Effects of CO₂ addition on red led-illuminated microalgal bioreactors treating municipal wastewater

Abstract

Use of red light coupled with carbon dioxide (CO₂) addition can potentially enhance wastewater treatment efficiency in microalgal photobioreactors (PBRs). This study investigated the effects of red light-emitting diodes (LEDs) irradiance and CO₂ addition on mixed microalgal culture, treating municipal wastewater. Batch operation of CO₂-enriched bench-scale microalgal PBRs resulted in high treatment efficiency of municipal wastewater. The PBRs were operated at irradiance ranging from 25 to 234 µmol/s.m² at 12:12 light-dark cycles, treating municipal wastewater containing 83, 50 and 13 mg/L of soluble chemical oxygen demand (SCOD), ammonia and phosphate, respectively, for 19 d. Up to 75% SCOD removal was achieved in a PBR operated at 182 µmol/s.m², with ammonia removal greater than 90%. However, high nitrite concentration in the bioreactors might have limited microbial growth, and affected the PBR performance. This study demonstrated the feasibility for achieving effective municipal wastewater treatment and carbon sequestration, at bench-scale.