Enrichment of waste sewage sludge for enhancing methane production from cellulose

Microbial and functional characterization of granulated sludge from full-scale UASB thermophilic reactor applied to sugarcane vinasse treatment

Considering the scarcity of data in the literature regarding phylogenetic and metabolic composition of different inocula, especially those from thermophilic conditions, this research aimed at characterizing the microbial community and preferable metabolic pathways of an UASB reactor sludge applied to the thermophilic treatment (55°C) of sugarcane vinasse, by means of shotgun metagenomics. After its metabolic potential was depicted, it was possible to observe several genes encoding enzymes that are of great importance to anaerobic digestion processes with different wastes as substrate, especially regarding the biodegradation of carbohydrates and ligninolytic compounds, glycerolypids, volatile fatty acids and alcohols metabolism and biogas (H2 and CH4) production. The genera identified in higher relative abundances for Bacteria domain were Sulfirimonas (37.52 ± 1.8%), possibly related to the sludge endogenic activity due to its strong relation with a peptidoglycan lyase enzymes family, followed by Fluviicola (5.01 ± 1.0%), Defluviitoga (4.36 ± 0.2%), Coprothermobacter (4.32 ± 0.5%), Fervidobacterium (2.93 ± 0.3%), Marinospirillum (2.75 ± 0.2%), Pseudomonas (2.14 ± 0.2%) and Flavobacterium (1.78 ± 0.1%), mostly related with carbohydrates fermentations and/or H2 production. For Archaea domain, Methanosarcina (0.61 ± 0.1%), Methanothermobacter (0.38 ± 0.0%), Methanoculleus (0.30 ± 0.1%), Thermococcus (0.03 ± 0.0%), Methanolobus (0.02 ± 1.8%), Methanobacterium (0.013 ± 0.0%), Aciduliprofundum and Pyrococcus (0.01 ± 0.0%) were the most dominant ones, being Methanosarcina the most related with methanogenesis. It was concluded that the robust inoculum description performed in this study may subside future biotechnological researches by using similar inocula (UASB sludges), focusing on the obtainment of value-added by-products by means of anaerobic digestion, such as volatile fatty acids, alcohols and biogas (H2 and CH4), by using several types of waste as substrate.

Medium-chain fatty acid production from thermal hydrolysed sludge without external electron donor supplementation

In this study, medium-chain fatty acid (MCFA) generation from mixed sludge (including primary sludge and waste activated sludge) was investigated without additional electron donors (EDs). 0.5 g COD/L of MCFAs was produced and the in situ generated ethanol could serve as the EDs during the anaerobic fermentation of mixed sludge without thermal hydrolysis process (THP) pretreatment. THP increased the MCFA production by approximately 128% in the anaerobic fermentation. During 102 days of operation, the fermentation of THP pre-treated mixed sludge stably generated 2.9 g COD/L MCFAs. The self-generated EDs could not maximize MCFA production, and external addition of ethanol improved MCFA yield. Caproiciproducens was the dominant chain-elongating bacteria. PICRUST2 revealed that both fatty acid biosynthesis and reverse β-oxidation pathways could participate in MCFA synthesis, and ethanol addition could enhance the contribution of the reverse β-oxidation pathway. Future studies should focus on the improvement of MCFA production from THP-assisted sludge fermentation.

Taxonomic and enzymatic basis of the cellulolytic microbial consortium KKU-MC1 and its application in enhancing biomethane production

Lignocellulosic biomass is a promising substrate for biogas production. However, its recalcitrant structure limits conversion efficiency. This study aims to design a microbial consortium (MC) capable of producing the cellulolytic enzyme and exploring the taxonomic and genetic aspects of lignocellulose degradation. A diverse range of lignocellulolytic bacteria and degrading enzymes from various habitats were enriched for a known KKU-MC1. The KKU-MC1 was found to be abundant in Bacteroidetes (51%), Proteobacteria (29%), Firmicutes (10%), and other phyla (8% unknown, 0.4% unclassified, 0.6% archaea, and the remaining 1% other bacteria with low predominance). Carbohydrate-active enzyme (CAZyme) annotation revealed that the genera Bacteroides, Ruminiclostridium, Enterococcus, and Parabacteroides encoded a diverse set of cellulose and hemicellulose degradation enzymes. Furthermore, the gene families associated with lignin deconstruction were more abundant in the Pseudomonas genera. Subsequently, the effects of MC on methane production from various biomasses were studied in two ways: bioaugmentation and pre-hydrolysis. Methane yield (MY) of pre-hydrolysis cassava bagasse (CB), Napier grass (NG), and sugarcane bagasse (SB) with KKU-MC1 for 5 days improved by 38-56% compared to non-prehydrolysis substrates, while MY of prehydrolysed filter cake (FC) for 15 days improved by 56% compared to raw FC. The MY of CB, NG, and SB (at 4% initial volatile solid concentration (IVC)) with KKU-MC1 augmentation improved by 29-42% compared to the non-augmentation treatment. FC (1% IVC) had 17% higher MY than the non-augmentation treatment. These findings demonstrated that KKU-MC1 released the cellulolytic enzyme capable of decomposing various lignocellulosic biomasses, resulting in increased biogas production.

