Enhancing humic acids production from cornstalk under fast hydrothermal conditions: Insights into new pathways of skeleton self-polymerization and branch growth.

Hydrochar, a sustainable fertilizer rich in humic substances, is made from lignocellulose through hydrothermal conversion. However, hydrothermal humification (HTH) is challenged by low yields and limited selectivity in the resulting hydrochar. This study proved humic-like acids production can be enhanced under fast non-catalytic conditions (260 âˆ¼ 280 °C, 0 âˆ¼ 1 h). A higher yield (by 14.1 %) and selectivity (by 40.2 %) in hydrochar of humic-like acids than conventional HTH (＜250 °C) were achieved. Meanwhile, decreased lignin derivatives, carbonyl and quinone groups, as well as increased sp2-C structures in the humic-like acids were observed. The synthesized humic-like acids exhibited a lower degree of aromatization and a higher molecular weight than commercial variants. Two pathways of humic-like acids formation of self-polymerization and the development of branched sidechains were hypothesized based on mass mitigation, carbon flow and aqueous phase compositions. This research contributes a novel approach to producing humic-like acids rich hydrochar for environmentally friendly fertilizer production.

Unraveling the relationship between soil carbon-degrading enzyme activity and carbon fraction under biogas slurry topdressing.

Biogas slurry, a by-product of the anaerobic digestion of biomass waste, predominantly consisting of livestock and poultry manure, is widely acclaimed as a sustainable organic fertilizer owing to its abundant reserves of essential nutrients. Its distinctive liquid composition, when tactfully integrated with a drip irrigation system, unveils immense potential, offering unparalleled convenience in application. In this study, we investigated the impact of biogas slurry topdressing as a replacement for chemical fertilizer (BSTR) on soil total organic carbon (TOC) fractions and carbon (C)-degrading enzyme activities across different soil depths (surface, sub-surface, and deep) during the tasseling (VT) and full maturity stage (R6) of maize. BSTR increased the TOC content within each soil layer during both VT and R6 periods, inducing alterations in the content and proportion of individual C component, particularly in the topsoil. Notably, the pure biogas slurry topdressing treatment (100%BS) compared with the pure chemical fertilizer topdressing treatment (CF), exhibited a 38.9% increase in the labile organic carbon of the topsoil during VT, and a 30.3% increase in the recalcitrant organic carbon during R6, facilitating microbial nutrient utilization and post-harvest C storage during the vigorous growth period of maize. Furthermore, BSTR treatment stimulated the activity of oxidative and hydrolytic C-degrading enzymes, with the 100%BS treatment showcasing the most significant enhancements, with its average geometric enzyme activity surpassing that of CF treatment by 27.9% and 27.4%, respectively. This enhancement facilitated ongoing and efficient degradation and transformation of C. Additionally, we screened for C components and C-degrading enzymes that are relatively sensitive to BSTR. The study highlight the advantages of employing pure biogas slurry topdressing, which enhances C component and C-degrading enzyme activity, thereby reducing the risk of soil degradation. This research lays a solid theoretical foundation for the rational recycling of biogas slurry.

Comprehensive study of the combined effects of biochar and iron-based conductive materials on alleviating long chain fatty acids inhibition in anaerobic digestion.

This study investigated the feasibility of alleviating the negative influence of long-chain fatty acids (LCFAs) on anaerobic digestion by biochar, micron zero-valent iron, micron-magnetite (mFe3O4) and their combination. The results demonstrate that co-addition of biochar and 6 g/L mFe3O4 (BC+6 g/L mFe3O4) increased cumulative methane production by 50% as suffered from LCFAs inhibition exerted by 2 g/L glycerol trioleate. The BC+6 g/L mFe3O4 did best in accelerating total organic carbon degradation and volatile fatty acids conversion, through successively enriching Bacteroides, Corynebacterium, and DMER64 to dominant the bacterial community. The proportion of acetotrophic Methanothrix that could alternatively reduce CO2 to methane by accepting electrons via direct interspecies electron transfer (DIET) was 0.09% with BC+6 g/L mFe3O4, nine times more than the proportion in control. Prediction of functional genes revealed the enrichment of the bacterial secretion system, indicating that BC+6 g/L mFe3O4 promoted DIET by stimulating the secretion of extracellular polymeric substances. This study provided novel insights into combining biochar and iron-based conductive materials to enhance AD performance under LCFAs inhibition.

