Industrial application of ceramic ultrafiltration membrane in cold-rolling emulsion wastewater treatment

A commercial ZrO2/α-Al2O3 ceramic ultrafiltration (UF) membrane system with a capacity of 24 m3 h−1 and cut off of 20 kDa was used to treat cold-rolling emulsion wastewater (CREW) from an iron and steel industry in Central China. The ceramic membrane exhibited high removal efficiency for oil and chemical oxygen demand (COD), with an average removal rate of 99.88% and 98.41%, respectively, which were better than other reported state-of-the-art ceramic membranes. In order to solve the problems of membrane fouling and low permeation flux in the treatment of CREW, the control strategies were proposed. The results showed that the membrane fouling can be mitigated by controlling the feed concentration in circulation tank, increasing the cross-flow velocity, and proper chemical cleaning. The membrane fouling mechanism revealed that the experimental data were well described by the combined model of cake filtration and pore blocking at low cross-flow velocity (4.0–4.3 m s−1). At high cross-flow velocity (5.2 m s−1), the pore blocking models fit the data well. After optimizing the process operation parameters, the continuous operation time of the UF membrane was prolonged by 1.5–2 times, the cleaning times were reduced by 40%. The total operating cost of this system is about $3.01/m3, which is cheaper than the conventional treatment process. In addition, the service life of the ceramic membrane tube was greatly extended to more than 8 years, thus saving the cost of replacement. These results indicate that the process is an economical and efficient method in the treatment of CREW.