Pathogen removal mechanisms in anoxic wastewater stabilization ponds

Anoxic wastewater stabilization ponds can reduce land requirements by as much as two-thirds of that required for facultative ponds and can avoid the environmental nuisances of odour and corrosion, compared with anaerobic ponds. When effluent reuse is to be considered, the aim of wastewater treatment is not only to reduce degradable organic matter but also to remove pathogenic microorganisms. There are many pathogenic agents in domestic sewage and determination of all of them is not practically feasible, so faecal coliform organisms are normally estimated as indicators of health risk. It has been found that the volumetric organic loading on ponds affects pathogen removal inversely and temperature has a positive effect. This was confirmed in the present studies on “anoxic” ponds and, in addition, other environmental factors (light, pH, DO and ORP) were found to have influenced pathogen removal in these ponds, which were loaded in the range between conventional loadings for anaerobic and facultative stabilization ponds. However, pathogen removal in anoxic ponds was not found to be significantly better or worse than in anaerobic or primary facultative ponds and, therefore, maturation ponds would be required following anoxic ponds to achieve an effluent quality suitable for unrestricted irrigation.