Research On Removal Of N, P And Organics In Artificial Algal System

Because of the nitrogen arbitrarily emissions, it has triggered a lot of environmentproblems, such as eutrophication problem of N and P. And ammonia is prisoner forwater biological, especially fish. In recent years, there were some reporters aboutsewage nitrogen removal. Algae sewage removal system, low operating cost, a drasticdecrease of surfaces, and it can realize better removal efficiency of N and P inwastewater, especially in some small and middle towns. Meanwhile, there was not adetailed study about nitrogen removal in alage sewage treatment system, also in ourcountry, very few people have proceed study of nitrogen mass balance.This experiment mainly research the removal efficiency of nitrogen, phosphorusand organic compounds in wastewater by Spirulina platensis. and Scenedesmusobliquus in a variety of conditions. Selecting the higher efficiency wastewater treatmentalgae as the better algae in the best condition, to study the mechanism analysis. In theanalysis, partly according to the amount change of TN in wastewater, org-N in algaeand mass N to research the N mass balance and towards in algal wastewater treatment.So providing new technology and practice guiding for the settlements wastewaterdeeply removal.The results showed that:(1) According to the algal growth characteristics, this study shows that theoptimum absorb wavelength of Spirulina platensis. is560nm and Scenedesmus obliquusis686nm. The relationship between algae density and water sample absorb wavelengthof Spirulina platensis. is y=3.749x-0.084（R2=0.9859） and Scenedesmus obliquus isy=5.3093x-0.0025（R2=0.9933）. The best inoculation date of Spirulina platensis andScenedesmus obliquus respectively were the eighth and ninth day.(2) According to the algal best growth condition, this study shows results of thebest illumination intensity is3000lux, the best light-dark ratio is12h:12h, the bestaeration mode is aerator aeration of Spirulina platensis. and Scenedesmus obliquus.(3) The final removal efficiency of TN, NH4+-N and TP by Spirulina platensis.were88.75±1.19%,100%and86.1±2.36%respectively. The totally removalefficiency of TN, NH4+-N and TP by Scenedesmus obliquus were83.83±0.26%,100%and84.46±3.46%respectively. But, less satisfactory results have been reached in theTOC removal effect by Spirulina platensis. and Scenedesmus obliquus, TOC removalrate was only14.36%by Spirulina platensis, and achieved17.36%removal efficiencyby Scenedesmus obliquus.(4) In the best condition, the average DO concentration was6.79-7.35mg/L, the average pH was8.34-9.21, the average temperature was27.6-28.7℃in sewageremoval by Spirulina platensis; the average DO concentration was6.77-7.3mg/L mg/L,the average pH was7.88-9.02, the average temperature was27.5-28.4℃in sewageremoval by Scenedesmus obliquus. Because of the proper pH, DO and temperature, itwas benefit for nitrifying bacteria and de nitrifying bacteria‘s growing, so it had causedNO3--N and NO2--N accumulation. When the HRT=8d, in Spirulina platensis sewageremoval, the phenomenon of NO3--N and NO2--N accumulation all occurred at the first4days. And in the Scenedesmus obliquus sewage removal, the phenomenon of NO3--Nand NO2--N accumulation all occurred at the first5days.(5) In finally, NO3--N had achieved a lower removal amount than NO2--N andNH4+-N by Spirulina platensis and Scenedesmus obliquus. At the same time, Spirulinaplatensis and Scenedesmus obliquus both had the different absorb capacity for variousnitrogen resources at the best treatment time, the absorb ranking was: NH3-N> NO3-Nand NO2-N.(6) In the low nitrogen and phosphorus tertiary, the average removal rate of TN bySpirulina platensis was significant higher than Scenedesmus obliquus, but it had aninsignificant differences among the average removal of NH4+-N、NO3--N、NO2--N、TPand TOC.(7) The proper treatment time was the sixth day of Spirulina platensis., and thebetter treatment time was the fifth day of Scenedesmus obliquus.(8) There were adaptive phase, logarithmic phase, Stable phase and decline phasein alage sewage removal, the sustances in sewage also tended to change. Water samplesabsorbance, turbidity, algal dry weight and chlorophyll-a concentration in algal all hadgradually increased with time, but only the chlorophyll-a concentration had a slightlyreduced at the eighth day in Spirulina platensis wastewater treatment.(9) In the best processing condition, the best hydraulic rentention time is12h ofwastewater treatment by Spirulina platensis.(10) In the best removal time, the organic nitrogen in Spirulina platensis dry weightwas about100.63mg（/algae g）. The mass of nitrogen was accouted for10%of algal dryweight, and the mass of Org-P was about1.4%of algal dry weight, N:P was nearly7:1.(11) We can conclude from the nitrogen balance analysis: TN in sewage can bedeeply removed by Spirulina platensis., about52.96%of them was been absorbed byalgae and then translated into itself Tissue cells organic nitrogen.