Start-up of co-digestion of poultry litter and wheat straw in anaerobic sequencing batch reactor by gradually increasing organic loading rate: Methane production and microbial community analysis

The dominant-substrate driven the enhanced performance in co-digestion of Pennisetum hybrid and livestock waste

Co-digestion has been considered a promising method to improve methane yield. The effect of the proportion of dominant substrate on the performance and microbial community of anaerobic digestion of Pennisetum hybrid (PH) and livestock waste (LW) was investigated. An obvious synergistic effect was obtained with an increase of 15.20%-17.45% in specific methane yield compared to the predicted value. Meanwhile, the dominant substrate influenced the relational model between methane yield enhancement rate and mixture ratio. For the LW-dominant systems, a parabolic model between enhancement rate and mixture ratio was observed with a highest value of 392.16 mL/g VS achieved at a PH:LW ratio of 2:8. While a linear pattern appeared for PH-dominant systems with the highest methane yield of 307.59 mL/g VS. Co-digestion selectively enriched the relative abundance of Clostridium_sensu_stricto_1, Terrisporobacter, Syntrophomonas, Methanosarcina and Methanobacterium, which boosted the performance of hydrolysis, acidogenesis, acetogenesis and methanogenesis processes.

Biochar mediated high-rate anaerobic bioreactors: A critical review on high-strength wastewater treatment and management

Treatment of high-strength wastewater is critical for the aquatic environment and receiving water bodies around the globe. Untreated or partially treated high-strength wastewater may cause severe damage to the existing water bodies. Various high-rate anaerobic bioreactors have been developed in the last decades for treating high-strength wastewater. High-rate anaerobic bioreactors are effective in treating industrial wastewater and provide energy in the form of methane as well. However, the physical or chemical properties of high-strength industrial wastewater, sometimes, disrupt the functioning of a high-rate anaerobic bioreactor. For example, the disintegration of granular sludge in up flow anaerobic sludge blanket reactor or membrane blocking in an anaerobic membrane bioreactor are the results of a high-strength wastewater treatment which hamper the proper functioning and may harm the wastewater treatment plant economically. Biochar, if added to these bioreactors, may help to alleviate the ill-functioning of high-rate anaerobic bioreactors. The primary mechanisms by biochar work in these bioreactors are direct interspecies electron transfer, microbial immobilization, or gene level alternations in microbial structure. The present article explores and reviews the recent application of biochar in a high-rate anaerobic bioreactor treating high-strength industrial wastewater.

Coupling of the Feammox - Anammox pathways by using a sequential discontinuous bioreactor

Treating nitrogenous compounds in wastewater is a contemporary challenge, prompting novel approaches for ammonium (NH4+) conversion to molecular nitrogen (N2). This study explores the classic anaerobic ammonium oxidation process (Anammox) coupled to the iron-dependent anaerobic ammonium oxidation process (Feammox) in a sequential discontinuous bioreactor (SBR) for NH4+ removal. Feammox and Anammox cultures were individually enriched and combined, optimizing the coupling, and identifying key variables influencing the enrichment process. Adding sodium acetate as a carbon source significantly reduces Fe3+ to Fe2+, indicating Feammox activity. Both Anammox and Feammox processes were successfully operated in SBRs, achieving efficient NH4+ removal (Anammox: 64.6 %; Feammox: 43.4 %). Combining these pathways in a single SBR enhances the NH4+ removal capacity of 50.8 %, improving Feammox efficiency. The Feammox process coupled with Anammox may generate the nitrite (NO2-) needed for Anammox. This research contributes to biotechnological advancements for sustainable nitrogenous compound treatment in SBRs.

Enhancement of anaerobic digestion of high salinity food waste by magnetite and potassium ions: Digestor performance, microbial and metabolomic analyses

The study investigated the effectiveness of magnetite and potassium ions (K+) in enhancing anaerobic digestion of high salinity food waste. Results indicated that both magnetite and K+ improved anaerobic digestion in high-salt environments, and their combination yielded even better results. The combination of magnetite and K+ promoted microorganism activity, and resulted in increased abundance of DMER64, Halobacteria and Methanosaeta. Metabolomic analysis revealed that magnetite mainly influenced quorum sensing, while K+ mainly stimulated the synthesis of compatible solutes, aiding in maintaining osmotic balance. The combined additives regulated pathways such as ATP binding cassette transport, methane metabolism, and inhibitory substance metabolism, enabling cells to resist environmental stress and maintain normal metabolic activity. Overall, this study demonstrated the potential of magnetite and K+ to enhance food waste anaerobic digestion in high salt conditions and provided valuable insights into the molecular mechanism.

Metataxonomic characterization of the microbial community involved in the production of biogas with microcrystalline cellulose in pilot and laboratory scale

Biogas, produced in anaerobic digestion, is a sustainable alternative for generating energy from agro-industrial and municipal waste. Information from the microbiota active in the process expands the possibilities for technological innovation. In this study, taxonomic annotations, and functional prediction of the microbial community of the inoculum of two processes were carried out: an industrial unit (pilot-scale urban solid waste plant-IU) and a laboratory-scale reactor fed with swine and cattle waste (LS). The biochemical potential of biogas was obtained using tested inoculum with microcrystalline cellulose, obtaining 682 LN/kgVS (LSC-laboratory scale inoculum and microcrystalline cellulose), and 583 LN/kgVS (IUC-industrial unit inoculum and microcrystalline cellulose), which is equivalent to a recovery of 91.5% of total biogas to LSC. The phyla Synergistota and Firmicutes were more abundant in LS/LSC. In the IU/IUC (treatment of restaurant waste and customs seizures), there was a greater microbiological variety and a predominance of the Bacteroidota, Cloacimonadota, Firmicutes and Caldatribacteriota. The genus Methanosaeta predominated in the process, and it was possible to infer the genes (K01895, K00193 and K00625) related to acetoclastic pathway, as well as endoglucanases that are involved in the metabolism of cellulose (LSC). Terpenoids, polyketides, cofactors, and vitamin metabolism were higher in reactors that received different substrates (IU; IUC). The taxonomic and functional differences revealed the importance of determining the microbiota in the analysis of the potential of an inoculum, combined with the use of microcrystalline cellulose, which can provide optimization information in the production of clean energy.

