. griseus were largely absent in the compost bacterial community and that they play a key role in the hydrolysis of non-dissolved nitrogen. This is the first study to identify the enzymes that enhance the hydrolysis of shrimp pond sludge and to show that the thermophilic bacterial community involved in composting has a low ability to secrete these enzymes.

Microbial explanation to performance stratification along up-flow solid-phase denitrification column packed with polycaprolactone

In this study, the fluctuating profiles of physicochemical and microbial characterizations along different filling heights of continuously up-flow solid-phase denitrification (SPD) columns packed with polycaprolactone (PCL) were investigated. It was found both the PCL filling area and non-filling area made significant contributions to treatment performance and denitrification mainly occurred near the bottom of the filling column. Nitrate displayed a high proportional removal (≥98.7%) among all the cases except the one with the lowest filling ratio (FR30) and highest NLR (3.99 ± 0.12 gN/(L·d)), while nitrite and ammonium displayed a weak accumulation in final effluents (nitrite ≤ 0.40 mg/L; ammonium ≤ 0.98 mg/L). The intensity of PCL hydrolysis in the top substrate was stronger than those in the middle or bottom. Both dissimilatory nitrate reduction to ammonium (DNRA) and microbial lysis contributed to ammonium accumulation, and nitrate was mainly removed via traditional denitrification and DNRA. JGI_0000069-P22_unclassified and Gracilibacteria_unclassified might contribute to denitrification.

Production of n-caproate using food waste through thermophilic fermentation without addition of external electron donors

The effectiveness of producing n-caproate from food waste without external electron donors (EDs) was investigated through batch and semi-continuous fermentation. The maximum concentration of n-caproate reached 10,226.28 mg COD/L during semi-continuous fermentation. The specificity for n-caproate was the highest at 40.19 ± 3.95%, and the soluble COD conversion rate of n-caproate reached up to 22.50 ± 1.09% at the end of batch fermentation. The production of n-caproate was coupled with the generation of lactate as an ED to facilitate chain elongation reactions. When lactate was used as the only substrate, n-butyrate (64.12 ± 20.11%) markedly dominated the products, instead of n-caproate (0.63 ± 0.07%). Microbial community analysis revealed that Caproiciproducens, Rummeliibacillus, and Clostridium_sensu_stricto_12 were the key genera related to n-caproate production. In addition to n-caproate, n-butyrate dominated the products in batch and semi-continuous fermentation with a maximum specificity of 47.59 ± 3.39%. Clostridium_sensu_stricto_7 was committed to producing n-butyrate from lactate.

Pilot-scale microaerobic hydrolysis-acidification and anoxic-oxic processes for the treatment of petrochemical wastewater

Microaerobic hydrolysis and acidification (MHA), as a promising pre-treatment method of industrial wastewater, is drawing increasing attention to enhance the hydrolysis-acidification rate and inhibit the production of toxic gas H₂S. In the present work, a pilot-scale MHA reactor coupled with anoxic-oxic (A/O) processes for treating the petrochemical wastewater was established and the mechanism and application of the MHA reaction were explored. The results showed that the ratio of VFA/COD was increased by 43-90% and low effluent S^2- concentration (less than 0.2 mg/L) was obtained after MHA treatment with 5.5-13.8 L air m^-3 h^-1 supply. The MHA sludge exhibited a good settleability, a higher protease activity and plentiful community diversity. In addition to the dominant anaerobic bacteria responsible for hydrolysis and acidification such as Clostridiales uncultured, Anaerovorax, Anaerolineaceae uncultured and Fastidiosipila, the sulfate reducing bacteria involving Desulfobacter, Desulfomicrobium and Desulfobulbus, the sulphur oxidizing bacteria involving Thiobacillus, Arcobacter and Limnobacter, the nitrifies such as Nitrosomonadaceae uncultured and Nitrospira, and denitrifies Thauera were also identified. MHA pre-treatment guaranteed the efficacy and stability of the following A/O treatment. The removal efficiency of COD and ammonium of the MHA-A/O system remained at around 78.3% and 80.8%, respectively, although the organic load fluctuated greatly in the influent.