Evaluation of activated pyrochar for boosting anaerobic digestion: Performances and microbial community.

In this study, the effects of CO2-activated/non-activated pyrochars (PCs) from cornstalk, cotton straw, and rice straw on anaerobic digestion (AD) performances and microbial characteristics were investigated. The maximum biogas production rate (2.2 L/L/d) with a methane content of 73% was obtained from the AD with CO2-activated cotton straw PC. The activated PC mainly played a strengthening role in the early and middle stages of AD. Specifically, the cornstalk PC could greatly relieve acid inhibition, and cotton straw PC had a significantly positive effect on the regulation of ammonia nitrogen concentration. The rare genera like Verrucomicrobia had obvious differences among groups of AD with PCs. Regarding differential metabolites, cornstalk PC-N2 displayed a positive correlation with isoleucyl-alanine, while exhibiting a negative correlation with deoxyinosine, and the corresponding relative expression levels were + 3.0 and -2.4, respectively. Overall, gas-activated PCs could promote methane production and affect the composition of microbial community.

Disentangling the impact of biogas slurry topdressing as a replacement for chemical fertilizers on soil bacterial and fungal community composition, functional characteristics, and co-occurrence networks.

The application of biogas slurry topdressing with drip irrigation systems can compensate for the limitation of traditional solid organic fertilizer, which can only be applied at the bottom. Based on this, we attempted to define the response of soil bacterial and fungal communities of maize during the tasseling and full maturity stages, by using a no-topdressing control and different ratios of biogas slurry nitrogen in place of chemical fertilizer topdressing. The application of biogas slurry resulted in the emergence of new bacterial phyla led by Synergistota. Compared with pure urea chemical topdressing, the pure biogas slurry topdressing treatment significantly enriched Firmicutes and Basidiomycota communities during the tasseling stage, in addition to affecting the separation of bacterial and fungal α-diversity indices between the tasseling and full maturity stages. Based on the prediction of community composition and function, the changes in bacterial and fungal communities caused by biogas slurry treatment stimulated the ability of microorganisms to decompose refractory organic components, which was conducive to turnover in the soil carbon cycle, and improved multi-element (such as sulfur) cycles; however it may also bring potential risks of heavy metal and pathogenic microbial contamination. Notably, the biogas slurry treatment reduced the correlation and aggregation of bacterial and fungal symbiotic networks, and had a dual effect on ecological randomness. These findings contribute to a deeper comprehension of the alterations occurring in soil microbial communities when substituting chemical fertilizers treated with biogas slurry topdressing, and promote the efficient and sustainable utilization of biogas slurry resources.

Co-pyrolysis of biomass and polyethylene: Insights into characteristics, kinetic and evolution paths of the reaction process.

Investigation on the distribution and mechanism of co-pyrolysis products is vital to the directional control and high-value utilization of agriculture solid wastes. Co-pyrolysis, devolatilization, kinetics characteristics, and evolution paths of corn stalk (CS) and low-density-polyethylene (LDPE) were investigated via thermogravimetric experiments. The co-pyrolysis behaviors could be separated into two stages: firstly, the degradation of CS (150- 400 °C); secondly, the degradation of CS (400- 550 °C). The devolatilization index (DI) increased with the addition of LDPE. Furthermore, a combination of devolatilization chemical analysis with product analysis to analyze the intrinsic mechanism during co-pyrolysis. The results indicated that the yield of alkanes and olefin in gas products increased with the addition of LDPE. Additionally, LDPE pyrolysis maybe abstract hydrogen from CS pyrolysis and evolved into hydrogen, methane, and ethylene. Further, the co-pyrolysis kinetic parameters were computed by using model-free isoconversion methods, which showed promotion of CS pyrolysis and the reduced activation energy. All the activation energy were declined, which indicated a "bidirectional positive effect" during co-pyrolysis. The mean activation energy of P-cellulose (P-CE), P-hemicellulose (P-HM), P-lignin (P-LG), and LDPE decreased by 23.49 %, 12.89 %, 15.36 %, and 27.82 %, respectively. This study further proves the hydrogen donor transfer pathway in the co-pyrolysis process of CS and LDPE, providing theoretical support for the resource utilization of agricultural solid waste.

Biogas slurry topdressing as replacement of chemical fertilizers reduces leaf senescence of maize by up-regulating tolerance mechanisms.

