Study On The Co-immobilized System Of Oedogonium Brevicingulatum And Activated Sludge And Its Reactor For The Removal Of Nitrogen And Phosphorus

Excessive discharge of nitrogen and phosphorus from municipal wastewater will cause eutrophication in aquatic environment.With the promulgation of "Action Plan for Prevention and Control of Water Pollution" by the Sate Council,China will accelerate the construction and renovation of municipal wastewater treatment facilities.Therein,sensitive areas of municipal wastewater should fully reach the level the level 1A standard of GB18918-2002 before the end of 2017.Therefore,it is urgent to research and develop new technologies in municipal wastewater treatment.Due to high efficiency,energy saving and resource reusing,algae-based biofilm technology has been paid more attentions in investigating nitrogen and phosphorus removal from municipal wastewater.In this paper,with elastic solid packing as immobilized substance,an immobilized algae-bacteria symbiotic system was established by Oedogonium brevicingulatum,a dominant alga identified from the secondary sedimentation tank in a municipal wastewater treatment plant,and activated sludge,from the oxidation ditch of this plant.First,we optimized the technological conditions of the system according to the removal efficiency of nitrogen and phosphorus,such as the ratio of algae and bacteria(algae/bacteria ratio),photoperiod,culturing time of biofilm and packing volume.Then,the effects of water quality conditions,e.g.,p H value,ratio of carbon to nitrogen(C/N),carbon sources and water temperature,on the removal efficiency were investigated.Based on the characteristics of the system,we designed and operated the immobilized algae-bacteria symbiotic biofilm reactor by using secondary sedimentation tank as a model,and then evaluated the removal efficiencies of nitrogen and phosphorus of the biofilm reactor.The following main conclusions have been obtained from this paper:(1)Within the algae/bacteria ratio ranging from 2:1~5:1,the removal efficiencies of nitrogen and phosphorus were highest of the 3:1 experimental group.Duo to the little difference of nitrogen and phosphorous efficiency between the light/dark ratio at 14 h: 12 h and 12 h: 12 h,12 h: 12 h experimental group was selected as the optimal light/dark ratio for energy saving.Within the hanging biofilm time from 0 ~72 h,48 h experimental group showed the best result.When the packing volume ranged from1/3~1,the packing volume full-filling displayed the highest results.Based on the above optimal technological conditions,the removal efficiency of ammonia nitrogen and orthophosphate achieved 100% and 70.71%,respectively in the experimental period of 12 hours.(2)The effects of water quality conditions on of removal efficiency the nitrogen and phosphorus by the symbiotic system were investigated and the results were as follows.Within the p H range from 6~9,the system at p H 7 showed the best removal efficiencies of ammonia nitrogen and orthophosphate,which were 100% and 66.56%,respectively.The C/N ratio of 50:2 was most beneficial in the range from 30:2~70:2,with the removal efficiency of ammonia nitrogen and orthophosphate 100% and 47.86%,respectively.Under different carbon source conditions,the ammonia nitrogen in all tested groups could be removed completely,while the phosphorus removal efficiencies were different.When glucose was used as carbon source,the removal efficiency of orthophosphate was higher(70.71%)than other experimental groups(sodium acetate or methanol as carbon source).With water temperature increasing from 10 oC to 30 oC,the removal efficiencies of ammonia nitrogen and orthophosphate first increased but then decreased,with the highest values of 100% at 20 oC.(3)A biofilm reactor was designed based on the above results of the immobilized algae-bacteria symbiotic system,which showed a continuous and stable removal efficiency on treatment of the simulated municipal wastewater.When the concentrations of ammonia nitrogen,orthophosphate and chemical oxygen demand(COD)of the influent were set at 2 mg/L,0.7 mg/L and 50 mg/L,respectively,with hydraulic retention time(HRT)of 12 h and running time for 24 days,the average concentration of ammonia nitrogen,orthophosphate and COD in the effluent were 1.38 mg/L,0.53 mg/L and 24.93 mg/L,respectively,which reached the discharging standard(the level 1A standard of GB18918-2002)of the municipal wastewater treatment plant.When the HRT ranged from 3-12 h,the effluent reached the discharging standard with the HRT more than 6 h.Moreover,when the HRT was reduced to 3 h,we also found that the ability of nitrogen and phosphorus removal can be improved by controlling the oxidation and reduction position(ORP)in the reactor(150-350 mv).When the ORP was set above 250 mv,the effluent can reach the discharging standards.Furthermore,the reactor showed a good stability with the change of influent water qualities during running time.According to economic benefit analysis,the running cost only increased 0.01 yuan(RMB)/m3(0.51 yuan(RMB)/m3 in winter)of the municipal wastewater plants which meeting expansion conditions.