Biomass production of marine microalga Tetraselmis suecica using biogas and wastewater as nutrients

Abstract

Anaerobic digestion is a suitable method for treating organic wastes and generating biogas. This biogas contains significant amount of CO2 and some other contaminants. The coupling of wastewater treatment with biogas purification using saline microalgae could effectively upgrade biogas (through photosynthetic CO2 fixation) and concurrently remove nutrients from the effluent, while producing valuable algal biomass. In this context, Tetraselmis suecica biomass production with the use of an impurity (CO2) in biogas to supply carbon, and nutrients (nitrogen and phosphorus) from anaerobically-digested piggery effluent (ADPE) was investigated at four operating pH set points (6.5, 7.5, 8.5 and 9.5). Results showed that pH 7.5 produced the optimum conditions for T. suecica growth and biogas-based CO2 removal, with the maximum biomass (59.8 mg L−1 d−1), lipid (25 mg L−1 d−1) and carbohydrate (6.5 mg L-1 d-1) productivities. Under this condition, CO2, total nitrogen and phosphorus removal efficiencies were 94.7%, 96% and 72%, respectively. Furthermore, the results showed no inhibitory effect of dissolved CH4 on the growth of T. suecica at pH 7.5, suggesting the technical feasibility of harnessing marine T. suecica for simultaneous nutrients removal from wastewaters, biogas upgrading, and production of energy-rich algal biomass. This process clearly harnesses anaerobically-digested piggery effluent not only as an asset but also uses an impurity (CO2) in biogas to produce valuable algal biomass.