Hydrothermal pretreatment contributes to accelerate maturity during the composting of lignocellulosic solid wastes

Alternating electric field as an effective inhibitor of bioavailability and phytotoxicity of heavy metals during electric field-assisted aerobic composting

Changing the form of the electric field in the electric field-assisted aerobic composting (EAC) system from direct current to alternating current is confirmed as a potential strategy to enhance compost humification to the level of hyperthermophilic composting. This study pioneered the comparative evaluation of the effects of different electric field forms on the immobilization and phytotoxicity of heavy metals during composting. The results demonstrated that the humic acid content and humification index of alternating electric field-assisted aerobic composting (AEFAC) were approximately 22.0 % and 33.7 % higher than that of EAC, respectively. Morphometric analysis of various HMs (Cu, Zn, Cr, Cd, and Pb) revealed that the amounts in the exchangeable and reducible fractions were obviously lower in AEFAC than in EAC. AEFAC reduced the bioavailability of multiple HMs to about 15.11-40.21 %, indicating the higher passivation efficiency of several HMs than EAC. PLS-PM analysis indicated that AEFAC inhibited HMs bioavailability mainly through physicochemical properties, humification parameters, and microbial communities. Phytotoxicity experiments confirmed that AEFAC improves the growth indicators of cultivated crops, resulting in a 26.2 % increase in plant height and a 36.2 % increase in root length compared to EAC. Moreover, compared with EAC, AEFAC reduces the accumulation of Cu, Zn, Cr, Cd, and Pb in cultivated plants by approximately 27.0 %, 30.9 %, 32.2 %, 8.6 %, and 10.9 %, respectively. This study provides the first proof of principle that AEFAC effectively promotes the passivation of HMs, providing a practical strategy for efficient and environmentally friendly compost disposal.

Effects of Trichoderma harzianum combined with Phanerochaete chrysosporium on lignin degradation and humification during chicken manure and rice husk composting

The purpose of this study was to investigate the effects of combined treatment of Trichoderma harzianum and Phanerochaete chrysosporium on lignin degradation and humification during aerobic composting. Chicken manure (CM) and rice husk (RH) were used as organic raw materials for composting. The basic physicochemical analysis indicated that the combined addition of Trichoderma harzianum and Phanerochaete chrysosporium effectively improved lignin degradation rate (16.60%), increased humic acid (HA) content (22.70 g/kg), and the germination index (GI) reached 110.99%. Fungal community revealed that the relative abundance of Ascomycota was 37.46-68.85%, 9.57-60.35%, 58.02-91.76%, 0.98-91.60% in CK, T1, T2, T3 and Basidiomycota was 7.81-36.03%, 7.84-3.55%, 4.42-9.60%, 0.06-8.05% in CK, T1, T2, T3 (in phylum); the relative abundance of Kazachstania was 0.001-68.48%, 0.62-14.60%, 7.06-25.45%, 0.001-38.16% in CK, T1, T2, T3 and Diutina was 2.67-7.97%, 1.11-34.42%, 15.79-64.41%, 0.25-35.34% in CK, T1, T2, T3 (in genus) during the composting. Especially, the combined addition of Trichoderma harzianum and Phanerochaete chrysosporium had more negative impact on the activity of Basidiomycota compared with CK and other treatments and Trichoderma harzianum treatment had the strongest inhibitory effect on Tausonia abundance compared with CK and other treatments. Correlation analysis indicated that moisture content influenced fungal community structure (r = -0.740, p < 0.01) which affected lignin degradation (r = -0.952, p < 0.01) and compost maturity level in the composting process. Fungi Functional Guild (FUNGuild) and correlation heatmap demonstrated that T3 could enhance the relative abundance of endophyte which may had the potential to improve the degradation of lignin. This study confirmed the positive effects of the combination of Trichoderma harzianum and Phanerochaete chrysosporium in enhancing lignin degradation and promoting compost maturity, providing a foundation for a deeper understanding of the mechanisms involved in lignin degradation and humification processes influenced by the fungal community during composting, ultimately contributing to the efficient utilization of agricultural waste resources.

