Use of activated carbon to reduce ammonia emissions and accelerate humification in composting digestate from food waste

Enhancing the decomposition and composting of food waste by in situ directional enzymatic hydrolysis: performance, ARGs removal and engineering application

This research utilized food waste (FW) as substrate, innovatively developed a directional multienzyme applied for accelerating FW hydrolysis and composting, and an in situ enzymatic hydrolysis combining in composting has been developed to manage FW. Results showed that the composting was achieved at 4 days and the humification index was increased by 2.60 compared with that of without enzymatic hydrolysis. FTIR analysis revealed that following multienzyme pretreatment, the primary constituents of FW, including protein, starch and lipid, underwent structural breakdown, among which protein exhibited the higher susceptibility to multienzyme action and was the first to disintegrated, and the structure also became looser. Moreover, the total antibiotic resistance gene (ARGs) was reduced more than 90 % in the proposed composting process. Analysis of microbial communities and metagenomes showed that multienzyme pretreatment reshaped microbial communities towards favoring FW hydrolysis and humification. The engineering application analysis further implied that the proposed composting approach is scale flexible, engineering applicable, economic viability and environmentally sustainability. It was anticipated that this study has the potential to trigger a paradigm shift in future in-situ treatment of FW to achieve full resource recovery towards zero solid discharge.

Simultaneous reduction of odorous and greenhouse gases emissions by thermophilic microbial agents during chicken manure composting

Odorous and greenhouse gases emissions from animal manure composting cause air pollution and nutrient loss. This research examined the effects of thermophilic fungal agent (F) and bacterial agent (B) on the emissions of odorous and greenhouse gases during chicken manure composting and explored the underlying mechanisms. The results indicated that the cumulative emission of ammonia (NH3), hydrogen sulfide (H2S), methane (CH4) and nitrous oxide (N2O) in F treatment decreased by 20.1 %, 34.2 %, 8.3 % and 26.1 %, respectively, in comparison to 25.3 % reduction in H2S and 9.3 % reduction in N2O in B treatment. F treatment increased the relative abundance of amoA, pmoA and nosZ, while lowering that of ureC, dsrB, mcrA and nirK. Furthermore, inoculation of thermophilic microbial agent significantly altered the evolution of bacterial communities during composting. Pearson correlation and co-occurrence network analysis revealed that Bacillus, Ammoniibacillus, Acinetobacter, Escherichia-Shigella and Oceanobacillus were closely related to gaseous emissions during composting. This study demonstrated that thermophilic fungal inoculation was efficient for mitigating odorous and greenhouse gases emissions during animal manure composting.

Particulate matter pollution alters the bacterial community structure on the human skin with enriching the Acinetobacter and Pseudomonas

Particulate matter (PM) has been recognized as a significant environmental contaminant with substantial effects on human health, although the impact of PM pollution on the skin microbiota is less understood. In this study, 78 skin microbiota samples from volunteers were obtained during periods of haze and non-haze in the spring and winter. The diversity, composition, and co-occurrence networks of the skin bacterial community were revealed using high-throughput sequencing. Acinetobacter sp. XSB125 and Pseudomonas sp. XSB6 were isolated and cocultured with PM collected during haze days. Significant seasonal variations were observed in the skin bacterial community, with winter samples showing greater diversities than spring samples. Supervised partial least squares discriminant analysis indicated that PM pollution influenced the skin bacterial community composition. Stronger interactions were detected in the network structure of the skin bacterial community during haze days. Differential and random forest analyses revealed that Acinetobacter and Pseudomonas, which are important resistant opportunistic pathogens, were significantly enriched during haze days in winter. To confirm the increases in Acinetobacter and Pseudomonas during haze days, an Acinetobacter strain and a Pseudomonas strain were isolated and cultured with the PM we collected during haze days. In vitro experiments confirmed that PM promoted the growth of the Acinetobacter and Pseudomonas strains. Function analysis revealed increased metabolic function and enrichment of antibiotic resistance- and pathogenicity-related functions during haze days, including the beta-lactamase gene and attachment invasion locus protein. These findings reveal the complex interplay between PM pollution and the skin microbiota, highlighting the need for further research into mitigation strategies to protect the public health from PM exposure.

Enhancing humification in high-temperature composting: Insights from endogenous and exogenous heating strategies

Livestock manure is difficult to manage for high moisture and nutrients. High-temperature composting (> 75 °C) reduces moisture. However, the humification process, crucial for nutrient recycling, remains poorly understood. This study investigated the humification mechanisms of endogenous-heating hyperthermophilic composting (HC) and exogenous-heating continuous thermophilic composting (CTC). Both methods significantly increased humus by 258.70 % in HC and 193.93 % in CTC. Spectral analysis showed stronger humification in the early stage for HC and in the later stage for CTC. Microbial activity primarily drove humification in HC, while environmental factors had more influence in CTC due to its simpler microbial structure. These results suggested that the polyphenol pathway, involving quinones and protein condensation, dominates humification in HC, while the Maillard reaction, with sugars and protein aggregation, dominates in CTC. Humification can be enhanced by increasing protein in HC and sugar in CTC. These findings provided strategies to improve humification efficiency and promote sustainable agriculture.

Interactions between fungi and bacteria hosts carrying MGEs is dominant for ARGs fate during manure mesophilic composting

The mycelial networks of fungi promote the interaction between the originally isolated bacteria, thereby potentially enhancing the exchange of nutrients and the horizontal transfer of genetic materials. However, the driving effect of fungi on antibiotic resistance genes (ARGs) during mesophilic facultative composting is still unclear. This study aims to elucidate the changes in ARGs and underlying mechanisms during the mesophilic composting of manure. Results indicated that reduction rates of ARGs in sheep and pig manure over a 90-day composting period were 34.68% and 60.10%, respectively. The sul1, sul2 and tetX were identified as recalcitrant ARGs in both composting treatments, with the additional unique recalcitrant gene addA observed in sheep manure. Fungal communities appeared to have a more significant influence on the cooperation between bacteria and fungi. Massive fungi interacted intensively with bacterial hosts carrying both ARGs and mobile genetic elements (MGEs). In sheep and pig manure, there were 53 and 38 potential bacterial hosts (genus level) carrying both ARGs and MGEs, associated close interactions with fungi. Structural equation modeling revealed that compost properties influence ARGs by affecting the abundance of core fungi and the hosts carrying MGEs, and that core fungi could also impact ARGs by influencing the bacterial hosts carrying MGEs. Core fungi have the potential to facilitate the horizontal transfer of ARGs by enhancing bacterial network interactions.

