Towards a mechanistic understanding of pond disinfection

Abstract

A broad overview of mechanisms of disinfection of waste stabilization ponds (WSPs) is based on a review of the literature on indicator micro-organisms in ponds, including our own recent experiments. There is appreciable evidence that sunlight is the single most important factor in WSP disinfection. Much of the uncertainty in the literature regarding pond disinfection may reflect the interaction of sunlight with other factors, including dissolved oxygen (DO) and pH, which fluctuate diurnally within WSPs owing to algal metabolism. Our experiments with WSP effluent (conducted in small, stirred reactors with well-controlled physico-chemical conditions) showed that different faecal indicators are inactivated by different components of the solar spectrum, and the rates of sunlight inactivation have differing dependencies on physico-chemical conditions. For example, F-specific DNA phage was inactivated only by solar UV-B (300–320 nm) at a rate unaffected by other factors, whereas enterococci and F-specific RNA phage were inactivated by a wide range of wavelengths (300–550 nm) by (DO-dependent) photo-oxidation. Sunlight inactivation of faecal coliforms was particularly complicated: at pHs < 8.5 only solar UV-B (300–320 nm) caused (slow) inactivation, but at higher pHs, the inactivation rate increased and a wider range of wavelengths (300–550 nm) contributed – suggesting photo-oxidative damage to membranes which sensitises faecal coliforms to high external pH. Our findings on the different influences of physico-chemical conditions for different indicators suggest difficulties in interpreting microbiological quality of WSP effluent in terms of a single indicator micro-organism. However, clearly disinfection in WSPs may be enhanced by increasing sunlight exposure, for example with shallower ponds or increased residence times.

Effects of Environmental Factors on the Disinfection Performance of a Wastewater Stabilization Pond Operated in a Temperate Climate

“…A neutral to slightly acidic pH has been reported as optimal for fecal bacteria growth [26], while pH levels higher than 9 have been reported to be effective in pathogen removal [9,[26][27][28]. Both the terms "removal" and "inactivation" are intended to refer to the conditions where indicator organisms lose their ability to be cultured using Standard Methods.…”

Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine

“…Phages are known to be susceptible to direct inactivation by sunlight in the UVB range, as well as to indirect inactivation by higher wavelengths (Davies-Colley et al, 2000). FX174 was shown to be one of the most sensitive viruses to sunlight irradiation among bacteriophages and human viruses (Hijnen et al, 2006;Love et al, 2010).…”

A Closer Look on Spatiotemporal Variations of Dissolved Oxygen in Waste Stabilization Ponds Using Mixed Models

“…Compared to ICA technology, it is not the best economic solution, as overly conservative designs can inflate capital and O&M costs of the plants and is not an optimal choice for pond upgrading [52]. Regarding MPs, two key mechanisms of disinfection process involve photo-oxidation, which essentially relies on the presence of DO and pH [54]. Indeed, it was concluded in Curtis et al [55] and Dixo et al [56] that sunlight-mediated disinfection can only have a considerable impact on fecal coliforms in the case of high DO and pH present.…”