SUNLIGHT WAVELENGTHS INACTIVATING FECAL INDICATOR MICROORGANISMS IN WASTE STABILIZATION PONDS

Waste stabilisation ponds (WSPs) are widely used in New Zealand for th e treatment of domestic sewage and other organic wastes. Traditionally , faecal coliforms have been used as the faecal indicator in WSPs and their receiving waters but there is increasing interest in alternative indicators. We studied the comparative inactivation kinetics under su nlight of two bacterial indicators in WSP effluent, and also those of two F-specific bacteriophages that may be models of the behaviour of v iral pathogens in WSPs. We investigated the wavelength-dependence of s unlight inactivation in rapidly-stirred, small reactors, with temperat ure, dissolved oxygen and pH control, using various plastics as ''long pass'' filters to screen different portions of the UV-visible spectrum . The UVB, UVA and blue-green visible radiation (<550nm wavelength) al l contributed appreciably to inactivation of enterococci and possibly FRNA phage, consistent with a photooxidation mechanism of action. In c ontrast, E. roll and presumed FDNA phage were inactivated mainly by WE , consistent with direct absorption by, and damage to, the DNA with mi nor or negligible contribution by longer wavelengths. Our results sugg est that E. coli may be a better bacterial indicator in WSPs than ente rococci. (C) 1997 IAWQ. Published by Elsevier Science Ltd.