Selection And Effect Evaluation Of Microalgae Purification For Alcohol Wastewater

The wastewater as the main pollutant of the cassava alcohol industry.About 13-16 tons of organic wastewater will be discharged per ton of alcohol production.After the treatment for wastewater,most of organic compounds has been removed,but it still contains more nutrients elements such as nitrogen and phosphorus.If it is misconduct will cause water eutrophication,so further treatment is needed.During the growth of microalgae,a large amount of nitrogen,phosphorus and other nutrients elements are absorbed,and CO₂ can be used as a carbon source to synthesize cellular biochemical components.The use of wastewater to culture microalgae can make full use of the nutrients elements in the wastewater,reduce the cultivation cost of microalgae,purification of water,get the microalgae biomass of a certain value,and obtain certain economic benefits.In this experiment,we screened the most suitable microalgae strains for the growth of alcohol wastewater from four types of microalgae,and finally determined the optimal culture conditions for this microalgae strain in alcohol wastewater.In this experiment,we screened out the most suitable microalgae strains for the growth of alcohol wastewater from four types of microalgae,determined the best culture conditions of the microalgae strains in alcohol wastewater,and finally compared the composition of amino acids and fatty acids in the culture medium and alcohol wastewater.The experimental results are as follows:1.Screening of algae suitable for growth in alcohol wastewaterOocystis borgei could not grow normally in alcohol wastewater.It's dry weight and Chla content in 12 d of alcohol wastewater were significantly lower than those in f/2 medium?P<0.05?.Chlorella vulgaris can grow normally in alcohol wastewater.The best growth test group is cultured in alcohol wastewater without dilution.After 12 days of culture,the dry weight of the treatment group?alcohol wastewater?was significantly lower than that of the control group?BG11??P<0.05?,but there was no significant difference in Chla content between the treatment group and the control group?P>0.05?.Scenedesmus quadricauda can grow normally in alcohol wastewater without dilution.The dry weight obtained by culturing for 12 days is 0.67±0.02 g·L^-1,and the content of Chla is 4.32±0.41 mg·L^-1.Significantly higher than other test groups?P<0.05?.Spirulina platensis can adapt to the growth environment of alcohol wastewater.With the increase of alcohol wastewater concentration,the dry weight and Chla content increase.Culture in 75%alcohol wastewater for 12 days.Its dry weight and Chla were the highest,1.05±0.07 g·L^-1 and 9.6±1.9 mg·L^-1,respectively.While cultured in alcohol wastewater without dilution were 0.96±0.09 g·L^-1 and 9.5±1.0 mg·L^-1,which showed no significant difference between 75%alcohol and alcohol without dilution?P>0.05?.Spirulina platensis grew better in alcohol wastewater without dilution,and its dry weight and Chla content were significantly higher than those of Oocystis borgei,common Chlorella vulgaris and Scenedesmus quadricauda?P<0.05?,so Spirulina platensis is a preferred algae strain for purifying alcohol wastewater.2.Effect of culture conditions on growth and purification of Spirulina platensis wastewater:The temperature had a extremely significant effect on the dry weight and Chla content of Spirulina platensis grown in alcohol wastewater?P<0.01?.When the temperature was30°C,the dry weight of Spirulina platensis cultured in alcohol wastewater was 1.31±0.02g·L^-1,and the Chla content was 12.1±0.5 mg·L^-1,which was significantly higher than other experimental groups?P<0.05?.The effect of temperature on COD_cr,TN and TP in alcohol wastewater from Spirulina platensis was extremely significant?P<0.01?.When the temperature was 30°C,the removal rate of COD_cr,TN and TP in Alcohol wastewater was21.0±0.8%,38.0±2.8%,and 59.0±1.9%separately,were significantly higher than the other experimental groups?P<0.05?.The illumination indensity had a significant effect on the dry weight and Chla content of Spirulina platensis grown in alcohol wastewater?P<0.05?.When the illumination indensity was 3000 lx,the average dry weight and Chla content of Spirulina platensis in ethanol wastewater was the highest which were 1.34±0.09 g·L^-1 and 11.1±2.1 mg·L^-1,respectively.The effect of light intensity on COD_cr,TN and TP in alcohol wastewater from Spirulina platensis