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Blend optimization and reagent consumption reduction: development of a pre-industrial prototype based on twin-screw extruder principle for sewage sludge liming – OptiChaux

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Submission summary

Annual French sewage sludge production is around 1.1 million of tons of dry matter. About 60% are used in agriculture. Before spreading, lime is usually added to sludges in order to stabilize them. This process allows olfactory nuisance decrease and fermenting processes reduction. Otherwise, such advantages only happen when the blend between sludge and lime is subtle. If not, there are areas of sludge with no lime that can start fermenting again. However, in practice, blends remain rough: to overcome this heterogeneity, professionals of sludge treatment are used to overdosing lime, its final concentration sometimes being twice. As a consequence, this overconsumption of lime leads to functioning costs and volumes increase and also to premature saturation of storage areas.
In order to optimise lime dispersion and to obtain a homogeneous blend while reducing its dosage, the Cemagref developed a process based on twin-screw extruder principle and patented a prototype. The blends are fine and lime consumption is clearly limited: it reaches 17% at laboratory scale while respecting sanitary recommendations. In industrial conditions, the goal is to reach about 20% (per dry content) of lime, which is half the average theoretical quantity. At a national scale, the saving is around 1 million of Euros, considering that the potential market is evaluated at 2 000 wastewater treatment plants.
This project aims at developing and producing a mobile demonstrator, less elaborated but as efficient as a corotary twin-screw extruder and adapted to technical and economical context of wastewater treatment plants. The demonstrator mobility is of major importance because it will allow us to perform in-situ objective comparison, with current tools and using the same lime and sludge as the plant.
To end in this finalised and industry-transferable tool, the project is organized in many steps including: extruder simplification, demonstrator elaboration, specifications, prototype optimization. Such a technical work will be accompanied by an exploitation plan.
At the end of the project, we intend to have a blender related to the final concept in is conception and principle and usable to perform tests and comparative experiments. A technical, environmental and economical evaluation of the different processes will be done, including mechanical and agronomical characteristics of the produced sludge. Moreover, a business plan will have started.

Project coordinator

Monsieur Jean-Christophe BAUDEZ (CENTRE NATIONAL DU MACHINISME AGRICOLE, DU GENIE RURAL, DES EAUX ET DES FORETS - CEMAGREF ANTONY) – jean-christophe.baudez@cemagref.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Cemagref CEMAGREF ANTONY
IFMA INSTITUT FRANCAIS DE MECANIQUE AVANCEE
Cemagref CENTRE NATIONAL DU MACHINISME AGRICOLE, DU GENIE RURAL, DES EAUX ET DES FORETS - CEMAGREF ANTONY

Help of the ANR 251,090 euros
Beginning and duration of the scientific project: January 2012 - 24 Months

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