Effect of magnetite on anaerobic digestion of distillers grains and beet pulp: Operation of reactors and microbial community dynamics.

It has been previously shown that magnetite (Fe3O4) nanoparticles stimulate the anaerobic digestion process in several anaerobic reactors. Here we evaluate the effect of magnetite nanoparticles on the efficiency of anaerobic digestion of distillers grains with solubles and sugar beet pulp in mesophilic batch experiments. The addition of magnetite nanopowder had a positive effect on the anaerobic digestion process. CH4 was produced faster in the presence of 50 mg of Fe3O4 per 1 g of added total solids than from treatments without addition of Fe3O4. These results demonstrate that the addition of magnetite enhances the methanogenic decomposition of organic acids. Microbial community structure and dynamics were investigated based on bacterial and archaeal 16S rRNA genes, as well as mcrA genes encoding the methyl-CoM reductase. Depending on the reactor, Bacteroides, midas_1138, Petrimonas, unclassified Rikenellaceae (class Bacteroidia), Ruminiclostridium, Proteiniclasticum, Herbinix, and Intestinibacter (class Clostridia) were the main representatives of the bacterial communities. The archaeal communities in well-performed anaerobic reactors were mainly represented by representatives of the genera Methanosarcina and Methanobacterium. Based on our findings, Fe3O4 nanoparticles, when used properly, will improve biomethane production.

Effect of the Organic Loading Rate Increase and the Presence of Zeolite on Microbial Community Composition and Process Stability During Anaerobic Digestion of Chicken Wastes.

This study investigates the effect of the organic loading rate (OLR) increase from 1.0 to 3.5 g VS L(-1) day(-1) at constant hydraulic retention time (HRT) of 35 days on anaerobic reactors' performance and microbial diversity during mesophilic anaerobic digestion of ammonium-rich chicken wastes in the absence/presence of zeolite. The effects of anaerobic process parameters on microbial community structure and dynamics were evaluated using a 16S ribosomal RNA gene-based pyrosequencing approach. Maximum 12 % of the total ammonia nitrogen (TAN) was efficiently removed by zeolite in the fixed zeolite reactor (day 87). In addition, volatile fatty acids (VFA) in the fixed zeolite reactor accumulated in lower concentrations at high OLR of 3.2-3.5 g VS L(-1) day(-1). Microbial communities in the fixed zeolite reactor and reactor without zeolite were dominated by various members of Bacteroidales and Methanobacterium sp. at moderate TAN and VFA levels. The increase of the OLR accompanied by TAN and VFA accumulation and increase in pH led to the predominance of representatives of the family Erysipelotrichaceae and genera Clostridium and Methanosarcina. Methanosarcina sp. reached relative abundances of 94 and 57 % in the fixed zeolite reactor and reactor without zeolite at the end of the experimental period, respectively. In addition, the diminution of Synergistaceae and Crenarchaeota and increase in the abundance of Acholeplasmataceae in parallel with the increase of TAN, VFA, and pH values were observed.

Impact of the substrate loading regime and phosphoric acid supplementation on performance of biogas reactors and microbial community dynamics during anaerobic digestion of chicken wastes.

This study evaluates the effects of increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) as well as phosphoric acid addition on mesophilic reactors' performance and biogas production from chicken wastes. Furthermore, microbial community composition in reactors was characterized by a 16S rRNA gene-based pyrosequencing analysis. Each step of increasing OLR impacted on the activity of microorganisms what caused a temporary decrease in biogas production. The addition of phosphoric acid resulted in the increased biogas production with values between 361 and 447 mL g(VS)(-1) from day 61 to day 74 compared to control reactor (309-350 mL g(VS)(-1)). With reactors' operation, Bacteroidetes phylotypes were noticeably replaced with Firmicutes representatives, and significant increase of Clostridium sp. was identified. Within Euryarchaeota, Methanosarcina sp. dominated in all analyzed samples, in which high ammonium levels were detected (3.4-4.9 NH4(+)-N g L(-1)). These results can help in better understanding the anaerobic digestion process of simultaneously ammonium/phosphate-rich substrates.

Microbial community diversity in anaerobic reactors digesting turkey, chicken, and swine wastes.

The microbial community structures of two continuous stirred tank reactors digesting turkey manure with pine wood shavings as well as chicken and swine manure were investigated. The reactor fed with chicken/swine wastes displayed the highest organic acids concentration (up to 15.2 g/l) and ammonia concentration (up to 3.7 g/l ammonium nitrogen) and generated a higher biogas yield (up to 366 ml/g(VS)) compared with the reactor supplied with turkey wastes (1.5- 1.8 g/l of organic acids and 1.6-1.7 g/l of ammonium levels; biogas yield was up to 195 ml/g(VS)). The microbial community diversity was assessed using both sequencing and profiling terminal restriction fragment length polymorphisms of 16S rRNA genes. Additionally, methanogens were analyzed using methyl coenzyme M reductase alpha subunit (mcrA) genes. The bacterial community was dominated by members of unclassified Clostridiales with the prevalence of specific clostridial phylotypes in each reactor, indicating the effect of the substrate type on the community structure. Of the methanogenic archaea, methanogens of the genus Methanosarcina were found in high proportions in both reactors with specific methanosarcinas in each reactor, whereas the strict hydrogenotrophic methanogens of Methanoculleus sp. were found at significant levels only in the reactor fed with chicken/swine manure (based on the analyses of 16S rRNA gene). This suggests that among methanogenic archaea, Methanosarcina species which have different metabolic capabilities, including aceticlastic and hydrogenotrophic methanogenesis, were mainly involved in anaerobic digestion of turkey wastes.