The BOD values as observed by the developed BOD biosensor reflect the concentrations of the dissolved organic substances which are assimilated/metabolized by the immobilized microbes [17]. The assimilation of organic substances in turn depends on the metabolic and physiological state of the immobilized biocatalyst, i.e., the microorganisms in use, their type, their phase of growth and density on the support. The prepared immobilized microbial membrane was therefore characterized w.r.t. the above stated parameters. The findings are depicted in Table 1.