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

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.