was significant?P<0.05?.When the illumination indensity was 3000 lx,The average removal rate of COD_cr,TN and TP in alcohol wastewater was the highest which were 20.1±1.0%,40.9±2.5%and 60.4±1.5%,respectively.The effect of different initial inoculum volume to the dry weight and Chla content of Spirulina platensis grown in alcohol wastewater are significant?P<0.05?.When the initial inoculum volume was 50%,the average dry weight of Spirulina platensis in ethanol wastewater got the highest,1.40±0.05 g·L^-1;when the initial inoculum volume was 30%,the average content of Chla got the highest,was 11.3±3.2 mg·L^-1.The initial inoculum volume had significant effects on COD_cr,TN and TP in the alcohol wastewater from Spirulina platensis?P<0.05?.When the initial inoculum volume was 10%,the average removal rate of COD_cr in alcohol wastewater got the highest,was 18.9±2.3%.When the initial inoculum volume was 50%,the average removal rate of TN in alcohol wastewater got the highest which was 43.6±3.1%.When the initial inoculum volume was 30%,the average value of TP removal rate in alcohol wastewater got the highest,was 62.7±3.0%;The effects of different concentration of CO₂ to the dry weight and Chla content of Spirulina platensis grown in alcohol wastewater were extremely significant?P<0.01?.When the 2.5%concentration of CO₂ was introduced,the dry weight of Spirulina platensis cultured in alcohol wastewater was 1.62±0.05 g·L^-1,and the Chla content was 12.1±0.7 mg·L^-1,which were significant higher than other experimental groups?P<0.05?.The effect of different concentration of CO₂ on COD_cr,TN and TP in alcohol wastewater from Spirulina platensis was extremely significant?P<0.01?.When the 2.5%concentration of CO₂ was introduced,The COD_cr,TN and TP removal rates were 24.9±0.6%,50.5±2.1%and 73.2±2.0%,respectively,which were significant higher than other experimental groups?P<0.05?.The orthogonal experiment showed that the initial inoculum volume and temperature were the critical factors to affect the dry weight and Chla content respectively.The most suitable temperature,illumination indensity and initial inoculum volume for growth of Spirulina platensis are at 30°C,3000 lx and 20%,respectively.The temperature was the key factor,affecting the removal of COD_cr,TN and TP in alcohol wastewater by Spirulina platensis.The most suitable temperature,light intensity and inoculation amount for removal of COD_cr,TN and TP in alcohol wastewater are at30°C,3000 lx and 20%,respectively,and the removal rate got highest.3.Amino acid and fatty acid content and evaluation of spirulina platensis cultured in medium and alcohol wastewaterA total of 16 amino acids were detected in culture medium and alcohol wastewater,and there was no significant difference between total amino acid content and individual amino acid content?P>0.05?,glutamic acid?Glu?and aspartic acid?Asp?and leucine?Leu?are the main amino acids;according to the amino acid score?AAS?and chemical score?CS?,lysine?Lys?and proline?Val?are the first limiting amino acids and the second limiting amino acid respectively;the essential amino acid content was 14.94±0.56 mg·g^-1 and 17.48±2.71mg·g^-1,respectively.The essential amino acid content of Spirulina platensis cultured in alcohol wastewater is higher than those of soybean cake and peanut kernel meal,which can fully satisfy the amino acid requirements of carp,tilapia,snapper,Chinese shrimp and penaeus monodon.It is a high-quality feed protein that can be utilized.Gas Chromatography of spirulina platensis cultured in medium and alcohol wastewater shows that the most abundant fatty acid was palmitic acid?C16:0?,accounting for 33.69%and 34.38%of total fatty acids,acid?C20:4n6?and nervonic acid?C24:1?,which have not been deteced from the spirulina platensis cultured in control group,have been detected from the one cultured in alcohol wastewater.Eicosapentaenoic acid?EPA,C20:5n-3?and docosahexaenoic acid?DHA,C22:6n-3?of the one cultured in the medium were higher than that cultured in the medium.Spirulina platensis cultured in alcohol wastewater contains linoleic acid?LA,C18:2n-6?,linolenic acid?LNA,C18:3n-3?,DHA and EPA,which are essential for the growth of shrimp and fish,therefore,it has the potential to be the feed for shrimp and fish;the chemical structure of Spirulina platensis cultured in alcohol wastewater meets the requirements of biodiesel for carbon chain structure,as a result,it is an energy algae that can be used to prepare biodiesel.