The effect of bacterial and archaeal populations on anaerobic process fed with mozzarella cheese whey and buttermilk.

Dairy wastes can be conveniently processed and valorized in a biorefinery value chain since they are abundant, zero-cost and all year round available. For a comprehensive knowledge of the microbial species involved in producing biofuels and valuable intermediates from dairy wastes, the changes in bacterial and archaeal population were evaluated when H2, CH4 and chemical intermediates were produced. Batch anaerobic tests were conducted with a mixture of mozzarella cheese whey and buttermilk as organic substrate, inoculated with 1% and 3% w/v industrial animal manure pellets. The archaeal methanogens concentration increased in the test inoculated at 3% (w/v) when H2 and CH4 production occurred, being 1 log higher than that achieved in the test inoculated at 1% (w/v). Many archaeal species, mostly involved in the production of CH4, were identified by sequencing denaturing gradient gel electrophoresis (DGGE) bands. Methanoculleus, Methanocorpusculum and Methanobrevibacter genera were dominant archaea involved in the anaerobic process for bioenergy production from mozzarella cheese whey and buttermilk mixture.

Recovery of Polyhydroxyalkanoates From Single and Mixed Microbial Cultures: A Review.

An overview of the main polyhydroxyalkanoates (PHA) recovery methods is here reported, by considering the kind of PHA-producing bacteria (single bacterial strains or mixed microbial cultures) and the chemico-physical characteristics of the extracted polymer (molecular weight and polydispersity index). Several recovery approaches are presented and categorized in two main strategies: PHA recovery with solvents (halogenated solvents, alkanes, alcohols, esters, carbonates and ketones) and PHA recovery by cellular lysis (with oxidants, acid and alkaline compounds, surfactants and enzymes). Comparative evaluations based on the recovery, purity and molecular weight of the recovered polymers as well as on the potential sustainability of the different approaches are here presented.

Pre-treatment and inoculum affect the microbial community structure and enhance the biogas reactor performance in a pilot-scale biodigestion of municipal solid waste.

During anaerobic digestion of municipal solid waste, organic matter is converted to methane, carbon dioxide, and other organic and inorganic compounds through a complex cooperation among different microbial groups with different metabolic activities. Here, culture-dependent and independent approaches provided evidence for examining the relationship between bacterial and archaeal communities and methane production in a pilot-scale anaerobic digestion. The abundance of aerobic and anaerobic functional groups of C and N cycles, such as cellulolytic, pectinolytic, amylolytic and proteolytic bacteria, was high at the beginning of the experiment and was drastically decreased after anaerobic digestion. In contrast, the ammonifiers increased in the biogas producing reactors in a higher pH environment. The methanogenic archaeal genera recovered were Methanobrevibacter, Methanobacterium, Methanoculleus and Methanocorpusculum, thus indicating that methane was formed primarily by the hydrogenotrophic pathway in the reactors. Moreover, the mechanical pretreatment effects, as well as the effect of pelleted manure as inoculum, were considered. The highest methane production was detected in the biodigesters with minced organic waste, thus indicating that pre-treatment of a heterogeneous starting matrix was essential for improving biogas production and stabilizing the process.

Anaerobic Process for Bioenergy Recovery From Dairy Waste: Meta-Analysis and Enumeration of Microbial Community Related to Intermediates Production.

Dairy wastes are widely studied for the hydrogen and methane production, otherwise the changes in microbial communities related to intermediate valuable products was not deeply investigated. Culture independent techniques are useful tools for exploring microbial communities in engineered system having new insights into their structure and function as well as potential industrial application. The deep knowledge of the microbiota involved in the anaerobic process of specific waste and by-products represents an essential step to better understand the entire process and the relation of each microbial population with biochemical intermediates and final products. Therefore, this study investigated the microbial communities involved in the laboratory-scale anaerobic digestion of a mixture of mozzarella cheese whey and buttermilk amended with 5% w/v of industrial animal manure pellets. Culture-independent methods by employing high-throughput sequencing and microbial enumerations highlighted that lactic acid bacteria, such as Lactobacillaceae and Streptococcaceae dominated the beginning of the process until about day 14 when a relevant increase in hydrogen production (more than 10 ml H2 gVS-1 from days 13 to 14) was observed. Furthermore, during incubation a gradual decrease of lactic acid bacteria was detected with a simultaneous increase of Clostridia, such as Clostridiaceae and Tissierellaceae families. Moreover, archaeal populations in the biosystem were strongly related to inoculum since the non-inoculated samples of the dairy waste mixture had a relative abundance of archaea less than 0.1%; whereas, in the inoculated samples of the same mixture several archaeal genera were identified. Among methanogenic archaea, Methanoculleus was the dominant genus during all the process especially when the methane production occurred, and its relative abundance increased up to 99% at the end of the incubation time highlighting that methane was formed from dairy wastes primarily by the hydrogenotrophic pathway in the reactors.

Integrated systems for biopolymers and bioenergy production from organic waste and by-products: a review of microbial processes.

Recently, issues concerning the sustainable and harmless disposal of organic solid waste have generated interest in microbial biotechnologies aimed at converting waste materials into bioenergy and biomaterials, thus contributing to a reduction in economic dependence on fossil fuels. To valorize biomass, waste materials derived from agriculture, food processing factories, and municipal organic waste can be used to produce biopolymers, such as biohydrogen and biogas, through different microbial processes. In fact, different bacterial strains can synthesize biopolymers to convert waste materials into valuable intracellular (e.g., polyhydroxyalkanoates) and extracellular (e.g., exopolysaccharides) bioproducts, which are useful for biochemical production. In particular, large numbers of bacteria, including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, Azotobacter chroococcum, Azotobacter beijerincki, methylotrophs, Pseudomonas spp., Bacillus spp., Rhizobium spp., Nocardia spp., and recombinant Escherichia coli, have been successfully used to produce polyhydroxyalkanoates on an industrial scale from different types of organic by-products. Therefore, the development of high-performance microbial strains and the use of by-products and waste as substrates could reasonably make the production costs of biodegradable polymers comparable to those required by petrochemical-derived plastics and promote their use. Many studies have reported use of the same organic substrates as alternative energy sources to produce biogas and biohydrogen through anaerobic digestion as well as dark and photofermentation processes under anaerobic conditions. Therefore, concurrently obtaining bioenergy and biopolymers at a reasonable cost through an integrated system is becoming feasible using by-products and waste as organic carbon sources. An overview of the suitable substrates and microbial strains used in low-cost polyhydroxyalkanoates for biohydrogen and biogas production is given. The possibility of creating a unique integrated system is discussed because it represents a new approach for simultaneously producing energy and biopolymers for the plastic industry using by-products and waste as organic carbon sources.