Optimization of Energy Production from Two-Stage Mesophilic–Thermophilic Anaerobic Digestion of Cheese Whey Using a Response Surface Methodology Approach

Spatial separation into acidogenic and methanogenic stages is considered a viable option to ensure process stability, energy efficiency and the better control of key anaerobic digestion (AD) parameters. The elucidation of the optimal modes of two-stage AD for the maximization of the recovery of biofuels (H2 and CH4) is still an urgent task, the main optimization criteria being the highest energy yield (EY) and energy production rate (EPR). In this work, a response surface methodology was used for an optimization of energy production from the two-stage mesophilic–thermophilic AD of cheese whey (CW). Three dilution rates of CW, providing values of 10.9, 14.53 and 21.8 g for the chemical oxygen demand (COD)/L in the influent and three hydraulic retention times (HRTs) (1, 2 and 3 days) in methanogenic biofilters at a constant HRT in an acidogenic biofilter of 0.42 days, were tested to optimize the EY and EPR. The desirability approach produced combined optimum conditions as follows: the dilution rate of the CW provided 17.58 g COD/L (corresponding to OLR of 6.5 g COD/(L·day)) in the influent and a HRT in the methanogenic biofilter of 2.28 days, both of which provided a maximum EPR of 80.263 kJ/(L·day) and EY of 9.56 kJ/g COD, with an overall desirability value of 0.883

A Review of Basic Bioinformatic Techniques for Microbial Community Analysis in an Anaerobic Digester

Biogas production involves various types of intricate microbial populations in an anaerobic digester (AD). To understand the anaerobic digestion system better, a broad-based study must be conducted on the microbial population. Deep understanding of the complete metagenomics including microbial structure, functional gene form, similarity/differences, and relationships between metabolic pathways and product formation, could aid in optimization and enhancement of AD processes. With advancements in technologies for metagenomic sequencing, for example, next generation sequencing and high-throughput sequencing, have revolutionized the study of microbial dynamics in anaerobic digestion. This review includes a brief introduction to the basic process of metagenomics research and includes a detailed summary of the various bioinformatics approaches, viz., total investigation of data obtained from microbial communities using bioinformatics methods to expose metagenomics characterization. This includes (1) methods of DNA isolation and sequencing, (2) investigation of anaerobic microbial communities using bioinformatics techniques, (3) application of the analysis of anaerobic microbial community and biogas production, and (4) restriction and prediction of bioinformatics analysis on microbial metagenomics. The review has been concluded, giving a summarized insight into bioinformatic tools and also promoting the future prospects of integrating humungous data with artificial intelligence and neural network software

Syntrophic Butyrate-Oxidizing Consortium Mitigates Acetate Inhibition through a Shift from Acetoclastic to Hydrogenotrophic Methanogenesis and Alleviates VFA Stress in Thermophilic Anaerobic Digestion

In anaerobic digestion (AD), butyrate is degraded by syntrophic consortium, but can accumulate in highly loaded AD systems. The effect of butyrate on the AD process attracts much less attention than propionate or acetate. In this work, an enrichment culture of the thermophilic butyrate-oxidizing syntrophic consortium was obtained by gradually increasing the initial butyrate concentration from 20 to 170 mM. Surprisingly, even the highest butyrate concentration did not significantly inhibit the methanogenic community, and the stage of acetate degradation was the limiting overall rate of the process. At 170 mM butyrate, the bacterial community changed towards the dominance of syntrophic acetate-oxidizing (SAO) bacteria related to Syntrophaceticus (42.9%), Syntrophomonas (26.2%) and Firmicutes (26.2%), while the archaeal community experienced a sharp decrease in the abundance of Methanosarcina thermophila (from 86.0 to 25.0%) and increase in Methanothermobacter thermautotrophicus (from 3.2 to 53.1%) and Methanomassiliicoccus (from 3.2 to 21.9%). Thus, the shift from acetoclastic methanogenesis to SAO coupled to hydrogenotrophic methanogenesis occurred as an adaptive strategy to overcome high acetate (~200 mM) build-up. Bioaugmentation with the obtained enrichment culture was effective in mitigating the butyrate-dominated VFA build-up during the AD of readily biodegradable waste, increasing the methane production rate, methane yield and volatile solids removal by more than 3.5, 6.2 and 2.9 times, respectively. Our study revealed that the thermophilic butyrate-oxidizing consortia as bioaugmented culture could be the potential strategy to alleviate the high organic load and VFA stress of AD