The Study On Utilization Of Wastewater Resource Based On The Cultivation Of Microalgae

Microalgae are auxoautotrophs which are high efficiency in photosynthesis, widelydistributed, rapidly multiply and highly valueable. Because of unique advantages,microalgae have been regarded as third-generation feedstock for biodiesel productionwhich could replace fossil fuel in the further. However, the culture cost and sustainableraw material supply are still the greatest bottlenecks that restrict large-scale biodieselproduction from microalgae. Therefore, except for the screening and cultivation ofmicroalgae for biodiesel and large-scale culture techniques, wastewater recycling andnutrients reusing become the key approaches to reduce cost.In this paper, water samples came from secondary effluent in Baotou northernsuburban water purification plant, and microalgae were separated, screened andidentified. Wastewater was reused to culture lipid-rich microalgae and vegetables. Thefeasibility was analyzed, characteristics of growth and lipid accumulation of XJ002inmunicipal wastewater were investigated to provide basis for utilization of wastewaterresource. The main contents and results of this study are as follows:1. Four algae strains were obtained from water samples by the plate dilute methods.With morphology and18S rDNA molecular identification, No.XJ001, XJ002, XJ006,XJ008strains were identified belonging to Nitzschia, Scenedesmus, Nannochloropsis,Chlorococcum respectively.2. XJ002was cultured with municipal wastewater, the effect of sterilization ofwastewater, content and composition of nutrients supplementation on the growth andlipid accumulation of microalgae were investigated. Results indicated that XJ002couldgrow in the crude municipal wastewater, and biomass yield of microalgae wereincreased under the conditions of supplementing50%and75%BG-11nutrients. Exceptfor Ca2+and trace mental solution, Fe3+, NaNO3, K2HPO4·3H2O, MgSO4·7H2O andNa2CO3could significantly influence (P＜0.05) the growth and lipid accumulation ofmicroalgae in crude municipal wastewater. With supplementing50%BG-11content of Fe3+（2.9mg·L-1）, NaNO3（0.75g·L-1）, K2HPO4（19.5mg·L-1）, MgSO4（37.5mg·L-1）and Na2CO3（10mg·L-1）, microalgae biomass yield could reach2.08g·L-1. It was1.93times higher than that cultured with crude wastewater, and thelipid productivity of17.58mg·L-1·d-1was4.92-fold and1.33-fold compared with theconditions of crude wastewater and BG-11respectively. Moreover, the cost ofcultivation was only30%~50%of the BG-11standard medium under the same cultureconditions.3. A single factor experiment and L18（37） orthogonal experiment wereconducted to study on the effect of five nutrients（N, P, Mg, Fe, C）. Results indicatedthe best growth conditions of XJ002were as follows: temperature25℃, light intensity5000Lx, initial pH6.5~7.5, NaNO32.25g·L-1, K2HPO4·3H2O40mg·L-1, MgSO4·7H2O56.25mg·L-1, FeCl3·6H2O9mg·L-1and Na2CO315mg·L-1. Under the optimumconditions XJ002biomass yield could reach3.04g·L-1which was2.8-fold comparedwith that cultured with crude wastewater. Besides, it was conducive to accumulation oflipid under the conditions of low concentration of nitrogen and high iron concentration.And the original concentration of phosphorus and carbon in crude wastewater couldsatisfy normal growth of microalgae.4. Microalgae wastewater was used as nutrient solution for hydroponic vegetableafter dealing with dilution and pH adjustment. Results indicated wastewater was useddirectly for hydroponic Lycopersicon and L. sativa after diluting to100times withoutpH adjustment. And wastewater was directly used to culture Lycopersicon after dilutingto20times and adjusting pH to6.0. Wastewater was directly used to culture L. sativaafter diluting to10times and adjusting pH to6.0. Moreover, low ratio of dilution couldguarantee the sufficient supply of nutrients in wastewater, and it avoided lossing toomuch nutrients due to dilution. The suitable pH in nutrient solution could satisfy thedemand of different plants.The cultivation of lipid-rich microalgae with municipal wastewater could producemass biomass and lipid productivity for biodiesel and reduce the microalgae cutivationcost. Reusing of wastewater could turn waste into wealth and reduce environmentalpollution from wastewater discharge. It has important realistic meaning for circulareconomy and sustainable development.