Caractérisation et traitabilité des sous-produits solides de l'assainissement pluvial

Abstract

Click to increase image sizeClick to decrease image sizeThe expression "sewerage solid by-products" designates all the solids produced by the operation and maintenance of streets and sewer systems, in the framework of an integrated approach of the urban wet weather discharges. As a part of the GARlH A5 research project, a specific study has been carried out in order to characterise the sewerage solid by-products (physico-chemical characteristics) and to assess their treatability (technologies, macro-economy... ) A literature review and a sampling study in Bordeaux have shown that the sewerage solid by-products are mainly mineral, with very low nutrient concentrations in comparison with sludge from waste water treatment plants, and with high pollutants loads, especially heavy metals and hydrocarbons. These solids, whose characteristics are highly variable from one site to another, are presently disposed of in landfills. According to the French law on waste products dated July 13th 1992, the future authorised land fills will only accept "ultimate waste products" after July 1st 2002. The sewerage solid by-products currently removed can not be considered as "ultimate waste products", and to comply with the regulation there will be a need to treat these solids in an attempt to recover as much material as possible for partial reuse. The inventory of the present treatment processes and technologies, by literature review and visits of plants, led to the definition of a typical treatment process with four main steps: screening, hydrocycloning, classification and dewatering. This treatment gives washed sands that can be reused, and by-products that need to be further treated in existing devices. The technical tools are quite well identified, however their performances are up to now not precisely known. A detailedcharacterisation of all by-products generated by the treatment process is also necessary in order to better assess their treatability or reuse.