Abstract: A method for cleaning industrial wastewater comprising pretreatment of the wastewater stream by intercepting and removing settleable solids prior to subjecting the stream to primary cleaning systems are disclosed. The method of pretreatment comprises pumping wastewater from a collecting reservoir or sewer through a hydrocyclone to separate the stream into an overflow of reduced solids content and an underflow of enhanced solids content. The overflow is directed to a holding tank or forebay of the primary cleaning system. The primary cleaning system comprises a gravity settler, a CPI (corrugated plate interceptor) system or API (American Petroleum Institute) separator for example. The gravity settler is operated to obtain an effluent essentially free of settleable solids and a sludge stream. The underflow with its enhanced solids content is screened to obtain a screened water stream and a sludge of screened solids which is directed to a collection container.