BIOSOLIDS LAND APPLICATION IN FRANCE: A COMPARATIVE STUDY WITH FERTILISERS FOR THE EFFECT ON PLANTS AND SOILS

This study looks at the behaviour of metal trace elements contained in sludges and fertilizers, when they are mixed with a clay soil. It has been made using plant containers, with three urban residual sludges and one industrial sludge, plus a fertilizer, placed in a plant house with controlled temperature and humidity. Some of the pots have been seeded with ryegrass and compared to controls.The addition of biosolids has increased the production of ryegrass plant matter and reduced its water consumption. The roots, have absorbed greater quantities of metal trace elements than the above ground parts, and blocked their transfer. No significant differences have been observed between the mixtures with or without biosolids, except for the industrial one which has induced higher levels. The flux of trace metal elements brought in by the biosolids has not produced a significant rise in the initial stock of soil metals.