As part of the Nereus project, CAPSO has installed new equipment at the Saint-Omer wastewater treatment plant to improve the sludge process and, in particular, to improve the dryness and heap of the sludge. To do this, the feeder pump and its discharge were replaced by the installation of a lime mixer and three conveyor screws. 

The advantages of lime

Lime simplifies the dewatering of organic and mineral sludge by increasing the dry matter content and improving their structure (simplified handling and storage). It stabilises and sanitises sludge in water treatment plants to control odours and add agronomic value. 

Sludge treatment with lime has the following advantages: 

• sludge reduction in order to achieve a better dry matter rate;
• sludge stabilization and hygienisation;
• inerting of heavy metals present in the sludge;
• improvement of sludge characteristics for disposal or subsequent use, such as agricultural recycling, to reduce odour, structure sludge, make it easier to use and increase their agronomic value;
• improvement of the quality of supernatants and filtrates (N, P).

Towards optimization

At the demo site, different lime at different rates were tested to determine which one meets the following regulatory conditions:

• dryness of limed sludge equal or greater than 30%;
• stack holding capacity equal or greater than 1.5m and stack angle greater than 30°.

As a result of this study, the Saint-Omer wastewater treatment plant can now dry its sludge according to regulations and therefore spread it on local fields.