Evaluation of a protease assay based on a natural protein for heavy metals inhibition of activated sludge.
An enzymatic assay employing 2,4,6-trinitrobenzenesulfonic acid to follow the hydrolysis reaction of peptide bonds of a natural protein by activated sludge was evaluated for assessing the inhibition caused by heavy metals on biological treatment processes. The individual and joint effects up to 20 mg/l of Cu(II) and Zn(II) on activated sludge of different ages (6, 10 and 14 days) between a pH range from 6 to 7 was investigated by means of a 2(4) factorial experimental design. From statistical results, it has been concluded that not only the four main effects of these variables have an important influence on protease activity of activated sludge but also some interactions among them. Experimental data showed that Zn(II) was less inhibitory towards proteases than Cu(II) and that their joint effects acted neither synergistically or antagonistically. Sludge age was the variable that more strongly affected the protease activity of activated sludge.