Effective factors in the treatment of kerosene-water emulsion by using UF membranes.

The effects of different parameters including membrane type (regenerated cellulose and polysulphone), transmembrane pressure (TMP), the content of oil in the feed, the flow velocity of the feed and pH on the ultrafiltration of an emulsion of kerosene in water were studied. It was found that the important factors affecting ultrafiltration were, in order, membrane type, pressure and oil concentration. The greatest flux at the optimum conditions here of 3 bar, an oil content of 3% (v/v) and with membrane type C30F was predicted as 108 L/(m(2)h) that was within the range of the confidence limit of the measured value of 106 L/(m(2)h). The normalised FTIR results of the virgin cellulosic membranes C30F and C100F showed more abundant OH groups. The bigger number of OH groups implies a greater hydrophilicity. The larger observed flux in the C30F is related to a higher number of pores as well (surface porosity) compared with the C100F membrane. In the "polarised regime" from 3 bar upwards, flux was independent of pressure for all membranes and was assumed to be determined by the back diffusion transport. Despite the fact that both the PS100H and C100F membranes had the same cut-off (100 kg/mol), the hydrophilic C100F showed a superior permeate flux. The strongest drop of flux with time due to oil fouling was observed for the C100F although it was hydrophilic. In the case of the PS100H, both FTIR and SEM showed that cake layer formation was not the cause of fouling. Meanwhile the SEM and FTIR results of fouled C100F provided evidence of adsorptive and gel formation fouling.

Experimental aspects of ultrasonically enhanced cross-flow membrane filtration of industrial wastewater.

Ultrasound based on-line cleaning for membrane filtration of industrial wastewater was studied. An ultrasonic transducer was assembled in the membrane module in order to get an efficient cleaning of membranes in fouling conditions. The focus of the studies was on the effects of the ultrasound propagation direction and frequency as well as the transmembrane pressure. The more open the membrane was the easier the membrane became plugged by wastewater colloids, when the ultrasound propagation direction was from the feed flow side of the membrane. If the membrane was tight enough, the ultrasound irradiated from the feed side of the membrane increased the flux significantly. However, in the circumstances studied, the power intensity needed during filtration was so high that the membranes eroded gradually at some spots of the membrane surface. It was discovered that the ultrasonic field produced by the used transducers was uneven in pressurised conditions. On the other hand, the ultrasound treatment at atmospheric pressure during an intermission pause in filtration turned out to be an efficient and, at the same time, a gentle method in membrane cleaning. The input power of 120 W (power intensity of 1.1 W/cm2) for a few seconds was sufficient for cleaning. The flux improvement was significant when using a frequency of 27 kHz but only minor when using 200 kHz.

Closing pulp and paper mill water circuits with membrane filtration.

In this study membrane filtration, ultrafiltration, and nanofiltration alone and as part of hybrid processes are considered as means to purify pulp and paper mill process waters suitable for reuse. Thermophilic aerobic biological treatment, pH adjustment, flocculation, and ozonation were tested as pretreatment methods on pilot or on laboratory scale. The aim was to increase flux and reduce fouling by various pretreatment steps and, thus, increase the competitiveness of the membrane process. The results were also evaluated by comparing the benefits obtained against the costs. It was discovered that benefits could be obtained with all the pretreatments tried. Thermophilic aerobic biology assisted in the removal of organic material and increased flux significantly, but the costs were the highest. The most cost-effective processes, however, seem to be pH-adjusted nanofiltration and flocculation nanofiltration hybrid processes, which is understandable because of their significantly lower investment costs compared to, for example, those of biological process. The pH adjustment increased the electrostatic repulsion between negatively charged solutes and membrane, thereby increasing the flux. Flocculation removed the foulants effectively from the feed and it both increased flux and reduced fouling. Yet, many noteworthy benefits were obtained also with ultrafiltration and ozonation. All of the hybrid processes tested could be applied at various points of the water circuit of an integrated pulp and paper mill for purification purposes. The eventual superiority and cost-effectiveness of the applied process remains to be determined case by case.