Application of polypropylene microfiltration membranes for separation of wastewater from car wash

Abstract

In the final stage of washing the car is waxed and rinsed with demineralized water, however, at an initial stage reusing treated effluents as process water is possible. In the current work, the application of microfiltration (MF) polypropylene (PP) membranes for treatment of carwash wastewater was investigated. To compare the transport properties, more hydrophobic PTFE capillary membranes were also used. The examined process is restricted by the fouling phenomenon, which has been thoroughly studied by filtering both the synthetic and real wastewaters. The use of different types of foaming agents and hydrowaxes, allowed to found that the membranes fouling was caused not only by the impurities removed from the car, but also by the mixtures of commercial washing agents. As a result, the permeate flux was quickly reduced, to a level of 100–200 LHM for PP membrane and to 50–150 LHM for PTFE membrane (TMP = 0.05 MPa). Regardless of the degree of feed contamination, the clean permeate with turbidity of 0.2–0.8 NTU was obtained. In the case PTFE membrane, the permeate turbidity was at a level of 2–3 NTU. The tested wastewaters (5–100 NTU) contained the particles with the size in the range of 0.1–400 μm. The removal of larger particles by prefiltration was found to increase the membranes fouling. It has been noted that rinsing the modules with water was not effective. Nevertheless, the membranes were cleaned using alkaline solutions (pH = 11.5–12.0) used at the car wash station to remove insects and to wash the wheel. This procedure was less effective for PTFE membranes, which experienced significantly greater irreversible fouling. It has been shown that the PP membranes used, in addition to removing turbidity, ensured the retention of Escherichia coli in almost 100%.