Cultivation And Flocculation Of Chlorella Sorokiniana In Swine Manure Wastewater

The development and application of energy from biomass is the most promising strategy to alleviate the energy crisis generated by the increasing depletion of fossil fuel resources.Microalgae as an important resource for bioenergy have many advantages,such as extensive distribution,rapid growth,high in lipid content and farmland saving.However,the expensive cost of nutrient in medium and energy consumption in harvest process restricts the commercial production of microalgae energy.Owning to the rapid development of pig husbandry,there is a dramatic increase in the swine manure wastewater,which brings a severe damage to the ecological environment.The integration of wastewater treatment and microalgae biomass production makes it possible to realize the wastewater purification and resourceful utilization of swine manure wastewater and to lower the cost for microalgae cultivation.130 strains of microalgae were isolated and purified from the waters around.A strain of microalgae indentified as Chlorella sorokiniana ZB was screened,which grew rapidly in diluted swine wastewater and had high oil content.In the research,the effect of ammonia nitrogen on the growth of C.sorokiniana ZB was studied and nutrient compositions in medium were optimized using response surface methodology(RSM).The results demonstrated that the addition of NH3-N(<500 mg/L)had no effect on the growth of C.sorokiniana ZB in autotrophic growth conditions,while NH3-N more than 30 mg/L would generate strong inhibition on cell growth in the heterotrophic/mixotrophic conditions(glucose existed in culture system).The optimal biomass productivity(553 mg/L d)was obtained,when C.sorokiniana ZB was cultivated in medium based on BG11 with 17.13 g/L of glucose,2.25 g/L of NaNO3 and 0.28 g/L of K2HPO4.The impacts of major water quality parameters of swine wastewater and inoculation concentration of algae seeds on biomass production of C.sorokiniana ZB were studied.The growth rate of C.sorokiniana ZB was increased with the increase of Chemical Oxygen Demand(COD)concentration(50-300 mg/L),while the growth of C.sorokiniana ZB would be significantly inhibited when COD content was higher than 1000 mg/L.Concentration of Total Nitrogen(TN)in wastewater would scarcely affect the algae growth,and inhibition of NH3-N on the growth of C.sorokiniana ZB was not so obvious,although NH3-N occupied the overwhelming proportion of nitrogen source.COD,Total Phosphorus(TP)and inoculation size which had significant impact on biomass production of C.sorokiniana ZB in swine manure wastewater were optimized using Box-Behnken RSM design.The optimal biomass production(125 mg/L d)was obtained when C.sorokiniana ZB was cultivated in swine wastewater containing 345 mg/L COD and 45 mg/L TP,with the initial inoculation concentration of 136 mg/L algae seeds(dry weight).The removal rates of TN,TP and COD reached 84%,88%and 38%respectively.Flocculation of C.sorokiniana ZB cultivated in swine wastewater and the effect of different organic matters on flocculation were investigated.The results demonstrated that microalgae cultivated in swine wastewater can be harvested efficiently through flocculation by increasing pH(>11)or by adding Al3+.The minimum amount of Al3+required for complete flocculation in wastewater would increase substantially,and flocculation efficiency became highly sensitive to pH.Tryptone could cause similar extent of inhibition on flocculation as in wastewater.Meanwhile,glucose could increase concentrations of Algogenic Organic Matter(AOM),inhibiting flocculation strongly at higher pH,including flocculation induced by Al3+ and autoflocculation.However,urea had little effect on flocculation of C.sorokiniana ZB.Moreover,the major factors:dilution times,pH and flocculants dosage,which had significant impact on flocculation efficiency of C.sorokiniana ZB in piggery wastewater,were optimized using RSM.The optimal flocculation efficiency(100%)was achieved at pH 8.5,7-folds of dilution and 52.14 mg/L of Al3+.Microalgae culture system was scaled up to 30 L and 350 L photobioreactor,and 200 m2 outdoor microalgae culture pond was built up and operated.The semi-continuous culture of C.ZB using swine wastewater was realized through the supplement of sodium acetate and phosphorus source,the highest biomass yield reached 430 mg/L d.The content of C16 and C18 dominated in the fatty acids of C.sorokiniana ZB,accounting for 94.39%of total fatty acids content,which could be used as the raw materials for the biodiesel.In addition,the crude protein content was 39.26%,the content of total amino acids was 340.1mg/g,in which the content of glutamic acid was the highest(38.1 mg/g),essential amino acids accounted for 42.75%of the total amino acids.Also the algae cultivated in wastewater could be taken as the substitutes of some protein feed.