Linking the electron transfer capacity with the compositional characteristics of dissolved organic matter during hyperthermophilic composting

Enhancing bioavailable carbon sources and minimizing ammonia emissions in distillery sludge and distiller's grains waste co-composting through deep eutectic solvent addition

This study introduced two deep eutectic solvents, ChCl/oxalic acid (CO) and ChCl/ethylene glycol (CE), into a 34-day co-composting process of distillery sludge and distiller's grains waste to address challenges related to NH3 emissions. The addition of DES increased dissolved organic carbon by 68% to 92%, offering more utilizable carbon for microorganisms. SYTO9/PI staining and enzyme activity tests showed the CE group had higher bacterial activity and metabolic levels during the thermophilic phase than the control. Bacterial community analysis revealed that early dominance of Lactobacillus and Lysinibacillus in CE accelerated the onset of the thermophilic phase, reduced pile pH, and significantly decreased urease production by reducing Ureibacillus. Consequently, CE treatment substantially dropped NH3 emissions by 73% and nitrogen loss by 54%. Besides, CE fostered a more abundant functional microbial community during the cooling and maturation phases, enhancing deep degradation and humification of organic matter.

Effect of soil organic matter-mediated electron transfer on heavy metal remediation: Current status and perspectives

Soil contamination by heavy metals poses major risks to human health and the environment. Given the current status of heavy metal pollution, many remediation techniques have been tested at laboratory and contaminated sites. The effects of soil organic matter-mediated electron transfer on heavy metal remediation have not been adequately studied, and the key mechanisms underlying this process have not yet been elucidated. In this review, microbial extracellular electron transfer pathways, organic matter electron transfer for heavy metal reduction, and the factors affecting these processes were discussed to enhance our understanding of heavy metal pollution. It was found that microbial extracellular electrons delivered by electron shuttles have the longest distance among the three electron transfer pathways, and the application of exogenous electron shuttles lays the foundation for efficient and persistent remediation of heavy metals. The organic matter-mediated electron transfer process, wherein organic matter acts as an electron shuttle, promotes the conversion of high valence state metal ions, such as Cr(VI), Hg(II), and U(VI), into less toxic and morphologically stable forms, which inhibits their mobility and bioavailability. Soil type, organic matter structural and content, heavy metal concentrations, and environmental factors (e.g., pH, redox potential, oxygen conditions, and temperature) all influence organic matter-mediated electron transfer processes and bioremediation of heavy metals. Organic matter can more effectively mediate electron transfer for heavy metal remediation under anaerobic conditions, as well as when the heavy metal content is low and the redox potential is suitable under fluvo-aquic/paddy soil conditions. Organic matter with high aromaticity, quinone groups, and phenol groups has a stronger electron transfer ability. This review provides new insights into the control and management of soil contamination and heavy metal remediation technologies.

Effects of additive on formation and electron transfer capacity of humic substances derived from silkworm-excrement compost during composting

Amending biochar or MnO2 is a common strategy to regulate humification during manure composting. However, how these additives affect the formation, spectrum characteristics (UV-vis, FTIR, EEM) of humic substances (HSs) in silkworm-excrement (SE) compost and their electron transfer capacities (ETC) remains unclear. Thus, the SE composting pilot separately added with 10% corncob biochar (CB) (w/w) and 0.5% MnO2 (w/w) was run to investigate the effects. The results revealed that adding 10% CB slightly affected the HA/FA (humic acids/fulvic acids) ratios, UV-vis and FTIR spectra of the final SE-compost HSs and EEM components in the FA, but remarkably improved fulvic-like (C1)/quinone-like (C3) substances and reduced humic-like (C2)/protein-like substances (C4) in the HA. Meanwhile, 0.5% MnO2 had a noticeable positive effect on the aromatization of SE-compost FA and HA but only weak impact on SUVAs and EEM components in these HSs except C4 in the FA. Moreover, 10% CB obviously reduced EAC/EDC of FA and HA in the final SE compost by 31.1%/22.0% and 19.7%/24.0%, while MnO2 improved EDC of these HSs by 6.5%/9.1% (FA/HA). These results showed MnO2 can be used as a useful amendment to enhance the promotion effect of SE-compost HA in the soil remediation other than CB. Further investigation is suggested to focus on the effects of adding MnO2 on SE-compost HSs enhancing soil remediation and its effect on ETC derived from other manure compost.

