Performance evaluation of pilot scale ion exchange membrane bioreactor for nitrate removal from secondary effluent

Eutrophication, driven by excessive nutrient concentrations in water bodies, is a critical global environmental issue affecting water quality, ecosystems, and human health. Discharging nutrient-rich secondary effluents from municipal wastewater treatment plants exacerbates this problem. This study aimed to assess the effectiveness of a pilot-scale Ion Exchange Membrane Bioreactor (IEMB) in removing nitrate from secondary treated effluent. The process involved Donnan dialysis (DD) followed by heterotrophic denitrification in an anoxic fixed bed bioreactor (FBBR). DD process demonstrated an efficiency of over 75 % when nitrate was externally spiked in the secondary treated effluent and over 90 % without spiking, reaching final concentrations below 5.65 mg NO₃–N/L and 1.1 mg NO₃–N/L, respectively. Furthermore, denitrification in FBBR was greater than 95 % at C/N ratio of 1.8–2 provided in the form of glycerol at an HRT of 2 h when nitrate was not spiked externally. Though sulphate accumulation occurred in the receiver (bio-side) during DD, denitrification outperformed sulphate reduction, as confirmed by the favourable oxidation-reduction potential (ORP) readings (−50 to −200 mV) in the FBBR reactor. Optimal conditions for nitrate removal, considering chemical and energy consumption, resulted in a cost of $0.237 per cubic meter of treated secondary effluent during continuous operation. A life cycle assessment (LCA) was also conducted to understand the environmental impacts of the IEMB. In light of these findings, IEMB showed a promising potential for tertiary wastewater treatment, providing an economical and sustainable solution for nutrient removal and indirect potable reuse of treated wastewater.