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Effect of Calcium and Magnesium Induced Hardness on the Toxicity of Lead to Microorganism in Aquatic Environment as Measured by Bio-Chemical Oxygen Demand

N. Nazar Khan

An experimental study was carried out to observe the effects of water hardness based on calcium and magnesium salt as sulphate at different concentrations ranging from 0 to 400 mg/L as CaCO3 to Pb toxicity for nitrifying (azobactor) at 20oC and 30oC. The rate constant (k) and ultimate biochemical oxygen demand (L) have been calculated from BOD data taken for 1 to 15 days using Thomas graphical method. Glucose was used as the source of carbon for microorganism. It was observed that the toxicity of Pb to azobactor decreased with increasing calcium as well as magnesium hardness at both the temperatures. The percentage reduction of BOD (over control as without hardness and Pb) was found to decrease from 51.99 to 18.83 and 54.52 to 19.45 for Ca hardness at 20oC and 30oC, respectively. Similarly, for Mg hardness at 20oC and 30oC, the percentage reduction of BOD was decreased from 51.99 to 14.85 and 51.94 to 15.25, respectively. Rate constant (k) values were found to follow the decreasing order as Mg hardness at 30oC > Mg hardness at 20oC > Ca hardness at 30oC > Ca hardness at 20oC.