| Microalgae investigation has been focused on in research all over the world. It could be used to produce animal feed, food additives, high-value added products (such as health supplements, cosmetics et al.), especially biofuels (such as biodiesel, bioethanol), due to its certain excellent advantages such as rapid growth, the least land demand, high biochemical compositions (protein, lipid). Microalgae could double their biomass within one day and their growth rate is100times that of terrestrial plants. Nonetheless, compared with heterotrophic or mixotrophic cultivation, the microalgae usually grow slowly in photoautotrophic culture due to the light attenuation. The algal biomass is usually not more than1g/L in photoautotrophic cultivation. Mixotrophic growth occurred when the microalgae are provided with CO2and organic carbon sources simultaneously. That could greatly reduce the dependence on light needed for pure photoautotrophic growth, stimulate the algal growth and increase the cells density significantly. However, the high cost of adding organic carbon to the medium will make mixotrophic cultivation uneconomical, In order to reduce the product cost, many researchers have explored techniques to culture microalgae with organic wastewater. By this means, nutrients from wastewaters are transferred to algal biomass, achieving economical microalgae cultivation and efficient wastewater treatment simultaneously. Because of the good performance of Chlorella vulgaris in mixotrophic cultivation, it was chosen as the model organism in this study.Monosodium glutamate (MSG) as a flavor enhancer is extensively used in food products throughout east and south-east Asia. The MSG production in China accounts for about half of world’s total output. After extraction of MSG from fermentation liquor the residual dark brown wastewater and effluent have high concentrations of COD, NH3-N, sulfate and a strong acidity. Without reasonable treatment the monosodium glutamate wastewater (MSGW) would cause serious pollution to the environment and damage to the ecology. As MSGW contains abundant nutrient substance, it could be feasible to reuse these organic substances using ecotechnological methods. The main works of this study were as follows:This paper seeks to evaluate the feasibility of growing Chlorella vulgaris with MSGW and assess the influence of MSGW concentration on the biomass productivity and biochemical compositions. The MSGW diluted in different concentrations was prepared for microalga cultivation. C. vulgar is growth was greatly promoted with MSGW compared with the inorganic BG11medium. C. vulgaris obtained the maximum biomass concentration (1.02g/L) and biomass productivity (61.47mg/L-d) with100-time diluted MSGW. The harvested biomass was rich in protein (36.01-50.64%) and low in lipid (13.47-25.4%) and carbohydrate (8.94-20.1%). The protein nutritional quality and unsaturated fatty acids content of algal increased significantly with diluted MSGW. These results indicated that the MSGW is a feasible alternative for mass cultivation of C. vulgaris.Light is one of the most important factors affecting microalgae growth and biochemical composition. The influence of illumination intensity on the biomass productivity and main composition of Chlorella vulgaris cultivated in diluted MSGW was investigated in laboratory. The Chlorella vulgaris was cultivated aseptically in100-fold diluted MSGW at four continuous illumination intensities (0,30,90,150,200and300μ mol/m2-s) at25℃. The growth of Chlorella vulgaris was stimulated greatly by the increasing of illumination intensity. Under150μ molm-2s-1, the microalgae obtained the maximum biomass concentration (1.458g/L) at the7th day and the greatest average specific growth rate (0.79d-1) of the first7days culture. The lipid contents under0,30,90and150μ molm-2s-1were12.6%,17.7%,16.9%,30.5%,21.4%and23.6%, respectively. The effects of illumination intensities on the contents of protein and carbohydrate were adverse.After microalgae harvest, the residule medium still contained abundant of nutrients, and high. If it is directly used to dilute the monosodium glutamate wastewater without treatment, that would lead to higher chromaticity and turbidity of the medium, blocking the light transmission. As a resoult the growth of microalgae will be negatively affected. In order to reduce the content of organic matter and decrease the chromaticity and turbidity of wastewater at the same time, the residule medium was excited to be treated by biological technology. We used two kinds of filters to conduct a immobilized biosystem. After inoculation with activated sludge and biofilm formation in the following 5days, the treatment efficiency of the immobilized biosystem on sewage was very well. The removal rate of COD, TN reached90%,50%respectively. During the actual operation process, we added two kinds of denitrifiers to the immobilized biosystem to enhance the contaminant removal. After46h the nitrogen removal was enhanced, the accumulation of nitrate during treatment was reduced. The chromaticity and turbidity of the effluent were10PCU,5NTU, respectively. It could be reused as water resource to dilutted the MSGW for microalgae cultivation. |
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