Worldwide physiological research has aimed to decelerate the aging of crop leaves by optimizing fertilization measures to improve crop or biomass yield. Solid organic fertilizers can be combined with chemical fertilizers to delay the aging of crop leaves. Biogas slurry is a liquid organic fertilizer produced by the anaerobic fermentation of livestock and poultry manure and other resources, and it can partially replace chemical fertilizers in field application via drip irrigation systems. However, the impact of biogas slurry topdressing on leaf aging remains unclear. This study investigated treatments with no topdressing (control, CK) and five topdressing patterns of biogas slurry replacing chemical fertilizer (nitrogen) at 100%, 75%, 50%, 25%, and 0% (100%BS, 75%BS, 50%BS, 25%BS, CF). The effects of different proportions of biogas slurry on leaf senescence rate, photosynthetic pigments, osmotic adjustment substances, antioxidant defense enzymes, and nitrogen metabolism related enzyme activities of maize were analyzed. Subsequently, the mechanisms of biogas slurry topdressing on the leaf senescence rate of maize were explored. The results showed that the mean decreasing rate of relative green leaf area (Vm) treated with biogas slurry decreased by 3.7%-17.1% and the duration of leaf area duration (LAD) increased by 3.7%-17.1% compared with the results for CK. The maximum senescence rate of 100%BS was delayed by 4.4 and 5.6 d compared to the results for CF and CK, respectively. During the senescence of maize leaves, the use of biogas slurry topdressing increased the content of chlorophyll, decreased the water loss and the accumulation rate of malondialdehyde and proline in leaves, and increased the activities of catalase, peroxidase, and superoxide dismutase in the later growth and development periods of maize. In addition, biogas slurry topdressing improved the nitrogen transport efficiency of the leaves and ensured continuous and efficient ammonium assimilation. Furthermore, there was a strong correlation between leaf senescence and the investigated physiological indices. Cluster analysis showed that the 100%BS treatment exhibited the most prominent effect on leaf senescence. Biogas slurry topdressing as a substitute for chemical fertilizer can be potentially used as an anti-aging regulation measure for crops to decrease the damage induced by senescence.

Deeper insights into the synergy of material transformation, microbial network, and energy balance during pilot thermophilic and mesophilic dry anaerobic digestion systems.

The present study investigated the synergistic characteristics between abiotic and biotic transformation with a view to improving the methane production efficiency of thermophilic and mesophilic sequencing batch dry anaerobic digestion (SBD-AD). The pilot scale experiment consisted of a lignocellulosic material based on a mixture of corn straw and cow dung. A leachate bed reactor was used for an AD cycle of 40 days. Several distinct differences are reflected in biogas (methane) production and VFA concentration and composition. A combination of first-order hydrolysis and a modified Gompertz model determined that the holocellulose (cellulose + hemicellulose) and maximum methanogenic efficiency at thermophilic temperatures were increased by 112.03 % and 90.09 %, respectively. Additionally, the methane production peak was extended by 3-5 days in comparison with that at mesophilic temperatures. The microbial community exhibited vastly different functional network relationships under the two temperature conditions (P < 0.05). The data indicate that Clostridales and Methanobacteria had preferable synergistic effects and that the metabolism of hydrophilic methanogens is necessary for the conversion of VFA to methane during thermophilic SBD-AD. The effect of mesophilic conditions on Clostridales was relative weakened, and acetophilic methanogens were mainly present. Moreover, simulation of the full-chain and operational strategy of SBD-AD engineering resulted in a decrease in heat energy consumption of 21.4-64.3 % at thermophilic temperatures and 30.0-90.0 % at mesophilic temperatures from winter to summer. Furthermore, the total net energy production of thermophilic SBD-AD was increased by 105.2 % in comparison with that at mesophilic temperatures, demonstrating strengthened energy recovery. Overall, raising the SBD-AD temperature to thermophilic levels has considerable application value for improving the treatment capacity of agricultural lignocellulosic waste.

Alleviating "inhibited steady-state" in anaerobic digestion of poultry manure by bentonite amendment: Performance evaluation and microbial mechanism.

