Experimental investigation and mathematical modelling of batch and semi-continuous anaerobic digestion of cellulose at high concentrations and long residence times

In the context of the anaerobic digestion of slowly biodegradable substrates for energy and chemicals production, this study investigated the anaerobic digestion of cellulose without any chemical pre-treatments using open (undefined) mixed microbial cultures. The anaerobic conversion of cellulose was investigated in extended-length (run length in the range 518–734 days) batch and semi-continuous runs (residence time 20–80 days), at high cellulose concentration (20–40 g L−1), at temperatures of 25 and 35 °C. The maximum cellulose removal was 77% in batch (after 412 days) and 60% (at 80 days residence time) in semi-continuous experiments. In semi-continuous experiments, cellulose removal increased as the residence time increased however the cellulose removal rate showed a maximum (0.17 g L−1 day−1) at residence time 40–60 days. Both cellulose removal and removal rate decreased when cellulose concentration in the feed was increased from 20 to 40 g L−1. Liquid-phase products (ethanol and short chain organic acids) were only observed under transient conditions but not at the steady state of semi-continuous runs. Most of the observed results were well described by a mathematical model which included cellulose hydrolysis and growth on the produced glucose. The model provided insight into the physical phenomena behind the observed results.

Conversion of dietary inositol into propionate and acetate by commensal Anaerostipes associates with host health

We describe the anaerobic conversion of inositol stereoisomers to propionate and acetate by the abundant intestinal genus Anaerostipes. A inositol pathway was elucidated by nuclear magnetic resonance using [13C]-inositols, mass spectrometry and proteogenomic analyses in A. rhamnosivorans, identifying 3-oxoacid CoA transferase as a key enzyme involved in both 3-oxopropionyl-CoA and propionate formation. This pathway also allowed conversion of phytate-derived inositol into propionate as shown with [13C]-phytate in fecal samples amended with A. rhamnosivorans. Metabolic and (meta)genomic analyses explained the adaptation of Anaerostipes spp. to inositol-containing substrates and identified a propionate-production gene cluster to be inversely associated with metabolic biomarkers in (pre)diabetes cohorts. Co-administration of myo-inositol with live A. rhamnosivorans in western-diet fed mice reduced fasting-glucose levels comparing to heat-killed A. rhamnosivorans after 6-weeks treatment. Altogether, these data suggest a potential beneficial role for intestinal Anaerostipes spp. in promoting host health.

Phytoremediation: A Synergistic Interaction between Plants and Microbes for Removal of Petroleum Hydrocarbons

Rapid industrialization leads to the deterioration of quality of life and the environment. Petroleum hydrocarbon pollution is one of the contributing factors to that. Petroleum hydrocarbons (PHCs) are natural products, and under high temperature and pressure, they are produced by the anaerobic conversion of biomass. Excessive use of PHCs leads to pollution in the agriculturally important soils and the ultimate source of potability of water, that is, groundwater which is gaining significant attention throughout the world. The fortuitous release of PHCs such as gasoline, diesel, and heating oil are common sources of groundwater contamination. The PHC concentrations in groundwater are often above drinking water standards and bioremediation actions have to be taken. Due to their organic nature, PHCs are difficult to degrade as unavailable for microbial action. Due to this, PHCs are the most widespread environmental contaminants. Plant-microbe synergistic association for remediation of PHCs is comprehensive and it is an effective tool for reclamation of soil and environment from these kinds of undesirable materials. In addition to providing plant growth promotion, microbes can degrade PHCs effectively.

Anaerobic Conversion of Biodegradable Municipal Solid Waste to Biogas: A Review

Huge quantity of Municipal Solid Waste (MSW) is generated daily. This waste comprises a biodegradable portion which can be converted into biogas (bioenergy) by anaerobic digestion (AD). This study reviews MSW and its management, AD feedstock and their characteristics, factors affecting biogas production in a biodigester and anaerobic co-digestion of Organic Fraction of MSW (OFMSW) with other substrates. Municipal solid waste is managed through waste diversion (reduction, reuse, recycling and recovery) and waste disposal (controlled incineration, landfilling and controlled dumping). AD feedstock includes agricultural waste/residues, animal wastes, energy crops, food waste, forestry crops and residues, organic industrial waste and wastewater, weeds, aquatic algae, sewage and OFMSW. The essential factors that influence the production of biogas are temperature, pH, mixing rate, carbon/nitrogen ratio, organic loading rate, micro and macro-nutrient availability, retention time, nature of the feedstock and digester type. Anaerobic co-digestion of OFMSW with other substrates results in improved AD process stability, enhanced biogas productivity, maximization of the capacity of available feedstock for anaerobic digestion. It is also a cost-effective and improved technique to optimize anaerobic digestion process via the increase in nutrients and bacterial variety in substrates. The generation rate and composition of MSW, as well as the characteristics of OFMSW feedstock for anaerobic digestion, are required for the design of a full-scale biodigester for municipal use. The information provided in this review is invaluable to researchers, governments, industries and other stakeholders interested in anaerobic conversion of biodegradable solids to bioenergy.