Differentiated strategies of animal-derived and plant-derived biochar to reduce nitrogen loss during paper mill sludge composting

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.

The influence of biochar from animal and plant on the transformation of phosphorus during paper mill sludge composting

Biochar has effect on phosphorus adsorption, release, and transformation. This study compared the influence of biochar derived from animal (AB) and plant (PB) during paper mill sludge composting. Results indicated AB not only accelerated sludge decomposition but also had significantly higher levels of available phosphorus (AP) than PB and CK (no biochar), with AP contents in the order of AB > PB > CK. Compared to CK, AB was found to increase the relative abundance of thermophilic bacteria, and PB diversified the microbial community. Based on Pearson and RDA results, TOC/TN ratio (C/N) and organic matter (OM) explained above 50% of the variance in microbial community and phosphorus fractions. Thermophilic bacteria with high levels of OM and C/N promoted the conversion among labile and moderately labile organic phosphorus, moderately labile inorganic phosphorus, and AP. Biochar could enhance the AP conversion pathway, leading to increased levels of AP.

Pulp-paper industry sludge waste biorefinery for sustainable energy and value-added products development: A systematic valorization towards waste management

The pulp-paper industry is one of the main industrial sectors that produce massive amounts of residual sludge, constituting an enormous environmental burden for the industries. Traditional sludge management practices, such as landfilling and incineration, are restricted due to mounting environmental pressures, complex regulatory frameworks, land availability, high costs, and public opinion. Valorization of pulp-paper industry sludge (PPS) to produce high-value products is a promising substitute for traditional sludge management practices, promoting their reuse and recycling. Valorization of PPIS for biorefinery beneficiation includes biomethane, biohydrogen, bioethanol, biobutanol, and biodiesel production for renewable energy generation. Additionally, the various thermo-chemical technologies can be utilized to synthesize bio-oil, hydrochar, biochar, adsorbent, and activated carbon, signifying potential for value-added generation. Moreover, PPIS can be recycled as a byproduct by incorporating it into nanocomposites, cardboard, and construction materials development. This paper aims to deliver a comprehensive overview of PPIS management approaches and thermo-chemical technologies utilized for the development of platform chemicals in industry. Substitute uses of PPIS, such as making building materials, developing supercapacitors, and making cardboard, are also discussed. In addition, this article deeply discusses recent developments in biotechnologies for valorizing PPIS to yield an array of valuable products, such as biofuels, lactic acids, cellulose, nanocellulose, and so on. This review serves as a roadmap for future research endeavors in the effective handling of PPIS.

The synergistic regulation of sewage sludge biodrying and greenhouse gas reduction by additives

As a dewatering method of high moisture solid waste sludge, biodrying still faces environmental problems such as material loss and greenhouse gas emission in the process of treatment. In this study, biochar and magnesium chloride were used to explore the synergistic effect of enhancing sludge biodrying and reducing greenhouse gas emissions. The highest temperature of biodrying was raised to 68.2 °C within 3 days, extending the longest high-temperature period to 5 days, which reduced the water content to 28.8 % in the single addition of biochar treatment. The complex addition increased the NH4+-N content of materials by 57.49 % and decreased the NO3--N content of materials by 40.62 %. The use of additives significantly reduced the emissions of CO2, CH4, and N2O compared to the no-addition treatment. The increase in dominant Actinomycetes and Chloroflexibacter was the main reason for the reduction in gas emissions.

Effects of adding lignocellulose-degrading microbial agents and biochar on nitrogen metabolism and microbial community succession during pig manure composting

This study assessed the influence of the additions of lignocellulose-degrading microbial agents and biochar on nitrogen (N) metabolism and microbial community succession during pig manure composting. Four treatments were established: CK (without additives), M (lignocellulose-degrading microbial agents), BC (biochar), and MBC (lignocellulose-degrading microbial agents and biochar). The results revealed that all treatments with additives decreased N loss compared with CK. In particular, the concentrations of total N and NO3--N were the highest in M, which were 21.87% and 188.67% higher than CK, respectively. Meanwhile, the abundance of denitrifying bacteria Flavobacterium, Enterobacter, and Devosia reduced with additives. The roles of Anseongella (nitrifying bacterium) and Nitrosomonas (ammonia-oxidizing bacterium) in NO3--N transformation were enhanced in M and BC, respectively. N metabolism pathway prediction indicated that lignocellulose-degrading microbial agents addition could enhance N retention effectively mainly by inhibiting denitrification. The addition of biochar enhanced oxidation of NH4+-N to NO2--N and N fixation, as well as inhibited denitrification. These results revealed that the addition of lignocellulose-degrading microbial agents individually was more conducive to improve N retention in pig manure compost.

A novel composting system for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer

Ammonia emissions not only lead to environmental pollution but also reduce the quality of compost products. Here, a novel composting system (condensation return composting system, CRCS) was designed for mitigating ammonia emissions. The results showed that the CRCS reduced ammonia emissions by 59.3% and increased the total nitrogen content by 19.4% compared with the control. By integrating the results of nitrogen fraction conversion, ammonia-assimilating enzyme activity, and structural equation modeling, it was found that the CRCS facilitated the conversion of ammonia to organic nitrogen by stimulating ammonia-assimilating enzyme activity and ultimately retained nitrogen in the compost product. Moreover, the pot experiment confirmed that nitrogen-rich organic fertilizer produced by the CRCS significantly increased the fresh weight (45.0%), root length (49.2%), and chlorophyll content (11.7%) of pakchoi. This study provides a promising strategy for mitigating ammonia emissions and producing nitrogen-rich organic fertilizer with high agronomic value.

