Abstract

Biological systems combining microalgae and bacteria have been identified as a system with great potential to provide sustainable sanitation solutions. This consortium has been conceived to be normally implemented in the form of high-rate algal-bacteria ponds (HRABP). However, these systems face limitations, associated with effluent clarification and limited loads. Application of membrane filtration to induce biomass retention and effluent clarification have been identified as way to overcome such constraints. However, the effects of decoupling solid retention time (SRT) from hydraulic retention time (HRT) are complex and sometimes difficult to determine or predict. In this study, a model (M-ALBA) was used to predict the performance of a membrane-assisted HRABP. M-ALBA represents an extension of the previously validated ALBA model, by incorporating a compartment providing membrane separation. M-ALBA considers the action of microalgae, heterotrophic bacteria, and nitrifying bacteria (ammonium oxidizers and nitrite oxidizers), including 34 state variables, 19 biological processes and gas-liquid mass transfer of O2, CO2, and NH3. Experimental data from previous study were used to evaluate the model accuracy. Different scenarios were simulated and analysed, using mass balances, considering SRT and HRT in the ranges 4.5–22.5 and 0.5–4.5 days, respectively. Results show how decoupling SRT from HRT improves effluent quality, by increasing nitrogen removal, while avoiding ammonia volatilization. Additionally, it allows operation at lower HRT values, achieving the best performance at HRT 1.5 days. The results obtained in this study contributed to a better understanding of the complex microalgae-bacteria dynamics in membrane-assisted HRABPs.