Experimental Study On Nitrogen And Phosphorous Removal From Municipal Wastewater By The Oscillatoria Biofilms

Wastewater reuse is a very important way of solving the shortage of water resourcesand reducing water pollution. However, the contents of nitrogen and phosphorous insecondary effluents from municipal wastewater treatment plants are relatively high andcan’t up to the requirements of reuse. Algal biofilm, as a technology of eco-friendly andclose to nature, is well suited for advanced treatment to remove nitrogen and phosphorus.This research mainly investigates the potential of nitrogen and phosphorous removal fromsynthetic wastewater by Oscillatoria tenuis biofilm systems. First, discusses the impactsof nitrogen sources, glucose, initial pH, different nitrogen and phosphorous concentrationsas well as N/P and Fe³⁺on nitrogen and phosphorous removal. And then examines theoperation efficiencies of algal biofilm reactor in batch and dynamic continuousexperiments. The main results of the thesis are as follows:1. Oscillatoria tenuis biofilm systems can remove nitrogen and phosphorouseffectively in semi-continuous conditions. The main mechanism of nitrogen andphosphorous removal is algal assimilation.（1） When （NH₄）₂SO₄, NaNO₂, NaNO₃, urea and peptone are used as nitrogen sources,Oscillatoria tenuis biofilms can uptake and utilize all of them effectively. But theabsorption rate of peptone is the lowest. The removal efficiencies of TN in different kindsof nitrogen source wastewater are as below: NaNO₂, NaNO₃>（NH₄）₂SO₄+NaNO₃> urea>（NH₄）₂SO₄> peptone.（2） Oscillatoria tenuis can utilize glucose for heterotrophic growth. The removal rateof TN increases along with the increasing of the glucose in wastewater. The removalefficiency of phosphorous is less affected by glucose which is less than200mg/L, but itdecreases dramatically when the glucose increases to300mg/L.（3） The initial pH of wastewater has a considerable effect on phosphorous removalwhile a smaller effect on nitrogen removal. When the initial pH ranges from5.0to10.0,the removal rates of TN and NH+4-Nare96.75%⁹7.46%and97.81%⁹8.59%,respectively. The removal rate of TP is about96%when the initial pH varies from5.0to 8.0and it reduces with the increase of pH that is above8.0. The removal efficiency of TPis only86.85%when the pH is up to10.0.（4） The uptake of nitrogen and phosphorous are related with their concentrations andN/P ratio. Keep the concentration of TN constant, N/P mainly influences phosphorousremoval: TP removal efficiency increases with the increase of N/P that ranges from4.8/1to14.1/1, whereas decreases with N/P which rises from14.1/1to28.0/1. N/P mainlyaffects nitrogen utilization keeping TP the same: the removal rate of TN falls off rapidly asN/P increases from14.5/1to28.0/1while less likely to be affected by N/P when N/Pchanges between5.3/1and14.5/1. And it gets the optimal effects of TN and TP removalwhen the N/P are14.1/1and14.5/1, that the removal rates of TN are97.02%and95.61%while TP are96.15%and96.05%.（5） Fe³⁺tends to have a smaller effect on nitrogen and phosphorous removal. Whenthe concentrations of Fe³⁺vary between0mg/L and5mg/L, the removal efficiencies ofNH₄⁺-N,TN and TP are97.58%⁹8.45%,98.94%⁹9.08%,97.54%⁹8.06%, respectively.（6） According to the orthogonal test, the optimum process conditions of nitrogen andphosphorous removal are: illuminate16hours, add glucose250mg to2L sewage everyday,adjust N/P of raw sewage around15/1and treat5days.（7） Oscillatoria tenuis can uptake nitrogen and phosphorous rapidly after starvation,so that the contents of nitrogen and phosphorous in cells are much higher after theexperiment.2. The algal biofilm reactor is of stable operation and achieves high nutrients removalefficiencies. The batch experiment shows that after3days treatment the remove rates ofNH₄⁺-N TN are96.54%,99.35%respectively while the TP remove rate is about97%fourdays later. During25days dynamic continuous experiment, the remove rates ofand TN are95.20%and97.22%, respectively; and the removal efficiency of TP stabilizesaround96%after the fluctuation caused by high concentrated influent.