The complex organic wastewater from agrochemical industry consists of a large number of solids and dissolved compounds. For the design and scale-up of any activated sludge reactor, it is desirable to know the kinetics of oxidation, which strongly depends upon the nature of wastewater and the microorganism. In the present work, the kinetics of aerobic biological oxidation of an agrochemical plant waste is investigated, having initial COD of 800-1200 mg/L. Experiments are performed at five different dissolved oxygen (DO) levels; viz. (i) 1.5 to 2.5 mg/L, (ii) 2.5 to 3.5 mg/L, (iii) 3.5 to 4.5 mg/L, (iv) 4.5 to 5.5 mg/L, and (v) 5.5 to 6.5 mg/L. For each DO level five mixed liquor suspended solids (MLSS) are studied in the range of 6000-20000 mg/L. The maximum percentage reduction of COD is 74.1%, 74.8%, 89.9%, 73.3% and 89.6% at different DO levels of 1.5-2.5 mg/L, 2.5 to 3.5 mg/L, 3.5 to 4.5 mg/L, 4.5 to 5.5 mg/L, and 5.5 to 6.5 mg/L and MLSS concentrations from 6000 to 20000 mg/L, respectively. An attempt is made to propose the kinetics of substrate utilization that does not actively support growth of organism. A kinetic model is proposed to understand the effect of DO and MLSS concentration.

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Treatment of agrochemical industry wastewater is difficult to carry out unless integration with some advanced oxidation process (AOP) is used. The present study deals with treatment of an agrochemical industry wastewater, first using activated sludge and then with sulfuric acid treated activated carbon (SAAC) in presence of Fenton reagent. During the activated sludge treatment the food-to-microorganisms (F/M) ratio is varied from 0.1 to 0.2 mg chemical oxygen demand (COD) per mg mixed liquor suspended solids (MLSS) by varying concentration from 6000 to 15000 mg L -1 . The dissolved oxygen (DO) concentration is varied from 2.0 to 4.0 mg L -1 in order to study its effect. The pH and oxidation-reduction potential (ORP) of the systems were monitored online for all the batch operations. The maximum percentage reduction in activated sludge treatment is found to be 72.65% at optimum conditions. The treated wastewater from activated sludge process is further treated with Fenton oxidation and H2O2/SAAC. The optimum dosing of H2O2, Fe 2+ and SAAC are determined. The maximum COD reduction using Fenton and H2O2/SAAC has been found to be 27.0% and 50.22%, respectively.