Sludge from wastewater treatment plants

Primary settling of suspended solids from the sewage (Primary sludge)
Activated sludge from the biological treatment (Secondary sludge)

Finally, for every 120 g of treated COD, or 1 person’s equivalent, 60 g of suspended solids in the form of sludge is being produced. At the same time, sewage treatment is a high energy consuming process.

In the past the produced sludge, rich of fertilizing elements, was used in the agriculture. Recently a certain number of undesirable compounds were found in the sludge (heavy metals, organic trace elements and residues of medicines), causing certain countries like Switzerland to prohibit sludge spreading in the agriculture. In these cases the sludge is being eliminated (incineration, wet oxidation, ..)

In countries where the use in agriculture of sludge from sewage plants is still allowed, the quality criteria are very strict.

Sludge digestion is a solution that has been used for decades to reduce the quantity of suspended solids in the sludge and to stabilise the remaining organic matter. Today, thanks to an improved control of the operational conditions (pre-thickening of the sludge, mixing of the digester, etc..) the digestion process can be optimised for energy production : up to 50% of the STPs consumption. On the other hand, the development of new technologies to enhance the sludge digestibility (thermolyse, ultra-sound, micro-crushing) allows even more the reduction of residual quantities and maximisation of the energy production (up to 30 – 100%).

Our contribution:

Advice regarding the set-up of an optimised sludge treatment process
Audits concerning the operation of existing digestion units
Advice regarding the optimisation of the operation
Set-up and execution of pilot research for the validation of new technologies (*)
Technical-economical feasibility studies
Comparative Eco Balance (Life Cycle Analysis) for the different processes (*)
Assistance during the realisation
Performance validation

EREP has built a tool for the energetic performance diagnostic on anaerobic process in WWTP.

> Download (Only French version)

> Information about sludge anaerobic treatment in WWTP (Only French version)

(*) In collaboration with local partners or specialists if the case arises