STUDY OF THE PHYTOPLANKTON GROWTH LIMITED BY N AND P IN A SMALL DOMESTIC SEWAGE-RECEIVING WATER BODY

In order to study the nitrogen and phosphorus limitation of algal blooms caused by domestic sewage treatment in the receiving water body. This study selected a receiving water body of a domestic sewage treatment system and conducted a highest and a gradient nutrient adding experiment. The highest concentrations of nitrogen and phosphorus were based on level A (ammonia nitrogen of 5 mg/L and phosphorus of 0.5 mg/L) in discharge standard of pollutants for municipal wastewater treatment plant in China (GB18918-2002). The highest addition experiment showed that chlorophyll a was significantly (P0.05) higher in the nitrogen and phosphorus addition group (+N, +P) than that in the single nitrogen addition group (+N) and single phosphorus addition group (+P) on the third day. And it indicated that both nitrogen and phosphorus were the limiting factors for algal growth in the studied water. The results also suggested that there was still a risk of algal bloom in the water body receiving treated domestic sewage in the short term. The gradient nutrient addition experiment showed that phosphorus should be below 0.27 mg/L or nitrogen should be below 1.0 mg/L to inhibit the growth of phytoplankton in the studied water. According to this nutrient value, a more strict discharge standard should be demanded to reduce the risk of algal blooms.