MICROBIOLOGICAL AND PHYSICOCHEMICAL STUDY OF WASTEWATER SELF-DEPURATION IN A DEEP POND SYSTEM

Abstract

A study of the chemical and microbiological self-depuration process of urban waste-waters in a deeppond stabilization system (15000 m') is presented. The pond is localized in the Campus of the University of Murcia (Spain). The study covers two independent periods of waste-water stabilization: November 1984-July 1985 and September 1985-March 1986. The pond was completely emptied between the two periods. Among the various physiological parameters studied, the following are presented in this paper: temperature, dissolved 0,, alkalinity, pH, and BOD,. Microbiological analysis inc1uded total and fecal coliforms, fecal streptococci, Clostridium perfringens, and coliphages, all of them being water pollution indicators. In the geographical area where the lagoon is located (SE Spain), the self-depuration process is relatively fast in surface waters (0-2 m). Periods of 30 to 50 days permit a significative decrease in the organic matter content (70% BOD,) and the microbial indicators (99.9% total and fecal coliforms, 90% C. perfringens; 100% fecal streptococci, ¡md 85% coliphages). Nevertheless, the selfdepuration process shows a diminished rate in the deep layers of the lagoon (under 2 m) because of the environmental conditions prevailing in them: low temperature and oxygen. The ¡atter aspect if magnified in periods of water stratification, when a pronounced anaerobiosis is generated under the thermoc1ine and the temperature remains below 15 ºC. In the area where the self-depuration system has been studied, the reutilization of the waters of deep pond systems does not present chemical or microbiological risks for certain uses (e.g., irrigation), if surface waters are used after an appropriate self-depuration periodo The latter depending on the organic load and the thermal regime under which the system has evolved.