Purification of Oil Contaminated Wastewater Using Sri Lankan Vein Graphite

Abstract

Oil contaminated wastewater comes from variety of sources such as crude oil production, oilrefinery, petrochemical industry, metal processing, lubricants, cooling agents, car washing,and restaurants, etc. Oil is a highly visible pollutant and it reduces the levels of dissolvedoxygen in water and increases the level of toxic hydrocarbons. Therefor it affects the aquaticlife and water environment.Water and oil cannot be easily separated from oil-water mixtures, as oil exists in droplets inthe oil-water mixture. Oil droplets which are greater than or equal to 150 microns is classifiedas free oil while oil droplets with size ranging between 20 and 150 microns are classified asdispersed oil mixture. Emulsified oil mixtures are oil-water mixtures with droplets smallerthan 20 microns and oil-water mixture with droplet sizes smaller than 5 microns are classifiedas soluble oil mixtures.High purity vein graphite available in Sri Lanka is well renowned for electrical conductivityand lubricity. Beside it also has higher adsorption capacity. In this study, vein graphite ofdifferent particle sizes (<65, 65-125, 125-150 and 150-500μm) with two purity grades (99+%and 95%) were used to treat oil-water mixtures (motor engine oil with distilled water) similarto service station waste water of different concentrations of oil.Minimum amount of graphite (weight) required to completely separate oil from water wasmeasured in each treatment. Most effective particle size of graphite for this treatment wasfound to be in the range of 125-150 μm. Oil separation capacity of high purity graphite (99+%) and less pure (95%) graphite was found to be similar to each other. Maximumconcentration of oil that can be treated with this method was found to be 400%. Final oilconcentrations of all samples treated with graphite were measured and the efficiency of thetreatment was found to be 99.98%.Keywords: Natural vein graphite, Absorption capacity, Waste water, Hydrocarbon