Deciphering the bioavailability of dissolved organic matter in thermophilic compost and vermicompost at the molecular level

Studies on compost dissolved organic matter (DOM) previously focus on its composition and humification, without considering DOM bioavailability to understand compost fertility. To decipher the fertility basis of compost, DOM bioavailability in thermophilic compost (TC) and vermicompost (VC) was investigated and linked with its molecular composition. Results showed that DOM bioavailability of VC (36 % BDOC) was generally higher than that of TC (22 % BDOC) due to containing more tannin-like substances. Inversely, only lipid-/carbohydrate-/protein-like substances contributed to DOM bioavailability in TC. Moreover, these differences of bioavailability expanded with C/N decreased in composting materials. Specifically, the %BDOC of VC with N-rich materials (C/N < 25) was 2.1-3.0 times higher than that in TC, while it was only 1.2-1.4 times for C-rich materials (C/N < 25), because N-surplus facilitated the formation of O-/N-containing aromatics (e.g., CHON and tannin) in VC, but inhibited the decomposition of organic materials into small bioactive molecules in TC.

Electric field applications enhance the electron transfer capacity of dissolved organic matter in sludge compost

Dissolved organic matter (DOM) plays an important role in heavy metal passivation and organic pollutant degradation owing to its redox ability. The structure and composition of DOM are determinants of redox ability changes during composting. Electric field-assisted aerobic composting (EAAC) has been shown to promote the degradation and humification of organic matter in compost. However, how EAAC affects the redox ability of DOM remains unclear. Hence, electron transfer capacity (ETC) of DOM extracted from EAAC was studied using the electrochemical method. Various spectral methods, such as excitation-emission matrix and ultraviolet and visible spectrophotometry were used to study the relationship of ETC with the compositional and structural changes of DOM. Results indicated that EAAC enhanced ETC of DOM at the later stage of composting, and ETC of DOM extracted from the final EAAC product was 10.4% higher than that of the control group. Spectral and correlation analyses showed that EAAC resulted in structural and compositional changes of DOM, and humification degree, aromatic compounds, molecular weight, and fulvic- and humic-like substance contents were improved in EAAC. This conversion increased ETC of DOM. Results of this study will contribute to the understanding of the redox of DOM and in expanding the application of EAAC products.

The microbial oxidation of pharmaceuticals in an anaerobic aqueous environment: Effect of dissolved organic matter fractions from different sources

Previous studies have demonstrated the importance of dissolved organic matter (DOM) on the biodegradation of trace organic contaminants occurred in the hyporheic zone. However, the role of diverse DOM fractions with distinct physicochemical properties on the biodegradation of pharmaceuticals under reducing conditions is scarcely known. To address this knowledge gap, DOMs derived from road-deposited sediment, soil, and active sludge (namely allochthonous DOM) and algae (namely autochthonous DOM) were collected and isolated into different fractions. Thereafter, the effect of DOM fractions on the anaerobic microbial oxidation of two typical pharmaceuticals, i.e., ritonavir (RTV) and tetracycline (TC) was explored by using simulated anaerobic microcosms. Mechanistic insights into how DOM fractions from different sources influence pharmaceutical biodegradation processes were provided by optical and electrochemical analyses. Results showed that humic acid and fulvic acid fractions from allochthonous DOM could enhance the biodegradation of TC (12.2 % per mgC/L) and RTV (14.5 % per mgC/L), while no significant impact was observed for that of hydrophilic fractions. However, autochthonous DOM promoted the biodegradation of TC (4.17 % per mgC/L) and inhibited that of RTV. Mechanistic analysis showed that the higher of humification and aromatization level of DOM components, the stronger their promotive effect on the biodegradation of TC and RTV. Further, the promotive mechanism could be attributed to the response of quinone moieties in DOM as extracellular electron acceptors that yields more energy to support microbial metabolism. These results provide a more comprehensive understanding of diverse DOM fractions mediating microbial anaerobic oxidation of trace organic pollutants, and extend our insights into contamination control and remediation technologies.

