Comparison of biological and chemical treatment processes as cost-effective methods for elimination of benzoate in saline wastewaters

•Treatability of hypersaline brine contaminated with benzoic acid was investigated.•Bacterial cultures obtained are suitable for treatment of hypersaline wastewater.•Long-term DOC removal of nearly 98% in continuous flow reactor.•Continuous reactor showed higher process stability than batch or fed-batch systems.•Instant elimination of about 85% of benzoic acid via chemical precipitation.

Eight mixed cultures able to degrade benzoic acid under saline conditions were established and kinetic parameters were determined in batch processes with cultures SBM002 (0.5 g d−1·g oDM−1), SBM003 (0.7 g d−1·g oDM−1) and SBM007 (2.2 g d−1·g oDM−1) showing the highest degradation rates. Treatability of an industrial waste water (12 g L−1 benzoic acid, 82 g L−1 NaCl) by these cultures was proven in a fed-batch system (SBM002 & SBM003) and a continuous flow reactor (SBM007). The performance of the continuous flow reactor was 15-times higher compared to the fed-batch system due to the change of inocula, higher concentration of ammonia as nutrient and less accumulation of possibly toxic catecholic compounds. Average DOC reduction was found to be 98% at 100 g L−1 NaCl and 1.2 g L−1 benzoic acid under these conditions. Pre-treatment of the waste water via chemical precipitation by acidification to pH 3.5 diminished the concentration of benzoic acid to 2.1 g L−1. In a combined chemical-biological process the volume of the bioreactor is reduced to 15% compared to a pure biological process. A comparison of operational costs for these three alternatives is presented.