Use of a membrane bioreactor for denitrification of brine from an electrodialysis process

Electrodialysis (ED) is an efficient process for the treatment of drinking water with high nitrate concentration. However it achieves only a transfer of pollution by producing concentrated brines. This study demonstrated the feasibility of ED brine denitrification in a membrane bioreactor (MBR). The results showed the high efficiency of the MBR despite the drastic conditions of nitrate concentration, pH and salinity of the ED concentrates. The denitrification kinetics close to 0.01 mgNO3–-N mgVSS–1 h–1 were in agreement with the literature values obtained with usual conditions. Next, the efficiency and performance of the hybrid process to treat ground water contaminated by nitrate was demonstrated in situ at Rodilhan (France). After ED treatment, the nitrate concentration of the treated water remained below the acceptable value (50 mg l–1) and a softening of the treated water was obtained. The membrane bioreactor allowed the almost total destruction of ED concentrate nitrate (99 %) with kinetics close to 0.3 kgNO3–-N kgVSS–1 d–1 and a sludge production of 0.5 gVSS gNO3–.

This study demonstrates the feasibility of the hybrid process combining a continuous separation Table 3 Physico-chemistry parameters of the ground water of Rodilhan (France) before and after ED and MBR treatment ED treatment MBR treatment Ground water pH Temperature, °C Concentration, mg l–1: NO3– NO2– Cl– HCO3– SO42– Na+ Ca2+ Mg2+ Treated water 0.95 7.14 24.7 0.56 7.09 24.5 0.1 0.04 5.5 15.5 EC norms Removal efficiency, % ED concentrate Permeate Removal efficiency, % 3.49 7.11 22.9 2.51 7.37 24.7 0.12 6.8 0.05 46.5 34.5 6.5–8.5 >30.5 • a complete elimination of nitrate by the use of Table 4 Operating conditions and MBR performances EDR concentrate, mg NO3– l–1 Hydraulic residence time, h Solids residence time, d Volumetric loading, gNO3–-N l–1 h–1 Biomass concentration mgVSS l–1 Permeate concentration, mg NO3– l–1 Nitrate removal efficiency, % Specific denitrification rate, mgNO3–-N mgVSS–1 h–1 Sludge production, gVSS gNO3-N–1 a biological denitrification of ED concentrate, • no direct contact between the denitrifying 500–600 0.02–0.03 1–10 0.01 0.5 of nitrate from polluted waters by electodialysis (ED) and their simultaneous biodegradation in a membrane bioreactor (MBR). The results showed that the MBR allowed efficient denitrification of ED concentrates despite the drastic conditions of nitrate concentration, pH and salinity. The denitrification kinetics close to 0.01 mgNO3–-N mgVSS–1 h–1 were in agreement with the literature values obtained with usual conditions [7–10]. Then, the efficiency and performance of the hybrid process to treat ground water contaminated by nitrate resulting from various agricultural and farm activities was demonstrated in situ at Rodilhan (France). The nitrate concentration of the treated water remained below the acceptable value (50 mg l–1) and the ED treatment induced a softening of the treated water. The high efficiency of the membrane bioreactor allowed the almost total destruction of nitrates (99 %) with kinetics close to 0.3 kgNO3–-N kgVSS–1 d–1 and a sludge production of 0.5 gVSS gNO3–-N–1. Despite this sludge production, this hybrid process present several advantages over classical processes: culture and the drinking water, the biological process ensuring only the concentrate denitrification, • a production of softening water ensured by electrodialysis, • a very good quality, ensured by the membrane bioreactor, of the treated concentrate without nitrate and particular compounds.