Comparing treatment methods for oily wastewater

Petroleum products such as oils, greases, and related additives are common components of industrial waste streams. These substances, whether released as a component in effluent or simply dumped on plant premises, can cause serious on-site environmental damage. Separating oils from wastewater is required in most industries. Although large quantities, as used in plant processes, are seldom overlooked, smaller amounts from other plant systems can be. Wastewater from manual washing operations, steam cleaners, and effluent from air compressors are in this second category. All states have laws which regulate the flow of wastewaters to the land or waters, and with some exceptions, the maximum oil content of any water released must not be greater than 10 ppm. A wide variety of devices are available. The equipment can be divided into two general groups depending on their basic operation. Some units separate and collect the oil from the oil/water waste stream. Others remove the water from the oil/water waste stream. Volumetric capacities, technical complexity, and costs of this equipment vary widely. The paper describes skimmer tanks, skimmer-filter units, absorber systems, evaporator systems, centrifuges, chemical clarifiers, membrane filters, and residue disposal.