in november 1935, a decision was made to convert the entire works to use the activated sludge system. renewal of the media in the primary and secondary bacteria beds ceased, and by september 1936, both of the media washing plants had been dismantled. railway tracks around the primary beds were removed during 1937. rolling stock on the railway consisted of one steam locomotive and two diesels, bought in 1935 from hudswell clarke. construction of a new sludge digestion plant and two secondary sludge digestion tanks was finished in june 1939, and two new settlement tanks were completed in 1940. five large lagoons were built at flixton in 1941, which could be used to store sludge in an emergency. the "mancunium" sank after hitting a mine in the mersey estuary in january 1941, but all of the crew were rescued. parts of the works were damaged by bombs in march and may 1941 and in january 1942. transport of sludge to the sea was maintained by borrowing the "shieldhall" from glasgow corporation, until a new "mancunium" was built by ferguson bros. of glasgow. it arrived at the works on 27 december 1946.