Performance of a membrane-coupled high-rate algal pond for urban wastewater treatment at demonstration scale

Abstract

The objective of this study was to evaluate the performance of an outdoor membrane-coupled high-rate algal pond equipped with industrial-scale membranes for treating urban wastewater. Decoupling biomass retention time (BRT) and hydraulic retention time (HRT) by membrane filtration resulted in improved process efficiencies, with higher biomass productivities and nutrient removal rates when operating at low HRTs. At 6 days of BRT, biomass productivity increased from 30 to 66 and to 95 g·m−3·d−1 when operating at HRTs of 6, 4 and 2.5 days, respectively. The corresponding nitrogen removal rates were 4, 8 and 11 g N·m−3·d−1 and the phosphorous removal rates were 0.5, 1.3 and 1.6 g P·m−3·d−1. The system was operated keeping moderate specific air demands (0.25 m3·m−2·h−1), resulting in reasonable operating and maintenance costs (€0.04 per m3) and energy requirements (0.29 kWh per m3). The produced water was free of pathogens and could be directly used for reusing purposes.