Influence of spent mushroom substrate and molasses amendment on nitrogen loss and humification in sewage sludge composting

Influence of microbial agents-loaded biochar on bacterial community assembly and heavy metals morphology in sewage sludge compost: Insights from community stability and complexity

Enhancing the passivation of heavy metals and increasing organic matter content during the composting of sewage sludge poses significant challenges for maximizing its utilization value. Results indicated that in the control, biochar, microbial agents and microbial agents-loaded biochar (BCLMA) groups, BCLMA addition led to a higher composting temperature, with increases of 17-62% in humic acid, 25-73% in germination index, and 30-35% in organic matter consumption. And the residual fraction of Cu, Zn, Cr and Cd were increased by 30%, 12%, 22% and 17%, respectively. Furthermore, BCLMA promotes community cohesion, robustness, and microbial nutrient cycling, and increases the relative abundance of heavy metals-degrading bacteria (Acinetobacter and Corynebacterium) and resistance genes. Structural equation model analysis revealed that heavy metal passivation is attributed to improved community cohesion and robustness, which facilitates the proliferation of heavy metal-resistant microorganisms. These results indicate that community robustness and cohesion are critical for mitigating the heavy metals bioavailability.

Spent mushroom substrate: A review on present and future of green applications

The cultivation of edible mushrooms plays a significant role in revitalizing numerous rural regions in China. However, this process generates a large amount of spent mushroom substrate (SMS). Traditional methods for handling SMS, such as random stacking and incineration, lead to resource waste and environmental pollution. The content of organic matter in SMS can range from 40% to 60%, and it also contains various beneficial elements such as trace minerals, making it a valuable resource for biomass. This review initially explores the unique characteristics of SMS and then summarizes the main methods of utilizing its resources. Presently, common resource utilization techniques for SMS include using it as a second-generation cultivation substrate, preparing animal feed and soil fertilizer, producing methane, bioethanol, hydrogen, bio-oil, and electrodes of energy storage devices, extracting enzymes and polysaccharides, and creating bioremediation materials for heavy metals and organic pollutants removal. While research has been conducted on these utilization methods, there are still relatively few large-scale industrial applications. This review also highlights existing challenges and potential solutions in the SMS utilization. Upcycling SMS via innovative and practical technologies presents a promising approach to transforming organic waste into economic value.

Status and development of spent mushroom substrate recycling: A review

The edible mushroom industry is the sixth largest after grain, cotton, oil, vegetables and fruits, and the annual production of edible mushrooms in China exceeds 40 million tons. Edible mushroom cultivation produces a class of by-products consisting mainly of mycelium remnants and lignocellulosic waste, known as Spent Mushroom Substrate (SMS) or Spent Mushroom Compost (SMC). SMS/SMC is rich in nutrients and active ingredients and has an extremely high recycling potential. This review paper summarizes SMS recycling strategies from the perspectives of "environmental remediation" and "circular economy", and briefly discusses the legitimacy, possible challenges and future research of SMS recycling. It is hoped that this will assist researchers in related fields and promote the development of the SMS recycling industry, thereby contributing to sustainable environmental and economic development.Implications: The efficient management of SMS is important for many countries around the world, particularly major mushroom producing countries. Traditional disposal methods (incineration, burial, piling) can cause serious damage to the environment and waste resources. The correct disposal method can protect the natural environment and provide certain economic benefits. This study presents the main methods of SMS processing from both an "environmental remediation" and "circular economy" perspective. In general, this paper emphasizes the importance of SMS processing, introduces the current mainstream processing methods and briefly discusses the legality of their processing methods.

Effects of different concentrations of biological maturity agents on nitrogen and microbial diversity of Auricularia heimuer residue compost

This study investigated the effects of different concentrations of biological maturity agents on the composting process of Auricularia heimuer residue by adding them to the composting process. By measuring the changes in physical and chemical indicators and microbial diversity during composting, the results showed that the addition of biological maturity agents had a certain promoting effect on compost temperature, humidity, pH, seed germination index, and vitality index. Appropriate composting days can promote the accumulation of ammonium nitrogen. The carbon content of humin and E4/E6 of treatments A, B, and E were significantly higher than those of the initial treatment. D0.CK treatment had the most types of resistance genes and the most abundant resistance genes. As composting progresses, the abundance of 13 resistance genes decreased. Adding high concentrations of biological maturity agents can activate the defense mechanism during the composting process, greatly ensuring the safety of fungi residue as a fertilizer.

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.

