nature of sewerage network cleaning waste

As it travels through the drainage systems, some of the matter entrained in the urban wastewater and storm water settles onto the floor. Commonly designated «cleaning grit», «cleaning sludge» or «cleaning waste», these sediments comprise waste that can be compared to household or bulky waste together with a mixture of organic matter and grit in extremely variable proportions depending on the type of networks involved.

In the main, there are three ways in which networks can be cleaned: suction using a hydrojet system through gulley holes, cleaning and suction in the large mains, and shovelling from grit chambers.

This grit has an average granulometry that is higher than the grit screened out by plant grit removers. It is also coated with an organic and mineral gangue having an OM content that is lower than that of pre-treatment grit (20% instead of 60% for pre-treatment grit).

The mineral core, i.e. grit, is generated by road and pavement deterioration, various urban sites, road-gritting during winter months and soil erosion etc.

Waste that can be likened neither to purification sludge nor to grit produced by pre-treatment operations.

On average, 10 L · hab^–1·year^–1 (or approximately 18 kg · hab^–1·year^–1) of grit is removed from cleaning waste.