The Purification And Response Of Chlorella Vulgaris To Aquaculture Wastewater

In recent years,with the improvement of the living standard,the demand for aquatic products is increasing,which has resulted rapid development in aquaculture industry.And the treatment to aquaculture wastewater caused scientists and entrepreneurs attention.The Takifug rubripes has been cultured extensively in northern of China,Japan and Korea because of its delicious taste,tender meat and high economic value.However,there is no report about purifying Takifug rubripes culturing wastewater(TRCW).In this paper,the microalgae of effectively purifying TRCW were screened,and the response of microalgae to the TRCW was also studied.The contents of NH4+-N,NO2+-N,NO3+-N,total nitrogen,total phosphorus and COD in TRCW from aquaculture company in Grand Port,Tianjin were 8.0 mg/L,5.0 mg/L,17.0 mg/L,42.0 mg/L,2.0 mg/L and 100.0 mg/L respectively.Analyzing the purification effect of Chlorella vulgaris,Spirulina and Dunaliella salina to TRCW,it was found that Chlorella vulgaris was best.And the content of NH4+-N,NO2--N,NO3--N,total nitrogen(TN),total phosphorus(TP)and COD in TRCW were removed by Chlorella vulgaris by 92%,71%,40%,53%,84%and 57%respectively.In order to reduce the cost of purifying wastewater,Chlorella vulgaris was immobilized.The optimum immobilization conditions obtained by orthogonal test were 4%sodium alginate(SA),2%polyvinyl alcohol(PVA),3%boric acid solution,2%calcium chloride and immobilization for 2 hours.And the NH4+-N,TP,NO2--N and COD in TRCW were removed by immobilized Chlorella vulgaris by 78%,68%,58%and 59%respectively.It is clear that the purification efficiency of immobilized Chlorella vulgaris is lower than that of free Chlorella vulgaris.However,immobilized Chlorella vulgaris can be used repeatedly,so it is still potential in purifying TRCW.The growth rate of Chlorella vulgaris cultured in TRCW was higher than that cultured in BG-11 medium.And the content of chlorophyll per cell in former was lower than that in later.There is no significant difference in net photosynthetic rate between cultured in TRCW and in BG-11 medium under lower light intensity.When light intensity is over 4000 Lux,the maximum net photosynthetic rate of the former was 1.3 times that of the latter.It indicated that TRCW inhibited photosynthetic process in Chlorella vulgaris.The nitrate reductase(NR),one of the key enzymes of nitrogen metabolism in cell,was also studied.It was found that the maximum NR activity in Chlorella vulgaris cultured in TRCW and in BG-11 medium were 0.12 ?g NO2-/mg Chl h and 0.07 ?g NO2-/mg Chl h respectively.And the former was 1.7 times the latter.It indicated that TRCW increased NR activity.The content of nitric oxide(NO),one of products of NR,was also increased by 32%by TRCW.The effect of NO on the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco),one of the key enzymes of carbon metabolism in cell,was studied.And it was shown that NO inhibited the Rubisco activity by post-translational protein modification.Hence,it was suggested that TRCW increased NR activity which produced more NO,and the NO reduced the photosynthetic rate by inhibiting Rubisco activity.