Research advances in deriving renewable energy from biomass in wastewater treatment plants

Abstract

Anaerobic digestion (AD) can be used to derive renewable energy from biomass in wastewater treatment plants, and the produced biogas represents a valuable end-product that can greatly offset operation costs. However, AD is a complex biological process involving many different kinds of microbial communities and biotransformation processes, and it is easily affected by start-up and operation conditions. In order to facilitate improvements in the AD process and enable predictions of biogas production quantities, this review discusses the microbial dynamics, scientific models, and reinforcement strategies of AD biogas production (i.e., sludge pre-treatment, bio-electrochemical and Fe/Fe₃O₄ technologies). During sludge pre-treatment, the focused-pulsed method can be introduced to promote cell lysis, and this requires specific treatment chamber designs. The bio-electrochemical method, especially in regard to the use of microbial electrolysis cells (MECs), can obviously improve biogas production while only consuming small amounts of energy. Mechanisms of AD-MEC systems and associated influencing factors are described in detail in this review. Engineered nanomaterials, which are increasingly being used in commercial products, may have detrimental or even beneficial effects on the sludge AD process. The use of low doses of Fe/Fe₃O₄ nanomaterials (≤0.5% (w/w)) as an economically viable and environmentally sustainable method for improving biogas production is discussed. In addition, removal methods for dissolved methane, which can have a negative environmental impact if not handled properly, in the anaerobic digester effluents are discussed in this review.