Influence mechanism of filling ratio on solid-phase denitrification with polycaprolactone as biofilm carrier

In this study, three up-flow fixed-bed bioreactors were constructed with three different filling ratios (filling volume/effective volume: 30%, 60% and 90%) of polycaprolactone (PCL). Above 98% of nitrate removal efficiency was achieved with low accumulations of nitrite and ammonium for each filling ratio. Low filling ratio of PCL had extensive folds and pores that favored the attachment and growth of microorganisms; however, excessive biomass restrained nitrate specific reduction rate (NaSRR). The most dominant genera were Comamonas (0.80-57.64%), Stenotrophomonas (2.59-54.39%), Acidovorax (7.32-23.55%), Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium (0.30-19.74%) and Thermomonas (0.12-14.58%). Nitrate reductase (EC 1.7.99.4), nitrite reductase (EC 1.7.2.1) and nitric oxide reductase (EC 1.7.2.5) predicted by PICRUSt2 were abundant in high influent nitrate load (NaL). According to the analysis of carbon balance model, the utilization rate (η) of PCL showed a highly positive correlation with influent NaL, indicating reducing filling ratio or HRT might be an effective measure to save cost for nitrate removal.

Compositional and functional succession of bacterial and fungal communities is associated with changes in abiotic properties during pig manure composting

While both bacteria and fungi are important for the degradation and humification of organic matter during composting, it is unclear to what extent their roles are associated with abiotic compost properties. This study evaluated changes in abiotic compost properties and the succession of bacterial and fungal communities during pig manure composting for 90 days. The compost rapidly reached thermophilic phase (>58 ℃), which lasted for 15 days. Both bacterial and fungal community compositions changed drastically during composting and while bacterial diversity increased, the fungal diversity decreased during the thermophilic phase of composting. Two taxa dominated both bacterial (Bacillales and Clostridiales) and fungal (Eurotiales and Glomerellales) communities and these showed alternating abundance fluctuations following different phases of composting. The abundance fluctuations of most dominant bacterial and fungal taxa could be further associated with decreases in the concentrations of fulvic acid, cellulose, hemicellulose and overall biodegradation potential in the compost. Moreover, bacterial predicted metabolic gene abundances dominated the first three phases of composting, while predicted fungal saprotrophic functional genes increased consistently, reaching highest abundances towards the end of composting. Finally, redundancy analysis (RDA) showed that changes in abiotic compost properties correlated with the bacterial community diversity and carbohydrate metabolism and fungal wood saprotrophic function. Together these results suggests that bacterial and fungal community succession was associated with temporal changes in abiotic compost properties, potentially explaining alternating taxa abundance patterns during pig manure composting.

Metagenomic analyses of microbial structure and metabolic pathway in solid-phase denitrification systems for advanced nitrogen removal of wastewater treatment plant effluent: A pilot-scale study

The pilot-scale solid-phase denitrification systems supporting with poly(3-hydroxybutyrateco-3-hydroxyvalerate) (PHBV) and PHBV-sawdust were constructed for advanced nitrogen removal from wastewater treatment plants (WWTPs) effluent, and the impacts of biomass blended carbon source on microbial community structure, functions and metabolic pathways were analyzed by metagenomic sequencing. PHBV-sawdust system achieved the optimal denitrification performance with higher NO₃^--N removal efficiency (96.58%), less DOC release (9.00 ± 4.16 mg L ^- 1) and NH₄⁺-N accumulation (0.37 ± 0.32 mg L ^- 1) than PHBV system. Metagenomic analyses verified the significant differences in the structure of microbial community between systems and the presence of four anaerobic anammox bacteria. Compared with PHBV, the utilization of PHBV-sawdust declined the relative abundance of genes encoding enzymes for NH₄⁺-N generation and increased the relative abundance of genes encoding enzymes involved in anammox, which contributed to the reduction of NH₄⁺-N in effluent. What's more, the encoding gene for electrons generation in glycolysis metabolism obtained higher relative abundance in PHBV-sawdust system. A variety of lignocellulase encoding genes were significantly enriched in PHBV-sawdust system, which guaranteed the stable carbon supply and continuous operation of system. The results of this study are expected to provide theoretical basis and data support for the promotion of solid-phase denitrification.

