Two-stage UASB reactor converting coffee drink manufacturing wastewater to hydrogen and methane

Abstract

In this study, the feasibility of a continuous two-stage up-flow anaerobic sludge blanket (UASB) reactor system, consisted of thermophilic (55 degrees C) dark fermentative H-2 production and mesophilic (35 degrees C) CH4 production from coffee drink manufacturing wastewater (CDMW), was tested. A recently proposed operational strategy was used to overcome a major drawback of the long start-up period of the UASB reactor. Firstly, a completely stirred tank reactor (CSTR) was operated for 8 days to prepare seeding. The seed was then directly transferred to the UASB reactor. Microbial aggregation took place in the initial period, and the floc size was gradually increased over time. In UASB reactor, the maximum H-2 yield of 2.57 mol H-2/mol hexose(added) and a stable H-2 production rate of 4.24 L H-2/L/h were observed at a hydraulic retention time (HRT) of 6 h and substrate concentration of 20 g Carbo. COD/L. In this novel method using CDMW, thermophilic H-2-producing granules with an average particle size of 1.3 mm was successfully developed after 100 days. The more bioenergy recovery was attempted in a post-treatment process using a mesophilic UASB reactor for CH4 production from the H-2 fermented effluent. The maximum CH4 yield of 325 mL of CH4/g COD was achieved with removing 93% of the COD at an organic loading rate of 3.5 g COD/L/d. The developed two-stage UASB reactor system achieved biogas conversion by 88.2% (H-2 15.2% and CH4 73%) and COD removal by 98%. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.