Effect of the initial pH on the anaerobic digestion process of dairy cattle manure

Influential factors in anaerobic digestion of rice-derived food waste and animal manure: A comprehensive review

Utilization of organic community wastes towards deriving sustainable renewable energy and adequate disposal of the residual has been an important topic of investigation. Anaerobic digestion and co-digestion of rice-derived food waste and animal manure for sustainable biogas generation is crucial from the view-point of community consumption. This paper presents an extensive review of the important and recent contributions in the related areas. The critical physico-chemical parameters involved in such digestion process are analyzed, including temperature, carbon-nitrogen ratio, microorganisms, pH, substrate characteristics, organic loading rate, hydraulic retention time, volatile fatty acids, ammonia, and light/heavy metal ions. Studies implied that the optimum yield of biogas production could be achieved only when the values of the parameters exist in the specific ranges. Few recent studies highlighted the use of emerging techniques including micro-aerobic system, additives, laser radiation, bio-electrochemical field, among others for efficiency enhancement of the digestion process and optimum yield. The entire study provided a set of important conclusions and future research directives are as well proposed.

Different bioaugmentation regimes that mitigate ammonium/salt inhibition in repeated batch anaerobic digestion: Generic converging trend of microbial communities

Bioaugmentation regimes (i.e., dosage, repetition, and timing) in AD must be optimized to ensure their effectiveness. Although previous studies have investigated these aspects, most have focused exclusively on short-term effects, with some reporting conflicting conclusions. Here, AD experiments of three consecutive repeated batches were conducted to determine the effect of bioaugmentation regimes under ammonium/salt inhibition conditions. A positive correlation between reactor performance and inoculum dosage was confirmed in the first batch, which diminished in subsequent batches for both inhibitors. Moreover, a diminishing marginal effect was observed with repeated inoculum introduction. While the bacterial community largely influenced the reactor performance, the archaeal community exhibited only a minor impact. Prediction of the key enzyme abundances suggested an overall decline in different AD steps. Overall, repeated batch experiments revealed that a homogeneous bacterial community deteriorated the AD process during long-term operation. Thus, a balanced bacterial community is key for efficient methane production.

The fecal microbiota of Holstein cows is heritable and genetically correlated to dairy performances

The fecal microbiota of ruminants constitutes a diversified community that has been phenotypically associated with a variety of host phenotypes, such as production and health. To gain a better understanding of the complex and interconnected factors that drive the fecal bacterial community, we have aimed to estimate the genetic parameters of the diversity and composition of the fecal microbiota, including heritabilities, genetic correlations among taxa, and genetic correlations between fecal microbiota features and host phenotypes. To achieve this, we analyzed a large population of 1,875 Holstein cows originating from 144 French commercial herds and routinely recorded for production, somatic cell score, and fertility traits. Fecal samples were collected from the animals and subjected to 16S rRNA gene sequencing, with reads classified into Amplicon Sequence Variants (ASVs). The estimated α- and β-diversity indices (i.e., Observed Richness, Shannon index, Bray-Curtis and Jaccard dissimilarity matrices) and the abundances of ASVs, genera, families and phyla, normalized by centered-log ratio (CLR), were considered as phenotypes. Genetic parameters were calculated using either univariate or bivariate animal models. Heritabilities estimates, ranging from 0.08 to 0.31 for taxa abundances and β-diversity indices, highlight the influence of the host genetics on the composition of the fecal microbiota. Furthermore, genetic correlations estimated within the microbial community and between microbiota features and host traits reveal the complex networks linking all components of the fecal microbiota together and to their host, thus strengthening the holobiont concept. By estimating the heritabilities of microbiota-associated phenotypes, our study quantifies the impact of the host genetics on the fecal microbiota composition. In addition, genetic correlations between taxonomic groups and between taxa abundances and host performance suggest potential applications for selective breeding to improve host traits or promote a healthier microbiota.