Dynamic responses of the inter-microbial synergism and thermodynamic conditions attribute to the inhibition-and-relief effects of chitosan towards anaerobic digestion

Wide commercial applications of chitosan in food preservation and green packaging fields inevitably lead to the universal existence in food, as well as the food waste (FW) processing system. However, whether and how the chitosan, a class of biomacromolecule substances, lead to dysfunction of anaerobic digestion (AD) process of FW remains less understood. Herein, chitosan exhibited an inhibition-and-relief effect with the AD process proceeding, and 80 mg/g-FW of chitosan decreased the net methane yield of FW by 24.7 %. The dynamic effect was ascribed to the varied fates of chitosan and the coupling biotic/abiotic influencing on multi-steps. Chitosan enhanced substrate flocs agglomeration, restraining the release of organics to liquid phase and reducing the binding affinity to enzymes. Among the various microorganisms involved in different steps, chitosan severely inhibited aceticlastic and hydrogenotrophic methanogen at the levels of microbial abundance, activity and function. Genome-centric metagenomics analyses revealed that transient chitosan decreased the coenzyme-based synergism of various microbial taxa involved in acetic acid generation/consumption metabolisms, including syntrophic propionate-oxidizing bacteria, syntrophic butyrate-oxidizing bacteria and methanogen. With the elimination of chitosan, these inhibitions were relieved, and the accumulated acetic acid and the more favorable thermodynamic conditions finally attributed to the recovery of AD performance.

Evaluation of the quality of products from multiple industrial-scale composting treatment facilities for kitchen waste and exploration of influencing factors

The aerobic composting process is extensively utilized to manage kitchen waste. Nonetheless, the variability in the quality of compost derived from engineering practices which significantly hinders its broader industrial application. This work investigated the final products of kitchen waste compost at multiple industrial-scale treatment facilities utilizing three distinct aerobic composting processes in a bid to explore key factors affecting compost quality. The quality evaluation was based on technical parameters like seed germination index (GI), and limiting factors such as heavy metal content. The results showed that most of the compost products failed to meet the established standards, with GI being the primary limiting indicator. Furthermore, maturity assessments suggested that compost with low GI exhibited reduced humification could not be recommended for agricultural use. The investigation delved into the primary determinants of GI, focusing on risk factors such as the oil and salt of kitchen waste, and the microbial community of the humification driving forces. The results indicated that products with low GI had higher oil and salt content and a relatively simple microbial community. A thorough analysis suggested that excessive levels oil and salt were potential influencing factors on GI, as they stimulated the activity of acid-producing bacteria like Lactobacillus, suppressed the activity of humification-promoting bacteria such as Actinomarinales, and influenced the decomposition and humification processes of organic matter and total nitrogen, thereby affecting product quality. The findings provide valuable insights for improving kitchen waste compost products for agricultural applications.

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.

Hydrothermal-enhanced pyrolysis for efficient NOX reduction and biochar valorization from food waste digestate

Pyrolysis has emerged as a promising technology for valorizing digestate resulting from the anaerobic digestion of food waste. However, the high NOX emissions during pyrolysis limit its application. This study proposed a hydrothermal coupled pyrolysis process to control the element transfer in digestate during biochar production. The efficient reduction of NOX emissions and the improvement of biochar adsorbability were realized. The hydrothermal process reduced the nitrogen content in solid digestate by 49.10 %-81.79 %, thus reducing the NOX precursors in syngas and the N-containing substances in bio-oil. Additionally, the specific surface area and the total pore volume of biochar were enhanced from 25 m2/g to 60-73 m2/g and 0.06 cm3/g to 0.12-0.14 cm3/g, respectively. More defects, oxygen-containing functional groups, and doped Ca on the biochar resulted in a high phosphate removal efficiency of 94 %. The proposed technology provides an efficient and environmentally friendly way to utilize the digestate.

Predicting maturity and identifying key factors in organic waste composting using machine learning models

The measurement of germination index (GI) in composting is a time-consuming and laborious process. This study employed four machine learning (ML) models, namely Random Forest (RF), Artificial Neural Network (ANN), Support Vector Regression (SVR), and Decision Tree (DT), to predict GI based on key composting parameters. The prediction results showed that the coefficient of determination (R2) for RF (>0.9) and ANN (>0.9) was higher than SVR (<0.6) and DT (<0.8), suggesting that RF and ANN displayed superior predictive performance for GI. The SHapley additive exPlanations value result indicated that composting time, temperature, and pH were the important features contributing to GI. Composting time was found to have the most significant impact on GI. Overall, RF and ANN were suggested as effective tools for predicting GI in composting. This study offers the reliable approach of accurately predicting GI in composting processes, thereby enabling intelligent composting practices.

