The oil-containing condensate from the compressor flows under pressure into the oil-water separator and through a first-stage filter, which is usually a pre-filter. A pressure relief vent usually helps reduce the pressure and avoid turbulence in the oil-water separator tank, allowing the gravitational separation of free oils. First-stage filters typically consist of polypropylene fibers, which adsorb the oil, but not the water. This means that oil droplets will stick to the surface of the polypropylene fibers. Due to their oil-attracting characteristics, these filters are aptly known as “oleophilic” filters. This type of filtration media usually floats on the surface of the water but gets heavier as it adsorbs oil droplets, sinking deeper near the end of its service life. After the first-stage filtration, the condensate flows through the main filters, which include second-stage and sometimes third-stage filters. These filters often rely on activated carbon (or organoclay for stronger emulsions) to purify and “polish” the condensate. In other words, depending on the type and size of the oil-water separator, the condensate will undergo one or two consecutive stages of filtration by activated carbon or organoclay. At the end of this process, the last remaining oil residues in the condensate have been collected. At an ambient temperature of 20 ℃, while there is 1-2 g/m³ of oil in the condensate after the first-stage filtration, there is approximately 2-3 mg/m³ of oil remaining in the condensate after it leaves the oil-water separator. The remaining water is sufficiently free from contaminants and can be safely discharged into the sewer system. The oil-water separator has done its job. And in the end, everybody benefits: The company that does the right thing and avoids fines and, most important of all, protects the environment.