Effect of biochar derived from biogas residue on methane production during dry anaerobic fermentation of kitchen waste

Synergy of multi-enzyme pretreatment and Paraclostridium benzoelyticum bioaugmentation: A dual strategy for enhancing methane production in dry anaerobic digestion of kitchen waste

Dry anaerobic digestion (DAD) of kitchen waste (KW) has low methane production due to the poor mass transfer and the low abundance of functional microorganisms. This study employed multi-enzyme pretreatment (PRE), bioaugmentation with Paraclostridium benzoelyticum (BIO), and their combination (COM) to enhance methane production. Interestingly, the COM group had the highest methane production, which was increased by 18.51 %, 9.91 % and 12.39 % compared with the control, PRE and BIO groups, respectively, which indicated that there was a synergy between multi-enzyme pretreatment and bioaugmentation. Further analysis of microbial community and metagenome was conducted to reveal the synergistic mechanism. The results showed that in COM group, the enrichment of the Rikenellaceae, Methanobacteriaceae and Methanosaetaceae was the directly reason for enhancing methane production. Additionally, key metabolic functions including biosynthesis of cofactors, methane metabolism and oxidative phosphorylation also played a pivotal role in boosting methane production. Furthermore, the enhancement of the hydrogenotrophic methanogenesis pathway has been demonstrated to be a critical factor in the synergistic effects. It provided a reliable theoretical basis for the practical application of the multi-enzyme pretreatment combined with Paraclostridium benzoelyticum bioaugmentation for DAD.

Alkaline catalytic liquefaction of pig manure fermentation residue in ethanol solvent for the production of high-quality biocrude oil

The widespread application of biogas projects generates substantial amounts of waste fermentation residue. Further treatment of fermentation residues facilitates resource utilization, ensures safe disposal, and is anticipated to enhance the economic returns of biogas projects. Herein, catalytic liquefaction of pig manure fermentation residue to produce biocrude oil was investigated using various alkaline catalysts at 340 ℃ with ethanol as the solvent. Biocrude oils were analyzed by elemental analysis, gas chromatography-mass spectrometry (GC-MS), thermogravimetric analysis, and kinetic analysis. The maximum biocrude oil yield (45.24 wt%) was obtained with the KOH catalyst. Additionally, the biocrude oil produced by the catalysis of CaO exhibited the maximum higher heating value at 44.18 MJ/kg. GC-MS results showed that KOH and K2CO3 considerably increased the content of phenols and hydrocarbons in the biocrude while reducing nitrogenous compounds. All alkaline catalysts effectively reduced the activation energy of biocrude oil compared to biocrude oil without catalyst. The maximum reduction in activation energy (18.73 %) was achieved with the addition of Na2CO3. More importantly, adding CaO not only increased the yield and higher heating value of biocrude oil but also reduced nitrogenous compounds and activation energy, improving the overall yield and quality. Overall, this work provides an effective and promising method to convert pig manure fermentation residue into green high-quality biocrude oil, simultaneously providing an economical and environmentally friendly waste management strategy for the fermentation industry.

Particulate matter pollution alters the bacterial community structure on the human skin with enriching the Acinetobacter and Pseudomonas

Particulate matter (PM) has been recognized as a significant environmental contaminant with substantial effects on human health, although the impact of PM pollution on the skin microbiota is less understood. In this study, 78 skin microbiota samples from volunteers were obtained during periods of haze and non-haze in the spring and winter. The diversity, composition, and co-occurrence networks of the skin bacterial community were revealed using high-throughput sequencing. Acinetobacter sp. XSB125 and Pseudomonas sp. XSB6 were isolated and cocultured with PM collected during haze days. Significant seasonal variations were observed in the skin bacterial community, with winter samples showing greater diversities than spring samples. Supervised partial least squares discriminant analysis indicated that PM pollution influenced the skin bacterial community composition. Stronger interactions were detected in the network structure of the skin bacterial community during haze days. Differential and random forest analyses revealed that Acinetobacter and Pseudomonas, which are important resistant opportunistic pathogens, were significantly enriched during haze days in winter. To confirm the increases in Acinetobacter and Pseudomonas during haze days, an Acinetobacter strain and a Pseudomonas strain were isolated and cultured with the PM we collected during haze days. In vitro experiments confirmed that PM promoted the growth of the Acinetobacter and Pseudomonas strains. Function analysis revealed increased metabolic function and enrichment of antibiotic resistance- and pathogenicity-related functions during haze days, including the beta-lactamase gene and attachment invasion locus protein. These findings reveal the complex interplay between PM pollution and the skin microbiota, highlighting the need for further research into mitigation strategies to protect the public health from PM exposure.

