INITIAL STUDIES ON THE TEMPERATURE-PHASED ANAEROBIC BIOFILTER PROCESS

The temperature-phased anaerobic biofilter (TPAB) process is a new hig h-rate anaerobic treatment system that includes a thermophilic biofilt er connected in series to a mesophilic biofilter providing for two-tem perature, two-phase treatment. Three TPAB systems with thermophilic:me sophilic reactor size ratios of 1:7, 1:3, and 1:1 were operated at sys tem hydraulic retention times (HRTs) of 24, 36, and 48 hours at temper atures of 56 degrees C in the thermophilic phase and 35 degrees C in t he mesophilic phase. The three TPAB systems achieved soluble and total chemical oxygen demand (GOD) reductions in excess of 97% and 90%, res pectively, for a synthetic milk substrate over a range of system COD l oadings from 2 to 16 g COD/L/d. There was little difference in perform ance between the three TPAB systems based on COD reduction and methane production, making it feasible to use a smaller thermophilic first ph ase in the TPAB system. At the 48-hour system HRT, the 6-hour thermoph ilic phase biofilter reached saturation loading at a COD load of 48 g/ L/d. After further increases in organic loading, the methane productio n decreased in the thermophilic first phase and increased in the corre sponding mesophilic second phase while levels of n-valeric and butyric acids increased significantly. It is proposed that a microbial popula tion shift occurred in the thermophilic first phase at high organic lo adings at low HRTs. Although a decrease in methane production from the thermophilic phase was observed, the performance of the overall two-s tage TPAB system did not decline. The TPAB systems were observed to ou tperform single-stage anaerobic filters operated at equivalent HRTs an d organic loadings.