L-tryptophan anaerobic fermentation for indole acetic acid production: Bacterial enrichment and effects of zero valent iron

Indole acetic acid (IAA) as a plant hormone, was one of the valuable products of anaerobic fermentation. However, the enriching method remained unknown. Moreover, whether zero valent iron (ZVI) could enhance IAA production was unexplored. In this work, IAA producing bacteria Klebsiella (63 %) was enriched successfully. IAA average production rate and concentration were up to 3 mg/L/h and 56 mg/L. With addition of 1 g/L ZVI, IAA average production rate and concentration was increased for 2 and 3 folds. Mechanisms indicated ZVI increased Na+K+-ATP activity and electron transport activity for 2 folds and 1 fold. Moreover, macro transcription determined indole pyruvate pathway activity like primary-amine oxidase, indole pyruvate decarboxylase and aldehyde dehydrogenase were increased for 146 %, 187 %, and 557 %, respectively. Therefore, ZVI was suitable for enhancement IAA production from mixed culture anaerobic fermentation.

Advances in sewage sludge application and treatment: Process integration of plasma pyrolysis and anaerobic digestion with the resource recovery

Sewage sludge (SS) is an environmental issue due to its high organic content and ability to release hazardous substances. Most of the treatments available are biological, thermal hydrolysis, mechanical (ultrasound, high pressure, and lysis), chemical with oxidation (mainly ozonation), and alkali pre-treatments. Other treatment methods include landfill, wet oxidation, composting, drying, stabilization, incineration, pyrolysis, carbonization, liquefaction, gasification, and torrefaction. Some of these SS disposal methods damage the ecosystem and underutilize the potential resource value of SS. These challenges must be overcome with an innovative technique for the improvement of SS's nutritional value, energy content, and usability. This review proposes plasma pyrolysis and anaerobic digestion (AD) as promising SS treatment technologies. Plasma pyrolysis pre-treats SS to make it digestible by AD bacteria and immobilizes the heavy metals. The addition of Char to the upstream AD process increases the quantity and quality of biogas produced while enhancing the nutrients in the digestate. These two processes are integrated at high temperatures, thus creating concerns about their energy demand. These challenges are offset by the generated energy that can run the treatment plant or be sold to the grid, generating additional cash. Plasma pyrolysis wastes can also be converted into biochar, organic fertilizer, or soil conditioner. These combined technologies' financial sustainability depends on the treatment facility's circumstances and location. Plasma pyrolysis and AD can treat SS sustainably and provide nutrients and resources. This paper explains the co-process treatment route's techno-economic prospects, challenges, and recommendations for the future application of SS valorization and resource recovery.

Rumen and Fecal Microbiota Characteristics of Qinchuan Cattle with Divergent Residual Feed Intake

Residual feed intake (RFI) is one of the indicators of feed efficiency. To investigate the microbial characteristics and differences in the gastrointestinal tract of beef cattle with different RFI, a metagenome methodology was used to explore the characteristics of the rumen and fecal microbiota in 10 Qinchuan cattle (five in each of the extremely high and extremely low RFI groups). The results of taxonomic annotation revealed that Bacteroidetes and Firmicutes were the most dominant phyla in rumen and feces. Prevotella was identified as a potential biomarker in the rumen of the LRFI group by the LEfSe method, while Turicibacter and Prevotella might be potential biomarkers of the HRFI and LRFI group in feces, respectively. Functional annotation revealed that the microbiota in the rumen of the HRFI group had a greater ability to utilize dietary polysaccharides and dietary protein. Association analysis of rumen microbes (genus level) with host genes revealed that microbiota including Prevotella, Paraprevotella, Treponema, Oscillibacter, and Muribaculum, were significantly associated with differentially expressed genes regulating RFI. This study discovered variances in the microbial composition of rumen and feces of beef cattle with different RFIs, demonstrating that differences in microbes may play a critical role in regulating the bovine divergent RFI phenotype variations.