COD, 2,4,6-trichlorophenol (TCP) and toxicity removal from synthetic wastewater in a rotating perforated-tubes biofilm reactor

Synthetic wastewater containing different concentrations of 2,4,6-trichlorophenol (TCP) was biologically treated using a novel rotating perforated-tubes biofilm reactor (RTBR) for chemical oxygen demand (COD), TCP and toxicity removal. Performance of the reactor was investigated as function of major operating variables such as the feed TCP and COD concentrations and A/Q (biofilm surface area/feed flow rate) ratio. A Box–Behnken statistical experiment design method was used by considering the feed TCP (0–400 mg L−1), COD (1000–4000 mg L−1) and A/Q ratio (23–163 m2 d m−3) as the independent variables while percent TCP, COD, and toxicity removals were the objective functions. The results were correlated with the quadratic model since this was found to be the most suitable one. Response function coefficients were determined by correlating the experimental data with the response function. Percent TCP, COD and toxicity removals estimated from the response functions were in good agreement with the experimental results. TCP, COD and toxicity removals increased with increasing A/Q ratio and decreasing feed TCP concentrations. Percent toxicity removals were always lower than TCP removals indicating presence or formation of some toxic by products from TCP biodegradation. For the feed TCP of 400 mg L−1, the optimum conditions resulting in maximum COD (99%), TCP (100%) and toxicity (93%) removals were A/Q ratio of nearly 165 m2 d m−3 and feed COD of 2985 mg L−1.