EFFECT OF STORAGE ON THE PERFORMANCE OF METHANOGENIC GRANULES

Anaerobic methanogenic granules were stored under anaerobic condition at 4 degrees and 22 degrees C for 1- to 18-month period to evaluate th e effect of storage on degradation of volatile fatty acids (VFAs), inc luding acetate, propionate and butyrate, and on methane production. Th e length of storage period affected the activities of different microb ial trophic groups. During storage at 22 degrees C, the degradation ra tes for all the three acids decreased gradually. At low temperature (4 degrees C), reduction in degradation rates of acetate and propionate was relatively slower than that at 22 degrees C. Reduction in butyrate degradation rate was faster (by 45%) during the first month of storag e at 4 degrees C, but the rate declined afterwards. Nevertheless, the granules maintained, although at reduced level, their metabolic activi ties for all three VFAs even after storage for 18 months. Higher decay coefficients were obtained at 22 degrees C than those at 4 degrees C. For a relatively short period (1-5 months), granules can be stored at ambient temperature (approx. 20-22 degrees C) with limited loss in th eir VFA degradation rates. However, granules can maintain higher level s of VFA degradation rates when they are stored at low (4 degrees C) r ather than at ambient temperature. Reactor studies indicated that the granules can completely recover their original VFA degradation rates i n three days when stored for 31 d at 22 degrees C. The granules stored at 22 degrees C for 9 months were used successfully as inoculum to st art a laboratory-scale reactor. The original VFA degradation rates of the granules were achieved after 15-20 d of reactor operation at 35 de grees C.