2.2. Structure of the oil-water separation technology
The oil-water separation technology has some structures such as grease trap, coagulation separation, absorption
separation and centrifugation. The structure of the oil-water separation technology uses in the factory named Grease
ECO (Daito Giken Co. Ltd.) is shown in Fig. 2. This equipment has the mechanism of separating and recovering oil
by specific gravity, and the mechanism of controlling and cycling wastewater. Wastewater flowed into this
equipment was so hot about 60 °C that oil and water can be separated easily due to the difference of specific gravity.
Wastewater was prevented from emulsify and then cost reduction was expected.The main unit has two tanks. Wastewater flows into the first tank with controlling flow rate and it separates into
oil-layer (upper) and water-layer (lower) due to the difference of specific gravity. The metallic rolling belt passes
over the surface of the oil-layer and the oil adhered to the belt is scrapped off by the metallic board to an oilcollecting
box. With the control of flow rate, controlling the oil viscosity by the heated metallic board enable the
equipment to recover oil. Wastewater from the first tank flows into the second tank. As it still contains a small
amount of oil, two layers is formed again. However, the oil layer of the second tank is relatively thin compared with
the first tank because most part of oil is recovered at the first tank. At the second tank, the middle layer of
wastewater flows into the outer pipe which has the inlet passage and the thin oil layer within the outer pipe
overflows into the inner pipe.
At the second tank, three layers are formed. The upper layer is oil which flows from the first tank and leave to
come to the surface. The lower layer is composed by the heavy contaminants except oil settled at the bottom. The
middle layer includes wastewater with least amount of oil and contaminants. Then, to obtain water with high purity,
the inlet passage is set at the middle part.
In this way, this equipment separated oil and water without chemical and biological treatment. Using the
difference of specific gravity and controlling flow rate, input energy to drive the machine was very low, 90 W h per
day. And, there were no change of water quality because chemicals were not used at all and there were no seasonal
change of treatment amount and it was easy to control treatment amount because biomaterials were not used at all.