Microbial mechanism for improving biogas production performance from boiling acidified pig manure feedstock

A short heat treatment (HT, 90 °C-100 °C, 5 min) was applied to two-phase anaerobic digestion (TPAD) of pig manure (PM) to investigate its effect on microbial inactivation in the acidified feedstock during the methanogenic phase. The results showed that no differences in biogas production at organic loading rate (OLR) below 4.28 g volatile solid (VS)/(L·d). However, as the organic load increased, the TPAD with HT exhibited greater biogas production and volatile organic acids removal than the control. By stabilizing pH, digestion of HT acidified feedstock at 9.56 g VS/(L·d) OLR resulted in a biogas yield of 340.1 mL/g VS, exceeding the control by 35.6 %. HT enriched syntrophic bacteria, Methanothrix and Methanobacterium methanogens, and one-carbon metabolizing genes in the methanogenic phase, enhancing energy storage and conversion. Accordingly, acidification followed by HT could be a potential method to improve microbial community and load tolerance in methanogenic phase of TPAD.

Comparing sewage sludge vs. digested sludge for starting-up thermophilic two-stage anaerobic digesters: Operational and economic insights

Despite advances in anaerobic digestion (AD), full-scale implementation faces significant challenges, particularly during the start-up phase, where inoculum selection is crucial. This study examines the impact of inoculum choice on the operational and economic performance of thermophilic digesters during the start-up phase. Methanogenic reactors R3 and R4 were inoculated with digested sludge (DiS) and diluted sewage sludge (DSS), respectively, and fed with hydrolyzed source-sorted organic fraction of municipal solid waste (SS-OFMSW) and thickened sewage sludge, which were processed in R1 and R2, serving as acidogenic reactors. A two-stage AD configuration was employed to mitigate inhibitory effects associated with the undigested inoculum (DSS). This approach enabled the establishment of methanogenic activity in R4 when the AD system is initiated with DSS. However, R3 outperformed R4, achieving 49 % of the feedstock's theoretical methane potential compared to 15 % in R4. Methane production and volatile solids (VS) processing costs in R4 were 18 and 3 times higher than in R3, respectively. R3's superior performance was attributed to DiS's diverse bacterial community, with over 66 % of genera involved in hydrolysis, volatile fatty acid production, and syntrophic methane production. In contrast, DSS was dominated by Trichococcus and Lactococcus (75.4 %), primarily involved in butyrate oxidation and lactate production. This study provides valuable insights into effective inoculum selection for the start-up of full-scale digesters.

Insight into response mechanism of short-chain fatty acids to refined microbial transformation order of dissolved organic matter ranked by molecular weight during dry anaerobic digestion

Dynamic transformation of dissolved organic matter (DOM) contributes to short-chain fatty acids (SCFAs) production during anaerobic digestion. However, the impact of refined transformation of DOM ranked by molecular weight (MW) on SCFAs has never been investigated. Results indicated that DOM conversion order was 3500-7000 Da>(MW>14000 Da) > 7000-4000 Da during hydrolysis stage, while it was independent of their MW in acidogenesis phase and followed a low to high MW order during methanogenesis stage. Proteins-like DOMs with different MW were closely related to SCFAs. Eight groups of microorganisms (e.g., Bacillus and Caldicoprobacter) responsible for the conversion of proteins-like DOMs to SCFAs. The possible routes linking environmental properties to microorganisms-proteins-like DOMs-SCFAs connections were constructed. Microbial activity modifications by regulating moisture, pH, NO3--N and NH4+-N can expedite the conversion of proteins-like DOMs to SCFAs. The study emphasizes the importance of MW-classification-based biotransformation of organic waste, offering a potential strategy to enhance anaerobic digestion performance.

