Bioconversion of Crude Glycerol to Hydrogen and Methane in Three-Stage Horizontal Anaerobic Fixed-Bed Reactors (HARFB)

Abstract

The anaerobic conversion of residual glycerol from biodiesel production is an excellent option for producing clean energy at a low cost. Crude glycerol (CG) is an excellent carbon source for microorganisms in Anaerobic Digestion (AD) process; however, it is a nutrient-limited waste. On the other hand, domestic Sewage (DS) is wastewater containing macronutrients, such as nitrogen and phosphorus. Therefore, feeding bioreactors with a blend of both wastes is an exciting approach. The objective of this study was to operate a system consisting of three horizontal anaerobic series reactors (HARFB) with fixed bed (R1, R2, and R3), fed with a mixture of crude glycerol and domestic sewage to evaluate the start-up strategy and best organic loading rate (OLR) to improve biogas production (H2 e CH4) as well as to analyze the dynamic changes in the anaerobic microbial consortium during the operation of the HARFB. The highest hydrogen generation was 10.3 moles H2 (m3 d-1) in reactor R1, and the highest methane yield was 312.0 and 283.9 L CH4 (m3 d-1) in R2 and R3, respectively. The three-stage system showed high efficiency in removing crude glycerol and Chemical Oxygen Demand (COD), with consumptions of 99.9%. In addition, there was a change in the relative abundance of microorganisms amongst R1, R2, and R3 and a considerable decrease in the diversity index in the fermentation reactor (R1). The results have shown the potential of applying HARFB reactors for energy recovery and alternative waste disposal.