Effects of micro-nano bubble water addition on maturation degree and microbial community during aerobic composting

In order to explore the effects of micro-nano bubble water (MNBW) on compost maturation and the microbial community in cow manure and straw during aerobic composting, we conducted composting tests using tap water with 12 mg/L (O12), 15 mg/L (O15), 18 mg/L (O18), and 21 mg/L (O21) dissolved oxygen in MNBW, as well as tap water with 9 mg/L dissolved oxygen as a control (CK). The results showed that O21 increased the maximum compost temperature to 64 °C, which was higher than the other treatments. All treatments met the harmless standards for compost. The seed germination index (GI) was largest under O21 and 15.1% higher than that under CK, and the non-toxic compost degree was higher. Redundancy analysis showed that the temperature, C/N, pH, and GI were important factors that affected the microbial community composition. The temperature, C/N, and pH were significantly positively correlated with Firmicutes and Actinobacteria (p < 0.05). Firmicutes was the dominant phylum in the mesophilic stage (2-6 days) and it accounted for a large proportion under O21, where the strong thermophilic metabolism increased the production of heat and prolonged the high temperature period. The bacterial genus Ammoniibacillus in Firmicutes accounted for a large proportion under O21 and it accelerated the decomposition of substrates. Therefore, the addition of MNBW changed the microbial community to affect the maturation of the compost, and the quality of the compost was higher under O21.

Effect evaluation of different green wastes on food waste digestate composting and improvement of operational conditions

This study attempted to determine the influence of diverse green wastes on food waste digestate composting and the improvement of operational conditions. Various effects of the green wastes (GW), with different types and sizes, initial substrate mixture C/N ratios, compost pile heights, and turning frequencies on the food waste digestate (FWD) composting were examined in the current work. The findings showed that the use of street sweeping green waste (SSGW) as an additive can maintain the thermophilic stage of the FWD composting for 28 days, while the end-product contained the greatest amounts of total phosphorus (TP, 2.29%) and total potassium (TK, 4.61%) and the lowest moisture content (14.8%). Crushed SSGW (20 mm) enabled the FWD composting to maintain the longest thermophilic period (28 days), achieving the highest temperature (70.2 °C) and seed germination index (GI, 100%). Adjusting the initial substrate mixture C/N ratio to 25, compost pile height to 30 cm, and turning frequency to three times a day could enhance the efficiency and improve the fertilizer quality of the co-composting of the FWD and SSGW. This study suggested that co-composting of FWD and SSGW (FWD/SSGW = 2.3, wet weight) is a promising technique for the treatment of municipal solid waste and provided significant theoretical data for the application of composting.

Continuous thermophilic composting of distilled grain waste improved organic matter stability and succession of bacterial community

Continuous thermophilic composting (CTC) is potentially helpful in shortening the composting cycle. However, its universal effectiveness and the microbiological mechanisms involved are unclear. Here, the physicochemical properties and bacterial community dynamics during composting of distilled grain waste in conventional and CTC models were compared. CTC accelerated the organic matter degradation rate (0.2 vs. 0.1 d-1) and shortened the composting cycle (24 vs. 65 d), mainly driven by the synergism of bacterial genera. Microbial analysis revealed that the abundance of Firmicutes was remarkably improved compared to that in conventional composting, and Firmicutes became the primary bacterial phylum (relative abundance >70 %) during the entire CTC process. Moreover, correlation analysis demonstrated that bacterial composition had a remarkable effect on the seed germination index. Therefore, controlling the composting process under continuous thermophilic conditions is beneficial for enhancing composting efficiency and strengthening the cooperation between bacterial genera.

A change in substance and microbial community structure during the co-composting of kitchen waste anaerobic digestion effluent, sewage sludge and Chinese medicine residue

Anaerobic digestion is a resource recovery method for organic waste, gaining attention due to carbon reduction. Disposing of anaerobic digestion effluent (ADE) is crucial for developing anaerobic digestion, but conventional wastewater treatment fails to effectively recover nutrients contained in the ADE. In the present study, the ADE without solid-liquid separation was mixed with sewage sludge and Chinese medicine residue for the composting, where the ADE could be recovered at high temperature through humification. Besides, the nitrogen balance, humification process, and microbial dynamics during the composting process were studied. The results showed that the group supplemented with ADE could increase the nitrogen retention efficiency by 2.21 % compared to the control group. High ammonia nitrogen content and salinity did not negatively affect the maturity and phytotoxicity of compost products and even increase the humification degree of compost products. Moreover, additional ADE may not alter microbial community structure, which could contribute to microbial succession. This is the first time to investigate the substance transformation and shift in microbial community structure while applying composting process for ADE treatment, in which the anaerobic-aerobic collaborative disposal process provides an alternative solution for the recovery of ADE.

Effect and its mechanism of potassium persulfate on aerobic composting process of vegetable wastes

Vegetable waste (VW) is a potential organic fertilizer resource. As an important way to utilize vegetable wastes, aerobic composting of VW generally has the problems of long fermentation cycle and incomplete decomposition of materials. In this study, 0.3-1.2% of potassium persulfate (KPS) was added to promote the maturity of compost. The results showed that the addition of KPS promoted the degradation of materials, accelerated the temperature rise of compost. KPS also promoted the formation of humic substances (HS). Compared with the control, HS contents of treatments with KPS addition increased by 7.81 ~ 17.52%. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) analysis reveal the mechanism of KPS affecting the composting process: KPS stimulated the degradation of various organic substances such as lignin at high temperature stage, and the degradation of lignin could accelerate the release and decomposition of other components; KPS made the structure of the material looser, with more voids and pores, and more specific surface area of the material, which was more suitable for microbial degradation activities. Therefore, the addition of KPS can promote the decomposition of organic matter in the early stage of composting, accelerate the process of thermophilic phase, and shorten the composting process and improve product maturity.

Product maturation and antibiotic resistance genes enrichment in food waste digestate and Chinese medicinal herbal residues co-composting

The land application of food waste digestate (FWD) requires a composting process to improve its soil amendment performance and alleviate environmental risks. This study proposed co-composting of Chinese medicinal herbal residues (CMHRs) and FWD as a means to improve the maturation performance and investigated the evolution of antibiotic resistance genes (ARGs). Results demonstrated that CMHRs addition effectively accelerated the maturity of FWD composting to less than 35 days, remarkably removed its remaining antibiotics by 83.0% and promoted the formation of humification substances. However, both quantitative PCR and 16S rRNA sequencing analysis indicated that a significant enrichment of ARGs and mobile genetic elements including frA1, tetX, blaTEM, InuB-01, aadA2-02 and IntI-1 was observed via the co-composting of FWD and CMHRs. These results indicated that the land application of products obtained from FWD and CMHRs co-composting is at risk of spreading ARGs, although the composting process could be significantly improved.

