High Rate Algal Ponds (HRAPs) are efficient treatment systems which minimise the effects of wastewater pollution by reduction of organic matter and inorganic nutrient content. The efficacy of these systems is well documented, however there remains little understanding of the mechanisms by which removal occurs or of the factors which may affect the efficiency of the removal process. This research attempts to elucidate the relationship between environmental parameters such as day length, pond temperature and incident surface irradiance and to relate these factors to the production of biomass and removal of nutrients within pond systems operated as continuous cultures and loaded with artificial sewage media.

Complex interactions were noted between the concentration of algal biomass in the ponds, as approximated by chlorophyll a measurements, and the efficiency of nitrogen removal which may have important implications for the management of these systems. Clear evidence of the time course of nitrification was also obtained. Equations have been developed which correlate the environmental variables with changes in pond biomass and nutrient removal. These equations can be used as a tool to aid the effective management of HRAPs as wastewater treatment systems.

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