Compost-derived humic and fulvic acid coupling with Shewanella oneidensis MR-1 for the bioreduction of Cr(Ⅵ)

The compost-derived humic acids (HA) and fulvic acids (FA) contain abundant active functional groups with strong redox capacity, which can function as an electron shuttles for promoting the reduction of heavy metals, thus changing the form of the pollutants in the environment and reducing their toxicity. Therefore, in this study, UV-Vis, FTIR, 3D-EEM, electrochemical analysis were applied to study the spectral characteristics and electron transfer capacity (ETC) of HA and FA. Upon analysis, the results showed an increasing trend of ETC and humification degree (SUVA254) for both HA and FA during composting. However, the aromatic degree (SUVA280) of HA was higher than FA. After 7 days of culture, 37.95% of Cr (Ⅵ) was reduced by Shewanella oneidensis MR-1 (MR-1) alone. Whereas, only if HA or FA existed, the diminution of Cr (Ⅵ) reached 37.43% and 40.55%, respectively. However, the removal rate of Cr (Ⅵ) by HA/MR-1 and FA/MR-1 increased to 95.82% and 93.84% respectively. It indicated that HA and FA acted as electron shuttles, mediating the transfer of electrons between MR-1 and the final electron acceptor, effectively facilitating the bioreduction of Cr (Ⅵ) to Cr (Ⅲ) and also determined via correlation analysis. This study suggested compost-derived HA and FA coupling with MR-1 exhibited excellent performance for the bioreduction of Cr (Ⅵ) to Cr (Ⅲ).

Fate of dissolved organic matter affected by oxytetracycline tolerant microorganisms during chicken manure composting

This study explored the interaction among the components of dissolved organic matter (DOM), environmental factors and oxytetracycline (OTC) tolerant bacteria during chicken manure composting using Parallel Factor Analysis (PARAFAC) and 16S rRNA sequencing analysis. The results revealed that the OTC residues in chicken manure may affect the transformation between the protein-like component (C1) and humus-like component (C2 and C3) during composting. The transformation of DOM components under the OTC stress was indirect by affecting the microbial community activity. The OTC tolerant bacteria that still exist after the high temperature period of composting had a significant positive correlation between the humification process. The correlations of the dissolved organic carbon (DOC), total nitrogen (TN), and core OTC tolerant bacteria with DOM components, which enhanced the cooperative function of DOM component transformation. To clarify the influence of OTC residue on the humification process can promote the composting carbon fixation and improve composting quality.

Black soldier fly pretreatment promotes humification and phosphorus activation during food waste composting

Black soldier fly (BSF) and thermophilic composting (TC) treatments are commonly adopted to manage food waste. In this study, 30 days of TC of food waste following seven days BSF pretreatment (BC) was compared to 37 days of TC of food waste (TC, the control). Fluorescence spectrum and 16S rRNA high-throughput sequencing analysis were used to compare the BC and TC treatments. Results showed that BC could decrease protein-like substances and increase humus substances more quickly, and that the humification index of compost products was 106.8% higher than that of TC, suggesting that the humification process was accelerated by BSF pretreatment resulting in a 21.6% shorter maturity time. Meanwhile, the concentrations of total and available phosphorus rose from 7.2 and 3.3 g kg-1 to 44.2 and 5.5 g kg-1, respectively, which were 90.5% and 118.8% higher in compost products from BC as compared to those in TC. Furthermore, BC had higher richness and diversity of humus synthesis and phosphate-solubilizing bacteria (PSB), with Nocardiopsis (53.8%) and Pseudomonas (47.0%) being the dominant PSB. Correlation analysis demonstrated that the introduction of BSF gut bacteria contributed to the effectiveness of related functional bacteria, resulting in a rapid humification process and phosphorus activation. Our findings advance understanding of the humification process and provide novel perspectives on food waste management.

Insight into the evolution characteristics on molecular weight of compost dissolved organic matters using high-performance size exclusion chromatography combined with a two-dimensional correlation analysis

The information on molecular weight (MW) characteristics of DOM and relevant evolution behaviors during composting are limited. In this study, DOM extracted from co-composting of chicken manure and rice husks were comprehensively analyzed by using high-performance size exclusion chromatography (HPSEC) combined with a two-dimensional correlation spectroscopy (2D COS) to explore the evolution characteristics of MW of compost DOM. The HPSEC detected at UV of 254 nm and at fluorescence (FL) Ex/Em wavelengths (315/410, 270/455 nm) all showed a gradual increase in both weight-average and number-average MW for DOM, suggesting that the large MW fractions were continuously generated and polymerized during composting. The 2D COS applied on HPSEC-UV and -FL further identified the key active MW chromophoric (i.e., 0.5, 7.2. 9.5, 26.3, 30.7, and 83.9 kDa) and fluorophoric (i.e., 0.55 and 3.5 kDa) molecules that mainly participated in the transformation processes of compost DOM. Moreover, these active MW species were preferentially formed by the order of small to large molecules. A hetero-2D COS analysis disclosed the change sequence in the order of 0.5 and 7.2 kDa chromophores → 3.5 kDa fluorophores, and the 0.55 and 3.5 kDa fluorophores → 26.3 and 83.9 kDa chromophores.

