Long term evaluation of a pilot scale multimodal algal bioprocess for treatment of municipal wastewater

The feasibility of Multimodal Algal-bacterial Bioprocess (MAB) for the treatment of primary clarified municipal wastewater was demonstrated at a pilot-scale MAB system (0.2 m3/d) installed and operated in Corvallis, Oregon, USA for one year. The system consisted of an anaerobic reactor; mixotrophic and phototrophic ponds followed by algal settlers and a final wetland cell (WC). The wastewater treatment performance was monitored weekly over the one-year period in terms of onsite parameters as pH, dissolved oxygen (DO), oxidation reduction potential (ORP), electrical conductivity (EC), total dissolved solids (TDS),turbidity and chemical parameters (COD, Nitrate-N, Amm.-N and reactive phosphorus). Algal biomass production and algal community analysis in the MAB was determined regularly. A continuous improvement in the mean DO (1.57-13.98 mg/L) and ORP (-140 to +86 mV) was observed throughout the study period. Higher mean pH (8.62) and DO (14 mg/L) in the ponds indicated high algal photosynthesis. The pilot-scale system maintained an average low final effluent turbidity (14.2 NTU), TSS (<30 mg/L) and COD concentrations (-78.3 mg/L) and achieved removal of nitrogen as Amm.-N (76%) and Nitrate-N (34%), phosphorus (DRP: 51%) throughout the experimental period. Particularly in summer, the overall treatment performance was high (70% COD removal; 78% Amm.-N removal; 38% Nit.-N removal; 53% DRP removal) owing to high algal-bacterial activity. The community analysis showed a predominance of diatoms and cyanophycean members in the winter and chlorophycean members especially species Chlorella (-80%) during summer. The average biomass productivities (VSS) in the treatment ponds ranged from 6.75 g/m2/d during winter to 11.47 g/m2/d during summer. Overall, the MAB can effectively treat municipal wastewater; produce quality final effluent and algal bioproducts with minimum energy inputs.