This study systematically evaluated the effects of bentonite as a possible additive to alleviate the "inhibited steady-state" induced by ammonia and acid accumulation during anaerobic digestion. Continuous stirred tank reactors fed with poultry manure were operated at 35 ± 1 °C either with bentonite or not. The results demonstrate that bentonite amendment increased average specific methane production by 35% as suffered from steady-state at an organic loading rate of 6.25 g VS/L·d. 16S rRNA gene amplicon sequencing revealed that the relative abundance of electron-donating Sedimentibacter and Syntrophomonas, and electrophilic Methanosarcina was increased by 110%, 91%, and 49%, respectively. The genera were identified as crucial for alleviating "inhibited steady-state", through establishment of a more robust syntrophic pathway of methanogenic acetate degradation. The enhancement might result from the accelerated electron transfer by bentonite, which is qualified for serving as an exogenetic electron mediator due to containing abundant redox-active metal elements.

Novel insights from lignocellulosic waste to biogas through regulated dry-wet combined anaerobic digestion: Focusing on mining key microbes.

Dry-wet combined anaerobic digestion is a novel approach for treating lignocellulosic waste by increasing the organic load of reactor while accelerating the conversion of organic acids. Here, we investigated the effect of regulated substrate ratios and initial pH in the dry acidogenesis stage on the bioconversion efficiency of dry-wet combined anaerobic digestion. Our data revealed microbial interactions and further identified key microbes based on microbial co-occurrence network analysis. On day three of acidification, the kinetic hydrolysis rate and acidification yield reached 1.66 and 60.07%, respectively; this was attributed to enhancement of the synergistic effect between Clostridiales and Methanosaeta, which increased the proportion of corn straw in the substrate or lowered the initial spray slurry pH to 5.5-6.5. With increased acidification capacity, acetoclastic methanogens were enriched in the wet methanogenesis stage; the syntrophic effect of Syntrophomonadales, Syntrophobacterales and Methanospirillum, meanwhile, was enhanced, leading to an overall improvement in biogas production.

Engineering and microbial characteristics of innovative lab and pilot continuous dry anaerobic co-digestion system fed with cow dung and corn straw.

Dry anaerobic digestion (dry-AD) allows high-solid digestion; however, dry-AD application is limited because it is prone to blockage and intermediate inhibition. Here, we reported innovative continuous dry co-digestion systems at both lab and pilot scales. The effects of digestate recirculation ratio, dry mass ratio of cow dung to corn straw (CD:CS), and TS content on the digestion performance were investigated. The effects of the three factors were ranked as follows: TS content > CD:CS > digestate recirculation ratio. The daily biogas production rate reached 0.386 NL/d/g VS with the optimal parameter combination, which was determined to be TS content of 30%, a substrate ratio of 1:3, and a digestate recirculation ratio of 40%. In addition, increasing the CD:CS and TS content increased digestate viscosity, which inhibited biogas production; however, increased abundance of Proteiniphilum and acetoclastic methanogens facilitated biogas production. This study provides empirical support for further application of dry-AD.

The hydrochar activation and biocrude upgrading from hydrothermal treatment of lignocellulosic biomass.

The production of hydrochar and biocrude from hydrothermal treatment of lignocellulosic biomass is getting increasing attention, but the quality of hydrochar and biocrude need further improvement before utilization. Many attempts have been carried out on the hydrochar activation and biocrude upgrading. However, different methods play different roles on the property of hydrochar and biocrude, this topic received scant attention in recent review papers. Therefore, the influence of different activation methods on hydrochar property, and the potential application of hydrochar were summarized in this study. Meanwhile, the research progress on biocrude upgrading is reported. Besides, the techno-economic analysis of hydrochar and biocrude from hydrothermal treatment of lignocellulosic biomass are also discussed. Finally, the research needs and future directions on hydrochar activation and biocrude upgrading were proposed. This paper could provide insights for further studies on the utilization of hydrochar and biocrude.

Evaluation of lignin inhibition in anaerobic digestion from the perspective of reducing the hydrolysis rate of holocellulose.

In this study, Anaerobic Digestion Model No. 1 (ADM1) were modified to simulate anaerobic digestion (AD) process of microcrystalline cellulose (MCC) and five lignocellulosic substrates, with the goal of predicting the hydrolysis rates of holocellulose fractions in environments with and without lignin inhibition. After model verification, the hydrolysis rate constant of MCC, i.e., the hydrolyzability of cellulose without lignin inhibition, was 3.227 d-1, while those of the holocellulose fractions of five lignocellulosic substrates (I_khyd) were in the range of 1.270 d-1 to 3.364 d-1 (average of 2.242 d-1), which demonstrated remarkable suppression of holocellulose hydrolysis by lignin. Lignin inhibition index (LII) was proposed as an indicator to intuitively quantify and characterize the lignin inhibitory strength in a specific substrate. A series of factors with the potential to affect the LII were analyzed sequentially. This study provides an advanced understanding of the participation and behavior of lignin in the AD process.

