Applicability of mathematical model for biomass production by indigenous microalgae based on cultivation characteristics at different wastewater treatment plants

Abstract

Outdoor biomass production by indigenous microalgae cultivation with treated effluent is strongly and complexly affected by fluctuating environmental conditions and water qualities in wastewater treatment plants (WWTPs), thus, mathematical models are required to discuss production performance. In this study, five-month outdoor cultivations with CO2 addition were conducted in two WWTPs (A and B) to reveal cultivation characteristics and examine the applicability of a previously developed model to different WWTPs. The limiting factor for microalgae growth in the treated effluent was different between WWTPs A (carbon) and B (phosphorus). Suspended solids (88 mg/L) in the culture at WWTP B were significantly lower than those at WWTP A (113 mg/L) due to phosphorus starvation in the culture at WWTP B. Meanwhile, Chlorophyceae dominated throughout the cultivation period at both WWTPs. The repeatability of the cultivation characteristics by the model at the same WWTP in different years was verified. It was revealed that application of the model to a new WWTP is difficult with regard to some coefficients. However, sensitivity analysis to identify the dominant coefficient affecting biomass productivity in the model and modification of the coefficient based on simple cultivation experiments resulted in the model being applicable to the new WWTP.