Performance and membrane fouling characteristics of a combined biofilm and membrane bioreactor for treatment of fluorescent whitening agent wastewater

A full-scale system, composed of one anoxic fixed biofilm reactor, four oxic fixed biofilm reactors and an activated sludge membrane bioreactor, was used to treat heavily organic loaded, high toxic and saline fluorescent whitening agent wastewater. This system was running steady during the experimental period of three months. Treatment performance and membrane fouling characteristics were investigated. The concentrations of chemical oxygen demand (COD), , and total nitrogen (TN) in effluent were 447, 27, 14 and 114 mg L−1, corresponding to the removal rates of 89%, 76%, 68% and 64%, respectively. A series of analyses, including Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, confocal laser scanning microscopy, scanning electron microscopy and protein and polysaccharide concentration measurements, represented that the sludge layer formed on the membrane surface contained both organic and inorganic foulants. Polysaccharides in bound extracellullar polymeric substances in mixed liquor were the main contributor to membrane fouling. Off-line tap water rinsing was proved to be a cost-effective method of fouling control.