Integrated The Biomass Production Of Oleaginous And Starch-rich Microalgae And Dairy Wastewater Treatment

Energy poverty and water quality deterioration are the two major global issues. Advancedwastewater treatment technologies and new energy resources development are important meansto solve the two major challenges mentioned above. A mutual-beneficial pattern whichwastewater treatment coupled with the production of clean, renewable microalgae-based biofuelshas received a lot of attention since it was reported by Oswald in1957[1]. In this thesis, thegrowth, morphology, lipid and starch accumulation of an oleaginous microalga Scenedesmusacuminatus and starch-rich, settleable microalga Desmodesmus insignis grown in BG-11medium and diluted dairy wastewater were investigated, respectively. The removal efficiency ofnitrogen and phophorus by these two microalgae from dairy wastewater was also analyzed.S. acuminatus was cultivated in four different initial NaNO3concentrations （18mmol/L,9mmol/L,6mmol/L and3.6mmol/L） of BG-11media and four different diluted concentrations（25%,50%,75%and100%） of dairy wastewater with3.0cm column photobioreactors,respectively. The highest biomass concentration reached9.49g/L in BG-11medium containing6mmol/L NaNO3, the maximum total lipid content was up to62.58%of dry biomass in BG-11medium containing3.6mmol/L NaNO3. The maximum biomass concentration of12.2g/L wasobtained in100%wastewater. The highest lipid content and neutral lipid content were gained in25%dilution of wastewater, total lipid content reached62.37%of dry biomass, neutral lipidcontents attained87.12%of total lipid and53.77%of dry biomass, respectively. The carbonchain length of fatty acids in S. acuminatus was between C14and C18which was very similarto the average carbon chain length of the petroleum diesel. S. acuminatus could effectivelyremove nitrogen and phosphorus from the different diluted dairy wastewater, the removalefficiency reached86.4⁹3.2%（N） and99.4%（P）.The volumetric total lipid content and volumetric total lipid productivity were employed toevaluate the lipids production capacity of S. acuminatus. The results showed that the highestvolumetric total lipid content （5.27g/L） and volumetric total lipid productivity （0.293g/L/d） of S.acuminatus grown in BG-11medium with3.6mmol/L were obtained. The maximum volumetrictotal lipid content（4.863g/L） and volumetric total lipid productivity（0.4052g/L/d） of S.acuminatus were gained in25%dilution of dairy wastewater. All data indicated that low dilution of diary wastewater （25%dilution） was suitable for lipid production of S. acuminatus.The mini-pilot cultivation of S. acuminatus were conducted in3cm light-path （workingvolume:24L） vertical flat plate glass photobioreactors（VFPGP） with25%dilution of dairywastewater. The results showed that the maximum biomass concentration of6.83g/L and totallipid content of50.07%based on dry biomass were obtained in VFPGP. The volumetric totallipid content and volumetric total lipid productivity were up to3.42g/L and0.19g/L/d,respectively.Desmodesmus insignis was grown in BG-11media containing four different initialconcentrations of NaNO₃（18mmol/L,9mmol/L,6mmol/L and3.6mmol/L） and dairywastewater diluted into four concentraions （25%,50%，75%and100%） with3.0cm columnphotobioreactors, respectively. The highest biomass concentration reached6.23g/L in BG-11medium containing9mmol/L NaNO₃, the maximum total carbohydrate and starch contents of D.insignis grown in BG-11medium containing18m mol/L NaNO₃were50.76%（d.w.） and40.95%（d.w.）, respectively. The highest biomass concentration and total carbohyadrate contentof D. insignis were obtained in100%dairy wastewater with10.31g/L and54.44%（d.w.）,respectively. The highest starch content of D. insignis was gained in75%of dairy wastewaterwith50.88%of dry biomass. D. insignis could also effectively remove nitrogen and phosphorusfrom different dilutions of diary wastewater. The removal efficiency reached78.05⁹0.34%（N）and95.76⁹8.74%（P）.The highest volumetric starch content （2.55g/L） and volumetric starch productivity（0.212g/L/d） of D. insignis were obtained in BG-11medium containing9mmol/L. Themaximum volumetric starch content and volumetric starch productivity of D. insignis grown in75%of dairy wastewater reached4.863g/L and0.4052g/L/d, respectively. All results manifestedthat high dilutions （100%or75%） of dairy wastewaters were suitable for biomass and starchaccumulation of D. insignis.The indoor scale-up cultivation of D. insignis was carried out in the same dimension ofVFPGP mentioned above with BG-11medium and75%of dairy wastewater, respectively. Themaximum biomass concentration, the total carbohydrate content, starch content, volumetricstarch content and volumetric starch productivity of D. insignis culvitated in BG-11medium were up to4.76g/L,52.28%（d.w.）,39.42%（d.w.）,1.39g/L and0.07g/L/d, respectively. Thehighest biomass concentration, the total carbohydrate content, starch content, volumetric starchcontent and volumetric starch productivity of D. insignis grown in75%of dairy wastewaterreachred9.57g/L,61.9%（d.w.）,48.75%（d.w.）,4.75g/L,and0.23g/L/d, respectively. D. insignishpossesses higher settling ability, cells in BG-11medium and in75%of diary wastewater couldfinish settlement within60and90minutes, respectively.The results from these two experiments proved that oleaginous microalga S. acuminatus andstarch-rich, settleable microlga D. insignis could be grown in dairy wastewater for feedstockproduction of biodiesel and bioethanol combined diary wastewater treatment for removingnitrogen and phosphorus.