Performance study and kinetic modeling of hybrid bioreactor for treatment of bi-substrate mixture of phenol-m-cresol in wastewater: process optimization with response surface methodology.

Performance of a hybrid reactor comprising of trickling filter (TF) and aeration tank (AT) unit was studied for biological treatment of wastewater containing mixture of phenol and m-cresol, using mixed microbial culture. The reactor was operated with hydraulic loading rates (HLR) and phenolics loading rates (PLR) between 0.222-1.078 m3/(m2 x day) and 0.900-3.456 kg/(m3 x day), respectively. The efficiency of substrate removal varied between 71%-100% for the range of HLR and PLR studied. The fixed film unit showed better substrate removal efficiency than the aeration tank and was more resistant to substrate inhibition. The kinetic parameters related to both units of the reactor were evaluated and their variation with HLR and PLR were monitored. It revealed the presence of substrate inhibition at high PLR both in TF and AT unit. The biofilm model established the substrate concentration profile within the film by solving differential equation of substrate mass transfer using boundary problem solver tool 'bvp4c' of MATLAB 7.1 software. Response surface methodology was used to design and optimize the biodegradation process using Design Expert 8 software, where phenol and m-cresol concentrations, residence time were chosen as input variables and percentage of removal was the response. The design of experiment showed that a quadratic model could be fitted best for the present experimental study. Significant interaction of the residence time with the substrate concentrations was observed. The optimized condition for operating the reactor as predicted by the model was 230 mg/L of phenol, 190 mg/L of m-cresol with residence time of 24.82 hr to achieve 99.92% substrate removal.