Comprehensive evaluation of spent mushroom substrate-chicken manure co-composting by garden waste improvement: physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter

The performance of garden waste on spent mushroom substrate (SMS) and chicken manure (CM) co-composting efficiency and humification is unclear. Therefore, this study investigated the impact of garden waste addition on SMS-CM co-composting physicochemical properties, humification process, and the spectral characteristics of dissolved organic matter (DOM). The results showed that garden waste improved the physicochemical properties of SMS-CM co-compost, the thermophilic period was advanced 2 days, the seed germination index increased by 30.2%, and the total organic carbon and total nitrogen content increased by 8.80% and 15.0%, respectively. In addition, garden waste increased humic substances (HS) and humic acid (HA) contents by 10.62% and 34.52%, respectively; the HI, PHA and DP increased by 31.53%, 43.19% and 55.53%, respectively; and the SUVA₂₅₄ and SUVA₂₈₀ of DOM also increased by 6.39% and 4.39%, respectively. In particular, HA content and DOM humification increase rapidly in the first 10 days. The increase of HA accounted for 52% of the total increase during composting. Fourier-transform infrared and two-dimensional correlation analysis further confirmed that garden waste could facilitate the degradation of organic molecules, including amino acids, polysaccharides, carboxyl groups, phenols, and alcohol, and contributed to the preferential utilization of carboxyl groups and polysaccharides and thus enhanced humification.

In situ generated oxygen distribution causes maturity differentiation during electrolytic oxygen aerobic composting

Electrolytic oxygen aerobic composting (EOAC) is an effective treatment with greater technical superiority and cost advantages for organic solid waste using in situ electrolytic oxygen as a feasible strategy to replace conventional aeration. However, the unclear effects of distribution and variation of in situ electrolytic oxygen on compost maturation in different depth zones of EOAC need further exploration. This study demonstrated that the humification of organic matter was faster at the bottom than in the middle and at the top. The main reason was that the higher oxygen content and lower moisture content in the bottom promoted microbial degradation and heat production, resulting in higher temperatures. The microbial analysis showed that the abundance of typical thermophilic bacteria (such as Cerasibacillus, Lactobacillus, and Pseudogracilibacillus) that could promote compost maturation was higher at the bottom than in the middle and at the top. The finding provided in-depth molecular insights into differentiated humification from bottom to top in EOAC and revealed its further practical engineering applications.

Reduction capacity of humic acid and its association with the evolution of redox structures during composting

The reducing capacity (RC) of compost-derived humic acid (HA) is related to the type and number of redox-active functional moieties in its structure and has a considerable environmental influence on its geochemical redox cycle. Composting treatment can affect the redox-active fractions of organic substances through microbial transformation and degradation. However, the relationship between the RC of compost-derived HA and its fluorescence component and infrared spectra remains unclear. In this study, we assessed the response of the organic reducing capacity (ORC) and inorganic reducing capacity (IRC) of compost-derived HA to the stabilization of organic solid waste materials by analyzing the redox-active functional groups of HA extracted at different composting times. The results demonstrated that the RC of compost-derived HA continuously increased during composting because of the formation of fulvic- and humic-like fluorescent components, which consist of amide, phenolic hydroxyl, quinone, and aromatic groups. Adsorption occurred between HA and FeCit by aliphatic and out-of-plane aromatic CH, which released free hydrogen and increased the Fe-binding site; consequently, ORC was obviously higher than IRC. The results of this study could provide an understanding of the transformation of the fluorescent substances and functional groups that affect redox properties during composting; therefore, this study has considerable significance for exploring the application of compost products.

Effect of ventilation quantity on electron transfer capacity and spectral characteristics of humic substances during sludge composting

