Among the buildings still to be seen at the Esholt works is the Sludge Disposal Building, later known as the Press House. It was in this building that the most innovative aspect of the new scheme was situated.

128 steam filter presses compressed the sludge, extracting the grease and leaving the remains suitable as fertiliser which could then be sold to farmers. The recovered grease was separated into three grades providing a variety of uses from railway axle grease to paint and polish.

Esholt Sludge Disposal Building in 1997 (Photo: Breedge Garnett)

The sewage works had its own laboratory and research team to investigate new uses for the grease extracts, resulting in a number of branded products for both home and export markets. Paint produced from one of the by-products was used to brighten up council houses across the district as well as Esholt Hall.

By 1949 the income from sales - over £3 million since 1900 - was meeting all the costs of operating the plant. Bradford was one of the few disposal authorities making a profit from its activities, at last proving that "where there's muck there's brass."

However, the continued success of the Esholt marketing operations depended on one factor - Bradford's woollen textile trade. Bradford's textile industry is now near to extinction and the Sludge Disposal Building is derelict but much of the Esholt complex is still in operation, continuing to benefit the city.

When looking for signs of Bradford's cultural and industrial heritage it is usual to begin among the mills of Little Germany and take in the gothic splendour of City Hall but it would be a mistake to forget the humble sewage works which, in a sense, made it all possible.

If you are digging deep into West Yorkshire's hidden history and would like to share your findings then please email us at: westyorkshire@bbc.co.uk