Biological treatment and toxicity removal from wastewaters containing chlorinated aromatic compounds in rotating perforated tubes and brush biofilm reactors

Rotating perforated tubes and rotating brush biofilm reactors were used for 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), COD and toxicity removals from synthetic wastewater. Box-Wilson and Box-Behnken statistical experiment design methods were used to evaluate the experimental results and determine the optimum operating conditions maximizing chlorophenol, COD and toxicity removals. Toxicity of wastewater was analyzed by dehydrogenase enzyme activity known as resazurin assay method.Both reactors were found to be very effective in removing chlorophenols over a large range of operating conditions. Chlorophenols and their degradation intermediates were the major toxic compounds causing low COD and chlorophenol removals. Nearly complete removal of chlorophenols required high biofilm surface area (high A/Q ratio) and high feed COD contents yielding high biomass densities. Percent chlorophenol and toxicity removals increased with increasing feed COD and A/Q ratio and with decreasing chlorophenol concentrations for both reactors. Percent COD removal increased with increasing feed COD up to a certain concentration and decreased with further increases in the feed COD. High A/Q ratio and low feed chlorophenol concentrations yielded high COD removals. To avoid inhibition of high chlorophenol concentrations on the biofilm microorganisms and to obtain high COD, chlorophenol and toxicity removals, the system should be operated at high A/Q ratio and feed COD.RTBR seemed to be more effective for removal of COD and chlorophenols when operated under the same A/Q ratio due to formation of thicker and denser biofilms on the tube surfaces. Similar trends were observed for percent toxicity removals.RTBR performed better than RBBR at high chlorophenol concentrations yielding high COD, chlorophenol and toxicity removals.