Technico-economic assessment of membrane filtration as post-treatment of biological denitrification for brackish groundwater

Abstract

This study examines a complementary treatment for denitrified water to improve its bacteriological and physicochemical quality, focusing on turbidity reduction. It combines sugarcane-based heterotrophic denitrification with a post-treatment system using conventional pretreatment (CP) and membrane filtration utilizing microfiltartion (MF) and ultrafiltration (UF) in various options like CP + MF, CP + UF, and CP + MF + UF. An economic assessment of these options is also included. The results demonstrate that sugarcane-based heterotrophic denitrification effectively removes 98 % of nitrates. However, sustaining this high level of efficiency requires careful control of parameters such as substrate availability, pH, and oxygen levels. Furthermore, the analysis of the treatment outcomes reveals that water quality achieved with the different post-treatment configurations includes approximately 94 % turbidity removal and 99 % bacterial reduction for the CP + MF configuration. Both CP + UF and CP + MF + UF configurations achieve around 99 % turbidity removal, with complete bacterial elimination. In terms of cost-effectiveness, the most economical option is CP + MF, with a treatment cost of 0.17$/m³ . The next most cost-effective option, CP + UF, comes at a moderate increase of 0.25$/m³ , providing higher water quality. Finally, the most advanced configuration, CP + MF + UF, delivers the highest water quality but at the highest cost of 0.35$/m³ . However, the study recommends using either MF or UF independently in scenarios where cost-efficiency is a critical consideration, whereas the CP + MF + UF option would only increase investment and operational costs.