Abstract
BackgroundMicroalgae as a viable biodiesel feedstock show great potential to approach the challenges of energy shortage and environment pollution, but their economic feasibility was seriously hampered by high production cost. Thus, it is in urgent need to reduce the cost of cultivation and improve the biomass and lipid production of microalgae. In this work, anaerobic digestion effluent from cattle manure combined with municipal wastewater was used as a cost-effective medium for cultivating microalgae and expected to obtain high biomass. The pretreatment of anaerobic digested effluent containing dilution rate, sterilization and nutrient optimization was investigated. Then, initial pH and light intensity for algal growth, lipid production and wastewater purification were optimized in this study.ResultsScenedesmus sp. could grow rapidly in 10% anaerobic digestion effluent from cattle manure combined with secondary sedimentation tank effluent without sterilization. Optimum nutrient additives for higher biomass were as follows: glucose 10 g/L, NaNO3 0.3 g/L, K2HPO4·3H2O 0.01 g/L, MgSO4·7H2O 0.075 g/L and trace element A5 solution 1 mL/L. Biomass of 4.65 g/L and lipid productivity of 81.90 mg/L/day were achieved during 7-day cultivation accompanying over 90% of COD, NO3−-N, NH4+-N, and 79–88% of PO43−-P removal with optimized initial pH of 7.0 and light intensity of 5000 l×. The FAME profile in ADEC growth medium consisted in saturated (39.48%) and monounsaturated (60.52%) fatty acids with the 16- to 18-chain-length fatty acids constituting over 98% of total FAME.ConclusionsThis study proves the potential of anaerobic digested effluent combined with municipal wastewater for microalgae culture, and provides an effective avenue for simultaneous microalgal lipid production and treatment of two kinds of wastewater.
Highlights
Microalgae as a viable biodiesel feedstock show great potential to approach the challenges of energy shortage and environment pollution, but their economic feasibility was seriously hampered by high production cost
The exponential growth period of microalgae in 0%, 5% and 10% anaerobic digested effluent from cattle manure (ADEC) basal medium lasted for 4 days, which was 1 day longer than that in 20% and 30% ADEC basal medium (Fig. 1a)
The biomass concentration of Scenedesmus sp. cultured in BG-11 medium was 3.50 g/L, while that in the medium containing 30% of ADEC was 2.29 g/L. This observation can be largely attributed to nutrients differences resulted from dilution ratio with modified BG-11 medium, which led to the inhibition of high concentration indicating that ADEC may not completely replace the nutrients in modified BG-11 medium
Summary
Microalgae as a viable biodiesel feedstock show great potential to approach the challenges of energy shortage and environment pollution, but their economic feasibility was seriously hampered by high production cost. It is in urgent need to reduce the cost of cultivation and improve the biomass and lipid production of microalgae. Anaerobic digestion effluent from cattle manure combined with municipal wastewater was used as a cost-effective medium for cultivating microalgae and expected to obtain high biomass. Due to over-reliance on fossil fuels, energy shortage and environmental pollution have become global issues In this context, the search for alternative, sustainable and green fuels such as biodiesel has become highly pronounced [1,2,3]. With the increase of biogas production, the large quantities of anaerobic digested effluent (ADE) would produce disastrous influence on the surrounding environment
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