Abstract:
Oil and grease is found in domestic as well as industrial wastewaters. Its removal
is one of the first steps in the treatment of wastewaters from a variety of industries, for
example oil refineries, petrochemical works, steel mills, metal finishing plants, cooking
oil and ghee factories, etc.
This study was undertaken to investigate the removal of oil and grease from
industrial and domestic wastewaters to achieve the National Environmental Quality Standards (NEQS) level of 10 mg/liter. For this purpose the techniques of gravity
separation and Dissolved Air Flotation (DAF) were employed. Research was conducted
in the following two steps.
Removal of oil and grease from synthetic samples by gravity
separation
Step 2 Development of a local Dissolved Air Flotation plant and using it
for the breaking and removal of emulsion from domestic and
industrial wastewater.
Step 1 was carried out with synthetic samples prepared by using lubricating oil,
cooking oil, ghee and a mixture of all the above three. Step 2 was performed on the
original
samples from Attock Oil Refinery (ARL). Murree Brewery and a domestic wastewater
sample.
Step I was carried out to find out the removal efficiencies of oil and grease at
retention times varying from 10 minutes to 2 hours and for different concentrations
ii
varying from 50 mg/liter to 500 mg/liter. A retention time of one hour was found to be sufficient for the separation of all oil concentrations.
In step 2 the samples were treated chemically prior to flotation by the addition of alum and polymer. The purpose of adding alum and polymer was to break the emulsion. The samples were then treated in the Dissolved Air Flotation unit at pressures varyino from 25 psi to 55 psi. A removal efficiency of 85% was achieved at 55 psi.
The results of this study show that free as well as emulsified oil can be effectively removed from the industrial and domestic wastewater by developing a local dissolved air flotation plant by using the parameters found out in this study.
