Abstract:
The present study involves the treatment of 4-nitrophenol (NP) bearing wastewater by biological treatment in a sequential batch reactor (SBR) without any adsorbent (called as blank-SBR) and an SBR loaded with granular activated carbon (GAC-SBR) and to compare the performance of two types of SBR’s.
First, separate adsorption study with GAC alone was done and the parameters like pH, dose, time and temperature were optimized. The optimum pH was found to be at the natural pH i.e. pH 6.4. Optimum dose was found to be 4 g/l. Optimum time of contact of the experiments was 3 h and the kinetics study showed that 2nd order kinetics best-represented the kinetic data. The intramolecular diffusion model showed that the presence of boundary layer is the rate limiting step in the adsorption model as shown by Weber-Morris plot. The isotherm study showed that the adsorption was endothermic in nature. The thermodynamic study shows that negative value of ΔG shows the spontaneity of the reaction. The positive value of ΔS shows the feasibility of the reaction.
During SBR study, sludge was first acclimatized to consume NP. SBR study was done for varying HRT and the optimum HRT was found to be 1.67 d. The experiments were further done at increased adsorbent dose in GAC-SBR for 100 mg/l. The optimum dose was found to be 2.5 g/l. The effect of increasing concentration was studied and the percentage removal was found to decrease from 92 to 55% when the concentration increased from 100 to 300 mg/l. The study was also done for the binary mixture of NP and 4-chlorophenol. Removal of each was found to be influenced by the presence of the other compound.
