Salomão Anselmo Silva

LIGHT PENETRATION IN WASTE STABILIZATION PONDS

Abstract The penetration of light into waste stabilization ponds was studied because of its importance in pathogen removal and algal productivity. The attenuation of light in ponds was dominated by light absorption by gilvin (also called dissolved yellow matter or humic substances) and algae, light scattering processes (turbidity) being of no importance. Gilvin exerts a strong influence over the spectral variation and longer wavelengths penetrate much better than short wavelengths. Estimates of attenuation coefficients in the u.v. suggest that these wavelengths are less penetrating than previously reported. Differences in algal concentrations cause the differences in light attenuation seen between ponds, though they also cause some spectral variation because short wavelengths are more affected by changes in algal biomass than long ones. In the absence of algae there appears to be a lower limit to the clarity of ponds dictated by gilvin and other substances. Secchi disks were found to be reliable instruments for measuring light penetration.

Vibrio cholerae O1 (El Tor) removal in waste stabilization ponds in northeast Brazil

Abstract A series of ten waste stabilization ponds (a 1-d anaerobic pond followed by nine 2-d ponds) was monitored for the removal of Vibrio cholerae O1. The anaerobic pond reduced the mean number of V. cholerae from 485 per litre of raw wastewater to 28, and there was then a very gradual removal in the next five ponds, after a cumulative retention time of only 11 d, to zero.

Enumeration of salmonellae in wastewater by the MPN technique

Abstract A comparative study of the use of double and single strength RV enrichment media for the enumeration of salmonellae by the MPN method was carried out. Of 53 samples of raw municipal wastewater and waste stabilization pond effluents examined 83% yielded higher numbers of positive tubes when the various volumes of the samples utilized for the estimations were inoculated into single strength RV enrichment medium than when inoculated into double strength medium. Extending the incubation period of the XLD agar plates from 24h to 48h at 37°C increased the number of confirmed positive tubes by 1–9% with a mean value of 3%. The effect of the strength of the enrichment medium used on the MPN values is discussed.