| With the rapid expansion of swine industy,a large amount of wastewater is produced.Anaerobic digestion of the wastewater from swine production facility is an efficient method to treat swine wastewater while producing methane gas as an energy source.However,the effluent after anaerobic digestion of swine manure still contains high content of nitrogen and phosphorus;if discharged directly to water bodies,the effluent will cause eutrophication of ecosystem.Finding a method which can efficiently reduce the nutrients levels in anaerobic digestion effluent is urgently needed.In general,microalgae grow well in wastwater by utilizing nitrogen,phosphorus and various other compounds in the wastewater.Therefore,growing microalgae production on anaerobic digestion derived effluent prodive a promising technology to reduce the nutrient load of anaerobic digestion effluent.In this work,we explored the use of freshwater microalgae Chlorella sp.for reducing the nutrients of the effluent of anaerobic digestion of swine manure.The algal growth,nutrient removal,and algal biomass composition were characterized..The main research performed in this work was summarized as follows:The strain was identified as Chlorellapyrenoidosa based on 18S rDNA.Use of flocculation as a pre-treatment menthod to physically remove the nutrient loading of the raw analerobic digestion efflulent was studied.To enable microlage effectively use nutrients in the anaerobic digestion effulent,a flocculation pretreatment of the effluent was performed to reduce the nutrient loading so the microlage can grow properly in the effluent.It was found that Poly aluminium chloride(PAC)and PAC with Cationic-type polyacrylamide was ideal for treating the anaerobic digestion effluent.The PAC coupling Cationic-type polyacrylamide(CAPM)flocculation reduced chemical oxygen demand,total nitrogen,total phosphorus concentrations by 33.54%,6.26%and 67.70%,respectively.When Chlorella sp.was grown in flocculation-treated effluent,effluent treated with PAC(CPAM as adjuvant)resulted in the best algal growth with the biomass increased 31.53%.Optimization of the growth and nutrient removal of C.pyrenoidosa LQ6 was researched through indoor cultivation system.The parameters optimized included Na2CO3 concentration(1.33 g/L),initial inoculum(1.0 g/L),lighting time over a day(24 h),light intensity(5,000～10,000 lx)，temperature(25 ℃),N/P ratio(7.0)and C℃ventilation(0.5%).Then after 360 hours cultivation,the biomass reached to 10.84 g/L,while the removal rate of chemical oxygen demand,total nitrogen,total phosphorus and ammonium nitrogen was 95.76%.97.71%、98.78%and 53.30%,respectively.The content of total cabohydrate,protein and lipid of the algal biomass were also determined.After 360 hours cultivation,the lipid production reached 62.6%,the total cabohydrate got 12.18%,while the protein production reached 3.15%.Then semi-continuous mode was studied for growing the C.pyrenoidosa using the effluent treated with PAC(CPAM as adjuvant).The update rate of 5%shown a better result.After 360 hours cultivation,the biomass reached to 9.79 g/L,while the removal rate of chemical oxygen demand,total nitrogen,total phosphorus and ammonium nitrogen was 96.41%、97.70%、99.42%and 64.81%,respectively.Pilot-scale cultivation of C.pyrenoidosa and nutrients removal was further investigated in outdoor using synthetic wastewater.After 10 days cultivation,the algal growth and nutrient removal using bubble column reactor were better than those using raceway pond.The biomass in bubble column reactor reached to 3.95 g/L,while total nitrogen and total phosphorus removal rate reached 71.54%and 71.54%,respectively.The impacts of different optical path(4,10,18 and 25 cm)were also investigated in outdoor cultivation.After 10 days cultivation,the biomass got 3.95、1.38、1.13 and 0.77 g/L,respectively.The results shown that the smaller the optical path were,the better biomass and nutrient removal rate were obtained.In addition,significantly higher lipid content(29.38%)was observed in this condition. |
PDF Full Text Request