Comparison of UASB and EGSB performance on the anaerobic biodegradation of 2,4-dichlorophenol

The anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors using glucose as main carbon source was studied. The performance of both systems was compared in terms of 2,4-DCP and COD removal efficiencies, methane production, stability, granular sludge adaptability as well as reversion of the bacterial inhibition. Both organic and 2,4-DCP loading rates were incrementally varied through the experiments. With loading rates of 1.9 g COD L-1 d-1 and 100 mg 2,4-DCP L-1 d-1, 75% and 84% removal efficiencies of this compound, accompanied by COD consumption efficiencies of 61% and 80% were achieved in the UASB and EGSB reactors, respectively. In these conditions, methane production reached 0.088 L CH4 g-1 COD in the EGSB reactor whereas in the UASB reactor was almost negligible. Decreasing the 2,4-DCP loading rate to 30 mg L-1 d-1 an improvement in the methane production was observed in both reactors (methanogenic activity of 0.148 and 0.192 L CH4 g-1 COD in UASB and EGSB reactors, respectively). Efficiency of dechlorination was improved in both reactors from around 30% to 80% by reducing to one-half the COD due to a decreasing of the 4-chlorophenol concentration accumulated in the effluents of both reactors. The dechlorination efficiency of the UASB reactor was dramatically inhibited at a 2,4-DCP feed concentration above around 210 mg L-1 because of 2,4-DCP accumulation in the effluent. SEM studies revealed no significant morphological changes in the sludge granules