Microbiological effluent control by UV-disinfection of a small-scale SBR system

Decentralized wastewater management systems, with the wastewater treated close to where it is generated, are considered by various researchers as an alternative to the traditional centralized system. The wastewater treatment facility should produce an effluent which is hygienically safe and can subsequently be utilized for watering lawns and irrigation. This article presents the operational data of such a small system and also presents disinfection efficiency data using a low-pressure UV lamp. To evaluate the SBR performance, several effluent parameters, such as BOD5, COD, and SSeff were measured and compared with the influent. The removal efficiencies were 90.9% for BOD5, 86.9% for CODt and 93.9% for SSeff (average values). Disinfection efficiency was evaluated through measurement of the controlled encountering coliform bacteria (total coliforms (TC) and faecal coliforms (FC) before and after the UV lamp), because of the central role they play in discharge pen-nits. To overcome disinfection problems that result from the influence of particle-associated organisms, a Mean Cell Retention Time (MCRT) of 20 d was used, in combination with a well-designed clarification phase. A clear reduction of the coliform form bacteria concentration was observed, which followed a similar pattern of the reduction of the SSeff. The Pearson correlation coefficient was used to express the degree of linear relationship between the TC and SSeff and FC and SSeff parameters.