Biodegradation of 2,4-dichlorophenol in sequencing batch anaerobic reactors.

Abstract

A synthetic wastewater containing 20 mg/L 2,4-dichlorophenol (2,4-DCP) and medium-strength carbonaceous co-substrate (7 g COD/L) was used to investigate the feasibility of treating chlorophenols in laboratory-scale sequencing batch upflow anaerobic sludge blanket reactors, designated as SBAR. The specific organic loading rate (SOLR) and specific 2,4-DCP loading rate (SDCPLR) tested were 0.35, 0.53, 0.70 g COD/g VSS/d and 1.0, 1.5 and 20 mg 2,4-DCP/g VSS/d, respectively. For each SOLR and SDCPLR operating condition, three different fill/react ratios, 0.33, 0.66 and 1.00 were examined in order to assess the performance of SBAR operating strategies. One continuous upflow anaerobic sludge blanket (UASB) reactor used as the control was operated at three SOLR and SDCPLR corresponding to those applied to SBARs. Experimental results show that laboratory-scale SBARs were able to treat 2,4-DCP contaminated wastewater in addition to medium-strength carbonaceous co-substrate. The over all removal efficiencies of SBARs were almost 100% for 2,4-DCP and ranged from 72.5% to 94.2% for carbonaceous co-substrate. Under studied conditions, the performance of the continuous flow reactor was quite similar to that of sequencing batch reactors. Removal efficiencies for the continuous flow reactor were almost 100% for 2,4-DCP and ranged from 84.2% to 93.3% for COD. The major biodegradation product of 2,4-DCP in both sequencing batch and continuous UASB reactors was 4-monochlorophenol. This experimental work also confirmed earlier observations that SOLR significantly influenced the overall COD removal efficiency of the SBAR, and SOLR based on fill time (SOLR)$\sb{\rm f}$ is an important design parameter for SBAR systems. Experimental data from this study were also compared with the simulated results obtained using a previously developed dynamic SBAR model. It was verified that this model can predict the SBAR performance reasonably well.