Subclass : TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE (processes for making harmful chemical substances harmless, or less harmful, by effecting a chemical change in the substances A62D 3/00 ; separation, settling tanks or filter devices  B01D ; special arrangements on waterborne vessels of installations for treating water, waste water or sewage, e.g. for producing fresh water, B63J ; adding materials to water to prevent corrosion C23F ; treating radioactively-contaminated liquids G21F 9/04 )