Abstract:Eutrophic seawater was treated with steel slag, Gracilaria lemaneiformis, and ‘steel slag-Gracilaria lemaneiformis’ system, respectively, and the feasibility of using steel slag for eutrophic seawater treatment was discussed. The results showed that, most phosphorus in the eutrophic seawater was removed by steel slag, while steel slag had no significant effect on nitrogen removement. When Gracilaria lemaneiformis with an initial density of 3g/L was used to treat mildly eutrophic seawater, in which concentration of nitrogen and phosphorus was 0.3~0.6mg/L, and 0.05~0.1mg/L, respectively, the removal rate of nitrogen and phosphorus is high. However, a low-removal rate of nitrogen and phosphorus was found in seriously eutrophic seawater (concentration of nitrogen was 4.8mg/L, and level of phosphorus was 0.8mg/L) treatment with Gracilaria lemaneiformis. And the ‘steel slag-Gracilaria lemaneiformis’ system obviously reduced nitrogen and phosphorus levels in eutrophic seawater, due to pthehysical adsorption and chemical precipitation of phosphorus by steel slag and the biological uptake of phosphorus and nitrogen by Gracilaria lemaneiformis.