The effect of hydraulic retention time on microalgae-based activated sludge process for Wupa sewage treatment plant, Nigeria

This study evaluated the efficiency of microalgae activated sludge (MAAS) for wastewater treatment by investigating the influence of hydraulic retention time (HRT) on MAAS using batch regime pilot scale photobioreactors at Wupa Wastewater Treatment Plant. The outcome of the study showed that MAAS has a comparably high wastewater treatment performance in comparison with the current Wupa Wastewater Treatment Plant (WWTPA) activated sludge (AS) method and is capable of treating wastewater to the defined Nigerian effluent standards. It was further revealed that treatment performance for most parameters were optimal from HRT₃ (6-day hydraulic retention time). Precisely, total nitrogen (TN), total phosphorus (TP), and BOD₅ had highest removal efficiency at HRT₃ with average total removal of 81.36%, 91.77% and 87.04% respectively. Correspondingly, the average percentage DO increment peaked at HRT₃ with a value of 269.7%. In addition, there was a general deterioration of SVI with increasing HRT, particularly after HRT₂ (4-day HRT). Notably, SVI₃₀ was significantly good at HRT₁ and HRT₂ with SVI values of 48.6 ml/g and 105.52 ml/g; however, from HRT₃ down to HRT₉, the SVI₃₀ became remarkably increases greater than that of HRT₁ and HRT₂, with values ranging from 685.61 to 1832.46 ml/g, which indicates a badly bulking sludge. The MAAS system is recommended as an attractive alternative to the conventional AS wastewater treatment in Nigeria and by extension West African subregion.