Optimisation of high rate algal ponds performance for post-treatment of upflow anaerobic sludge blanket reactor effluents

Abstract

Upflow anaerobic sludge blanket (UASB) reactors are widely used for wastewater treatment in tropical regions, yet the resulting effluent requires further post-treatment to meet the quality standards for a safe discharge or reuse. This study proposes a novel technology for the post-treatment of effluents from UASB reactors, high rate algal ponds (HRAP). Firstly, experimental data from two pilot HRAP treating the primary effluent from an UASB reactor was used to calibrate a mathematical biokinetic model (BIO_ALGAE). Then, different operational strategies were simulated by varying the HRAP hydraulic retention time (HRT) (4, 6, and 8 days) and footprint, water quality, and bioenergy production, considering a wastewater treatment plant of 10,000 population equivalent. Experimental results showed a removal efficiency of 70% for the chemical oxygen demand, 42% for total suspended-solids, 57% for ammonium nitrogen, and 30% for orthophosphate in the pilot plant. According to the calibrated model output, the quality of the effluent is similar with HRT of 6 and 8 days, but with a HRT of 4 days N removal would be compromised. Bearing in mind that the lower the HRT, the lower the footprint of the wastewater treatment plant, 6 days seems a important trade-off. The findings of this study are promising, presenting a new conception for treating effluents from UASB reactors. This could enhance the quality of wastewater treatment in tropical countries and suggest potential uses for the generated by-products.