Inhibition insights of hydrothermal liquid digestate in anaerobic digestion: Impact on organics conversion and inhibitor degradation

Hydrothermal liquid digestate has been widely accepted as a substrate in anaerobic digestion (AD) for energy recovery. However, the potential negative impacts of hydrothermal liquid digestate on AD remain unclear. In this study, the organic biodegradability of hydrothermal liquid digestate produced from hydrothermal treatment (HTT) at different temperatures was analyzed, and the formation and degradation process of potential inhibitory substances were discussed. Results demonstrated that the AD lag phase of hydrothermal liquid digestate increased from 3 days at raw liquid digestate to 5-21 days. When the HTT temperature reached 220 °C, the methane yield decreased by 48%, and more than 71% of the organics in the hydrothermal liquid digestate were not utilized by AD. Biorefractory substances, such as fulvic and humic acids, accumulate in the hydrothermal liquid digestate. Potential inhibitory substances from Maillard reactions mainly affect the methanogenesis of AD. Most inhibitory substances were degraded within 7-22 days, with the degradation rate following the order of pyrroles > pyrazines > ketones > imidazoles > indoles. The AD community structure and methane conversion were partially re-established after most inhibitory substances were degraded. This study provides valuable information on eliminating the potential negative effects of hydrothermal liquid digestate on AD.

Ammonia assimilation is key for the preservation of nitrogen during industrial-scale composting of chicken manure

Nitrogen loss from compost is a serious concern, causing severe environmental pollution. The NH4+-N content reflects the release of NH3. However, the nitrogen conversion pathway that has the greatest impact on NH4+-N content is still unclear. This study attempted to explore the key pathways, core functional microorganisms, and mechanisms involved in the transformation of ammonia nitrogen during composting. KEGG (Kyoto Encyclopedia of Genes and Genomes) metabolic pathways revealed that ammonia assimilation was dominated by the glutamate dehydrogenase (GDH) pathway (53.4%), which is crucial for nitrogen preservation. The combined analysis of KEGG, NR species annotation, and co-occurrence network identified 20 easy-to-regulate obligate core nitrogen-transforming functional microorganisms, including 18 ammonia-assimilating bacteria. Furthermore, the effects of environmental parameters on the obligate core functional microorganisms were investigated. The present study results provided a theoretical basis for the utilization of ten ammonia-assimilating bacteria, such as Paenibacillus, Erysipelatoclostridium, and Defluviimonas to improve the quality of compost.

Impacts of digestate-based compost on soil property and nutrient availability

The treatment of digestate from food waste (DFW) has emerged as the bottleneck for food waste anaerobic digestion. DFW generally contains abundant nutrients that can be recycled by composting. However, the effect of DFW-based compost on soil improvement has not been extensively explored. In this study, soil properties were improved by adding various amounts of DFW-based compost, and the growth conditions of Pak choi were monitored. The results indicated that the DFW-based compost could provide nitrogen, calcium, magnesium, and organic matter, thereby enhancing the growth of Pak choi, accumulating chlorophyll, and improving photosynthesis efficiency. As the amount of added DFW-based compost increased from 0% to 20%, the fresh biomass, leaf weight, and root weight of Pak choi increased by 242%, 262%, and 99%, respectively. The total chlorophyll content was 2.62 mg g-1 in control and increased to 12.45 mg g-1 in the group with 20% DFW-based compost, benefiting the photochemical efficiency of Pak choi. However, the growth was inhibited when the addition amount exceeded 20%, potentially due to excessive nutrient supplementation. Overall, the addition of 20% of DFW-based compost was suggested to promote the growth of Pak choi by providing proper nutrients.

Proteolysis Analysis and Sensory Evaluation of Fermented Sausages using Strains Isolated from Korean Fermented Foods

We studied the proteolysis and conducted a sensory evaluation of fermented sausages using strains derived from Kimchi [Pediococcus pentosaceus-SMFM2021-GK1 (GK1); P. pentosaceus-SMFM2021-NK3 (NK3)], Doenjang [Debaryomyces hansenii-SMFM2021-D1 (D1)], and spontaneous fermented sausage [Penicillium nalgiovense-SMFM2021-S6 (S6)]. Fermented sausages were classified as commercial starter culture (CST), mixed with GK1, D1, and S6 (GKDS), and mixed with NK3, D1, and S6 (NKDS). The protein content and pH of GKDS and NKDS were significantly higher than those of CST on days 3 and 31, respectively (p<0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the NKDS had higher molecular weight proteins than the GKDS and CST. The myofibrillar protein solubility of the GKDS and NKDS was significantly higher than that of the CST on day 31 (p<0.05). The GKDS displayed significantly higher pepsin and trypsin digestion than the NKDS on day 31 (p<0.05). The hardness, chewiness, gumminess, and cohesiveness of the GKDS were not significantly different from those of the CST. The GKDS exhibited the highest values for flavor, tenderness, texture, and overall acceptability. According to this study, sausages fermented using lactic acid bacteria (GK1), yeast (D1), and mold (S6) derived from Korean fermented foods displayed high proteolysis and excellent sensory evaluation results.

