Experimental Research On Optimization Of Algal Biofilm And Removal Of Nitrogen And Phosphorus

More and more severe eutrophication has brought enormous pressure to aquatic environment, which makes it absolutely necessary and eagerly to come up with a high efficiency and low consumption technology to reduce the discharge of exogenous nutrients, especially nitrogen (N) and phosphorus (P). Algal biofilm is formed by algae attached on the surface of carriers, which can assimilate nutrients (especially N and P) effectively in the process of algal photosynthesis to decontaminate wastewater. However, current research on algal biofilm mostly focused on wastewater treatment efficiency with little reference to optimization (particularly in the selection of carrier) and mechanism of N and P removal.In the paper, firstly, three common fresh water algae were selected from Hydrodictyon, Oedogonium, Chlorella pyrenoidosa, Scenedesmus obliquus, Anabaena flos-aquae and Oscillatoria agardhii via their own growth rate and removal efficiency of N and P in synthetic wastewater treatment. Secondly, at room temperature and continuous illumination (3500lx), nine kinds of algal biofilm were prepared by attaching three optimized algae on the surface of three carriers, i.e. stereo elastic carrier, half-soft carrier and soft carrier, respectively, which were applied in synthetic wastewater treatment, and the objective algal biofilm was selected according their respective removal rate for N and P, algal biofilm dehydrogenase activity (DHA) and expolysaccharide (EPS) contents. Afterwards, treatment efficiencies of schoolyard domestic sewage were tested under static and dynamic conditions by algal biofilm reactor, and the feasibility of algal biofilm application technology in wastewater treatment was evaluated. Finally, the tentative exploration was carried out in N and P removal mechanism by algal biofilm.The main results are summarized as following:(1) Scenedesmus obliquus, Anabaena flos-aquae and Oscillatoria agardhii are screened for their higher average specific growth rate and removal rate of COD, NH4+-N and TP in simulated domestic wastewater;(2) among nine kinds of algal biofilm, the target algal biofilm is determined as Anabaena flos-aquae attached on the surface of stereo elastic carrier for its highest removal rates of NH4+-N93.55%and TP92.21%, as well as the DHA and EPS contents with values of42.18g/(h·m2) and99.57×10-2g/m2, respectively;(3) the integrated process of algal biofilm and inclined plate sedimentation is very effective to treat schoolyard domestic sewage in HRT three days, and in continuous operation process of ten days, the average concentration of COD, NH4+-N, TN and TP in effluent were42.67,3.29,6.51and0.43mg/L, respectively;(4) the sequence of utilization priority of different N by algal biofilm is NH4+-N, urea, NO2-and NO3-, while its adsorption order of different of P shows:ortho-phosphate> metaphosphate> polyphosphate>organic phosphate;(5) the yield coefficients of N and P by algal biofilm are determined as YN=.72(mg/m2chla)/(mg/L NH4+-N), YP=2.50(mg/m2chla)/(mg/L PO43--P);(6) biokinetic coefficients of algal biofilm (containing reaction rate constant and half-saturation constant) were determined as k=1.24(mg/L NH4+-N)/(mg/m2chla)/d, Km=17.88mg/L for nitrogen and k=0.35(mg/L PO43--P)/(mg/m2chla)/d, Km=7.29mg/L for phosphorus.