Effects Of Factors For Removal Of Nitrogen And Phosphorus And Adsorption/Absorption Of Phosphorous By Algal Biofilm

The excessive discharge of nutrients, especially nitrogen and phosphorus, was the key factor causing eutrophication. Traditional sewage treatment technology cannot remove nitrogen and phosphorus effectively and synchronously. Sewage treatment by algal biofilm which can overcome the disadvantages of tradition is a potential biological technology. Algal biofilms were formed by Anabaena flos-aquae and Scenedesmus obliqnus attached on the surface of flexible polyvinyl chloride (PVC) carriers in synthetic wastewater. Experiments were carried out to study the effects of pH, N/P,temperature, illumination intensity and photoperiod in N and P removal by algal biofilm. Afterwards, the adsorption/absorption of phosphorous by algal biofilm was studied under certain conditions, and the essential elements and approximate molecular formula of Anabaena flos-aquae were analyzed finally. The main results are summarized as follows:(1) Effects of factors for removal of nitrogen and phosphorus. ①Removal of N and P under temperature (25℃) and continuous illumination (3500 lx) by algae in sewage, pH 8 is a critical value. Removal rates of NH4+-N and PO43--P were unsatisfactory when the pH was under 8, while it has improved when pH was above 8. The removal rates of NH4+-N and PO43--P were above 91% and 93%, respectively, when pH was 10. ②Taking removal quantity and removal rate of NH4+-N and PO43--P simultaneously into account under temperature (26 ±2℃) and continuous illumination (3500 1x), the N:P ratio (PO43--P concentration was 1.5 mg/L) was optimal at 10:1, which removal rates of NH4+-N and PO43--P were 67.6%,70.5% and 91.8%,92.5%, respectively; and the N:P ratio (NH4+-N concentration was 20 mg/L) was optimal at 16:1 at which removal rates of NH4+-N and PO43--P were 49.7%,56.4% and 91.8%,91%, respectively.③Orthogonal experiment showed that suiTable temperature and continuous high-illumination intensity contribute to removing nutrients by algae. The importance order was B (illumination intensity)>A (temperature)> C (photoperiod), and levels of factor A and B was significant on biomass growth and removal of phosphate, but not for nitrate. The optimal combination were temperature (25℃), illumination (6000 lx) and photoperiod (24 h:0 h).(2) Adsorption/absorption of phosphorous by algal biofilm was studied under temperature (28℃) and continuous illumination (40001x). Adsorption of phosphorous by Anabaena flos-aquae and Scenedesmus obliqnus reached equilibrium at 240 min. The surface-adsorbed P by Anabaena flos-aquae was 28.1% of total P of cell, and Scenedesmus obliqnus was 23.5%. Langmuir sorption model was good appropriate type for this sorption and linear regression coefficient was 0.996,0.950, respectively. The maximum adsorption of phosphorous and adsorption constant by Anabaena flos-aquae were 0.625 mg/mg,0.233 L/mg, while Scenedesmus obliqnus were 0.577 mg/mg,0.188 L/mg, respectively.(3) Algae could excessively absorb phosphorous. Essential elements of algae include C, H, O, N, P and S, and total P of cell accounted for 1.58% of dry weight under sufficient nutrient for Anabaena flos-aquae whose approximate molecular formula was C65.78H112.62O55.97N7.53PS0.74 in this study. Training 3 d under P-limit, excessively absorb phosphorous of Anabaena flos-aquae would be consumed mainly and the approximate molecular formula was C128H257～290O105～109N12～15PS1.2.