Effects of fungal agents and biochar on odor emissions and microbial community dynamics during in-situ treatment of food waste

The effects of the co-addition of fungal agents and biochar on physicochemical properties, odor emissions, microbial community structure, and metabolic functions were investigated during the in-situ treatment of food waste. The combined addition of fungal agents and biochar decreased cumulative NH₃, H₂S, and VOCs emissions by 69.37%, 67.50%, and 52.02%, respectively. The predominant phyla throughout the process were Firmicutes, Actinobacteria, Cyanobacteria, and Proteobacteria. Combined treatment significantly impacted the conversion and release of nitrogen from the perspective of the variation of nitrogen content between different forms. FAPROTAX analysis revealed that the combined application of fungal agents and biochar could effectively inhibit nitrite ammonification and reduce the emission of odorous gases. This work aims to clarify the combined effect of fungal agents and biochar on odor emission and provide a theoretical basis for developing an environmentally friendly in-situ efficient biological deodorization (IEBD) technology.

Co-digestion of food waste and hydrothermal liquid digestate: Promotion effect of self-generated hydrochars

Hydrothermal treatment (HTT) can efficiently valorize the digestate after anaerobic digestion. However, the disposal of the HTT liquid is challenging. This paper proposes a method to recover energy through the anaerobic co-digestion of food waste and HTT liquid fraction. The effect of HTT liquid recirculation on anaerobic co-digestion performance was investigated. This study focused on the self-generated hydrochars that remained in the HTT supernatant after centrifugation. The effect of the self-generated hydrochars on the methane (CH₄) yield and microbial communities were discussed. After adding HTT liquids treated at 140 and 180 °C, the maximum CH₄ production increased to 309.36 and 331.61 mL per g COD, respectively. The HTT liquid exhibited a pH buffering effect and kept a favorable pH for the anaerobic co-digestion. In addition, the self-generated hydrochars with higher carbon content and large oxygen-containing functional groups remained in HTT liquid. They increased the electron transferring rate of the anaerobic co-digestion. The increased relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota was observed with adding HTT liquid. The results of the principal component analysis indicate that the electron transferring rate constant had positive correlationships with the relative abundance of Methanosarcina, Syntrophomonadaceae, and Synergistota. This study can provide a good reference for the disposal of the HTT liquid and a novel insight regarding the mechanism for the anaerobic co-digestion.

Effect of biodrying of lignocellulosic biomass on humification and microbial diversity

By optimizing the carbon to nitrogen (C/N) ratio, this study accomplished an improved level of humification and microbial diversity in the biodrying process of lignocellulosic biomass. The results demonstrated that C/N ratio of 20 accelerated the decomposition of refractory lignocellulose, resulting in lower greenhouse gas emissions and the production of highly mature fertilizer with a germination index of 119.0% and a humic index of 3.2. Moreover, C/N ratio of 20 was found to diversify microbial communities, including Pseudogracilibacillus, Sinibacillus, and Georgenia, which contributed to the decomposition of lignocellulosic biomass and the production of humic acid. Hence, it is recommended to regulate the C/N ratio to 20:1 during the biodrying of biogas residue and wood chips to promote the economic feasibility and bioresource recycling.

Sustainable management and recycling of anaerobic digestate solid fraction by composting: A review

The aim of the study was to review and discuss the management and recycling of anaerobic digestate solid fraction by composting process in the context of circular bioeconomy and sustainable development. The conversion of the solid fraction into compost can be recognized as novel process-enhancing supplements for land reclamation. Moreover, the solid fraction of the digestate is a valuable substrate for compost production, both as a monosubstrate and as a valuable additive for other raw materials to enrich in organic matter. These results should serve as reference point to target adjusting screws for anaerobic digestate solid fraction by composting process improvement, its implementation in modern bioeconomy perspective as well as provide a guideline for effective waste management.

Biochar as smart organic catalyst to regulate bacterial dynamics during food waste composting

The impact of wheat straw biochar (WSB) on bacterial dynamics succession during food waste (FW) composting was analyzed. Six treatments [0(T1), 2.5(T2), 5 (T3), 7.5 (T4), 10 (T5), and 15 %(T6)] dry weight WSB were used with FW and saw dust for composting. At the highest thermal peak at 59 ℃ in T6, the pH varied from 4.5 to 7.3, and electrical conductivity among the treatments varied from 1.2 to 2.0 mScm1. Firmicutes (25-97 %), Proteobacteria (8-45 %), and Bacteroidota (5-50 %) were among the dominate phyla of the treatments. Whereas, Bacillus (5-85 %), Limoslactobacillus (2-40 %), and Sphingobacterium (2-32 %) were highest among the identified genus in treatments but surprisingly Bacteroides was in greater abundance in the control treatments. Moreover, heatmap constructed with 35 various genera in all the treatments showed that Gammaproteobacterial genera contributed in large proportion after 42 days in T6. Additionally, a dynamic shift from Lactobacillus fermentum to higher abundance of Bacillus thermoamylovorans was reported on 42 days of FW composting. Biochar 15 % amendment can improve FW composting by influencing bacterial dynamics.

Manganese dioxide eliminates the phytotoxicity of aerobic compost products and converts them into a plant friendly organic fertilizer

This study mainly confirmed the exogenous substances (pomace, biochar, MnO₂) and the quorum sensing of bacterial communities jointly regulate the metabolic conversion of toxic substances in manures and agricultural wastes, and converts them into a plant-friendly organic fertilizer through aerobic composting and pot experiment. The results showed the composting products had positive performance in bacterial communities, physicochemical indicators, and phytotoxicity. Meanwhile, the addition of exogenous substances could significantly improve seed germination index, promote metabolites conversion, and optimize bacterial community structure. Furthermore, the exogenous substances mainly regulated the functions of the three bacterial communities by quorum sensing system, then promoted the beneficial metabolites, and inhibited the harmful metabolites. Finally, pot experiments suggested compost products could significantly promote plant growth. Thus, these important discoveries extend the knowledge of the previous work and provide an economical and simple method to convert wastes into organic fertilizers that are friendly to plants and soil.

