The use of ultrafiltration membranes made of various polymers in the treatment of oil-emulsion wastewaters

Emulsion wastes contain considerable amounts of mineral oil (up to several score of kg/m³), which hardly undergo biochemical decomposition. Therefore, such wastes cannot be drained into the sewage system without previous treatment, even if they are very diluted. Recently, ultrafiltration (UF) has become appreciated as a suitable method of emulsion waste treatment. It was the aim of this investigation to determine the suitability of polyacrylonitrile (PAN) and poly(vinyl chloride) (PVC) membranes for the UF of spent emulsion wastewaters. Oil-emulsions were ultrafiltered in an apparatus equipped with tubular membranes made in our laboratory. The process was carried out in batch mode at a constant concentration and also in the concentration mode. The efficiency of UF was determined by measuring the flux rate and retention coefficient of oil and chemical oxygen demand (COD). In the first stage of the investigation the UF of model emulsions was carried out at pressures of 0.05-0.3 MPa and a linear velocity of 1-4 m/sec. The flux rate depends on pressure according to the power function (J_v = A_r * (P)^b), while at linear velocity on the linear function (J_v = A + B * u). The obtained permeate does not contain oil and the reduction of COD most often exceeds 99%. The second stage of the investigation comprised the influence of the oil concentration (concentration range 1-20%) on the efficiency and effectiveness of the UF process, on two previously selected membranes at constant pressures, linear velocity, and temperatures. In the third stage of the investigation the actual emulsion was concentrated up to 90% of volume reduction. The flux rate drop depends on the kind of emulsifying oil, and the retention coefficient of oil was 95-99% and COD was -91-98%.