Study On Influencing Factors And Mechanism Of Removal Of Nitrogen And Phosphorus By Scenedesmus Obliquus Algal Biofilm

Municipal sewage contains large amounts of nitrogen, phosphorus and other nutrients, resulting in severe eutrophication, sewage treatment plant and the traditional nitrogen and phosphorus removal from secondary effluent nitrogen and phosphorus concentrations were still too high to efficient and simultaneous remove nutrients in water. Algae film wastewater treatment technology with eco-friendly, efficient low energy, natural treatment process characteristics, for advanced treatment of urban wastewater has great potential for development. This paper selected Scenedesmus obliqnus as the experiment algae attached on elastic carrier surface to formed algal film, for studying the effect of nitrogen source forms, algae vaccination concentration, concentration of phosphorus, light cycle, starvation and stirring interval on the removal capacity of nitrogen and phosphorus by algal film. Optimal experiment condition of orthogonal experimental was used to study the biological absorption of nutrients by algal film and the major element in algae cells. Main results are as follows:(1)① With nitrate as the nitrogen source of algal film was more conducive to algae growth. Algal biomass increased 7.76 mg/L with sodium nitrate as nitrogen source, and the removal efficiency of nitrogen and phosphorus were 94.61%,95.63%,respectively; while algal biomass increased 1.05 mg/L only with ammonium as the nitrogen source, the removal efficiency of nitrogen and phosphorus were 50.2% and 95.5%, respectively. ② Removal rate of nitrogen and phosphorus increased as the initial algae liquid vaccination concentration of algae increased, the maximum removal rate were 96.22,97.52%, respectively.③ The maximum biomass increment was 10.77 mg/L when the concentration of phosphorus was 20 mg/L with the nitrogen concentration 20 mg/L, while the maximum removal rate of nitrogen and phosphorus were 92.7%, and 99.46%, respectively, when the concentration f the concentration of phosphorus was 10 mg/L. ④ The optimal photoperiod was 16:8 whose biomass and biofilm formation were highest,13.27mg/L,2.85 mg/L, respectively; and the removal rate of nitrogen and phosphorus were 97.49%,97.65% respectively; continuous light or no light was detrimental to the growth of algae and the removal of nitrogen and phosphorus. ⑤ Appropriate starvation was favor to the biomass increment of algal film. Biomass maximum increment was 9.28 mg/L with starvation of 1 d, while the highest removal rate of nitrogen and phosphorus,96.23%, 97.27%, respectively, appeared on starvation of 2 d. Excessive starvation was not conducive to algae growth. ⑥ Algae biomass maximum increment was 9.02 mg/L with sirring interval for 8 h, the removal rate of nitrogen and phosphorus was highest at this condition,96.15% and 94.07%, respectively. ⑦ Orthogonal experiment showed that, appropriate starvation, stirring and the photoperiod were benefic al to the removal of nutrients by algal film. Optimal condition was photoperiod(L:D) of 16:8, starvation of 2 d, phosphorus concentration of 5 mg/L and stirring interval of 8 h.(2) The bio-absorption was the major operation for the removal of nitrogen and phosphorus by algal film. The chemical removal proportion was only accounted for 4.9% which can be negligible with nitrate as the nitrogen source; The chemical removal of phosphorus accounted for 26.9% of the total removal rate, and biological absorption accounted for a larger proportion.The main elements within algae cells were C, N, H, O, P and S, whose ratio changes with the action time of algae film system, molecular type similar to theory molecular was C106.03H191.06O71.52N13.73PS0.35, appeared on the third day. During the experiment, polysaccharides, fatty acids, proteins and phospholipid polymers of algae cells participated in the adsorption and absorption of nitrogen and phosphorus.