The biodegradation and COD removal of 2-chlorophenol in a granular anoxic baffled reactor

• This work presents an AnBR for biodegradation of halogenated aromatics.
• The AnBR was very efficient in biodegrading and dehalogenating 2-chlorophenol.
• The AnBR biodegraded 2-chlorophenol to a much greater extent than does ABR.
• A large and dense granule was developed in the AnBR under anoxic condition.
• AnBR is a viable option for biodegradation of halogenated organics.

The present work was designed to developed a granular anoxic baffled reactor (AnBR) and to investigate its performance in the treatment of 2-chlorophenol (2-CP). The acclimation and enrichment of microorganisms in activated sludge to degrade 2-CP was effectively accomplished. Then the influence of inlet 2-CP, hydraulic retention time (HRT), salinity, and type of electron acceptor (nitrate or organic compound) on the performance of AnBR in biodegradation of 2-CP was investigated. The increase of inlet 2-CP from 50 to 500 mg/L at a fixed HRT of 24 h did not adversely affected the AnBR where over 99% of inlet 2-CP was biodegraded. Decreasing the HRT stepwise from 24 to 4 h at an inlet 2-CP of 200 mg/L did not inhibit the rate of biodegradation (>99%). The increase of over 20 g/L salinity in the feed stream strongly inhibited the rate of 2-CP biodegradation in the AnBR, whereas the bioreactor could efficiently tolerate concentrations below 20 g/L NaCl. Moreover, the rate of 2-CP biodegradation under anoxic denitrifying metabolic conditions (presence of nitrate) was much greater than that under anaerobic metabolic conditions (absence of nitrate). Accordingly, the AnBR process is a feasible, simple, low-cost, and thus appropriate process for efficiently biodegrading toxic chlorinated organic compounds.