Identifying the specific pathways to improve nitrogen fixation of different straw biochar during chicken manure composting based on its impact on the microbial community

The application of straw biochar to chicken manure composting mitigated nitrogen loss. However, the impact of biochar derived from different types of straw on nitrogen fixation in chicken manure composting is discrepant, and the specific pathways remain unclear. Therefore, this study aimed to clarify the specific pathways of maize straw biochar (M) and rice straw biochar (R) to improve nitrogen fixation during chicken manure composting. The nitrogen losses in control (no addition, CK), M, and R composting were 51.84 %, 33.47 %, and 38.24 %, respectively, suggesting that adding straw biochar effectively improved nitrogen fixation. Microbial community analysis suggested that inhibiting denitrification and NH4+-N transformation by microorganisms was the primary means of improving nitrogen fixation. Meanwhile, biochar addition reduced the number of bacteria participating in nitrogen transformation and strengthened the NO3--N and total organic nitrogen transformation processes, among which the effect of M composting was stronger. The stronger effect was attributed to the significant role of the core microorganisms in M composting in shifting the transformation processes of the nitrogen components (P < 0.05). Therefore, the function of different straw biochar was determined by its different impacts on the microbial community, highlighting the important role of microbial community variability.

Synergistic effects of rice husk biochar and aerobic composting for heavy oil-contaminated soil remediation and microbial community succession evaluation

Soil petroleum pollution is an urgent problem in modern society, which seriously threatens the ecological balance and environmental safety. Aerobic composting technology is considered economically acceptable and technologically feasible for the soil remediation. In this study, the combined experiment of aerobic composting with the addition of biochar materials was conducted for the remediation of heavy oil-contaminated soil, and treatments with 0, 5, 10 and 15 wt% biochar dosages were labeled as CK, C5, C10 and C15, respectively. Conventional parameters (temperature, pH, NH₄⁺-N and NO₃^--N) and enzyme activities (urease, cellulase, dehydrogenase and polyphenol oxidase) during the composting process were systematically investigated. Remediation performance and functional microbial community abundance were also characterized. According to experimental consequences, removal efficiencies of CK, C5, C10 and C15 were 48.0%, 68.1%, 72.0% and 73.9%, respectively. The comparison with abiotic treatments corroborated that biostimulation rather than adsorption effect was the main removal mechanism during the biochar-assisted composting process. Noteworthy, the biochar addition regulated the succession process of microbial community and increased the abundance of microorganisms related to petroleum degradation at the genus level. This work demonstrated that aerobic composting with biochar amendment would be a fascinating technology for petroleum-contaminated soil remediation.

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.

Biochar improved the composting quality of seaweeds and cow manure mixture and altered the microbial community

The beneficial effects of biochar addition during composting have been proved for many feedstocks, like manures and crop straws. However, the effect of biochar on the quality of composting product with seaweed as the feedstock and the bacterial response has not been investigated. In this study, the wheat straw biochar addition on the quality of the composting product and the bacterial response was explored at the rate of 0-10%. The results showed that biochar addition at the optimal rate (5%, w/w) could increase the germination index and the ratio of the optical density of humic acid at 460 nm to that at 660 nm (E4/E6) of the composting product, which indicated the decreased biotoxicity and enhanced compost maturity. The significant increase of the nitrate nitrogen (NO₃ ^--N) content of the composting product proved the improvement of N cycling during composting process with biochar addition. The bacterial community of composting product was shifted and the relative abundance of some beneficial taxa (e.g., Muricauda and Woeseia) was significantly increased with biochar addition. Furthermore, the relative abundance of some bacterial genes related to amino acid metabolism and carbohydrate metabolism was also increased with biochar addition. The results of our study provided the positive effect of biochar addition on the composting of seaweed and could help to produce high quality seaweed fertilizer by composting with biochar addition.

Influence of thermally activated peroxodisulfate pretreatment on gaseous emission, dissolved organic matter and maturity evolution during spiramycin fermentation residue composting

Aerobic composting combined with appropriate pretreatment is promising to achieve the utilization of antibiotics fermentation residues (AFRs). This research studied the effect of thermally activated peroxodisulfate (TAP) pretreatment on greenhouse gas (GHGs) emission, dissolved organic matter (DOM) and maturity evaluation during spiramycin fermentation residue (SFR) composting. Three treatments were conducted from co-composting of SFR and wheat straw, while 90% and 99.9% residual spirmycin removal pretreatment SFR by TAP were provided and compared with raw SFR. The cumulative CO₂ and NH₃ emissions increased by 17.2% and 30.8% after TAP pretreatment removed 99.9% residual spiramycin in SFR, while the cumulative CH₄ and N₂O emission decreased by 34.0% and 5.27%, respectively. The DOM, humic acid (HA)/fulvic acid (FA) and NH₄⁺/NO₃^- analysis confirmed that the composting maturity was improved with the increasing of HA and NO₃^- content by TAP pretreatment.