Impact of Hot Water Extraction on the Compaction Efficiency and Material Properties of Miscanthus giganteus in Pellet Production

The present study aimed to determine the effect of material modification by hot water extraction (HWE) on the compaction efficiency of shredded Miscanthus giganteus stalks in the pellet production process. Samples were prepared to differ in the number of HWE cycles: HWE I was subjected to a single cycle, HWE II was subjected to two cycles, and HWE III was subjected to three cycles and unmodified material. An analysis of the compaction process was carried out to evaluate the effect of HWE on density and energy consumption. In this study, HWE pre-treatment was applied to improve biomass compaction efficiency and material properties, improving biofuel production's sustainability and efficiency. A small change was found in glucose and xylose content, suggesting that HWE slightly affects these sugars. It was found that HWE significantly increased the density of compacted Miscanthus giganteus biomass, with a peak density of 388.7 kg·m-3 after the first HWE cycle. Ash content was reduced by 50% after one HWE cycle, making the biomass more suitable for biofuel applications. Furthermore, pretreatment with HWE reduced energy consumption during compaction, enhancing process efficiency. This study highlights the role of hot water extraction (HWE) in improving miscanthus compaction, enhancing density, reducing ash, and lowering energy use.

Prediction of the impact of tobacco waste hydrothermal products on compost microbial growth using hyperspectral imaging combined with machine learning

The insufficient understanding of the impact of hydrothermal products on the growth characteristics of compost microorganisms presents a significant challenge to the broader implementation of hydrothermal coupled composting for tobacco waste. Traditional biochemical detection methods are labor-intensive and time-consuming, highlighting the need for faster and more accurate alternatives. This study investigated the effects of hydrothermal treatment on tobacco straw products and their influence on compost microorganism growth, using hyperspectral imaging (HSI) technology and machine learning algorithms. Sixty-one tobacco straw samples were analyzed with a hyperspectral camera, and image processing was used to extract average spectra from regions of interest (ROI). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were applied to assess four key variables: nicotine content, total humic acid content, Penicillium chrysogenum H/C ratio, and Bacillus subtilis OD600 ratio. The effects of hydrothermal treatment on compost were classified as promoting, inhibiting, or neutral regarding microbial growth. The Competitive Adaptive Reweighted Sampling (CARS) method identified the most influential wavelengths in the 900-1700 nm spectral range. The Random Forest (RF) model outperformed SVM, KNN, and XGBoost models in predicting microbial growth responses, achieving R c = 0.957, RMSE = 3.584. Key wavelengths were identified at 1096 nm, 1101 nm, 1163 nm, 1335 nm, and 1421 nm. The results indicate that hyperspectral imaging combined with machine learning can accurately predict changes in the chemical composition of tobacco straws and their effects on microbial activity. This method provides an innovative and effective means of improving the resource usage of tobacco straws in composting, enhancing sustainable waste management procedures.

Carbon-mediated modulation pathways of phytotoxicity in chicken manure composting

Compost phytotoxicity affects the safety of organic fertilizers returned to the field, thus hindering the breeding cycle, so it is essential to reduce the compost phytotoxicity. The phytotoxicity of compost was estimated utilizing the germination index (GI) and the aqueous substances (organics and ions) present in compost correlated closely with GI. This study assessed the effect of carbon additives from different plant sources (mushroom substrates (MS), cornstalks (CS) and garden substrates (GS)) on maturity parameters (temperature, pH, EC, C/N), content of aqueous carbon and nitrogen matters, salt ions, heavy metal ions, and microbiome of piles when composting with chicken manure and especially focused on their effect on GI. Results showed that all additives significantly improved GI (85.25%-106.28%). The primary factors influencing seed germination were Mg2+ and SO42- in CM compost, acetic acid and NH4+ in CM + MS compost, humic acid in CM + CS compost, and dissolved total nitrogen in CM + GS compost. During composting, the growth of heavy metal passivating bacteria (Bacillus) and organic matter degrading bacteria (Desemzia and Turicibacter) can be promoted by decreasing aqueous carbon and nitrogen substances (volatile fatty acids, NH4+, dissolved total nitrogen, amino acids) and increasing the content of humic acid, which improved the composting environment and provided favorable conditions for the germination of seeds, thereby increasing GI. Therefore, GS showed the best potential for accelerating degradation of organic matter and improving GI during composting with chicken manure.