Simultaneous carbon dioxide reduction and enhancement of methane production in biogas via anaerobic digestion of cornstalk in continuous stirred-tank reactors: The influences of biochar, environmental parameters, and microorganisms.

The composition of biogas produced by anaerobic digestion (AD) is typically not ideal due to high CO2 content. In the study, cottonwood biochar was used as an enhanced mediator for the continuously stirred tank reactor AD of cornstalk. The effects of substrate loading and biochar dosage on biogas composition, volatile fatty acids (VFAs), NH3-N, and microbial community characteristics were systematically explored. The results showed that the highest volumetric biogas production rate with biochar was 1.40 L/L/d, at the same time, the CO2 content in the biogas decreased by 5.90%, while the CH4 content increased by 7.40%, compared with the values in AD without biochar. Moreover, VFAs were degraded effectively, in particular, the propionic acid concentration decreased by 55.7%. Besides, microbial abundance had positive correlations with environmental parameters. This study could provide valuable information for both the elucidation of strengthening mechanisms of biochar and further large-scale engineering application.

Sequencing batch dry anaerobic digestion of mixed feedstock regulating strategies for methane production: Multi-factor interactions among biotic and abiotic characteristics.

This study investigated the synergistic effects and regulation strategy of multiple factors for improving methane production in sequencing batch dry anaerobic digestion (SBD-AD) using corn stalks (CS) and cow dung (CD). The regulation of the spray frequency (SF) and inoculum content (IC) significantly improved methane yield, which increased feedstock ratios (FRs) by 12.4-121.3%. Moreover, the relationship between SF and IC produced distinct interaction modes. An FR of 4:6 increased the SF to 2 h for the CD-rich condition, and an FR of 6:4 decreased the SF during a 6 h interval and increased the IC for the CS-rich condition, resulting in increases in methane yield and the conversion efficiency of volatile fatty acids (VFAs). Methanogenesis (Methanogens) played a key role in SBD-AD. The nutrient substrate (NH4-N+) and key enzyme activities of methanogens were significantly affected such that the synergistic effect of the acetoclastic and hydrogenotrophic methanogenesis pathways was likely strengthened.

Efficient acetogenesis of anaerobic co-digestion of food waste and maize straw in a HSAD reactor.

In this study, food waste and maize straw were used as feedstock, and the two-phase high-solid anaerobic digestion (TP-HSAD) technology was used to optimize the process parameters of leachate reflux in acid-production stage. Results indicated that compared with other waste activated sludge, pig manure digestate (PM) as leachate can achieve better hydrolysis and acidification effect. The increase of leachate reflux ratio can shorten the fermentation time of the acid-producing stage and increase the fermentation efficiency. When the reflux ratio was 32:1, peak concentration of volatile fatty acids (VFAs) was 45.4 g/L and the volatile solids (VS) removal rate was 61.7%. Reflux frequency has minimal effect on the concentration of VFAs and the degree of degradation of VS, but a higher reflux frequency will prolong the reaction time of acid-production stage. When PM is used as reflux leachate, the HSAD reactor can improve the hydrolysis and acidification of the anaerobic fermentation.

A pilot-scale biomass pyrolytic poly-generation plant performance study and self-sufficiency assessment.

This work studied the influence of pyrolysis temperature on the energy and mass balance of pyrolysis of rice husk (RH), cotton stalk (CS) and fruit branch (FB) in a pilot-scale biomass pyrolytic poly-generation plant. The paper presents energy balance and self-sufficiency assessment of pilot-scale pyrolysis plant processing different types of biomass. The results also include characterization of the pyrolysis products. The volatile matter varied from 6.5 to 25.8% at different temperatures for the three feed stocks, which can be used as indexes for the degree of carbonization of biochar. The yield of pyrolysis gases enriched with H2, CH4 and other alkanes, and olefins increased significantly with increasing pyrolysis temperature from 550 to 650 °C. With a lower heating value >17.1 MJ/m3, an energy self-sufficient system is possible using only the pyrolysis gas. Biomass pyrolytic poly-generation technology offers a promising means of converting abundant agricultural residues into energy and added-value products.