water. Wiper blades remove the oil from the drums depositing it into the collection trough where it is pumped to a storage location. Drum skimmers are lightweight and have a high oil recovery rate. The drums can be either smooth or grooved. These types of skimmers are generally used in oil spill response and various industrial operations. Disc Disc skimmers are oleophilic skimmers that use a disc constructed from PVC, steel or aluminum and can be either smooth or grooved. They are capable of recovering high volumes of oil with very little water. They can be equipped with either a single or multiple discs. The discs can be driven by hydraulic, electric, diesel or air motors. DISCOIL technology patented by OCS in the year 1970, is able to recover all the hydrocarbons on the surface of water: 98% of oil with the only 2% of water. It is hydraulic type and able to operate also in classified areas, as ATEX Zone 0, 1 and 2. Non-oleophilic Non-oleophilic skimmers are distinguished by the component used to collect the oil. A metal disc, belt or drum is used in applications where an oleophilic material is inappropriate, such as in a hot alkaline aqueous parts washer. The skimmer is generally turned off whenever there is no oil to skim thus minimizing the amount of water collected. Metal skimming elements are nearly as efficient as oleophilic skimmers when oil is present. Weir Weir skimmers function by allowing the oil floating on the surface of the water to flow over a weir. There are two main types of weir skimmer, those that require the weir height to be manually adjusted and those where the weir height is automatic or self-adjusting. Whilst manually adjusted weir skimmer types can have a lower initial cost, the requirement for regular manual adjustment makes self-adjusting weir types more popular in most applications. Weir skimmers will collect water if operating when oil is no longer present. To overcome this limitation most weir type skimmers contain an automatic water drain on the oil collection tank. See also List of waste-water treatment technologies References Machines Oil spill remediation technologies Water pollution Water technology