Techno-economic assessment of industrial food waste composting facility: Evaluating bulking agents, processing strategies, and market dynamics

Techno-economic assessment (TEA) of a valorization of bulking agent (BA) ratios on the food waste compost value chain is made to assess economic feasibility. TEA was performed with two plans (Plan A: existing composting facilities; Plan B: new composting facilities) and each plan was under four scenarios. The BA (i.e. corn stalks, garden waste, and watermelon seedlings) ratio of 5 % (S1), 10 % (S2), 20 % (S3), and garden waste with a ratio of 20 % (S4). Results indicate that S2, with a net present value (NPV) of 128.9 million, represents Plan A's most economically viable scenario. Although the total operating costs of S4 were 18.9 %-23.5 % higher, 25.6 %-42.2 % higher total revenue made S4 have an NPV of 92.9 million, making it the most viable scenario in Plan B. All scenarios show positive NPV within a ± 20 % fluctuation range. Organic fertilizer price, government subsidies, and processing capacity were the key factors influencing NPV.

Mitigation of ammonia and hydrogen sulfide emissions during aerobic composting of laying hen waste through NaOH-modified biochar

The impact of NaOH-modified biochar on the release of NH3 and H2S from laying hens' manure was examined for 44 days, using a small-scale simulated aerobic composting system. The findings revealed that the NaOH-modified biochar reduced NH3 and H2S emissions by 40.63% and 77.78%, respectively, compared to the control group. Moreover, the emissions of H2S were significantly lower than those of the unmodified biochar group (p < 0.05). The increased specific surface area and microporous structure of the biochar, as well as the higher content of alkaline and oxygenated functional groups, were found to facilitate the adsorption of NH3 and H2S. This enhanced adsorption capability was the primary reason for the significant reduction in NH3 emissions. Furthermore, during the high-temperature phase of composting, there was a notable alteration in the microbial community. The abundance of Limnochordaceae, Savagea, and IMCC26207 increased significantly which aided in the conversion of H2S to stable sulfate. These microorganisms also influenced the abundance of functional genes involved in sulfur metabolism, thereby inhibiting cysteine synthesis, along with the decomposition and conversion of sulfate to sulfite. This led to a significant decrease in H2S emissions. This study provides valuable data for the selection of deodorizers in the composting process of egg-laying hens. The results have significant implications for the application of NaOH-modified biochar for odor reduction in aerobic composting processes.

Ca(H2PO4)2 and MgSO4 activated nitrogen-related bacteria and genes in thermophilic stage of compost

This study was conducted to investigate the effects of Ca(H2PO4)2 and MgSO4 on the bacterial community and nitrogen metabolism genes in the aerobic composting of pig manure. The experimental treatments were set up as control (C), 1% Ca(H2PO4)2 + 2% MgSO4 (CaPM1), and 1.5% Ca(H2PO4)2 + 3% MgSO4 (CaPM2), which were used at the end of composting for potting trials. The results showed that Ca(H2PO4)2 and MgSO4 played an excellent role in retaining nitrogen and increasing the alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) contents of the composts. Adding Ca(H2PO4)2 and MgSO4 changed the microbial community structure of the compost. The microorganisms associated with nitrogen retention were activated. The complexity of the microbial network was enhanced. Genetic prediction analysis showed that the addition of Ca(H2PO4)2 and MgSO4 reduced the accumulation of nitroso-nitrogen and the process of denitrification. At the same time, despite the reduction of genes related to nitrogen fixation, the conversion of ammonia to nitrogenous organic compounds was promoted and the stability of nitrogen was increased. Mantel test analysis showed that Ca(H2PO4)2 and MgSO4 can affect nitrogen transformation-related bacteria and thus indirectly affect nitrogen metabolism genes by influencing the temperature, pH, and organic matter (OM) of the compost and also directly affected nitrogen metabolism genes through PO43- and Mg2+. The pot experiment showed that composting with 1.5% Ca(H2PO4)2 + 3% MgSO4 produced the compost product that improved the growth yield and nutrient content of cilantro and increased the fertility of the soil. In conclusion, Ca(H2PO4)2 and MgSO4 reduces the loss of nitrogen from compost, activates nitrogen-related bacteria and genes in the thermophilic phase of composting, and improves the fertilizer efficiency of compost products. KEY POINTS: • Ca(H2PO4)2 and MgSO4 reduced the nitrogen loss and improved the compost effect • Activated nitrogen-related bacteria and altered nitrogen metabolism genes • Improved the yield and quality of cilantro and fertility of soil.

