Investigation On Method And Characteristic For Removal Of Nitrogen And Phosphorus From Wastewater By Immobilized Microalgae

With the continuous development of the economy and society,a large amount of waste water generated by industry,such as inrich N,P and organic matter etc,has caused serious damage to the ecosystem and human health,and can even cause eutrophication of water bodies.In recent years,there have been many studies at home and abroad showing that algae has great potential in wastewater treatment,and the use of an algae to remediate polluted water can effectively reduce the content of N,P and organic matter in wastewater.The treatment of wastewater by the microalgae system not only conforms to the concept of ecology,but also realizes the recycling utilization of water resources.It has important environmental significance and good application prospects.In this rearch,Chlorella vulgaris,Chlorella pyrenoidsa and Scenedesmus quadricauda were used as experimental materials,and sodium alginate?SA?and polyvinyl alcohol?PVA?were used for immobilization carriers to immobilize microalgae,the improvement of the traditional method of immobilizing microalgae on a single carrier was done and then the immobilizing microalgae were used to remove CODcr,NH₃-N and TP from wastewater.Firstly,the optimal immobilization conditions were selected by orthogonal experiments,and the immobilized carriers were screened.Secondly,the reaction conditions were used to optimize the process conditions,and the best process conditions were selected.Finally,the laboratory test of immobilized Chlorella vulgaris treated sewage was studied..The final research results obtained mainly include the following points:1.In the study of the growth regularity and growth characteristics of different microalgae,the optimal conditions for the growth of Chlorella vulgaris,Chlorella pyrenoidsa and Scenedesmus quadricauda were determined as 25°C,pH 7,and light intensity 3000 Lx.The removal rates of CODcr were 48%,34%,and 45%for Chlorella vulgaris,Chlorella pyrenoidsa and Scenedesmus quadricauda,respectively.The removal rates for NH₃-N were64%,52%,and 50%,respectively.The removal rate of TP was 66%,54%,and 49.5%,respectively.Therefore,Chlorella vulgaris has the best removal effect on CODcr,NH₃-N and TP in wastewater.2.Orthogonal experiment table optimization of the composite carrier and crosslinker ratio experiment set up 4 factors 4 lever L₁₆?4⁵?orthogonal test,obtained for CODcr,NH₃-N and TP,the impact of the factors on the experimental size of the PVA>activated carbon>boric acid>immobilization time,PVA>boric acid>activated carbon>immobilization time,boric acid>activated carbon>immobilization time>PVA,optimum ratio of carrier and cross-linking agent is 1.0%PVA?2%of SA?,2%of boric acid?2.0%of calcium chloride?,0.5%of activated carbon,and immobilization for 11 h.3.Under the optimal conditions of orthogonal experiment,the response surface method was used to perform the second optimization.Finally,the response surface analysis showed that the optimum conditions for SA-PVA composite immobilized Chlorella vulgaris treatment wastewater were:Chlorella vulgaris density 3.8×10⁶ cells/m L,immobilized particle diameter 3.2 mm,glucose content 0.34%,the nitrogen-phosphorus ratio was 24.58.4.The test of sewage treatment by immobilized Chlorella vulgaris was done in the laboratory,the optimum conditions are:pH 7,treatment time 12 d,and light intensity 5000 Lx.The effluent concentrations of CODcr,NH₃-N,and TP in the wastewater were 98 mg/L,12.76mg/L,and 0.59 mg/L,respectively.The removal rates were 88.71%,80.14%,and 87.36%,respectively,and the treatment results showed that the concentrations of CODcr,NH₃-N,and TP were much lower than the maximum allowable daily average emission load of the "National Standards for Urban Domestic Sewage Discharge"?GB18596-2001?,which reached the national emission standards.