Use of chlorine in the control of filamentous bulking in an activated sludge system from beef industry

Abstract

There are various processes for treating urban and industrial sewage; the most common is activated sludge. Among the major operational problems is the excessive growth of filamentous microorganisms. The present work aimed to study the initial effects of a dosage of chlorine to control bulking in lab bench scale using a Jar-test. Although results of the monitoring of the treatment effluent system indicate good efficiency, Thiothrix I and Type 0675 bacteria were identified. In the first phase, doses were tested in the return sludge with sodium hypochlorite of 125 g L-1 of active chlorine. A concentration of 25 mg L-1 showed a positive effect after 1 h of sedimentation, breaking the filaments. In the second phase, concentrations of 20 to 27 mg L-1 were tested, relating them to the total suspended solids and settled volume at 1 h. The concentration of 25 mg L-1 showed a positive effect: the total suspended solids of return sludge showed values of 4933 mg L-1 and a settled volume of 947 mL L-1, whereas the control was 943 mL L-1. This concentration helped sedimentation of sludge, but has affected the activities of other microorganisms. A possible explanation for why only high doses had a positive effect on the bacteria could be due to the presence of a sheath that acted as a protective cover against external agents in this species of bacteria.