Effects of Bacillus-based inoculum on odor emissions co-regulation, nutrient element transformations and microbial community tropological structures during chicken manure and sawdust composting

This study aims to evaluate whether different doses of Bacillus-based inoculum inoculated in chicken manure and sawdust composting will provide distinct effects on the co-regulation of ammonia (NH3) and hydrogen sulfide (H2S), nutrient conversions and microbial topological structures. Results indicate that the Bacillus-based inoculum inhibits NH3 emissions mainly by regulating bacterial communities, while promotes H2S emissions by regulating both bacterial and fungal communities. The inoculum only has a little effect on total organic carbon (TOC) and inhibits total sulfur (TS) and total phosphorus (TP) accumulations. Low dose inoculation inhibits total potassium (TK) accumulation, while high dose inoculation promotes TK accumulation and the opposite is true for total nitrogen (TN). The inoculation slightly affects the bacterial compositions, significantly alters the fungal compositions and increases the microbial cooperation, thus influencing the compost substances transformations. The microbial communities promote ammonium nitrogen (NH4+-N), TN, available phosphorus (AP), total potassium (TK) and TS, but inhibit nitrate nitrogen (NO3--N), TP and TK. Additionally, the bacterial communities promote, while the fungal communities inhibit the nitrite nitrogen (NO2--N) production. The core bacterial and fungal genera regulate NH3 and H2S emissions through the secretions of metabolic enzymes and the promoting or inhibiting effects on NH3 and H2S emissions are always opposite. Hence, Bacillus-based inoculum cannot regulate the NH3 and H2S emissions simultaneously.

Electron transfer and microbial mechanism of synergistic degradation of lignocellulose by hydrochar and aerobic fermentation

In response to the problem of asynchronous fermentation between lignocellulose and perishable materials in compost, the combined technology of low-temperature hydrochar and compost has been studied. Hydrochar was prepared through low-temperature hydrothermal reactions and applied to aerobic fermentation. The response relationship between lignocellulose content, electron transfer capability, and microbes was explored. The results showed that a pore structure with oxygen-containing functional groups was formed in hydrochar, promoting electron transfer during composting. With the rapid increase in composting temperature, the lignocellulose content decreased by 64.36 mg/g. Oceanobacillus, Cerasibacillus, Marinimicrobium, and Gracilibacillus promoted the degradation of lignocellulose and the carbon/nitrogen cycle during aerobic fermentation, and there was a significant response relationship between electron transfer capability and functional microbes. The combined application of hydrochar and aerobic fermentation accelerated the degradation of lignocellulose. This study provides technical support for the treatment of heterogeneous organic waste.

Change of core microorganisms and nitrogen conversion pathways in chicken manure composts by different substrates to reduce nitrogen losses

Due to the rapid development of animal husbandry, the associated environmental problems cannot be ignored, with the management of livestock and poultry manure emerging as the most prominent issue. Composting technology has been widely used in livestock and poultry manure management. A deeper understanding of the nitrogen conversion process during composting offers a theoretical foundation for selecting compost substrates. In this study, the effects of sawdust (CK) and spent mushroom compost (T1) as auxiliary materials on nitrogen as well as microbial structure in the composting process when composted with chicken manure were investigated. At the end of composting, the nitrogen loss of T1 was reduced by 17.18% relative to CK. When used as a compost substrate, spent mushroom compost accelerates the succession of microbial communities within the compost pile and alters the core microbial communities within the microbial community. Bacterial genera capable of cellulose degradation (Fibrobacter, Herbinix) are new core microorganisms that influence the assimilation of nitrate reduction during compost maturation. Using spent mushroom compost as a composting substrate increased the enzyme activity of nitrogen assimilation while decreasing the enzyme activity of the denitrification pathway.

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.

Biochar enhanced organic matter transformation during pig manure composting: Roles of the cellulase activity and fungal community

Fungal degradation of cellulose is a key step in the conversion of organic matter in composting. This study investigated the effects of adding 10% biochar (including, prepared from corn stalk and rape stalk corresponding to CSB and RSB) on organic matter transformation in composting and determined the role of cellulase and fungal communities in the conversion of organic matter. The results showed that biochar could enhance the conversion of organic matter, especially in RSB treatment. Biochar could increase cellulase activity, and RSB could enhance 33.78% and 30.70% the average activity of cellulase compared with the control and CSB treatments in the mesophilic to thermophilic phase, respectively. The results of high throughput sequencing demonstrated that Basidiomycota dominant in mesophilic phase, and Ascomycota dominant in other phases of composting. The redundancy analysis showed that Alternaria, Thermomycees, Aspergillus, Wallemia, and Melanocarpus might be the key fungi for the degradation of organic matter, and Fusarium, Penicillium, and Scopulariopsis may promote the conversion of organic matter. Network showed that the addition of RSB changed the interactions between fungal communities and organic matter transformation, and RSB treatment enriched members of Ascomycota related to organic matter transformation and cellulase activity. These results indicated that RSB improved organic matter conversion by enhancing the role of cellulase and fungal communities.