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

Sewage sludge contains various classes of organic pollutants, limiting its land application. Sludge composting can effectively remove some organic pollutants. This review summarizesrecent researches on concentration changes and dissipation of different organic pollutants including persistent organic pollutants during sludge composting, and discusses their dissipation pathways and the current understanding on dissipation mechanism. Some organic pollutants like PAHs and phthalates were removed mainly through biodegradation or mineralization, and their dissipation percentages were higher than those of PCDD/Fs and PCBs. Nevertheless, some recalcitrant organic pollutants could be sequestrated in organic fractions of sludge mixtures, and their levels and ARG abundance even increased after sludge composting in some studies, posing potential risks for land application. This review demonstrated that microbial community and their corresponding degradation for organic pollutants were influenced by different pollutants, bulking agents, composting methods and processes. Further research perspectives on removing organic pollutants during sludge composting were highlighted.

Thermal pretreatment enhances the degradation and humification of lignocellulose by stimulating thermophilic bacteria during dairy manure composting

This study investigated the effect of thermal pretreatment (TP) on the lignocellulose degradation and humification during dairy manure composting and the underlying microbial mechanism. The results showed that TP accelerated temperature rise and elevated composting temperature by increasing 26% initial content of simple organics. The degradation of cellulose, hemicellulose and lignin was 78, 10 and 109% higher in thermal pretreatment composting (TPC) than traditional composting (TC), respectively. Moreover, TP significantly improved the humification degree of composts, as indicated by 14 and 38% higher humus content and humification indexes in TPC, respectively. 16S rRNA sequencing showed that TP increased the relative abundance of thermophilic bacteria in TPC, of which Thermobifida, Planifilum, Truepera and Thermomonospora were potentially involved in lignocellulose biodegradation and humification. Canonical correspondence analysis revealed that TP changed the main factor determining the bacterial community evolution from dissolved organic carbon (DOC) in TC to temperature in TPC.

On-Site Blackwater Treatment Fosters Microbial Groups and Functions to Efficiently and Robustly Recover Carbon and Nutrients

Wastewater is considered a renewable resource water and energy. An advantage of decentralized sanitation systems is the separation of the blackwater (BW) stream, contaminated with human pathogens, from the remaining household water. However, the composition and functions of the microbial community in BW are not known. In this study, we used shotgun metagenomics to assess the dynamics of microbial community structure and function throughout a new BW anaerobic digestion system installed at The Netherlands Institute of Ecology. Samples from the influent (BW), primary effluent (anaerobic digested BW), sludge and final effluent of the pilot upflow anaerobic sludge blanket (UASB) reactor and microalgae pilot tubular photobioreactor (PBR) were analyzed. Our results showed a decrease in microbial richness and diversity followed by a decrease in functional complexity and co-occurrence along the different modules of the bioreactor. The microbial diversity and function decrease were reflected both changes in substrate composition and wash conditions. Our wastewater treatment system also decreased microbial functions related to pathogenesis. In summary, the new sanitation system studied here fosters microbial groups and functions that allow the system to efficiently and robustly recover carbon and nutrients while reducing pathogenic groups, ultimately generating a final effluent safe for discharge and reuse.