Effects of adding corn steep liquor on bacterial community composition and carbon and nitrogen transformation during spent mushroom substrate composting

BACKGROUND

Carbon and nitrogen are essential energy and nutrient substances in the composting process. Corn steep liquor (CSL) is rich in soluble carbon and nitrogen nutrients and active substances and is widely used in the biological industry. Nonetheless, limited research has been done on the effect of CSL on composting. This work firstly reveals the effect of adding CSL to bacterial community composition and carbon and nitrogen conversion during composting. This study provides the choice of auxiliary materials for the spent mushroom substrate compost (SMS) and some novel knowledge about the effect of bacterial community on C and N cycling during composting of SMS and CSL. Two treatments were set up in the experiment: 100% spent mushroom substrate (SMS) as CK and SMS + 0.5% CSL (v/v) as CP.

RESULTS

The results showed that the addition of CSL enhanced the initial carbon and nitrogen content of the compost, altered the bacterial community structure, and increased the bacterial diversity and relative abundance, which might be beneficial to the conversion and retention of carbon and nitrogen in the composting process. In this paper, network analysis was used to screen the core bacteria involved in carbon and nitrogen conversion. In the CP network, the core bacteria were divided into two categories, synthesizing and degrading bacteria, and there were more synthesizing bacteria than degrading bacteria, so the degradation and synthesis of organic matter were carried out simultaneously, while only degrading bacteria were found in the CK network. Functional prediction by Faprotax identified 53 groups of functional bacteria, among which 20 (76.68% abundance) and 14 (13.15% abundance) groups of functional bacteria were related to carbon and nitrogen conversion, respectively. Adding CSL stimulated the compensatory effect of core and functional bacteria, enhanced the carbon and nitrogen transformation ability, stimulated the activity of low-abundance bacteria, and reduced the competitive relationship between the bacterial groups. This may be why the addition of CSL accelerated the organic matter degradation and increased carbon and nitrogen preservation.

CONCLUSIONS

These findings indicate that the addition of CSL promoted the cycling and preservation of carbon and nitrogen in the SMS composts, and the addition of CSL to the compost may be an effective way to dispose of agricultural waste.

Antibiotic and heavy metal resistance genes in sewage sludge survive during aerobic composting

Municipal sewage sludge has been generated in increasing amounts with the acceleration of urbanization and economic development. The nutrient rich sewage sludge can be recycled by composting that has a great potential to produce stabilized organic fertilizer and substrate for plant cultivation. However, little is known about the metals, pathogens and antibiotic resistance transfer risks involved in applying the composted sludge in agriculture. We studied changes in and relationships between heavy metal contents, microbial communities, and antibiotic resistance genes (ARGs), heavy metal resistance genes (HMRGs) and mobile genetic elements (MGEs) in aerobic composting of sewage sludge. The contents of most of the analyzed heavy metals were not lower after composting. The bacterial α-diversity was lower, and the community composition was different after composting. Firmicutes were enriched, and Proteobacteria and potential pathogens in the genera Arcobacter and Acinetobacter were depleted in the composted sludge. The differences in bacteria were possibly due to the high temperature phase during the composting which was likely to affect temperature-sensitive bacteria. The number of detected ARGs, HMRGs and MGEs was lower, and the relative abundances of several resistance genes were lower after composting. However, the abundance of seven ARGs and six HMRGs remained on the same level after composting. Co-occurrence analysis of bacterial taxa and the genes suggested that the ARGs may spread via horizontal gene transfer during composting. In summary, even though aerobic composting is effective for managing sewage sludge and to decrease the relative abundance of potential pathogens, ARGs and HMRGs, it might include a potential risk for the dissemination of ARGs in the environment.

Effects of two types nitrogen sources on humification processes and phosphorus dynamics during the aerobic composting of spent mushroom substrate

Aerobic composting is increasingly regarded as a promising technology for the recycling of spent mushroom substrate (SMS), and an applicable nitrogen source is necessary to improve the process. This study is the first to investigate the effects of protein-like N source (chicken manure, CM) and high-N source (urea, UR) on humification process and P dynamics during SMS composting. The effect of different N sources on microbial succession was also studied. Results showed that CM addition achieved a longer thermophilic phase (16 d vs 9 d), greater germination indices (131.6% vs 106.3%), and higher total phosphorus content (13.1 g/kg vs 6.56 g/kg) in the end products, as compared to UR. The addition of CM showed beneficial effects on humification and stabilization, including decreased weight loss and fluctuations in the level of functional groups. The P produced in the compost was interconverted and leached in the P pool. In this case, the P detected in the compost was in the form of orthophosphate and MgNH₄PO₄⋅6H₂O crystal as inorganic P and orthophosphate monoester as organic P. The most abundant microorganisms at the phylum level mainly include Firmicutes, Actinobacteria, and Proteobacteria, accounting for more than 88% of the total microorganisms. The addition of CM to SMS compost resulted in higher organic matter degradation rates. This work clarified the role of various N sources in SMS composting and presented an appropriate waste management method beneficial to bioresource technology and sustainable development of the edible fungi business.

