Initial studies on the temperature‐phased anaerobic biofilter process

Abstract

The temperature‐phased anaerobic biofilter (TPAB) process is a new high‐rate anaerobic treatment system that includes a thermophilic biofilter connected in series to a mesophilic biofilter providing for two‐temperature, two‐phase treatment. Three TPAB systems with thermophilic:mesophilic reactor size ratios of 1:7, 1:3, and 1:1 were operated at system hydraulic retention times (HRTs) of 24, 36, and 48 hours at temperatures of 56°C in the thermophilic phase and 35°C in the mesophilic phase. The three TPAB systems achieved soluble and total chemical oxygen demand (COD) reductions in excess of 97% and 90%, respectively, for a synthetic milk substrate over a range of system COD loadings from 2 to 16 g COD/L/d. There was little difference in performance between the three TPAB systems based on COD reduction and methane production, making it feasible to use a smaller thermophilic first phase in the TPAB system. At the 48‐hour system HRT, the 6‐hour thermophilic phase biofilter reached saturation loading at a COD load of 48 g/L/d. After further increases in organic loading, the methane production decreased in the thermophilic first phase and increased in the corresponding mesophilic second phase while levels of n‐valeric and butyric acids increased significantly. It is proposed that a microbial population shift occurred in the thermophilic first phase at high organic loadings at low HRTs. Although a decrease in methane production from the thermophilic phase was observed, the performance of the overall two‐stage TPAB system did not decline. The TPAB systems were observed to outperform single‐stage anaerobic filters operated at equivalent HRTs and organic loadings.