EFFECT OF AERATION ON KINETICS OF BOD EXERTION

Abstract

Biochemical Oxygen Demand (BOD) is the measure of the oxygen used in bacteria mediated oxidation of organic substances in water and wastewater. Rate of BOD exertion depends on concentration and nature of the substrate, micro-organisms, electron acceptors, nutrients, temperature, pH, toxicants etc. Theoretically an infinite time is required for complete biochemical oxidation of organic matter, but the measurement is made over 5-days at 20°C or 3-days at 27°C with or without dilution. Researchers have worked to further reduce the time of measurement. Kaurbe et. al, (1977), Cullimore et. al, (1990), Kylie et. al, (2001) etc, have investigated BOD measurement primarily to minimize the time and negate the measurement difficulties such as low solubility of oxygen, limited linear working range, time consuming procedures; questionable accuracy and questionable reproducibility. BOD is exertion in activated sludge plants where wastewater is continuously aerated and concentration of MLVSS is maintained is 70-80 % in six hours. Keeping these in view, it was felt necessary to investigate BOD exertion in the presence of continuous supply of air and varying micro environmental attributes such as seed, buffer temperature etc. Experiments were conducted with the solution of glucose-glutamic acid (GGA) in dilution water as the only source of carbon in the presence of continuous supply of air. Process was monitored by measuring pH, DO concentration, TOC and BOD. Results show increased rate of degradation. Rapid reduction of carbon (TOC) was noticed with continuous aeration as compared to normal condition i.e. without aeration. TOC degradation with and without continuous air supply were found to be (0.38-0.42) and 0.29 per day respectively (at 27°C). The effect of the following variables of kinetics of BOD exertion with or without aeration were monitored:- III Effect ofAeration on netics ofBOD ertion • Aeration Device: Two simple aeration devices a)Shaker-Incubator mechanism (S-I) b) Diffuser-Incubator Mechanism(D-I), were used for this experiment. The results show around 1.3-1.7 times increase in the k' value as compared to without aeration method. Also, two aeration devices were compared and the results shows that D-I gave better outcome. Kea results confirmed the same that Diffuser-Incubator mechanism is a better aeration device. • Amount of buffer (Buffer Capacity): Due to formation of the acid at early stages of degradation, there is a dip in pH of the system. So, the Buffering Capacity of the solution was increased. 0.26 mol/l of base/pH unit gave the best results. Decrease in rate of degradation was noticed if the BC was increased further. Also, the pH goes in alkaline condition. In addition, DO also decrease when pH vary from optimum conditions(6.5-8). • Amount of seed (F/M): The effect of the nature and amount of the seed sludge used on substrate degradation has also been observed. In one of the experiments TOC degradation of GGA has been found to be as high as 0.55/day(at 27°C). • Nature and concentration of substrate: The system was analyzed by reducing the initial concentration of GGA. It was observed that the rate of degradation was increased with decrease in concentration. Other substrates like sucrose, glycine, glutamic acid, municipal wastewater were also analyzed. Sucrose and glutamic acid gave value of 0.43 and 0.56 respectively. But Glycine gave a poor BOD and TOC exertion results. Unkown Municipal Waste Water samples were also tested and it was observed that the concentration of BOD decreased to half of its initial concentration in about 1.5 days. Perusal of the results gave an indication that the rate of degradation increase with aeration. It is also affected by the nature and concentration of substrate, micro-environmental attributes and availability of DO etc.