Oily Wastewater Treatment

In recent years, large quantities of effluents have been produced by the vegetable oil and catering industries. The latter also discharge considerable amounts of oily wastewater containing animal and/or vegetable oil, inorganic salt and surfactant. If the effluent is discharged untreated, it can cause serious environmental problems due to its high biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Removing oil from wastewater is therefore an important aspect of pollution control.

Conventional treatment techniques include gravity settling, chemical emulsion breaking, coagulation and flocculation. However, these techniques experience various disadvantages e.g. complex operation procedures, the generation of large volumes of sludge and low efficiency in the case of smaller-diameter oil droplets.

The authors investigate the influence of operational parameters - such as feed temperature, transmembrane pressure (TMP) and crossflow velocity (CFV) - on the separation behaviour of the microfiltration (MF) process. To achieve a good balance between flux and rejection, an optimal temperature was found to be between 30 and 40 degrees C. Experiments also demonstrated that CFV and TMP and should be maintained at values of around 4 m/s and 0.15 MPa, respectively.

The MF continuous process was run for 500 min under the optimized conditions. After adding baffle with an overflow in the feed tank, the steady flux was around 90 (L/m2 h) with the concentrated multiple of 16, and the oil concentration in permeate was less than 12 mg/L.

The reverse osmosis (RO) process was adopted to further treat permeate from the MF process, in order to improve the permeate quality. The continuous process was operated for 420 min with a temperature of 20-30 degrees C, transmembrane pressure of 1.3 MPa and crossflow velocity of 3m3/h. The permeate flux was 24 (L/m2 h) and the water recovery rate reached 95%. In the RO permeate the TOC is almost zero, suggesting that the permeate is free of oil. The conductivity of the RO permeate is lower than 50ms/cm. The general properties of the final permeate are comparable to that of tap water.

The results demonstrate that the two stage membranes combining MF and RO provide a feasible and reliable process for the treatment of vegetable oily wastewater.

I observered so many petrochemical plant in which waste water contain various and multigrade oil. For couple of the months I had tacked this problem and found concentration of oil in the waste water flowing out from the menthol plant is higher as compare to the others, that is why I had to consume alway more time in menthol plant to help the technical people to detect concentration of the oil in waste water. regards Kamran Saeed email:kspuri@hotmail.com tele: 00966500193412 Kamran Saeed - 17/03/2010 - 15:07