Thermophilic anaerobic treatment and biogas generation from wastewater produced in an advanced biorefinery process

Abstract

Anaerobic digestion can be an alternative method for treating wastewater from second‐generation biorefineries while simultaneously producing biogas. However, the feasibility of the process and key operational parameters by which wastewater produced in lignocellulosic biorefineries affects reactor performance remain poorly understood. This study evaluated the thermophilic anaerobic treatment of wastewater from the hydrothermal biomass pretreatment stream of a lignocellulosic biorefinery. Reactor performance, effects of wastewater on methanogenic activity, and microbial community composition were examined. A maximum methane production rate of 0.4 normal L CH 4 L −1 per day and a yield of 175 normal L CH 4 kg −1 chemical oxygen demand (COD) were obtained at an organic loading rate of 8.5 kg COD m −3 per day and 0.75 days of hydraulic retention time. The lignocellulosic wastewater exhibited low acetoclastic‐specific methanogenic activity (0.37 g CH 4 ‐COD g −1 volatile solids per day), resulting in suboptimal methane reactor performance despite its relatively high soluble COD content. The wastewater imposes selective pressure with a specialized microbiota comprising bacteria from the extremophile order MSBL9, Fervidobacterium , Candidatus Caldatribacterium , Oscillospirales , and Acetomicrobium , as well as Methanosarcina thermophila and Methanothermobacter archaea. Despite the adaptation and high specialization of the microbial community, wastewater from advanced biorefineries exhibited inhibitory properties that adversely affected methanogenic activity.