Biological saccharification coupled with anaerobic digestion using corn straw for sustainable methane production

In this study, accumulated fermentable sugars from biosaccharified corn straw were used to generate methane through anaerobic digestion (AD). The results showed that reducing sugars from biosaccharification expanded corn straw (BECS) treated with Clostridium thermocellum XF811 accumulated with yields of 94.9 mg/g. The BECS used for AD was converted into a high methane yield (7436 mL), which was 49.3 % higher than that of expanded corn straw (ECS). High-throughput microbial analysis suggested that Methanoculleus and Methanobacterium greatly contributed to the high methane yield. Industrial experiments demonstrated that the methane production from BECS by AD was 72,955 m³, which increased by 13.2 % compared to that from ECS. Biosaccharification pretreatment accelerated ECS destruction and accumulated sugars, thereby increasing methane yields. This study provides a strategy for producing clean energy from lignocellulose biomass.

Study on Degradation of 1,2,4-TrCB by Sugarcane Cellulose-TiO2 Carrier in an Intimate Coupling of Photocatalysis and Biodegradation System

1,2,4 trichlorobenzene (1,2,4-TrCB) is a persistent organic pollutant with chemical stability, biological toxicity, and durability, which has a significant adverse impact on the ecological environment and human health. In order to solve the pollution problem, bagasse cellulose is used as the basic framework and nano TiO₂ is used as the photocatalyst to prepare composite carriers with excellent performance. Based on this, an intimate coupling of photocatalysis and biodegradation (ICPB) system combining photocatalysis and microorganisms is constructed. We use the combined technology for the first time to deal with the pollution problem of 1,2,4-TrCB. The biofilm in the composite carrier can decompose the photocatalytic products so that the removal rate of 1,2,4-TrCB is 68.01%, which is 14.81% higher than those of biodegradation or photocatalysis alone, and the mineralization rate is 50.30%, which is 11.50% higher than that of photocatalysis alone. The degradation pathways and mechanisms of 1,2,4-TrCB are explored, which provide a theoretical basis and potential application for the efficient degradation of 1,2,4-TrCB and other refractory organics by the ICPB system.

Antibiotic removal potential for low greenhouse gas emission process of anaerobic digestion (AD) producing volatile fatty acids (VFAs)

This study aimed to investigate the antibiotic of sulfachloropyridazine (SCP) reduction and its effects on volatile fatty acids (VFAs) accumulation and microbial community structures during the process of anaerobic digestion (AD) producing VFA. Results showed that initial SCP concentrations have a positive correlation with reduction of SCP and accumulation of VFAs. The removal rates of SCP were 22.21%, 30.00%, 39.31% and 42.59% and the maximum production of VFAs were 3947, 6180, 6462 and 6032 mg/L for initial SCP concentrations of 25, 50, 75 and 100 mg/kg·TS, respectively. SCP only altered bacterial composition by hastening growth of specific bacterial taxa, but didn't increase bacterial α-diversity.

New insights of anaerobic performance, antibiotic resistance gene removal, microbial community structure: applying graphite-based materials in wet anaerobic digestion

The addition of carbonaceous materials into anaerobic digestion (AD) has gained widespread attention due to their significant effects on anaerobic performance and antibiotic resistance gene (ARG) removal. This study selected graphite, graphene, and graphene oxide (GO) as additives to investigate variations in AD performance, ARG removal, microbial community diversity and structure in wet AD systems. The results indicated that the addition of graphite-based materials in wet AD systems could increase degradation of solid organic matters by 0.91%-3.41% and utilization of soluble organic fractions by 10.43%-13.67%, but could not stimulate methane production. After the addition of graphite and graphene, ARG removal rates were effectively increased to 90.85% and 94.22%, respectively. However, the total ARG removal rate was reduced to 77.46% with the addition of GO. In addition, the microbial diversity in the wet AD process was enhanced with the addition of GO only, graphite and graphene led to a reduction in it. As for bacterial community, graphite and graphene increased the abundance of Thermotogae from 43.43% to 57.42% and 58.74%, while GO increased the abundance of Firmicute from 49.90% to 56.27%. For the archaeal community, the proportion of hydrogenotrophic methanogens was improved when adding each graphite-based material; however, only GO increased Methanosaeta that was acetoclastic methanogens. Finally, methanogens were found as the ARG host, and ARGs that belong to the same subtype might exist in the same host bacteria.