Changes in the characteristics of dissolved organic matter during sludge treatment: A critical review

Dissolved organic matter (DOM) of sludge is a heterogeneous mixture of high to low molecular weight organic substances which is including proteinaceous compounds, carbohydrates, humic substances, lipids, lignins, organic acids, organic micropollutants and other biological derived substances generated during wastewater treatment. This paper reviews definition, composition, quantification, and transformation of DOM during different sludge treatments, and the complex interplay of DOM with microbial communities. In anaerobic digestion, anaerobic digestion-refractory organic matter, particularly compounds showing polycyclic steroid-like, alkane and aromatic structures can be generated after pretreatment. During dewatering, the DOM fraction of low molecular weight proteins (< 20,000 Dalton) is the key parameter deteriorating sludge dewaterability. During composting, decomposition and polymerization of DOM occur, followed by the formation of humic substances. During landfill treatment, the composition of DOM, particularly humic substances, are related with leachate quality. Finally, suggestions are proposed for a better understanding of the transformation and degradation of DOM during sludge treatment. Future work in sludge studies needs the establishment and implementation of definitions for sample handling and the standardization of DOM methods for analysis, including sample preparation and fractionation, and data integration. A more detailed knowledge of DOM in sludge facilitates the operation and optimization of sludge treatment technologies.

Impacts of bio-carriers on the characteristics of soluble microbial products in a hybrid membrane bioreactor for treating mariculture wastewater

To gain greater insights into impacts of bio-carriers on the fate and characteristics of soluble microbial products (SMPs) for mariculture wastewater treatment, the hybrid membrane bioreactor (HMBR) and conventional membrane bioreactor (CMBR) were investigated. Both protein and polysaccharide exhibited lower level in HMBR (8.95 ± 0.28 mg/L and 20.49 ± 1.3 mg/L for anoxic stage, 5.16 ± 0.22 mg/L and 17.85 ± 0.92 mg/L for aerobic stage) than CMBR (14.6 ± 0.68 mg/L and 28.3 ± 2.99 mg/L for anoxic stage, 10.53 ± 0.68 and 26.04 ± 3.15 mg/L for aerobic stage). Three-dimensional fluorescence excitation emission matrix (EEM) revealed bio-carriers reduced the production of aromatic protein-like components in anoxic and aerobic supernatant and caused a blue-shift of soluble microbial product in aerobic stage. Molecular weight (Mw) distribution indicated that bio-carriers ameliorated the excretion of biopolymer (Mw > 500 kDa) in anoxic supernatant and intermediate Mw fractions (20-500 kDa) in aerobic supernatant. Moreover, little changes were observed in SMPs with Mw < 3 kDa down the whole treatment process of both systems. Gas chromatography-mass spectrometry (GC-MS) demonstrated that the major SMPs were long-chain alkanes and aromatics in all units of both systems and fewer aromatics were detected in HMBR. For anoxic stage, more peaks were identified in the HMBR (138) than CMBR (115), while for aerobic stage, more compounds were observed in the CMBR (94) than HMBR (70). Over 50% of the compounds in the anoxic supernatant for the HMBR were the same as in the CMBR. And 27 compounds were the same in aerobic supernatant for the HMBR and CMBR. Fewer compounds in the HMBR effluent (52) was observed, compared to CMBR effluent (80). Approximately 25.7% of compounds in the aerobic stage of the HMBR were rejected by membrane, while this value decreased to 14.9% in the CMBR.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting

The aim of this work was to investigate how the initial C/N ratio during composting of chicken manure/corn stover mix affected the succession of dominant bacteria in the mix which led to the reduction of the total losses of N and C in the composting process. 16S rDNA sequencing indicated that the succession of predominant bacteria was significantly affected by the temperature and the initial C/N ratio during composting. Redundancy analysis showed that higher C/N appeared to promote the relative abundance of nitrogen fixing bacteria Thermoactinomyces, Planifilum, Flavobacterium, Bacillaceae, Pseudomonas,Sphingobacterium, Paenibacillus, Bacillus and Thermobifida, while compressing the denitrifying bacteria Pusillimonas, Ignatzschineria, Alcanivorax, Cerasibacillus, Truepera and Erysipelothrix. C/N ratio of 30:1 yielded the least C/N losses in the composting process, indicating that adjustment to the initial C/N ratio could affect nitrogen transforming bacteria to reduce the total losses of N and C and improve compost quality.

