DO Concentration as a Fuzzy Control Parameter for Organic Substrate Removal in SBR Processes

Abstract

Dissolved oxygen (DO) concentration profiles were characterized during the aerobic organic substrate removal phase in a sequencing batch reactor (SBR) for the treatment of a chemical industrial wastewater. In the initial stage (0–10 min), DO concentration rose sharply to a peak level. Subsequently, the DO was slowly decreased and approached a plateau during the COD removal phase. When the organic substrate was consumed, the DO concentration rose sharply from the previous plateau. This was an indication of the end of the COD removal phase, and showed an inflection point on the DO profile. At a fixed aeration rate, the initial peak DO concentration was related to the initial COD concentration. The initial COD can be estimated based on on-line monitoring of the initial DO data. Changing the aeration rate to control DO at a proper level (about 2 mg/L) during the initial stage (10 min) not only ensures oxygen supply and saves aeration energy, but also simplifies operational management. A method of fuzzy control of the aeration rate using on-line DO monitoring was developed. The inflection point on the DO profile can be used as an indication to terminate aeration. Fuzzy control of the aeration rate and aeration duration for COD removal was constructed based on the DO profile. Test results with the fuzzy control demonstrated an improved treatment efficiency by 35% and saved aeration energy by 50% in comparison with that without fuzzy control when COD removal was 85–90%.