Liquid hot water as sustainable biomass pretreatment technique for bioenergy production: A review

In recent years, lignocellulosic biomass has emerged as one of the most versatile energy sources among the research community for the production of biofuels and value-added chemicals. However, biomass pretreatment plays an important role in reducing the recalcitrant properties of lignocellulose, leading to superior quality of target products in bioenergy production. Among existing pretreatment techniques, liquid hot water (LHW) pretreatment has several outstanding advantages compared to others including minimum formation of monomeric sugars, significant removal of hemicellulose, and positive environmental impacts; however, several constraints of LHW pretreatment should be clarified. This contribution aims to provide a comprehensive analysis of reaction mechanism, reactor characteristics, influencing factors, techno-economic aspects, challenges, and prospects for LHW-based biomass pretreatment. Generally, LHW pretreatment could be widely employed in bioenergy processing from biomass, but circular economy-based advanced pretreatment techniques should be further studied in the future to achieve maximum efficiency, and minimum cost and drawbacks.

An efficient strategy to improve enzymatic hydrolysis of naked oat straw pretreated by Irpex lacteus

The objective of this study was aiming at developing an efficient strategy to promote enzymatic hydrolysis of naked oat straw and deciphering the potential mechanism. Irpex lacteus and Phlebia acerina were employed to inoculated on the naked oat straw for 4 weeks which the changes of fiber components, fermentation losses, lignin-degrading enzymes production pattern were determined weekly. Furthermore, the 72 h enzymatic hydrolysis of ultimately fermented naked oat straw were also evaluated. The acid detergent lignin was degraded at about 25% along with the moderate dry matter and cellulose loss which both showed selective degradation. The lignin-degrading enzymes production patterns of the two fungi were different which lignin peroxidase was not detected in Irpex lacteus treatment. In addition, the activities of cellulolytic enzymes were higher in Phlebia acerina treatment. After 72 h enzymatic hydrolysis, the reducing sugar content and hydrolysis yield pretreated by Irpex lacteus was 12.92 g/L and 69.49%, respectively. It was much higher than that in sterilized substrate and Phlebia acerina treatment. Meanwhile, the hydrolysis yields of glucose, sum of xylose and arabinose were all improved by Irpex lacteus which were 30.96% and 25.62%, respectively, and showed significant enhancements compared to control and Phlebia acerina treatment. Irpex lacteus is one of effective white rot fungi which could promote the enzymatic hydrolysis of naked oat straw obviously.

Biogas Production from Anaerobic Co-Digestion of Spent Mushroom Substrate with Different Livestock Manure

Spent mushroom substrate (SMS) is defined as the biomass waste generated during industrial mushroom cultivation. Utilization of SMS has been extensively researched and has immense potential as a sustainable substrate for generating biogas that can offset fossil fuel use. This closed loop energy generation process that can be set up in mushroom plants will reduce the dependence on fossil fuels and has the potential to reduce greenhouse gas emissions, which will benefit the environment. Anaerobic co-digestion of SMS with different agricultural wastes such as livestock manure would result in enhanced biogas production. In this study, the anaerobic co-digestion of SMS was carried out by combing yellow back fungus SMS along with chicken, dairy and pig manure. SMS combined with chicken manure yielded a slightly higher cumulative methane yield when compared with the combination of dairy manure and pig manure. Factors such as the total solids (TS) and the relative ratio of manure to SMS loading had a significant impact on the cumulative methane yield, volatile solids removal, with a particularly prominent synergistic effect. The synergistic effect was also closely related to the C/N ratio, and under experimental conditions (TS = 15%, SMS relative ratio of 50% and C/N ratio = 25.6), the cumulative methane yield of SMS with chicken manure (CM) was increased by 414% compared with that obtained using SMS or CM separately. We carried out a multiple linear regression (MLR) analysis, a statistical technique that uses several explanatory variables to predict the outcome of a response variable. Our analysis concluded that by using operating conditions (TS = 15%, and SMS ratio = 38.9), we were able to achieve the maximum cumulative methane yield (CMY).