Effects of moisture and carbon/nitrogen ratio on gaseous emissions and maturity during direct composting of cornstalks used for filtration of anaerobically digested manure centrate

This study investigated the maturity and gaseous emission during direct composting of cornstalks used as organic media for filtration of anaerobically digested manure centrate. Effects of moisture and carbon/nitrogen (C/N) ratio on composting performance were evaluated. Results show that cornstalks could effectively retain suspended solids and organic matter in digested manure centrate to lower their C/N ratio and attain microbial inoculation. Filtered cornstalks became more compostable when their moisture decreased from 76% to 60% or C/N ratio increased from 12 to 24. Nevertheless, such adjustment aggravated the emission of greenhouse and odours gases during composting. Regardless of composting conditions, the phylum Firmicutes was the most dominant with reduced abundance during composting. Similar reduction also occurred to several abundant phyla, including Atribacteria, Synergistetes and Euryarchaeota. By contrast, the phylum Bacteroidetes, Chloroflexi, Proteobacteria and Actinobacteria enriched as composting progressed. In addition, compost maturity was insignificantly affected by matrix moisture and C/N ratio.

Heat Energy and Gas Emissions during Composting of Sewage Sludge

The composting of sewage sludge and maize straw mixtures was investigated in this study. The aim was to analyze the influence of different proportions of sewage sludge and maize straw in the mixtures on composting process dynamics (expressed by heat production) and gas emissions. The results showed that all examined mixtures reached a strong thermophilic phase of composting; however, the lowest dynamic of temperature growth was observed in the case of the biggest sewage sludge content (60% of sewage sludge in the composting mixture). The ammonia concentration inside bioreactor chambers was directly related to the content of sewage sludge in the composted mixture. Excessive contents of sewage sludge had a considerable effect on very low C/N ratios and high losses through ammonia emissions. Tests were carried out in reactors with a capacity of 160 dm3 under controlled conditions. All mixtures were aerated by the average air-flow of about 2.5 dm3∙min−1, i.e., the minimum air-flow that allows a temperature of about 70 °C to be reached and a sufficiently long thermophilic phase, which ensures proper composting.

Degradation mechanism of lignocellulose in dairy cattle manure with the addition of calcium oxide and superphosphate

Cellulose and lignin belongs to refractory organic matters in the traditional composting. In this research, the degradation of lignocellulose in dairy cattle manure was investigated through adding calcium oxide (CaO) and superphosphate (SSP). In the presence of CaO and SSP, the degradation rate of cellulose and lignin were improved by 25.0% and 8.33%, respectively. The results indicated that the pH value in system would be slightly higher with the addition of CaO and SSP. Besides, the pH value of all cow manure piles were about 8.4 after composting rotten, which could be well neutralized by the gradually acidified soil in the southwest of China with the full effect of fertilizer released. In addition, the abundance of Bacillales, Actinomycetes, and Thermoactinomycetaceae in the experimental groups (AR) was slightly better than that in the control groups (CK) during composting, which led to a conclusion that an elaborate physical-chemical-multivariate aerobic microorganism evolution model of cellulose degradation products (PCMC) was deduced and the physical-chemical-multivariate aerobic microorganism model of lignin cycle degradation (PCML) was developed.