Humic substances (HSs) can ameliorate soil pollution by mediating electron transfer between microorganisms and contaminants. This capability depends on the redox-active functional structure and electron transfer capacity (ETC) of HS. This study mainly aimed to analyze the effects of different ventilation quantities on the ETC and spectral characteristics of HS (including humic acids (HAs) and fulvic acids (FAs)) during sludge composting. HS was extracted from compost with different ventilation quantities (0.1, 0.2, and 0.3 L kg^-1 dry matter min^-1, denoted as VQ1, VQ2, and VQ3, respectively). The ETC of HS was measured by electrochemical method. Excitation-emission matrix (EEM) spectroscopy, ultraviolet and visible (UV-Vis) spectrophotometry, and Fourier transform infrared (FT-IR) spectroscopy were conducted to understand the evolution of HS composition during composting. Results indicated that the ETC of HA and FA increased during composting, and VQ2 had stronger ETC and electron recycling rate than VQ1 and VQ3 at the end of composting. UV-Vis analysis revealed that the humification degree, aromatization degree, and molecular weight of HA and FA increased during composting, while the content of lignin decreased. EEM-PARAFAC results suggested that VQ2 accelerated the degradation of protein-like substances. FT-IR revealed a decrease trend in polysaccharide and aliphatic, and the carboxyl content increased in VQ2 and VQ3 while decreased in VQ1. Correlation analysis was used to study the relationship between HS components and ETC. The results advance our further understanding of the pollution remediation mechanism of HS.

Enhancement effects of dissolved organic matter leached from sewage sludge on microbial reduction and immobilization of Cr(VI) by Geobacter sulfurreducens

Sewage sludge has a high concentration of dissolved organic matter (DOM) which contains compounds that can serve as electron donors or shuttles for metal reduction by dissimilatory metal reducing bacteria (DMRB). In this study, Cr(VI) removal by G. sulfurreducens, a common DMRB present in anaerobic soils, was examined in the presence or absence of sludge DOM. Two different types of sludge DOM were tested; composted sludge DOM (C-DOM) and anaerobically digested sludge DOM (A-DOM). Both sludge DOMs enhanced Cr(VI) reduction by G. sulfurreducens, but C-DOM was more effective likely because it had higher concentrations of humic substances that served as electron shuttles. Transcriptomic studies indicated that G. sulfurreducens utilizes several different mechanisms to tolerate chromium including extracellular Cr(VI) reduction and immobilization by outer membrane c-type cytochromes and electrically conductive pili, intracellular Cr(VI) reduction by triheme cytochromes and NAD(P)H FMN reductase proteins, and chromium efflux by several P-type ATPase and RND transporter proteins. Microscopy experiments also showed that Cr(III) crystals formed on the surface of the cells, indicating that extracellular Cr(VI) reduction and adsorption was involved in the chromium removal process. These results help provide insight into the potential use of sewage sludge as an additive to enhance the bioremediation of chromium contaminated soils.

Effects of radiation with diverse spectral wavelengths on photodegradation during green waste composting

Composting is currently the best way to dispose of green waste (GW), which contains lignocellulose and other refractory substances that can prolong composting time. Although the natural degradation of litter involves photodegradation, few studies have considered the effects of photodegradation on GW composting. The current research investigated the influence of radiation with different spectral wavelengths (light-transmitting films were used to filter sunlight) on composting efficiency. Among six treatments that differed in the spectral wavelength of radiation, a no-UV-A treatment (the radiation between 320 nm and 380 nm was blocked by light-transmitting film) produced the best-quality compost product in only 34 days. Compared to the control (the full spectrum of light), the no-UV-A treatment increased total porosity, humus coefficient, optimal particle-size, and germination index by 10%, 2%, 3%, and 9%, respectively; increased available phosphorus, available potassium, and nitrate nitrogen by 21%, 17%, and 21%, respectively; decreased electrical conductivity, residual organic matter, and ammonium nitrogen by 9%, 13%, and 14%, respectively; and increased dehydrogenase, cellulase, and laccase activity by 76%, 66%, and 23%, respectively. These results indicated that the no-UV-A treatment resulted in the most complete degradation of lignocelluloses, the best nutrient properties, and the highest level of microbial activity in the GW compost. In addition, the bulk density, water-holding capacity, total porosity, void ratio, particle-size distribution, and coarseness index of the compost product were the closest to ideal ranges with the no-UV-A treatment and indicated that the no-UV-A compost product had the best granular structure in support of aeration, water drainage, and water retention. In a phytotoxicity assay, the compost produced by the no-UV-A treatment had the highest root length, seed germination rate, and germination index, indicating that the compost product was non-phytotoxic, mature, and suitable for use in agriculture and forestry.