Impact of biochar, calcium magnesium phosphate fertilizer and spent mushroom substrate on humification and heavy metal passivation during composting

The effects of exogenous additives (biochar, calcium magnesium phosphate fertilizer, and spent mushroom substrate) on humification process and heavy metal passivation during pig manure composting were investigated. The aerobic composting trial were carried out in 60 L reactors for 49 d. The calcium magnesium phosphate fertilizer, biochar, and spent mushroom substrate amendment treatments all accelerated the organic matter degradation and increased the temperature, decreased the volatile fatty acid content by 45%-49.0% and promoted humification of the compost (increasing the humic acid content and humus index). The biochar passivated Cu best, calcium magnesium phosphate fertilizer passivated Zn best (passivation rate 13.85%), and spent mushroom substrate passivated Cd, Cr, and Pb best (passivation rates 25.47%-47.91%). The additives amendment improved Cu, Zn, Cd, Cr, and Pb passivation performance by promoting composting humification process.

Mechanism that allows manno-oligosaccharide to promote cellulose degradation by the bacterial community and the composting of cow manure with straw

The new sugar source manno-oligosaccharide can regulate the structure of the microbial community. This study investigated the effects of adding manno-oligosaccharide at four different levels (0, 0.1%, 0.5%, and 1% w/w compost) to composting cow manure and straw on lignocellulose degradation and the bacterial community. Adding 0.5% manno-oligosaccharide had the greatest effects on accelerating the composting process, reducing its toxicity, and improving the stability of the product. After composting for 25 days, adding 0.5% manno-oligosaccharide decreased the hemicellulose, cellulose, and lignin contents to 2.25%, 11.25%, and 7.07%, respectively, compared with those under CK. Manno-oligosaccharide promoted the degradation of lignocellulose by increasing the abundances of Thermobifida, Streptomyces, and Luteimonas. In addition, manno-oligosaccharide inhibited pathogenic bacteria and increased the abundances of functional genes related to metabolism. Finally, adding 0.5% manno-oligosaccharide mainly affected the degradation of lignocellulose by enhancing the C/N ratio and the abundances of Streptomyces and the secretion system during composting according to redundancy analysis.

Effects of different lignocellulosic wastes on alleviating acidification of L-lactic acid production from food waste fermentation

In this study, the effects of different lignocellulosic wastes on alleviating acidification in the fermentation of lactic acid (LA) from food waste (FW) were studied. Amongst three lignocellulosic wastes, spent mushroom substance (SMS) could reach 95.22% lignin removal efficiency through simple NaOH pretreatment. Results showed pretreated SMS was best choice for FW co-fermentation, the maximum LA concentration could reach 46.12 g/L. And the NaOH solution as neutraliser could save 5.69 mL compared with the other two lignocellulosic wastes. The reason for alleviating acidification was 4.71% calcium salt in SMS and the porous structure of SMS. Then, 50% of pretreated liquid (PL) produced in SMS pretreatment was reused in the co-fermentation process. Compared with the group with 0% PL loading, that with 50% PL loading showed an increase in LA concentration and optical purity of L-LA, reaching 50.95 g/L and 96.28%, and NaOH consumption also further decreased by 24.65%.

Effects of bamboo biochar on nitrogen conservation during co-composting of layer manure and spent mushroom substrate

Layer manure (LM) and spent mushroom substrate (SMS) are two kinds of nitrogen (N) rich solid wastes generate in the poultry breeding and agriculture production. Composting is an effective way to recycle the LM and SMS. However, a large amount of N in the LM and SMS was lost via volatilisation during composting, with negative environmental and economic consequences. This study investigated the effect of incorporating biochar at the ratio of 5%, 10%, and 15% (w/w) during co-composting of LM and SMS on ammonia (NH3) and nitrogen oxide (N2O) volatilisation and N retention. After the 35-day composting, the results showed that the pile temperature and seed germination index in biochar treatments were significantly improved in comparison with control treatment. The nitrogen in all treatments was lost in the form of N2O (0.05∼0.1%) and NH3 (13.1∼20.2%). Likewise, the total nitrogen loss was 28.9%, 20.3%, and 24.9%, respectively, of which N2O-N accounts for 0.05∼0.10%. Compared with control treatment, the total amount of NH3 volatilisation in biochar treatments of 5%BC, 10%BC and 15%BC was decreased by 21.2%, 33.1%, and 26.1%, respectively. The total amount of N2O emission was decreased by 39.0%, 13.2%, and 1.6%, respectively. Adding 10% and 15% biochar can significantly reduce NH3 volatilisation while adding 5% biochar treatment didn't significantly reduce NH3 emissions but showed the best performance in reducing N2O emission. The addition of 10% biochar in co-composting of LM and SMS is the recommended dosage that exhibited the best performance in improving composting quality and reducing nitrogen loss.