STABILITY ENHANCEMENT OF ANAEROBIC-DIGESTION THROUGH MEMBRANE GAS EXTRACTION UNDER ORGANIC SHOCK LOADS

A novel submerged silicone membrane extraction technique for removing the dissolved gases, CO2 and H-2, was explored as a method for enhanci ng the stability of anaerobic digesters under shock loads. The effecti veness of this strategy was demonstrated during a five-fold step incre ase in the feed concentration from 4 kg m(-3) to 20 kg m(-3) Chemical Oxygen Demand (COD) to two anaerobic chemostats, a control and a membr ane reactor, operating under steady state. Data revealed that membrane extraction of CO2 enabled neutral pH values to be maintained during t he shock, in contrast to the control; and this appeared to enhance ace tate degradation. In addition, while liquid phase hydrogen removal was only partially successful due to a biofilm building up on the membran e, it also appeared to enhance the rate of volatile fatty acid degrada tion, and hence improved reactor stability. Flee sizes were monitored during the course of the shock load experiment and found to decrease f rom 46 mu m to 30 mu m over 35 days in the control, but from 37 mu m t o < 5 mu m in the membrane reactor. This decrease in hoc size was post ulated to be due to the growth of a relatively pure methanogenic biofi lm on the membrane. (C) 1998 Society of Chemical Industry.