The UK produces c.1.2 million tons of sludge p.a. with disposal costs of £50-200 per ton. With low cost disposal routes becoming excluded and difficulties of recycling liquid sludge to land, there is a strong drive to reduce sludge volumes. In addition to process changes to minimise sludge production, improved sludge dewatering has the potential to deliver substantial cost benefits.
Control of dewatering is usually manual and chemical dosing without online monitoring leads to sub-optimal dewatering or excess chemical addition. Effective online control/monitoring of dewatering also provides a good control stage in a HACCP analysis (Hazard Analysis and Critical Control Points) for compliance with legislation on use of sludge in agriculture.
The project researched possible control strategies including measurements on the sludge and the centrate/filtrate. Non-contact sensing (optical scatter, fluorescence and gas phase methods) and other high reliability approaches were used to find a suitable control measurement.
- Reduced sludge disposal costs and coagulant chemicals.
- Robust on-line dewatering data for management information.
- Freeing operator time for other tasks.