| With the rapidly increasing global energy demands and fossil fuel crisis, more attention has been paid to the production of alternative energy sources in the recent past. Microalgae is one of the most potentially viable energy sources of the third generation biofuel, which could be used as an alternative renewable source of fuel to partially replace fossil fuels in the future. Microalgae can utilize organic carbon, inorganic nitrogen and phosphate contents in wastewater to generate biomass suitable for biodiesel conversion. Large quantities of untreated anaerobic digestion wastewater resulting from the recent expansions in agricultural productions, as well as the increase in the number of biogas plants, has become one of the major environmental concerns. Therefore, integration of anaerobic digestion wastewater treatment and algae biomass production could be one of viable ways to reduce the risk of nitrogen and phosphorus pollutions from anaerobic digestion.Major objectives of current research were as follows:(i) isolated a new species of microalgae from wild in order to promote biomass production and figured out their optimal growth conditions;(ii) cultured those species in diluted anaerobic digestion wastewater using batch and fed-batch cultivation processes in order to improve biomass production, and also increased the amount of nutrients removed therefrom. Five novel strains of unicellular green algae were isolated from freshwater samples collected from20locations in China. The morphological and genomic identification of this strain was carried out using18s rRNA and ITS1analysis, and all of those strains were found to have a close relationship with Desmodesmus sp. The characterization of biomass of five selected strains under autotrophic conditions was carried out.The two strains, Desmodesmus EJ13-4and EJ15-2, achieved dry cell weights of0.620and0.621g/L, respectively after14days of cultivation, while their lipid content reached24.1%and23.9%(mainly the fatty acid methyl esters (FAMEs) with C16-C18).Environmental factors for cultivation of Desmodesmus EJ13-4and EJ15-2were optimized using response surface methodology (RSM). The optimal biomass of Desmodesmus EJ13-4was0.667g/L under24℃,120umol/(m2-s) and15:9(day:night). The optimal temperature, light intensity and photo-period (day/night cycle) for Desmodesmus EJ15-2that resulted in a relatively high biomass production (up to0.741g/L) were30℃,98umol/(m2·s) and14:10(day:night), respectively.Three levels of initial anaerobic digestion wastewater dilution ratio (diluted40times,20times and10times) were used in this study. Desmodesmus EJ13-4and EJ15-2grew well in anaerobic digestion wastewater and the highest biomass production after14days were0.427and0.443g/L respectively. Moreover, they could remove77.7%-86.5%of total nitrogen (TN),89.6%-100%of ammonia nitrogen (NH4-N) and100%of phosphate (PO4-P) from dulited anaerobic digestion wastewater. Results indicated that diluted20times anaerobic digestion wastewater was an optimal dilution for Desmodesmus sp. due to the resultant high biomass concentration.Desmodesmus sp. was cultured in anaerobic digestion wastewater for nutrients removal and biomass production, and the results were compared with both fed-batch and batch cultivations. The Desmodesmus sp. EJ13-4was able to remove6.363,5.981and0.195mg/L/d of TN, NH4-N and PO4-P respectively after40days of fed-batch cultivation while biomass concentration reached1.048g/L. As with Desmodesmus sp. EJ15-2, the removed amount of TN, NH4-N and PO4-P were5.904,6.706and0.161mg/L/d respectively, while the biomass concentration peaked at1.039g/L. When compared to batch experiments, the amount of nutrients removed and the biomass production in fed-batch increased twice and three times respectively. |
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