Linking Microbial Community Succession With Substance Transformation in a Thermophilic Ectopic Fermentation System

Ectopic fermentation system (EFS) is an effective technology for treating mass livestock manure. However, the associations between microbial communities and substance transformation remain controversial. This study aimed to investigate chicken manure EFS lasting 170 days using 16S rRNA sequencing and electrochemical, spectroscopic, and chromatographic analyses. The results showed a noticeable transformation of protein-like substances into humus-like substances. Meanwhile, the electron–accepting capacity increased persistently, effectively reflecting the humification of organic substances. The contents of phenols that promoted electron transfer continued to increase from 2.80 to 6.00%, which could be used as a maturity indicator for EFS. During the heating period, the dominant microbial communities were Chloroflexi and Proteobacteria, whereas thermotolerant bacteria Cyanobacteria and Planctomycetes were significantly enriched from 1.64 to 50.15% during the continuous thermophilic period of EFS. The correlation analysis manifested that these thermotolerant bacteria were the major functional bacteria for the formation of phenols and the key to driving the humification of organic substances. This study provides insights into understanding the humification mechanisms and implementing regulatory strategies in EFS.

The Addition of Biochar and Hyper-Thermal Inoculum Can Regulate the Fate of Heavy Metals Resistant Bacterial Communities during the Livestock Manure Composting

In the present investigation the effects of biochar and hyper-thermal inoculum on the heavy-metal-resistant bacteria (HMRB) during livestock manure composting were studied. An experiment was performed on composting livestock manure and wheat straw amended with biochar and hyper-thermal inoculum. Physicochemical properties, enzyme activity, heavy metals (HMs), and bacterial activities were monitored, and a comprehensive assessment was analyzed during the composting process. The results showed that the dominant phyla of Proteobacteria, Bacteroidota, Actinobacteriota, and Chloroflexi were enriched, but this was not the case with Firmicutes. The abundance of Galbibacter, Thermobifida, Sphaerobacter, and Actinomadura was significantly different in CT15 and BHCT15. In addition, this study showed that the selected factors are less correlated with HMRB compared with the CT group. Therefore, this study could provide new insights into the effect of biochar and hyper-thermal inoculum amendments on the fate of HMRB under HMs and high temperature stress during livestock manure composting.

Recognize and assessment of key host humic-reducing microorganisms of antibiotic resistance genes in different biowastes composts

Humic-reducing microorganisms (HRMs) can utilize humic substance as terminal electron mediator promoting the bioremediation of contaminate, which is ubiquitous in composts. However, the impacts of HRMs on antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in composts and different HRMs community composition following the types of biowastes effected the spread of ARGs have not been investigated. Herein, the dynamics and mobility of ARGs and HRMs during protein-, lignocellulose- and lignin-rich composting were investigated. Result show that ARGs change significantly at the thermophilic phase, and the relative abundance of most ARGs increase during composting. Seven groups of HRMs communities are classified as primary host HRMs of ARGs, and most host HRMs groups from protein-rich composts. Conclusively, regulating methods for inhibiting ARGs spread for different composts are proposed. HRMs show a higher ARGs dissemination capacity in protein-rich composts than lignocellulose- and lignin-rich composts, but the spread of ARGs can be inhibited by regulate physicochemical parameters in protein-rich composts. In contrary, most HRMs have inhibitory effects on ARGs spread in lignocellulose- and lignin-rich composts, and those HRMs can be used as a new agent that inhibits the spread of ARGs. Our results can help in understanding the potential risk spread of ARGs by inoculating functional bacteria derived from different biowastes composts for environmental remediation, given their expected importance to developing a classification-oriented approach for composting different biowastes.

Hyperthermophilic Composting Technology for Organic Solid Waste Treatment: Recent Research Advances and Trends

Organic solid waste is considered a renewable resource that can be converted by various technologies into valuable products. Conventional thermophilic composting (TC), a well-studied and mature technology, can be applied to organic solid waste treatment to achieve waste reduction, mineralization, and humification simultaneously. However, poor efficiency, a long processing period, as well as low compost quality have always limited its wide application. In order to overcome these shortages, hyperthermophilic composting (HTC) has been recently put forward. This paper reviews the basic principle, process flow, operation parameters, research advances, and application status of HTC. Compared with the TC process, the shorter composting period and higher temperature and treatment efficiency, as well as more desirable compost quality, can be achieved during HTC by inoculating the waste with hyperthermophilic microbes. Additionally, HTC can reduce greenhouse gas emission, increase the removal rate of microplastics and antibiotic residues, and achieve in-situ remediation of heavy metal-polluted soils, which greatly improve its application potential for organic solid waste treatment. This paper also proposes the limitations and future prospects of HTC technology for a wider application. As a result, this review advances our understanding of the HTC process, which promotes its further investigation and application.