L. Weaver*, J. Webber, N. Karki, K. Thomas, M. Mackenzie, S. Lin, A. Inglis and W. Williamson
1 Institute of Environmental Science & Research Ltd., Christchurch 8041, Canterbury, New Zealand
Waste stabilisation ponds (WSP) offer a sustainable and economical method of treatment for wastewater across the world. Pathogen removal mechanisms occurring within ponds are largely unknown and only a few studies have been conducted on virus removal. While it is clear that sunlight (UV) and temperature play a major role in removal of pathogens in WSP’s there are other mechanisms present in these complex systems that also play their part in removal of pathogens such as viruses. Our work investigated virus (and indicator organism) removal efficiencies of WSP, particularly the effect of controlled pH and dissolved oxygen (DO) on virus removal, in the presence and absence of sunlight. The results of this study demonstrated that if the pH and DO levels in the WSP remain elevated, similar levels of removal of indicator and virus can be achieved in the presence and absence of direct sunlight: die off rate (k) was ln -5.5 to -9.5 day-1. Results from two summers showed a similar removal rate for virus (4-5 log) but a lower removal for indicator organisms was seen in the second summer when the ambient temperature was lower. Only E. coli showed a significant negative correlation between sunlight and removal rate. By maintaining WSP with high pH and DO levels efficient removal of virus can be achieved using these sustainable, economic treatment methods.