Insights into the influence of digestate-derived biochar upon the microbial community succession during the composting of digestate from food waste

The by-product from the anaerobic digestion of food waste (FW) called the digestate (DFW) needs proper disposal because of its high environmental burden. Composting can transform DFW into a nutrient-containing soil improver via a series of microbial metabolic activities. However, the long composting time and high amount of ammonia emission are the key concerns of DFW composting. In the present study, the effect of DFW-derived biochar (BC-DFW) on microbial succession and its involvement in nitrogen transformation and humification during DFW composting were investigated. The results indicated that the BC-DFW accelerated bacterial and fungal evolution, and the bacterial diversity was augmented by increasing the amount of BC-DFW. In particular, Cryomorpha, Castellaniella, Aequorivita, and Moheibacter were enriched by the addition of BC-DFW, thereby enhancing the degradation of organic matter and nitrogen transformation and increasing the germination index. The group with 25% BC-DFW contained a higher relative abundance of Cryomorpha (2.08%, 2.47%) than the control (0.39%, 1.72%) on days 19 and 35 which benefited the degradation of organic matter. The group with 25% BC-DFW quickly enhanced the growth of Nitrosomonas, thereby accelerating the conversion of ammonium-nitrogen to nitrate-nitrogen and reducing the phytotoxicity of the composting product.

Persistence and remote sensing of agri-food wastes in the environment: Current state and perspectives

Food demand is expected to increase globally by 60-110% from 2005 to 2050 due to diet shifts and population growth. This growth in food demand leads to the generation of enormous agri-food wastes (AFWs), which could be classified into pre-consumption and post-consumption. The AFW represents economic losses for all stakeholders along food supply chains, including consumers. It is reported that the direct financial, social, and environmental costs of food waste are 1, 0.9, and 0.7 trillion USD/year, respectively. Diverse conventional AFW management approaches are employed at the different life cycle levels (entre supply chain). The review indicates that inadequate transportation, erroneous packaging, improper storage, losses during processing, contamination, issues with handling, and expiry dates are the main reason for the generation of AFWs in the supply chain. Further, various variables such as cultural, societal, personal, and behavioral factors contribute to the AFW generation. The selection of a specific valorization technology is based on multiple physicochemical and biological parameters. Furthermore, other factors like heterogeneity of the AFWs, preferable energy carriers, by-products management, cost, end-usage applications, and environmental legislative and disposal processes also play a crucial role in adopting suitable technology. Valorization of AFW could significantly impact both economy and the environment. AFWs have been widely investigated for the development of engineered added-value biomaterials and renewable energy production. Considering this, this study has been carried out to highlight the significance of AFW cost, aggregation, quantification, and membrane-based strategies for its management. The study also explored the satellite remote sensing data for Spatio-temporal monitoring, mapping, optimization, and management of AFW management. Along with this, the study also explained the most recent strategies for AFW valorization and outlined the detailed policy recommendation along with opportunities and challenges. The review suggested that AFW should be managed using a triple-bottom-line strategy (economic, social, and environmental sustainability).

Effect of different-sized bulking agents on nitrification process during food waste digestate composting

Food waste digestate (FWD) disposal is a serious bottleneck in anaerobic digestion plants to achieve a circular bioeconomy. FWD could be recycled into nitrogen-rich compost; however, the co-composting process optimisation along with bulking agents is required to reduce nitrogen loss and unwanted gaseous emissions. In the present study, two different-sized bulking agents, namely, wood shaving (WS) and fine sawdust (FS), were used to investigate their impact on FWD composting performance along with the nitrogen dynamics. The mixing of FWD with different bulking agents altered the physiochemical characteristics of composting matrix and the effective composting performance was observed through reduced ammonium nitrogen and increased seed germination index during 28 days of composting. The carbon loss of 19-22% through CO2 emission indicated similar carbon mineralisation with both types of sawdust; however, the nitrogen transformation pathways were different. Only WS treatment demonstrated the nitrification process, whereas the nitrogen loss was higher with FS. A total nitrogen loss of ∼15% was observed in treatments with FS, whereas WS treatments displayed a nitrogen loss of 12%. The outcome of the present study could significantly contribute to the practical aspect of the FWD composting operation with the promotion of the bio-recycling economy.

Mechanism analysis of humification coupling metabolic pathways based on cow dung composting with ionic liquids

This study focused on how adding ionic liquids (IL) affects composting humification. During the warming and thermophilic phases, addition of IL increased precursors content, and increased the polymerization of humus (HS) at later stages. Furthermore, the final HS and humic acid (HA) content of experimental groups (T) groups 129.79 mg/g and 79.91 mg/g were higher than in control group (CK) 118.57 mg/g and 74.53 mg/g, respectively (p < 0.05). IL up-regulated the gene abundance of metabolism for carbohydrate and amino acid (AA), and promoted the contributions of Actinobacteria and Proteobacteria, which affected humification. The redundancy analysis (RDA) results showed that the citrate-cycle (TCA cycle)(ko0020), pentose phosphate pathway (ko00030), pyruvate metabolism (ko00620), glyoxylate and dicarboxylate metabolism (ko00630), propanoate metabolism (ko00640), butanoate metabolism (ko00650) positively correlated with HA and HI. HA and humification index (HI) positively correlated with AA metabolic pathways, and fulvic acid (FA) was negatively correlated with these pathways. Overall, metabolism for carbohydrate and AA metabolism favored compost humification. ILs improved metabolism for carbohydrate and amino acid metabolism, thus enhancing humification.

