Changes in enzymatic and microbiological activity during adaptation of a conventional activated sludge (CAS) to a CAS-oxic-settling-anaerobic (OSA) adapted process

Abstract

The production of excess sludge in the conventional activated sludge (CAS) process is an important aspect of the operation of wastewater treatment plants. The oxic-settling-anaerobic (OSA) process is one of the most promising strategies among those to achieve a reduction in the excess sludge produced. Cell decay occurs at a low oxidation–reduction potential and subsequent degradation reactions seem to be the major causes of sludge reduction in the OSA process. As a consequence of previous exposure of the sludge to anaerobic conditions in the sludge holding tank, an increase of enzymatic and microbiological activity in the aeration reactor could enhance the degradation of the released material. In this study, the results of a pilot plant running sequentially as a CAS and a CAS-OSA system are shown not only in the terms of the crucial aspect of excess sludge reduction, but also in terms of enzymatic and microbiological activities in the sludge from the aeration tank. Specifically, the application of the OSA strategy with a sludge anaerobic exposure time (SAET) of 5.5 h achieved a 33.6% reduction of the produced sludge in comparison with the CAS approach. Similarly, this system showed an average increase of 23.2, 22.6 and 7.59% in the specific oxygen uptake rate (SOUR), dehydrogenase, and protease activity, respectively, and a negligible change in glucosidase activity compared to the conventional process. At the same way, the OSA process with a SAET of 8 h led to a reduction of 38.9% of produced sludge and an average increase of 27.9, 11.31, 28.7 and 26.57% in SOUR, dehydrogenase, protease, and glucosidase activity, respectively, compared to control unit.