Sludge bio-drying followed by land application could control the spread of antibiotic resistance genes

The process of sludge bio-drying has been adopted in response to the increasing amount of residual sewage sludge. It has been demonstrated that sludge bio-drying effectively reduces both antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), whereas ermF, tetX, and sulII become enriched in response to the dynamic development of the microbial community. The present study further demonstrated that the land application of sludge bio-drying products under current application rate did not cause an increase in the abundance of quantified ARGs in the soil but the persistence of ARB should be paid attention. Although land application introduced ermF, tetX, and tetG into the soil, these soon decreased to control levels. Furthermore, the decay rate varied between soil types, with red soil being the most persistent based on kinetics modeling. The fate of ARGs could also be attributed to the dynamics of the microbial community during land application, and the genus Parasegetibacter, which can degrade extracellular DNA, might play a key role in the control of ARGs. In summary, sludge bio-drying following land application could constitute an effective means of controlling the spread of ARGs, and microbial community changes contributed the most to the fate of the ARGs during the entire treatment chain (residual sewage sludge → bio-drying process → land application).

Effect of Ca(OH)2 dosing on thermophilic composting of anaerobic sludge to improve the NH3 recovery

The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH₃ gas recovery during composting processes has the potential benefit of producing high-value microalgal biomass. However, the majority of produced ammonia does not evaporate as NH₃ gas but retains as NH₄⁺-N in the compost after fermentation. The present study investigates the effects of the timing of Ca(OH)₂ dosing (on days 2, 5, and 9), and the Ca(OH)₂ dose (1.1-2.6 mmol/batch), on lab-scale thermophilic composting of anaerobic sludge. The effects on NH₃ recovery, organic matter degradability, and microbial activity are evaluated. Ca(OH)₂ dosing immediately improved the emission of NH₃, with yields 50-69% higher than those under control conditions. The timing of the dosing did not influence NH₃ recovery or organic matter degradability. Higher Ca(OH)₂ doses resulted in higher NH₃ recovery, while microbial activity was temporarily and marginally inhibited. The pH of the compost reached 10-11.5 but quickly dropped to 8-8.5 within a day, probably because of neutralization of Ca(OH)₂ by the emitted CO₂ and release of NH₃, which maintained the microbial activity. The present study indicated that Ca(OH)₂ dosing would be useful to apply during thermophilic composting for NH₃ recovery to cultivate high-value microalgal biomass, which enables this process to obtain a more economic benefit.

Soil organic carbon mineralization in relation to microbial dynamics in subtropical red soils dominated by differently sized aggregates

The dynamics of eroded and retained soil organic carbon (SOC) may provide critical clues for evaluating impacts of soil erosion on global carbon cycling. Distribution patterns of soil aggregates in eroded and deposited environments are shaped by selective transport of water erosion. Therefore, detecting the pattern of SOC mineralization in soils dominated by aggregates of different sizes is essential to accurately explore the dynamics of eroded and retained SOCs in eroded and deposited environments. In the present study, the characteristics of SOC mineralization and its relationship to microbial dynamics in subtropical red soils dominated by different sizes of soil aggregates were investigated. The results demonstrated that the SOC mineralization rate of soils dominated by graded aggregates were significantly different, indicating that SOC mineralization in eroded and deposited environments are shaped by selective transport of water erosion. The highest mineralization rate was found in soils containing 1-2 mm aggregates at the initial stage of the experiment, and the daily average mineralization rate of the < 0.5 mm aggregates was significantly higher than that of the 2-3 mm aggregates. During the incubation, fungal communities exhibited a low dynamic character, whereas the composition of bacterial communities in all treatments changed significantly and had obvious differences relative to each other. Bacterial species diversities and relative abundances in the <0.5mm and the 2-3mm aggregates showed opposite dynamic characteristics. However, there were no statistical interactions between the dynamics of microbial communities and the changes of SOC or soil water content. Changes in bacterial community structure had no significant impact on the mineralization of SOC, which might be related to the quality of SOC or the specific utilization of carbon sources by different functional groups of microorganisms. Mineralization of the eroded and retained SOCs with specific qualities in relation to their functional microorganisms should be further explored in the future.