Pretreatment and composting technology of agricultural organic waste for sustainable agricultural development

With the continuous development of agriculture, Agricultural organic waste (AOW) has become the most abundant renewable energy on earth, and it is a hot spot of research in recent years to realize the recycling of AOW to achieve sustainable development of agricultural production. However, lignocellulose, which is difficult to degrade in AOW, greenhouse gas emissions, and pile pathogenic fungi and insect eggs are the biggest obstacles to its return to land use. In response to the above problems researchers promote organic waste recycling by pretreating AOW, controlling composting conditions and adding other substances to achieve green return of AOW to the field and promote the development of agricultural production. This review summarizes the ways of organic waste treatment, factors affecting composting and problems in composting by researchers in recent years, with a view to providing research ideas for future related studies.

Exogenous microbial antagonism affects the bioaugmentation of humus formation under different inoculation using Trichoderma reesei and Phanerochaete chrysosporium

This study was aimed at exploring the effect of antagonism of Trichoderma reesei (T.r) and Phanerochaete chrysosporium (P.c) on humification during fermentation of rice (RS) and canola straw (CS). Results showed that exogeneous fungi accelerated straw degradation and enzyme activities of CMCase, xylanase and LiP. P.c inhibited the activity of LiP when co-existing with T.r beginning, it promoted the degradation of lignin and further increased the production of humus-like substances (HLS) and humic-like acid (HLA) in later fermentation when nutrients were insufficient. The HLS of RTP was 54.9 g/kg RS, higher than the other treatments, and displayed more complex structure and higher thermostability. Brucella and Bacillus were the main HLA bacterial producers. P.c was the HLA fungal producer, while T.r assisted FLA and polyphenol transformation. Therefore, RTP was recommended to advance technologies converting crop straw into humus resources.

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.

Microflora for improving the Auricularia auricula spent mushroom substrate for Protaetia brevitarsis production

Mushroom cultivation is a sustainable agricultural waste utilization method, but the lack of high-value utilization of the produced spent mushroom substrate (SMS) has hindered the development of mushroom cultivation-based circular agricultural systems. Conversion and utilization of SMS via Protaetia brevitarsis larvae (PBL) have proven to be a high-value AASMS utilization strategy. However, Auricularia auricula SMS (AASMS), which contains woodchips, is less palatable and digestible for PBL. To solve this problem, in this investigation, we screened out microflora (MF) for AASMS fermentation by comparing the fermentation performance as well as the effect on PBL feed intake, weight gain, and AASMS phytotoxic compound removal efficiency. In addition, by bacterial community analysis, the genera Luteimonas, Moheibacter, and Pseudoxanthomonas were predicted to be functional bacteria for AASMS fermentation and contribute to palatability and digestibility improvement.

•

Larvae frass microflora can ferment Auricularia auricula spent mushroom substrate

•

The fermentation can improve feed intake, weight gain, and phytotoxic removal efficiency

•

The genera Luteimonas, Moheibacter, and Pseudoxanthomonas were functional bacteria

Emerging challenges for the agro-industrial food waste utilization: A review on food waste biorefinery

Modernization and industrialization has undoubtedly revolutionized the food and agro-industrial sector leading to the drastic increase in their productivity and marketing thereby accelerating the amount of agro-industrial food waste generated. In the past few decades the potential of these agro-industrial food waste to serve as bio refineries for the extraction of commercially viable products like organic acids, biochemical and biofuels was largely discussed and explored over the conventional method of disposing in landfills. The sustainable development of such strategies largely depends on understanding the techno economic challenges and planning for future strategies to overcome these hurdles. This review work presents a comprehensive outlook on the complex nature of agro-industrial food waste and pretreatment methods for their valorization into commercially viable products along with the challenges in the commercialization of food waste bio refineries that need critical attention to popularize the concept of circular bio economy.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.