Identification of Optimal Fermentation Temperature for Dry-Fermented Sausage Using Strains Isolated from Korean Fermented Foods

This study aims at identifying the optimal fermentation temperature for dry-fermented sausage using strains isolated from Kimchi (GK1, Pediococcus pentosaceus-GK1; NK3, P. pentosaceus-NK3), Doenjang (D1, Debaryomyces hansenii-D1), and commercial fermented sausage (S6, spontaneously generated Penicillium nalgiovense-S6). The microbial population, pH, moisture content, color, thiobarbituric acid reactive substance (TBARS), volatile basic nitrogen (VBN), and electronic nose (E-nose) were analyzed to identify the optimal fermentation temperature. The dry-fermented sausages were inoculated with three types of starter cultures [CS (commercial starter culture), GD (GK1 + D1 + S6), and ND (NK3 + D1 + S6)]. The fermentation was performed for 3 days at 20 °C and 25 °C, and dried for 28 days. The Lactobacillus spp. plate count and TBARS showed significantly higher values in the 25 °C group than in the 20 °C group (p < 0.05). The Staphylococcus spp. plate count of GD and ND were significantly higher than CS group at all temperatures. On day 31, the moisture content and VBN values of all groups were less than 35 % and 20 mg%, respectively. According to E-nose, the highest amount of acetoin was detected at the GD group fermented at 25 °C. Thus, the optimal fermentation temperature is expected at 25 °C after using GD in the manufacturing of dry-fermented sausages.

Thermophilic semi-continuous composting of kitchen waste: Performance evaluation and microbial community characteristics

This study evaluated the feasibility, system stability, and microbial community succession of thermophilic semi-continuous composting of kitchen waste (KW). The results revealed that treatment performance was stable at a 10 % feeding ratio, with an organic matter (OM) degradation efficiency of 81.5 % and seed germination index (GI) of 50.0 %. Moreover, the OM degradation efficiency and GI were improved to 83.4 % and 70.0 %, respectively, by maintaining an optimal compost moisture content (50-60 %). However, feeding ratios of ≥ 20 % caused deterioration of the composter system owing to OM overloading. Microbial community analysis revealed that Firmicutes, Actinobacteria, Chloroflexi, Proteobacteria, and Gemmatimonadetes were dominant. Additionally, moisture regulation significantly increased the Proteobacteria abundance by 57.1 % and reduced the Actinobacteria abundance by 57.8 %. Moreover, network analysis indicated that the bacterial community stability and positive interactions between genera were enhanced by moisture regulation. This information provides a useful reference for practical KW composting treatment in the semi-continuous mode.

A revolving algae biofilm based photosynthetic microbial fuel cell for simultaneous energy recovery, pollutants removal, and algae production

Photosynthetic microbial fuel cell (PMFC) based on algal cathode can integrate of wastewater treatment with microalgal biomass production. However, both the traditional suspended algae and the immobilized algae cathode systems have the problems of high cost caused by Pt catalyst and ion-exchange membrane. In this work, a new equipment for membrane-free PMFC is reported based on the optimization of the most expensive MFC components: the separator and the cathode. Using a revolving algae-bacteria biofilm cathode in a photosynthetic membrane-free microbial fuel cell (RAB-MFC) can obtain pollutants removal and algal biomass production as well as electrons generation. The highest chemical oxygen demand (COD) removal rates of the anode and cathode chambers reached 93.5 ± 2.6% and 95.8% ± 0.8%, respectively. The ammonia removal efficiency in anode and cathode chambers was 91.1 ± 1.3% and 98.0 ± 0.6%, respectively, corresponding to an ammonia removal rate of 0.92 ± 0.02 mg/L/h. The maximum current density and power density were 136.1 mA/m2 and 33.1 mW/m2. The average biomass production of algae biofilm was higher than 30 g/m2. The 18S rDNA sequencing analysis the eukaryotic community and revealed high operational taxonomic units (OTUs) of Chlorophyta (44.43%) was dominant phyla with low COD level, while Ciliophora (54.36%) replaced Chlorophyta as the dominant phyla when COD increased. 16S rDNA high-throughput sequencing revealed that biofilms on the cathode contained a variety of prokaryote taxa, including Proteobacteria, Bacteroidota, Firmicutes, while there was only 0.23-0.26% photosynthesizing prokaryote found in the cathode biofilm. Collectively, this work demonstrated that RAB can be used as a bio-cathode in PMFC for pollutants removal from wastewater as well as electricity generation.

Role of multistage inoculation on the co-composting of food waste and biogas residue

Effect of diverse Lactobacillus amylophilus, Geobacillus thermoleovorans, and Bacillus subtilis inoculation patterns on the co-composting performance of food waste and biogas residue was explored. Experimental results revealed that, compared to the single-stage inoculation and non-inoculation groups, the multistage inoculation pattern prolonged the thermophilic period during composting, consequently improving organic matter decomposition and humification [with a high germination index (120.9%)]. In addition, it could promote the development of humic substances [with a high humus index (4.3) and biological index (1.4)] and lower emissions of carbon dioxide (CO₂), methane (CH₄), and ammonia (NH₃). Additionally, it could improve the microbial variety and the amounts of functional bacteria (i.e., Chloroflexi) in compost, which might be advantageous for the decomposition of refractory organic materials and plant growth. Therefore, the multistage inoculation pattern is recommended for organic waste composting in terms of its gas emissions, compost quality and efficacy benefits.

Evaluation of key microbial community succession and enzyme activities of nitrogen transformation in pig manure composting process through multi angle analysis

This experiment aimed to investigate changes in enzyme activity, microbial succession, and nitrogen conversion caused by different initial carbon-to-nitrogen ratios of 25:1, 35:1 and 20:1 (namely CK, T1 and T2) during pig manure composting. The results showed that the lower carbon-to-nitrogen ratio (T2) after composting retained 19.64 g/kg of TN which was more than 16.74 and 17.32 g/kg in treatments of CK and T1, respectively, but excessive conversion of ammonium nitrogen to ammonia gas resulted in nitrogen loss. Additional straw in T1 could play the role as a bulking agent. After composting, TN in T1 retained the most, and TN contents were 63.51 %, 67.34 % and 56.24 % in CK, T1 and T2, respectively. Network analysis indicated that many types of microorganisms functioned as a whole community at various stages of nitrogen cycle. This study suggests that microbial community structure modification might be a good strategy to reduce ammonium nitrogen loss.

