Biogas optimisation processes and effluent quality: A review

Since the first use of anaerobic digestion technology to generate biogas in 1895 to power street lights in Britain and also as a Municipal Solid Waste Management technique in the US in 1939, significant advances have been developed to optimise the process in a sustainable manner. In practice, optimising anaerobic digesters to increase biogas production dependent on a balanced pH (neutral), tolerable volatile fatty acids and alkalinity levels by anaerobic bacteria. Others include maintaining suitable temperature regime, providing suitable organic loading rate to prevent noxious conditions, well-balanced carbon to nitrogen ratio to limit ammonia build-up and appropriate choice of substrates. In terms of biomass, lignocellulose substrates constitute the most abundant bioresource. This resource however requires modification of the chemistry of the structure to improve its biodegradation, biogas production and effluent quality. There have been attempts by most researchers to improve lignocellulose biomass utilization in anaerobic digesters through delignification to prevent non-productive binding of bacteria as well as reduce the crystalline in cellulose with the aim of making the holocellulose fractions bioavailable. However, none of the techniques so far applied for the purpose of optimising biogas production has attained the maximum theoretical biogas yield of 120,000-650,000 L t(-1). Techniques frequently applied include among others; pretreatment (chemical, biological, physical or their combinations), co-digestion, application of inoculum or bio-augmentation, and supplementing anaerobic digesters with micronutrients and nanoparticles. This review thus highlights research findings from authors in relation to factors influencing effective degradation of lignin based biomass in other to ascertain the best possible strategies to scale up the process.