Cellular Method for Evaluation of Noxiousness of Inorganic Pollutants in Industrial Wastes: Calculation of a Safety Index for Monitoring Sludge Discharge

This article deals with a biological test of safety applicable to industrial wastes. The test is based on the measurement of the growth rate of cultured human cells exposed to waste samples with different dilutions. As a first approach, 15 chemicals in which discharge concentrations are submitted to sanitary regulations were tested one by one. For Zn, Cu, Ni, Cd, Ag, Co, Mg, sulfates, and fluorides, it was possible to detect concentrations that are below the allowed limit. For Hg, Al, As(V), Cr(III), Fe, and Pb, the concentrations that affect cell growth are higher than the allowed limit. Tests were also performed using actual samples (liquid effluent from a laundry and sludge from waste-water treatment plants). Results indicate that, in contrast to chemical analyses, the current biological test has the advantage of providing an indication of global toxicity, integrating all substances and factors that can be harmful to life processes. From the sludge data and the observed threshold of concentration that does not affect cell growth, a numeric safety index has been calculated which indicates the amount of sludge that could be dispersed, as a fertilizer, per hectare of agricultural soil. Such an index could be conveniently used for designing sewage sludge disposal strategies.