Impact of Heavy Metals ions on BOD Exertion

Abstract

Abstract Metal Ion Effect In the normal BOD measurement process, microbial matter is taken from some source which is known to be rich in bacteria and capable of undergoing BOD exertion process. It has been established that the type of inoculum becomes important for a study where BOD exertion is measured at different concentrations of heavy metal ions. Wastewaters were digested to grow the bacteria, separately, in Luria broth (LB) medium and then used as seed. Experiments were conducted to determine BOD in presence of some identified heavy metal ions i.e. cobalt, nickel, copper, zinc, silver and cadmium using mixed flora as seed collected from dairy wastewater and distillery wastewater developed in the LB medium. The metal ions were taken in a wide concentration range from 0.2 mM to 10.0 mM to study their effect at different levels of concentrations. A standard mixture of Glucose-glutamic acid (1:1) was taken as food. Industrial wastewater was not used as source of food simply to avoid any inconsistency in the composition of the sample water. Experiments were also conducted to measure optical density at 600nm of microbial medium containing different concentrations of the metal ion. Microbes are expected to show greater optical density in the absence of metal ions while in presence of the metal ions, there is a fall in the absorbance values. The extent of fall depends on the concentration of the metal ions added. In most of the cases, changes in absorbance values correspond to the corresponding changes in BOD. This indicates that the inhibition in BOD is due to the decay of microbial matter. This hypothesis works very well for almost all metal ion environments. Hence, the extent of BOD suppression/ increase is directly related to the decay/ growth of the microbial matter. BOD values were determined in replicas of three bottles for each set of combination of metal ion concentration and by measuring DO levels using membrane based DO meter. Only average values were taken for further calculations. A decre