Sludge Management

Three issues that need to be addressed

Three issues govern the development of new technical solutions: producing safer sludge, in smaller amounts and of better quality.

1- Producing safer sludge :

The issue here is to ensure that organic matter is recycled, but that all environmental and health risks are eliminated.

In order to do this, it is necessary to monitor the whole system :

• collection of wastewater ;
• policing of the network, i.e. control what is allowed to enter the system ;
• certification for sludge production and disposal systems ;
•  development and implementation of processes ;
• their integration within the treatment plant ;
• end use

2- Producing less sludge :

The issue here is to reduce, either partially or totally, the organic matter in the sludge through destruction and/or concentration - either at the beginning or at the end of the process.

3- Producing better quality sludge :

The issue here is to produce re-useable and "odourless" sludge. By limiting the fermentation process, odour can be controlled at all stages - from the treatment plant, through to land application.

Agricultural recycling

Agricultural recycling is possible for raw, limed, composted or dried biosolids (treated sludge.)

• fertilizer (raw biosolids) and lime (limed biosolids) ;
• carbon-based materials (green wastes) which produce humus (composted biosolids) ;
• concentrated fertilizer, possibly supplemented with commercial fertilizers (dried biosolids).

Landfill sites

At landfill sites sludge is mixed with household waste.

The waste decomposes in oxygen-free conditions, resulting in the production of biogas, which can then be used as an energy source (for heating, electricity, etc.)

Destruction by incineration, co-incineration

Thermal oxidization in the gas phase or incineration provides a final treatment for the sludge.

The organic matter in the sludge is destroyed, leaving only a very small quantity of mineralized by-products.

The co-incineration of sludge with household waste results in a synergy between treatment processes and the reuse of different urban wastes.

Hydrothermal Oxidation - a new approach

Hydrothermal Oxidation has been used for over 40 years in the United States. This alternative approach is now beginning to make its presence felt in Europe.

Liquid sludge, is oxidized by wet air (40 bars, 240°C, pure oxygen supply) in order to remove most of the organic components without producing smoke.

With regards to the last two treatment processes, the mineral matter produced by the processes is most often reused by the civil engineering sector for use as underlay for roads, ballast, pre-fabricated concrete, etc.