A Kinetic Approach to the Biodegradation of Dairy Waste Discharged into the Coastal Waters Around Mumbai City, India

Abstract

The pollution of coastal waters around cities is largely due to unregulated discharge of industrial, agricultural and domestic wastes. Mumbai City has a large dairy industry which processes raw milk into several food products and in the process, large amounts of water effluents containing dissolved sugars, proteins and fats are produced. These effluents are released into the marine waters after a meagre preliminary treatment. Thus, the marine environment is adversely affected and marine life gets depleted. The health of a water body is defined by physicochemical parameters like BOD, COD, DO and pH. Dairy waste is rich in microorganisms which help in its biodegradation by wet oxidation. The carbonaceous organic matter in dairy waste is oxidized in the presence of microorganisms: Carbon in organic matter + O2 -------> CO2 + H2O + Biomass. The kinetics of biodegradation of dairy waste by wet oxidation has been studied in detail with particular reference to the effects of i) salinity [(Cl-)= 0 to 20000 mg per litre] and ii) temperature on the rate of biodegradation. The biodegradation follows first order kinetics and the oxidation rate was monitored by estimating the dissolved oxygen present initially and at regular time intervals during the reaction using the Alsteberg azide modification of the Winkler method. The study confirmed the negative impact of salinity on the rate of biodegradation of dairy waste. Thermodynamics plays an important role in chemical reactions occurring in the oceans during degradation of organic wastes. The effect of temperature (20 and 27 degrees Celsius) on the rate of degradation of dairy waste was studied and the energy of activation and other thermodynamic activation parameters like enthalpy of activation, free energy of activation and entropy of activation were evaluated using the Arrhenius equation, and correlated with the reaction mechanism of the biodegradation reaction. From the dissolved oxygen values obtained, the BOD values were calculated at different salinities and temperatures and correlated with the rates of biodegradation of the organic wastes under study. The kinetics of biodegradation of a synthetic sample, Lactose-Peptone was also studied.