Remediation of dairy wastewater by Euglena gracilis WZSL mutant and ?-glucan production

According to the concept of circular economy, food industry wastewater should be considered a secondary raw material that could be exploited, thus reducing the resources escaping from the production system. We aimed to assess the circular sustainability of dairy wastewater treatment by evaluating the possibility of transforming it from a cost to a valuable resource. We tested the non-photosynthetic WSZL mutant of Euglena gracilis as a bio-remediating organism for raw dairy wastewater to recover the resources herein present for biomass growth and simultaneously provide a source of paramylon, a high commercial value glucan. This mutant is an obligate osmotroph, which can synthesize paramylon up to 90% of the cell dry weight with the proper carbon source. We tested the mutant on the wastewater produced by a small dairy facility located near Pisa (Italy) using an indoor bench-scale fermenter allowing the alga to grow inside a dialysis tubing immersed in the effluent. We monitored the effluent variation of biochemical oxygen demand (BOD5), soluble chemical oxygen demand (COD), total suspended solids (TSS), ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N), orthophosphate (PO43--P), electric conductivity and pH. The alga can reduce the pollutant concentration to values allowing indirect discharge of the wastewater into public sewage plants and can be therefore considered a promising organism for tertiary treatment of dairy wastewater. The cells produced about 2.6 g L-1 of paramylon from 3.2 g L-1 biomass, an amount greater compared with that produced by batch cultures, confirming the possibility of recovering wastewater resources and transforming them in a high-value product. © 2020, Springer Nature B.V.