Efficient methane production from anaerobic co-digestion of poultry litter with wheat straw in daily sequencing batch reactor: Effects of carbon-to-nitrogen ratio, total solids, and hydraulic retention time

This study performed co-digestion of poultry litter (PL) with wheat straw in the daily anaerobic sequencing batch reactor considering operation parameters of carbon-to-nitrogen ratio (C/N, 11.6 to 28.4), total solids (TS, 2.6 to 9.4%), and hydraulic retention time (HRT, 7.6 to 24.4d). The inoculum with a diverse microbial community structure included 2% of methanogens (Methanosaeta) was chosen. Experimental performance by central composite design showed continuous methane production with the highest biogas production rate (BPR) obtained at C/N = 20, TS = 6%, and HRT = 7.6d, being (1.18 ± 0.14 L/L_R/d). A significant modified quadratic model (p < 0.0001) for predicting BPR was built (R²= 0.9724). The operation parameters and process stability both affected the release of nitrogen, phosphorus, and magnesium in the effluent. The results provided new support for the novel reactor operations for efficient bioenergy production from PL and agricultural wastes.

Ammonia tolerance and microbial community in thermophilic co-digestion of sewage sludge initiated with lignocellulosic biomass

Rice straw is a useful lignocellulosic biomass for controlling ammonia inhibition in the thermophilic anaerobic digestion of sewage sludge. However, it is challenging to procure rice straw throughout the year because of its seasonal production. This study investigated methane production in a laboratory-scale digester by gradually decreasing rice straw addition to solid thermophilic sewage sludge digestion. The decrease in rice straw did not accumulate volatile fatty acids and stabilized methane production. Even with increased sludge concentration without rice straw, methane production continued under high ammonia conditions. Ammonia tolerance of the digested sludge of the experimental digester was higher than that of conventionally digested sludge. The cellulose-degrading bacteria Clostridia and high ammonia-resistant archaea Methanosarcina were dominant in the experimentally digested sludge. The community was maintained for over 200 days after discontinuing the rice straw supply. These findings suggest that anaerobic digestion initiation with rice straw is appropriate to facilitate ammonia-tolerant communities.

Promoting the Circular Economy on an Island: Anaerobic Co-Digestion of Local Organic Substrates as a Possible Renewable Energy Source

The local waste co-digestion is an interesting option to tackle in reduced and isolated areas like the islands. The islands have limited territory and scarce fuel production. Moreover, organic waste can create serious environmental problems in soil, water and air. Anaerobic co-digestion (AcoD) is a technology fulfilling the concept of waste-to-energy (WtE) based on local resources. The valorisation of organic waste through AcoD on an island would prevent environmental impacts, while being a source of renewable energy. In this study, cow manure (outdoor and indoor), pig slurry, bird manure, kitchen waste, sewage sludge and oily lacteous waste produced on Island Terceira (Portugal) were tested in mesophilic -35 °C- Biochemical Methane Potential (BMP) co-digestion assays. The goals were to analyse the recalcitrant and high potential produced waste and to estimate the energetic supply source on the island. The cow manure and pig slurry were used as inocula and specific methanogenic activities (SMAs) were carried out. The results showed that both substrates have a significant methanogenic activity-SMA 0.11 g-COD/(g-VSS.d) and 0.085 g-COD/(g-VSS.d), respectively. All the studied combinations were feasible in AcoD, showing TS removals in the range of 19-37%; COD removals in the range 67-78% and specific methane yields from 0.14 to 0.22 L/gCOD removed, but some differences were found. The modified Gompertz model fitted the AcoD assays (R² 0.982-0.998). The maximum biogas production rate, Rmax. was highest in the AcoD of Cow+Pig+Oily and in the Cow+Pig+Sludge with 0.017 and 0.014 L/g-VS_added.day, respectively, and the lowest in Cow+Pig+Bird with 0.010 L/g-VS_added. In our AcoD studies, the bird manure limited the performance of the process, since it was recalcitrant to anaerobic degradation. On the other hand, the oily lacteous waste showed a great potential in the anaerobic digestion. The estimated biogas production, from the best-studied condition, could cover the 11.4% of the energy supply of the inhabitants. These preliminary results would prevent the environmental impact of organic waste on the island and promote the use of local waste in a circular economy scenario.

Employing micro-aeration in anaerobic digestion of poultry litter and wheat straw: Batch kinetics and continuous performance

In this study, different micro-aeration (MA) strategies for anaerobic digestion (AD) of poultry litter (PL) and wheat straw (WS) were examined. MA at different stages (pretreatment, middle, pretreatment plus middle, and daily) in batch AD of WS showed that daily MA had the highest increase (16.5 %) of the cumulative methane yield (CMY) compared to the control. Batch co-digestion (Co-AD) of WS and PL with daily MA obtained a furtherly improved (15.1 %) CMY of 225.44 N mL CH₄/g vS _added. The modified Gompertz model and Cone model were good in fitting the methane yield kinetics of MA engaged AD process (R² greater than 0.99). Daily MA shortened the lag phase of Co-AD by 3.4 %. The sequencing batch reactor for the Co-AD of WS and PL showed an increased (21.5 %) daily methane yield when 0.5-h/d MA was employed. The results provided support for the application of micro-aeration in the AD of agricultural wastes.