Simultaneous production of methane and acetate by thermophilic mixed culture from carbon dioxide in bioelectrochemical system

A thermophilic bioelectrochemical system was operated with mixed culture at 60 °C, while introducing only carbon dioxide. Methane production was initially observed in a membrane-less single chamber without a mediator, but eventually acetate was also found as 10.5 g/L after 137 days of operation. Comparing the microbial communities before and after the electricity supply using next-generation sequencing technology, acetoclastic methanogens such as Methanosaeta concilii were increased, and this result also indicates the production of acetate in bioelectrochemical CO₂ conversion system. With the advent of sulfate-reducing bacteria, Desulfotomaculum peckii was considered to be an acetate production promoter. These high production results for both methane and acetate can be applied to CO₂ storage using excess electricity for value-added chemicals.

Role of Humic Acid Chemical Structure Derived from Different Biomass Feedstocks on Fe(III) Bioreduction Activity: Implication for Sustainable Use of Bioresources

Humic acids (HAs) are redox-active components that play a crucial role in catalyzing relevant redox reactions in various ecosystems. However, it is unclear what role the different compost-derived Has play in the dissimilatory Fe(III) bioreduction and which chemical structures could accelerate Fe reduction. In this study, we compared the effect of eighteen HAs from the mesophilic phase, thermophilic phase and mature phase of protein-, lignocellulose- and lignin-rich composting on catalyzing the bioreduction of Fe(III)-citrate by Shewanella oneidensis MR-1 in temporarily anoxic laboratory systems. The chemical composition and structure of different compost-derived HAs were analyzed by UV–Vis spectroscopy, excitation-emission matrices of the fluorescence spectra, and 13C-NMR. The results showed that HAs from lignocellulose- and lignin-rich composting, especially in the thermophilic phase, promoted the bioreduction of Fe(III). They also showed that HA from protein-rich materials suppressed significantly the Fe(II) production, which was mainly affected by the amount and structures of functional groups (e.g., quinone groups) and humification degree of the HAs. This study can aid in searching sustainable HA-rich composts for wide-ranging applications to catalyze redox-mediated reactions of pollutants in soils.

Aerosolization behavior of prokaryotes and fungi during composting of vegetable waste

Aerobic composting is one of the most effective ways to treat biowaste. However, microorganisms, including prokaryotes (i.e. bacteria and archaea) and fungi, are inevitably released from the compost as bioaerosols during biowaste composting. The release pattern of bioaerosols was analyzed during vegetable waste composting through onsite direct sampling of bioaerosol, compost on the pile surface, and compost inside the windrows to have a systematic understanding of the aerosolization behavior of bacteria, archaea, and fungi during composting. A total of six and three dominant microbial phyla were detected in the vegetable compost and aerosol, respectively. The overall aerosolization index of archaea and bacteria was 0-79 and 0-214, respectively, while that of fungi ranged from 0 to 397. The major preferentially aerosolized microorganism phyla included Bacteroidetes (bacteria) and Basidiomycota (fungi). Furthermore, the aerosolization index of bacterial and fungal genera was 0-22,500 and 0-9000, respectively. Seven major preferentially aerosolized bacterial genera, including Brevundimonas, Massilia, Chryseobacterium, Chryseobacterium, Kurthia, Burkholderia-Paraburkholderia, and Acinetobacter were detected with aerosolization indices of 171, 491, 1478, 22,460, 5525, 4014, and 631, respectively. With regard to fungal genera, Cochliobolus, Sclerotinia, and Aspergillus were noted to get easily aerosolized, with maximum aerosolization indices of 7344, 8582, and 439, respectively. The microbial number in the aerosol from composts ranged from 400 to 4800 cell/m³. Besides, more than 90% of easily aerosolized microbial genera were Gram-negative and pathogenic. Thus, the microorganisms released from vegetable compost may have certain detrimental effect on human health.

