Enhancement of granule formation and sludge retainment for tetrachloroethylene (TCE) removal in an upflow anaerobic sludge blanket (UASB) reactor

Tetrachloroethylene (TCE) in wastewater was effectively removed at 35 degreesC over 200 days in an upflow anaerobic sludge blanket (UASB) reactor in order to investigate the formation of TCE degrading granules. Anaerobic unacclimated sludge and glucose were used as seed and primary substrate, respectively. TCE degrading massive initial granules were developed after 1.5 months of start-up, which grew at an accelerated pace for 7 months and then became fully-grown. Gradual granulation took place and the fine particles became coarse granules as the operation continued. The TCE degrading granular sludge cultivated had a maximum diameter of 2.5 mm and specific methanogenic activity (SMA) of 1.32 g chemical oxygen demand (COD)/g total suspended solid (TSS) day. The granules settled satisfactorily (sludge volume index-SVI = 28 ml/g) and had a maximum specific. methane production rate (SMPR) of 1.16 g COD/g TSS day. Approximately 94% of the total soluble COD removed was converted to methane with a sludge yield of 0.055 g TSS/g COD. 94% COD and 90% TCE removal efficiencies were achieved when the reactor was operating at loading rates as high as 160 mg TCE/1-day and 14 g COD/1.day, respectively after 230 days of continuous operation. Microscopic examinations indicated that-the granules were mainly comprised of Methanothrix and Methanosarcina-like bacteria. They were the main methanogens on the inner surface-of the granules, plus a small amount of Methanobrevibacterium sp. and Methanococcus sp. (C) 2002 Elsevier Science Ltd. All rights reserved.