Improved Short-Chain Fatty Acids Production and Protein Degradation During the Anaerobic Fermentation of Waste-Activated Sludge via Alumina Slag-Modified Biochar

As the by-product in the biological sewage treatment, waste-activated sludge (WAS) always suffers from the difficulty of disposal. Anaerobic fermentation to achieve valuable carbon sources is a feasible way for resource utilization of WAS, whereas the process is always restricted by its biochemical efficiency. Hence, the WAS was used as the feedstock in this study. Alumina slag-modified biochar (Al@BioC) respectively from pine wood (PW) or fresh vinegar residue (FVR) was employed to stimulate the process of short-chain fatty acids (SCFAs) production during the anaerobic treatment of WAS. The results indicate that the addition of Al@BioC could facilitate the distinct increase in SCFAs yield (42.66 g/L) by 14.09% and acetate yield (33.30 g/L) by 18.77%, respectively, when compared with that in regular fermentation without Al@BioC addition. Furthermore, protein degradation was also improved. With the Al@BioCPW added, the maximum concentration of soluble protein reached 867.68 mg/L and was 24.39% higher than the initial level, while the enhancement in the group with Al@BioCFVR and without biochar addition was 12.49% and 7.44%, respectively. According to the results of 16S rDNA sequencing, the relative abundance of acid-producing bacteria (Bacteroidota and Firmicutes) was enriched, enhancing the pathways of protein metabolisms and the ability to resist the harsh environment, respectively. Moreover, Proteiniphilum under Bacteroidota and Fastidiosipila under Firmicutes were the main microorganisms to metabolize protein. The above results might provide a novel material for harvesting the SCFAs production, which is conducive to harmless disposal and carbon resource recovery.

Inhibition of Verticillium Wilt in Cotton through the Application of Pseudomonas aeruginosa ZL6 Derived from Fermentation Residue of Kitchen Waste

To isolate and analyze bacteria with Verticillium wilt-resistant properties from the fermentation residue of kitchen wastes, as well as explore their potential for new applications of the residue. A total of six bacterial strains exhibiting Verticillium wilt-resistant capabilities were isolated from the biogas residue of kitchen waste fermentation. Using a polyphasic approach, strain ZL6, which displayed the highest antagonistic activity against cotton Verticillium wilt, was identified as belonging to the Pseudomonas aeruginosa. Bioassay results demonstrated that this strain possessed robust antagonistic abilities, effectively inhibiting V. dahliae spore germination and mycelial growth. Furthermore, P. aeruginosa ZL6 exhibited high temperature resistance (42°C), nitrogen fixation, and phosphorus removal activities. Pot experiments revealed that P. aeruginosa ZL6 fermentation broth treatment achieved a 47.72% biological control effect compared to the control group. Through activity tracking and protein mass spectrometry identification, a neutral metalloproteinase (Nml) was hypothesized as the main virulence factor. The mutant strain ZL6ΔNml exhibited a significant reduction in its ability to inhibit cotton Verticillium wilt compared to the strain P. aeruginosa ZL6. While the inhibitory activities could be partially restored by a complementation of nml gene in the mutant strain ZL6CMΔNml. This research provides a theoretical foundation for the future development and application of biogas residue as biocontrol agents against Verticillium wilt and as biological preservatives for agricultural products. Additionally, this study presents a novel approach for mitigating the substantial amount of biogas residue generated from kitchen waste fermentation.

Mechanism of improving anaerobic fermentation performance of kitchen waste pretreated by ionizing irradiation-part 1: rice

Ionizing irradiation, as a new pretreatment method for the anaerobic fermentation of organic pollutants, is featured with fast reaction speed, good treatment effect, no need to add any chemical reagents, and no secondary pollution. This study explores the mechanism of improving anaerobic fermentation performance of rice samples pretreated by cobalt-60 gamma irradiation through the influence on fermentation substrate, acidogenic phase and methanogenic phase. The results reveal that the soluble chemical oxygen demand of the irradiated rice sample at an absorbed dose of 9.6 kGy increases by 12.4 times due to the dissolution of small molecules of fat-soluble organic matter. The yield of biogas in the acidogenic phase increases by 22.2% with a slight increase in hydrogen gas content. The yield of biogas and methane gas content in the methanogenic phase increases by 27.3% and 15%, respectively. Microbial genome analysis, performed with MiSeq high-throughput sequencing and metagenomic methods, suggests the microbial abundance and metabolic functions in the anaerobic fermentation process change significantly as a result of the pretreatment by gamma irradiation.

A comprehensive review on the preparation of biochar from digestate sources and its application in environmental pollution remediation

The preparation of biochar from digestate is one of the effective ways to achieve the safe disposal and resource utilization of digestate. Nevertheless, up to now, a comprehensive review encompassing the factors influencing anaerobic digestate-derived biochar production and its applications is scarce in the literature. Therefore, to fill this gap, the present work first outlined the research hotspots of digestate in the last decade using bibliometric statistical analysis with the help of VOSviewer. Then, the characteristics of the different sources of digestate were summarized. Furthermore, the influencing factors of biochar preparation from digestate and the modification methods of digestate-derived biochar and associated mechanisms were analyzed. Notably, a comprehensive synthesis of anaerobic digestate-derived biochar applications is provided, encompassing enhanced anaerobic digestion, heavy metal remediation, aerobic composting, antibiotic/antibiotic resistance gene removal, and phosphorus recovery from digestate liquor. The economic and environmental impacts of digestate-derived biochar were also analyzed. Finally, the development prospect and challenges of using biochar from digestate to combat environmental pollution are foreseen. The aim is to not only address digestate management challenges at the source but also offer a novel path for the resourceful utilization of digestate.

