Oil–Water Emulsion Separation and Cleaning Performance Study by Cross-Flow Membrane Filtration

Oil–water emulsion discharge or reuse is a major problem for the environment and ecological systems. This discharge cannot mix with fresh water, owing to the high oil content, total dissolved solids, and chemical oxygen demand (COD). Membrane separation is a unique process to reprocess oily wastewater. The membrane has additional advantages compared with other commercial processes, such as adsorption, distillation, and centrifugation, for example, less energy requirement, no addition of chemicals, and a reduction of the COD to within permissible limits. Transient flux decline and foulant deposition during the operating time are the main drawbacks of the membrane separation process. Transient flux decline could be minimized by using a cross-flow setup. In a cross-flow filtration unit, the cell consists of a flat sheet comprising a polyamide membrane with pore diameters under the microfiltration range. During experiments, the membrane was first fouled, and the fouled membrane was cleaned using a cleaning agent. The membrane fouling experiment was conducted at a 138-kPa transmembrane pressure (TMP) difference in the laminar flow zone. The membrane cleaning operation was essential to recover the initial hydraulic membrane permeability. Deionized water, the anionic surfactant [i.e., sodium dodecyl sulfate (SDS)], and the chelating agent [i.e., ethylenediaminetetraacetic acid (EDTA)], were used to recover the original flux value. A thorough study was conducted into how the membrane performance was improved with variation of chemical agent doses.