MAJOR PATHWAYS FOR NITROGEN REMOVAL IN WASTE-WATER STABILIZATION PONDS

A study on the factors influencing nitrogen removal in waste water sta bilization ponds was undertaken in an eight-pond series in Werribee, A ustralia. Nitrogen species including Kjeldahl nitrogen, total ammonia nitrogen, nitrite and nitrate were monitored monthly from March 1993 t o January 1994. At the same time, pH, temperature, chlorophyll a conte nt and dissolved oxygen were also recorded. Highest nitrogen removal o ccurred during the period with highest levels of chlorophyll a content and dissolved oxygen, but the rate of nitrogen removal was not relate d to temperature and pH. Enhanced photosynthetic activities resulting from an increased phytoplankton abundance due to prolonged detention t ime caused an increase in dissolved oxygen, and created an optimum con dition for nitrification to occur. In this process, ammonia was oxidiz ed to nitrite and nitrate which were subsequently reduced to elemental nitrogen. Apart from nitrification-denitrification which was the majo r nitrogen removal pathway in the study system, algal uptake of ammoni um, nitrate and nitrite as nutrient sources also contributed to the ni trogen removal. The role of phytoplankton and zooplankton in the treat ment process in waste stabilization ponds was discussed.