Wood biochar enhances methanogenesis in the anaerobic digestion of chicken manure under ammonia inhibition conditions

The process of breaking down chicken manure through anaerobic digestion is an effective waste management technology. However, chicken manure can be a challenging feedstock, causing ammonia stress and digester instability. This study examined the impacts of adding wood biochar and acid-alkali-treated wood biochar to anaerobically digest chicken manure under conditions of ammonia inhibition. The results highlighted that only the addition of 5 % acid-alkali-treated wood biochar by volume can achieve cumulative methane production close to the typical methane potential range of chicken manure. The treated wood biochar also exhibited highest total ammonia nitrogen removal compared to the Control treatment. Scanning Electron Microscope revealed growing interactions between biochar and methanogens over time. Real-time polymerase chain reaction showed that treated wood biochar produced the highest number of bacterial biomass. In addition, 16S amplicon-based sequencing identified a more robust archaeal community from treated biochar addition. Overall, the acid-alkali treatment of biochar represents an effective method of modifying biochar to improve its performance in anaerobic digestion.

Elucidation of microbial interactions, dynamics, and keystone microbes in high pressure anaerobic digestion

High-pressure anaerobic digestion (HPAD) is a promising technology for producing biogas enriched with high methane content in a single-step process. To enhance HPAD performance, a comprehensive understanding of microbial community dynamics and their interactions is essential. For this, mesophilic batch high-pressurized anaerobic reactors were operated under 3 bars (H3) and 6 bars (H6). The experimental results showed that the effect of high-pressure (up to 6 bar) on acidification was negligible while methanogenesis was significantly delayed. Microbial analysis showed the predominance of Defluviitoga affiliated with the phylum Thermotogae and the reduction of Thiopseudomonas under high-pressure conditions. In addition, the microbial cluster pattern in H3 and H6 was significantly different compared to the CR, indicating a clear shift in microbial community structure. Moreover, Methanobacterium, Methanomicrobiaceae, Alkaliphilus, and Petrimonas were strongly correlated in network analysis, and they could be identified as keystone microbes in the HPAD reactor.

A revolving algae biofilm based photosynthetic microbial fuel cell for simultaneous energy recovery, pollutants removal, and algae production

Photosynthetic microbial fuel cell (PMFC) based on algal cathode can integrate of wastewater treatment with microalgal biomass production. However, both the traditional suspended algae and the immobilized algae cathode systems have the problems of high cost caused by Pt catalyst and ion-exchange membrane. In this work, a new equipment for membrane-free PMFC is reported based on the optimization of the most expensive MFC components: the separator and the cathode. Using a revolving algae-bacteria biofilm cathode in a photosynthetic membrane-free microbial fuel cell (RAB-MFC) can obtain pollutants removal and algal biomass production as well as electrons generation. The highest chemical oxygen demand (COD) removal rates of the anode and cathode chambers reached 93.5 ± 2.6% and 95.8% ± 0.8%, respectively. The ammonia removal efficiency in anode and cathode chambers was 91.1 ± 1.3% and 98.0 ± 0.6%, respectively, corresponding to an ammonia removal rate of 0.92 ± 0.02 mg/L/h. The maximum current density and power density were 136.1 mA/m2 and 33.1 mW/m2. The average biomass production of algae biofilm was higher than 30 g/m2. The 18S rDNA sequencing analysis the eukaryotic community and revealed high operational taxonomic units (OTUs) of Chlorophyta (44.43%) was dominant phyla with low COD level, while Ciliophora (54.36%) replaced Chlorophyta as the dominant phyla when COD increased. 16S rDNA high-throughput sequencing revealed that biofilms on the cathode contained a variety of prokaryote taxa, including Proteobacteria, Bacteroidota, Firmicutes, while there was only 0.23-0.26% photosynthesizing prokaryote found in the cathode biofilm. Collectively, this work demonstrated that RAB can be used as a bio-cathode in PMFC for pollutants removal from wastewater as well as electricity generation.