Odor removal by and microbial community in the enhanced landfill cover materials containing biochar-added sludge compost under different operating parameters

Odor problem has become a growing concern for municipal solid waste (MSW) operators and communities located close to landfill sites. In this study, nine laboratory-scale landfill reactors were used to simulate in-situ odor control by a novel landfill cover material consisting of biochar-added sludge compost under various operating parameters. Characterization of odor removal and microbial community in the cover layer under various operating parameters was conducted using gas chromatograph-mass spectrometry and 454 high-throughput pyrosequencing, respectively. Results showed that H₂S (76.9-86.0%) and volatile organic sulfur compounds (VOSCs) (12.3-21.7%) were dominant according to their theoretical generated odor concentrations. The total odor REs calculated using the theoretical odor concentrations in the landfill reactors were different than using the measured odor values, which were ranked from high to low as: R6 > R5 > R7 > R4 > R8 > R9 > R3 > R2 > R1, showing the largest discrepancy of 25.3%. The optimum combination of operating parameters based on the theoretical odor concentration was different with that based on the measured odor concentrations. Moreover, although Firmicutes (12.21-91.48%), Proteobacteria (3.55-51.03%), and Actinobacteria (4.01-47.39%) were in general the three major bacterial phyla found in the landfill covers, the detailed bacterial communities in the cover materials of the simulated reactors varied with various operating parameters. Alicyclobacillus and Tuberibacillus showed positive correlations with the removal efficiencies (REs) of chlorinated compounds, H₂S, aromatic compounds, volatile organic sulfur compounds (VOSCs), and organic acids. The correlations of Rhodanobacter, Gemmatimonas, Flavisolibacter and Sphingomonas were strongly positive with ammonia RE and relatively positive with REs of organic acids, VOSCs, and aromatic compounds. These findings are instrumental in understanding the relationship between the structure of microbial communities and odor removal performances, and in developing techniques for in-situ odor control at landfills.

Insights into the succession of the bacterial microbiota during biodrying of storage sludge mixed with beer lees: Studies on its biodiversity, structure, associations, and functionality

Biodrying was first used for post-treatment of storage sludge mixed with beer lees. In this study, dynamic changes in dissolved organic matter (DOM), bacterial community structure, bacterial associations as well as metabolic functions were investigated using Excitation-Emission Matrix (EEM) spectra, high-throughput sequencing, network and correlation matrix analyses, and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). Furthermore, a hypothetical model was proposed to better understand the biodrying process. The results showed that desired performance was obtained and DOM variations revealed that biodrying can increase biostability of the matrix. The bacterial communities differed among different stages of the biodrying. At the phylum level, the dominant phyla were Proteobacteria and Bacteroidetes in the mesophilic and cooling phases, whereas Firmicutes became the most dominant phylum in the thermophilic phase. At the genus level, the dominant bacteria in the mesophilic and cooling phases were not obvious, while Ureibacillus and Bacillus were the dominant genera in the thermophilic phase. Network and correlation matrix analyses were useful tools for insights into the bacterial interactions. PICRUSt metagenome inference indicated that metabolism, genetic information processing, and environmental information processing were the primary metabolic pathways. These results allowed us to advance a hypothetical model explaining how succession in bacterial associations regulates the dynamics of a biodrying system.

Effect of temperature on thermophilic composting of aquaculture sludge: NH3 recovery, nitrogen mass balance, and microbial community dynamics

Development of thermophilic composting for maximizing NH₃ gas recovery would enable the production of a nitrogen source which is free from pathogen/heavy metal, for the cultivation of high-value microalgae. The present study examined the effect of NH₃ recovery, nitrogen mass balance, and microbial community dynamics on thermophilic composting of shrimp aquaculture sludge. The emission of NH₃ gas at 60 and 70 °C was 14.7% and 15.6%, respectively, which was higher than that at 50 °C (9.0%). The nitrogen mass balance analysis revealed that higher temperatures enhanced the solubilization of non-dissolved nitrogen and liberation of NH₃ gas from the produced NH₄⁺-N. High-throughput microbial community analysis revealed the shift of the dominant bacterial group from Bacillus to Geobacillus with the rise of composting temperature. In conclusion, thermophilic composting of shrimp aquaculture sludge at 60-70 °C was the most favorable condition for enhancing NH₃ gas recovery.