Extreme thermophilic (70 degrees C), VFA-fed UASB reactor: Performance, temperature response, load potential and comparison with 35 and 55 degrees C UASB reactors

The paper evaluates the reactor performance, load potential and temperature response of a 70 degrees C, VFAs-fed UASB reactor, seeded with mesophilic granular sludge. Batch experiments were, in addition, conducted to assess t he effect of temperature on the achievable residual VFAs in the 70 degrees C effluent. The performance of similarly-fed and seeded 35 and 55 degrees C UASB reactors was also tested. At a short HRT (2-3 h) and a moderate VLR o f 12-20 g COD l(-1) d(-1), the 70 degrees C UASB achieved 66-74% VFAs remov al (acetate and butyrate 84-90%, propionate < 20%), while the 35 and 55 deg rees C UASB reactors removed 98-99% of VFAs at a VLR of 34-35 g COD l(-1) d (-1) and an HRT of about 1.1 h. The doubling of the OLR, by halving the slu dge beds of the 35, 55 and 70 degrees C UASB reactors, to about 3.68, 3.54 and 2.6 g COD g VS-1, respectively, had no significant effect on the overal l VFAs removal in these reactors. Temperature shifts (70-->55-->70 degrees C) in the 70 degrees C UASB led to a higher VFAs removal at 55 degrees C (m ainly propionate, 46%). In the batch experiments, 92-94 of the 70 degrees C effluent residual VFAs were removed at 35 and 55 degrees C and 72% of acet ate and < 7% of VFAs were removed at 70 and 80 degrees C, respectively. The 70 degrees C UASB reactor survived starvation at 20 degrees C for ca. a mo nth and recovered fast after temperature was reset to 70 degrees C. (C) 199 9 Elsevier Science Ltd. All rights reserved.