Year-long performance assessment of an on-site pilot scale (100 L) photobioreactor on nutrient recovery and pathogen removal from urban wastewater using native microalgal consortium

Abstract

The study was carried out as part of the Indo-Dutch collaboration project to ascertain the efficacy of the algal system for the treatment of urban wastewater. The study was done at Barapullah drain in New Delhi, using a pilot-scale (100 L) bubble column microalgae photobioreactor (PBR). The year-long study was intended to find the impact of seasonality coupled with varying hydraulic retention times (HRTs) on the PBR performance in terms of nutrient recovery, microbial contamination reduction, biomass productivity, and theoretical biomethane potential.To begin with, native microalgae consortium was enriched and cultivated in PBR directly on the Barapullah drain wastewater at the drain site. After achieving maximum recovery of nutrients in the batch mode, the PBR was operated in continuous mode at HRTs ranging from 1 to 3 days during summer, while 2–3 days during monsoon, autumn, and winter. The maximum and minimum biomass productivity obtained was 260 mg L−1 d−1 at the HRT of 1 day during summer and 77 mg L−1 d−1 at the HRT of 2 days during winter. At peak overall PBR performance at HRT of 2 days, the nutrient removal rate was 37.2 ± 6.2 mgCOD L−1 d−1, 39.3 ± 6 mgN L−1 d−1, and 4.7 ± 0.7 mgP L−1 d−1. Nearly 5 log removal of total and faecal coliform was obtained during summer and monsoon. However, the overall performance reduced during winters. The natural sedimentation of grown biomass achieved 81–95% of biomass settling at different HRTs. The areal footprint of the PBR is 1.42 m2 KLD−1, which was significantly lower than other pilot-scale microalgal wastewater treatment technologies. The obtained results at this lower HRT (2 days) even under non-optimized process parameters represent vital improvements over earlier reports with significantly higher HRTs. Results thus highlight the feasibility and scalability of the technology.