Evolution of an activated sludge system under starvation conditions

In this work, the evolution of several physical-chemical and microbiological variables in starvation conditions of an activated sludge are studied. An activated sludge pilot plant was used to study starvation condition effect on biomass. The experiment was studied over a 21-day period, during which no organic material was added to the system. Suspended solids, volatile suspended solids (VSS), pH, dissolved chemical oxygen demand (CODd), dissolved organic carbon (DOC), oxygen uptake rate (OUR), specific oxygen uptake rate (SOUR), identification of microorganisms and total and active cells counting were all monitored. At last of the experiment, an important decrease in the reactor biomass was observed, which may be related both to: the intracellular component degradation from endogenous metabolism, and to the solid depletion occurred, specially, over the first 4 days. Sludge degradation throughout the experiment led to a decrease in the respiratory and enzymatic activity of the microorganisms of the system. During identification tests, some of the typical microbial groups, usually found in an activated sludge, had disappeared and others opportunists appeared. Sludge flocculation capacity decreased with microbial activity diminution and/or microorganism death. From the results obtained, it may be deduced that significant biomass reduction is achieved in first days, specifically, the first one. The highest solid decrease is produced during the first day. Thus, may be interesting to use with an activated sludge system a starvation period of 24 h before stabilization. This can suppose operation and economic benefits.