This study investigated the improvement of operating efficiency through physical cleaning and chemical enhanced backwashing (CEB) using ceramic membranes with high permeability and chemical safety compared to organic membranes. The turbidity and DOC (Dissolved Organic Carbon) concentrations were selected to ensure that the degree of contamination was always constant. The operating pressures were fixed at 100, 200, and 300 kPa, and the filtration was terminated when the effluent flow rate decreased to 30% or less from the initial value. After filtration, backwashing was performed at a pressure of 500 kPa using 500 mL backwash water. The membrane was cleaned by dipping in NaOCl, and a new washing technique was proposed for steam washing. In this study, we investigated the recovery rate of membranes by selectively performing physical cleaning and CEB by changing the influent water quality and operating pressure conditions.

Flux recovery through chemical cleaning was investigated using small-sized membrane modules for application in drinking water treatment using river water as feed. This study focused on the causes of membrane fouling by evaluating the cleaning efficiency with several chemical agents at various conditions. Sodium hypochlorite and sodium hydroxide as basic chemicals, and citric acid, nitric acid, oxalic acid, and sulfuric acid as acidic chemicals were used in the experiment. Each chemical was prepared at concentrations of 0.1, 1, 3, and 5%. The mini-module was made of four strings of polyvinylidene fluoride hollow fibers with pore diameter of 0.038 μm. Flux was tested at constant pressure of 0.5 bar. The experiment was operated at the temperature range of 18.1–25.3°C. To compare the effect of water temperature, cleaning test was performed at the range of 0–5°C. Also, the effect of combination of chemicals was tested with cleaning sequences of base–acid–base and acid–base–acid. The surface characteristics of the membrane were also investigated using Scanning electron microscopy and tensile strength analyses. Prior to the chemical cleaning, flux of fouled membrane was measured using deionized water. Duration of chemical cleaning was set at 30 min, 1, 2, and 4 h, and then, the flux was checked. For the control, pure water flux was measured using virgin hollow fiber membranes. Among the chemicals, sodium hypochlorite showed the highest flux recovery rate of 44.0% at 1% concentration. On the other hand, for the acidic chemicals, the highest was only 38.1% recovery rate at 1% oxalic acid. Recovery efficiency increased as the concentration of chemicals and cleaning time increased. Organic or biofilm was considered as the main foulant as observed from the experimental results. In addition, the cleaning efficiency was better in basic than acidic.

This research was carried out to evaluate the suitable operating condition for both nanofiltration (NF) and reverse osmosis (RO) membranes for the reuse of wastewater effluent from membrane bioreactor (MBR). Various parameters such as pH, conductivity, total dissolved solids, UV₂₅₄, dissolved organic carbon, total nitrogen and total phosphorus were analysed for the permeate from the NF and RO to compare the membrane performance. Batch experiments were conducted using a lab-scale NF and RO systems. Effluent from the MBR system treating synthetic wastewater was used as feed water to NF and RO. Filtration tests were performed at the operating pressure ranging from 0.2 to 1.0 MPa. Flux was measured at every 5 min, and the permeate was collected at the end of each experiment. Although the permeate flux and salt rejection increased in proportion to the operating pressure for NF, the increase in salt rejection was tapered off at a certain range of the operating pressure over 0.6 MPa for RO. As a result, an optimum operating pressure should be considered when using RO for treating the effluent from MBR. On the other hand, a better performance would be expected at higher operating pressure when using NF. The removal rates for various components in the feed slightly decreased by less than 5% as the recovery rate increased from 50 to 80%. Therefore, the optimization of the operating pressure and recovery rate should be considered when NF and RO systems were applied effectively to wastewater reuse purpose.