Effect of hydraulic retention time and treated urban wastewater ratio on progressive adaptation of an inoculated microalgae in membrane photobioreactors

Currently, there is a growing concern about water scarcity. The rising demand for wastewater treatment systems that facilitate the reuse of wastewater has resulted in a focus on the use of microalgae in sustainable treatments. These methods not only eliminate nutrients from the wastewater but also produce biomass that can be used to obtain high-value products. This study aimed to observe the effect of different hydraulic retention times (HRTs) and treated urban wastewater (TUWW) percentages on the growth of microalgae biomass and nutrient consumption in membrane photobioreactors. Microalgae biomass growth increases with HRT regardless of the percentage of TUWW. Biomass concentration stabilises at between 40% and 60% TUWW but significantly increases when 100% TUWW is used, resulting in the highest biomass concentrations. As HRT increases, ammonium and total nitrogen consumption also rise. A positive trend in ammonium consumption was observed with increasing TUWW, reaching its peak with 100% TUWW. The optimal conditions for biomass growth and nutrient removal are achieved with a 7-day HRT and 100% TUWW as influent, which was confirmed as optimal with the response surface methodology. [Display omitted] •Microalgae biomass exhibits a positive correlation with HRT.•Microalgae growth increases at wastewater percentages higher than 60%.•A total nitrogen consumption of 23.14 mg N/L was reached for the longest HRT studied.•A phosphates consumption of 4.51 mg PO43−/L was reached for the longest HRT studied.•The optimal operational parameters are an influent 100% of wastewater and a 7-day HRT.