Proceedings

Sewage sludge disposal is an increasing issue in all the European countries. The recycling in agriculture, provided that sewage sludge is human health and environment friendly, is encouraged by the European commission. In fact this disposal route leads to the recycling of valuable plants nutrients (N and P) and participates to the maintenance of the organic matter level in European soils. Nevertheless, some European countries promote sewage sludge incineration. The reduction of the water content of sludge after dewatering, in other words the improvement of the sludge dewaterability is beneficial to both disposal routes. The main objective of the present R&D was to assess if the conditioning of sewage by adding an organic flocculants/ lime based product association, could improve its dewaterability. Another issue tackled here, was the effect of this new conditioning process, on the characteristics of both dewatered sludge and filtrate.

The dewatering of sewage sludge conditioned by adding an organic flocculants/ lime based product was studied upstream a centrifuge, a belt filter and a filter press. The effect of the nature of the lime-based product and of its dose on the total solids of the dewatered sludge and on the PO4 3- content of the filtrates was monitored during these industrial trials.

The results obtain in the course of the trials with the centrifuge confirmed the few results already published, in term of sludge quantity and phosphate reduction. The trials conducted on the belt-filter for more than one year showed a reduction by around 10% of the dewatered sludge production (no need of a blending equipment) and the easy and secure (no dust) implementation of sludge liming.

KEY WORDS Biosolids, Sludge Quantity reduction, Sanitisation, Stabilisation, Structuration, Stockpilling ability, Agricultural Recycling, Incineration, Composting.