Wastewater Treatment and Biodiesel Production Using Microalgae Cultivated in Municipal Wastewater in Semi-Pilot Scale: Mashhad City Wastewater Case Study

The conventional activated sludge technique in wastewater treatment is an expensive process and suffers from problems such as large amounts of sludge, high energy consumption, high turbidity in the effluent, and not effectively respond to variations in the composition of wastewater. The use of municipal wastewater for microalgae production and its conversion to value-added products such as biodiesel in conjunction with wastewater treatment is a new approach in the wastewater treatment industry. But due to the lack of sufficient information, it has not been extended to a commercial level and most reported activities are at the research level. Specifically, in simultaneous wastewater treatment and microalgae production in a semi-pilot scale very few publications exist. In this study, for the first time, simultaneous wastewater treatment and microalgae production was conducted in a semi-pilot 500 l open pond raceway. The objectives of this study were, on one hand, evaluation of the potential of algae-based treatment for removal of nutrients and COD and, on the other hand, evaluation of the potential of wastewater to produce microalgae in a semi-pilot scale in an open pond raceway. The results indicated that in week-long cultivation, biomass concentration of the broth reached 1.25 g/L with the lipid content of 25%. Harvesting of microalgae using chemical flocculation resulted in 83% recovery of algal solid content. The dried microalgae, during direct acidic transesterification with 76% yield, produced biodiesel with proper fatty acid profile mainly based on Palmitic, Oleic, and Linoleic acids that accounted for 49.5% of total lipid content. The simultaneous wastewater treatment results indicated COD removal of approximately 50% along with total nitrogen removal of 25%, and phosphate removal of 50% was achieved. This study indicated that microalgae production using wastewater is a promising approach to the development of green technology to produce value-added products.