Dewatering of sludge

Cellulose – which comes fom toilet paper – is sieved from the raw wastewater (influent) by means of a fine sieve. This reduces the load of solid matter in the subsequent biological wastewater treatment process, thus reducing the energy consumed for biological treatment.

The CADoS research project is seeking to enhance significantly both the water line and the sludge line. The process reduces operational costs in the water line while it also greatly simplifies the processing of sludge. At the same time it creates possibilities for using the separated sieved material as a raw material for biogas and for the production of bioplastics.

Present situation
Wastewater is cleaned with bacteria in the biological treatment process of the Ulrum wastewater treatment plant. The dirt in the wastewater is food for the bacteria. This causes the bacteria mass (sewage sludge) to grow. The surplus sewage sludge is thickened on-site and then taken by tanker trucks to a central processing plant at Garmerwolde in the province of Groningen. This is where the sewage sludge, after bio-fermentation with additives like polymer and iron chloride, is dewatered by a pressure installation. Subsequently, third parties thermally dry the dewatered sludge, after which it is taken by truck to cement furnaces in the south of the Netherlands. The furnaces incinerate the sludge as waste. The residual ash becomes part of the cement. The cement is a raw material for products like paving such as kerbstones and cement bricks.

Cellulose Assisted Dewatering of Sludge (CADoS)
A trial installation will be used at the Ulrum wastewater treatment plant mid-2014, which will reduce the operational costs of the existing treatment process in the water line. Even more important, it will significantly simplify sludge processing:

  • existing processes such as the thickening of sludge will be eliminated;
  • doses of chemicals used for sludge processing will be substantially reduced. The produced sieved material (containing about 40% dry matter) is a raw material that will be transported by road to a raw material customer in the region;
  • the released waste will be reduced in volume closer to source and reused regionally as a raw material. This means fewer transport movements.