Mitigation of NH3 and N2O emissions during food waste digestate composting at C/N ratio 15 using zeolite amendment

Composting of food waste digestate (FWD) is challenging as it requires more bulking agents, and the nitrogen loss is inevitable. To address these issues, FWD composting was conducted at a relatively lower C/N ratio of 15 with zeolite amendment in the dosage range of 5-15%. The impact of zeolite addition on nitrogen loss, NH₃ and N₂O emissions was assessed during FWD composting. The results showed that the addition of 10-15% zeolite could significantly reduce the phytotoxic nature of FWD and the compost maturity level could be reached in 10-21 days. Furthermore, ∼45% total nitrogen loss could be reduced by mitigating NH₃ and N₂O emissions upon 10 and 15% zeolite amendment. The outcome of the present study could be used as an effective strategy for composting FWD in any part of the world as the FWD characteristics are similar irrespective of the type of food waste.

Succession of Microbial Community during the Co-Composting of Food Waste Digestate and Garden Waste

Microorganisms are of critical importance during the composting process. The aim of this study was to reveal the bacterial and fungal compositions of a composting pile of food waste digestate and garden waste, where the succession of the microbial communities was monitored using Illumina MiSeq sequencing. We explored the efficiency of composting of different microorganisms to judge whether the composting system was running successfully. The results showed that the composting process significantly changed the bacterial and fungal structure. Firmicutes, Proteobacteria, and Bacteroidota were the dominant phyla of the bacterial communities, while Ascomycota was the dominant phylum of the fungal communities. Moreover, the highest bacterial and fungal biodiversity occurred in the thermophilic stage. The physical and chemical properties of the final compost products conformed to the national standards of fertilizers. The efficient composting functional microbes, including Cladosporium, Bacillus and Saccharomonospora, emerged to be an important sign of a successfully operating composting system.

Mechanism of digestate-derived biochar on odorous gas emissions and humification in composting of digestate from food waste

Emissions of odorous gases and prolonged composting duration are the key concerns in the composting of digestate from food waste (DFW). In this study, different amounts of biochar derived from DFW (BC-DFW) were introduced in the composting process of DFW to decrease the emissions of ammonia (NH₃) and volatile sulfur compounds (VSCs) and composting duration. The addition of BC-DFW increased the temperature and germination index during DFW composting. The group with 25% BC-DFW exhibited a 30% smaller composting duration. Significant amounts of NH₃ and VSCs emissions were observed in the initial phase of DFW composting. Dimethyl disulfide (DMDS) was a prominent contributor to the odor associated with VSCs. The addition of BC-DFW facilitated the adsorption of NH₃ and VSCs, and the corresponding contents decreased by 5-21% and 15-20%, respectively. Moreover,the BC-DFW accelerated the transformation of ammonium-nitrogen (NH₄⁺-N) to nitrate-nitrogen (NO₃^--N), thereby alleviating the NH₃ volatilization. The addition of 25% BC-DFW minimized the NH₃ emission and enhanced the generation of humic-acid-like matter, thereby promoting humification. Therefore, the addition of 25% BC-DFW was optimal for promoting the degradation of organic matter and humification and odor emission reduction (e.g., NH₃, DMDS).

Inhibitory Effects of the Addition of KNO3 on Volatile Sulfur Compound Emissions during Sewage Sludge Composting

Odor released from the sewage sludge composting process often has a negative impact on the sewage sludge treatment facility and becomes a hindrance to promoting compost technology. This study investigated the effect of adding KNO₃ on the emissions of volatile sulfur compounds, such as hydrogen sulfide (H₂S), dimethyl sulfide (DMS), and carbon disulfide (CS₂), during sewage sludge composting and on the physicochemical properties of compost products, such as arylsulfatase activity, available sulfur, total sulfur, moisture content, and germination index. The results showed that the addition of KNO₃ could inhibit the emissions of volatile sulfur compounds during composting. KNO₃ can also increase the heating rate and peak temperature of the compost pile and reduce the available sulfur loss. The addition of 4% and 8% KNO₃ had the best effect on H₂S emissions, and it reduced the emissions of H₂S during composting by 19.5% and 20.0%, respectively. The addition of 4% KNO₃ had the best effect on DMS and CS₂ emissions, and it reduced the emissions of DMS and CS₂ by 75.8% and 63.0%, respectively. Furthermore, adding 4% KNO₃ had the best effect from the perspective of improving the germination index of the compost.

Recent Advances on Innovative Materials from Biowaste Recycling for the Removal of Environmental Estrogens from Water and Soil

New technologies have been developed around the world to tackle current emergencies such as biowaste recycling, renewable energy production and reduction of environmental pollution. The thermochemical and biological conversions of waste biomass for bioenergy production release solid coproducts and byproducts, namely biochar (BC), hydrochar (HC) and digestate (DG), which can have important environmental and agricultural applications. Due to their physicochemical properties, these carbon-rich materials can behave as biosorbents of contaminants and be used for both wastewater treatment and soil remediation, representing a valid alternative to more expensive products and sophisticated strategies. The alkylphenols bisphenol A, octylphenol and nonylphenol possess estrogenic activity comparable to that of the human steroid hormones estrone, 17β-estradiol (and synthetic analog 17α-ethinyl estradiol) and estriol. Their ubiquitous presence in ecosystems poses a serious threat to wildlife and humans. Conventional wastewater treatment plants often fail to remove environmental estrogens (EEs). This review aims to focus attention on the urgent need to limit the presence of EEs in the environment through a modern and sustainable approach based on the use of recycled biowaste. Materials such as BC, HC and DG, the last being examined here for the first time as a biosorbent, appear appropriate for the removal of EEs both for their negligible cost and continuously improving performance and because their production contributes to solving other emergencies, such as virtuous management of organic waste, carbon sequestration, bioenergy production and implementation of the circular economy. Characterization of biosorbents, qualitative and quantitative aspects of the adsorption/desorption process and data modeling are examined.