Salinity fluctuations in AnMBR. BioXtreme

High and fluctuating salinity are becoming more common in industrial wastewaters, particularly when striving for closing water loops. Owing to the challenge for anaerobic reactor systems, this study investigated the impact of high and fluctuating salinity on the anaerobic conversion capacity and membrane filtration in an anaerobic membrane bioreactor treating phenol-containing wastewater. The reactor was operated during 180 days in a range of sodium concentrations from 8 to 37 gNa+.L-1. COD and phenol removal efficiencies of about of 99% were achieved at sodium concentrations below 26 gNa+.L-1 under step-wise salinity changes. A maximum phenol conversion rate of 113.8 mgPh.L-1.d-1 was determined. At 37 gNa+.L-1, phenol and COD removal efficiency decreased to 86% and 82% respectively, whereas the biomass specific methanogenic activity was 0.12±0.05 gCOD-CH4.gVSS-1.d-1. Concomitantly, 84% of cells with compromised membranes and a 99% biomass stress index were observed. Moreover, as a result of the applied large salinity fluctuations, phenol and COD removal efficiencies were reduced transiently to a minimum of 42% and 28%, respectively. Likewise, the particle size decreased from 65.6 μm to 4.3 μm. Transmembrane pressures above 400 mbar and membrane resistance to filtration over 25 x 1012 m-1 were observed. Concurrently, capillary suction time increased by a factor of three (32.5 s.L.gTSS−1) and biomass exhibited low relative hydrophobicity (11.4 ± 4.7%). The cake layer resistance to filtration contributed with 85% of the total resistance. The microbial community was dominated by bacteria belonging to Clostridiales and archaea by Methanosarcinales and Methanobacteriales order. A salinity change larger than 14 gNa+L-1 reduced the microbial richness and diversity substantially.