A novel extractive membrane bioreactor for treating biorefractory organic pollutants in the presence of high concentrations of inorganics: application to a synthetic acidic effluent containing high concentrations of chlorophenol and salt

Traditional bioprocesses have difficulties treating biorefractory organic pollutants in waste streams that contain high concentrations of inorganics. A novel hybrid process, combining liquid–liquid extraction and a membrane bioreactor, has been designed to treat such an effluent. To demonstrate the viability of this process, a synthetic wastewater was designed to represent the sort of effluent that often results from the speciality organic chemicals sector. This model effluent contains high concentrations of chlorophenols (CPs) (1000 mg l−1), salts (15% w/w) and has a pH of less than 1. Experimental work was combined with process design to estimate the likely treatment costs for such an effluent. The proposed treatment process has three advantages. 1. The water insoluble solvent serves as a barrier to prevent the salts and acids in the raw wastewater from entering the bioreactor where they are inhibitory. 2. Due to their acidity, CPs are easily extracted from the acidic effluent, leaving a low concentration (<100 mg l−1). They are stripped from the solvent into an alkaline aqueous stripping stream at a moderate concentration. The bioreactor can then be operated at much higher CP concentrations than the stringent regulatory discharge standard of 100 mg l−1. At the higher concentration the biodegradation rate of the CPs increases by over a twenty-fold. 3. Two hydrophilic ceramic membranes effect oil/water (o/w) emulsion separation and biomass separation. These are operated alternately for each purpose in opposing directions. Thus one filtration serves as backflush of the other and vice versa, reducing membrane fouling. This process could also be used for treating other wastewaters containing organic priority pollutants that are either acids or bases.