Determinação da toxicidade aguda e crônica de hexavalente [Cr(VI)] para a biomassa em sistemas de lodo ativado, aplicando a respirometria como técnica de avaliação

Abstract

Biological processes of wastewater treatment systems can suffer operational instability caused by the presence of toxic pollutants in concentrations that inhibit the activity of organisms present. Heavy metals have received most attention, since, even in minute concentrations, some are extremely toxic to a wide variety of organisms. From this assumption, the present study aimed to evaluate the toxicity of hexavalent chromium [Cr(VI)] for microbial biomass of activated sludge systems using respirometry as evaluation tool. for assessment of acute and chronic Cr(VI) toxicity at six concentrations (5, 10, 20, 40, 80 and 160mg/L) were studied. An experimental investigation was carried out with two pilot scale activated sludge systems (RBS1 and RBS2) operated simultaneously under sequencing batch regime. The first RBS1 received sewage, while the second , RBS2 , a part from sewage also received the potassium dichromate. The excess sludge RBS2 was compared with that of RBS1 for analysis of chronic toxicity of chromium. Sudden additions of chromium sludge RBS1 allowed evaluation of acute toxicity. Through respirometric tests it was possible top determine the maximum specific growth rate (µ ) of heterotrophic and autotrophic bacteria, used in this work as the main criterion for assessing the kinetics of processes using organic material and nitrification respectively. COD, TKN and total volatile and fixed suspended solids were also analyzed. Using RBS1-control reactor as a reference for maximum growth of microorganisms, the results showed that in the acute toxicity tests heterotrophic bacteria react at all concentrations Cr(VI), reducing (µ ) in more than 50 % when exposed to 20mgCr(VI)/L autotrophic obtained half (µ m ) of 5mgCr(VI)/L, showing complete inhibition with 160mgCr(VI)/L. In chronic toxicity tests heterotrophic bacteria showed maximum growth range of 85% to 40mgCr(VI)/L, whereas the daily addition of Cr(VI) to microorganisms favored acclimation, whereas autotrophic reacted only in the early days of addition of Cr(VI).