The treatment and disposal of coagulant sludge was a major and increasing proportion of water treatment operating costs. Optimisation of sludge treatment was needed to reduce costs while ensuring that the revised regulatory limit for acrylamide monomer (0.1µg/l) is met.
Efficient thickening (de-watering) of the dilute sludges from clarification and backwash settlement was central to efficient sludge management. Many widely used, continuous "rake type" thickeners, were underperforming due to: overdosing of polyacrylamide floculant-aid causing sludge blankets to congeal; inadequate design of inlet arrangements so there was insufficient floc shear; oversizing of thickened sludge transfer pumps.
The research was undertaken by WRc and British Hydraulics Research (BHR) who optimise thickener operation and demonstrated compliance with acrylamide limits by:
- Identifying benchmarks for sludge thickener performance
- Developing tools and procedures for assessing thickener performance
- Auditing a sample of thickeners
- Producing a step-by-step guide to auditing and optimising thickeners.
- Performance benchmarks will allow underperformance (and underlying causes) to be identified rapidly
- Cost-effective improvements to thickener operation to reduce operating and disposal costs
- Ability to demonstrate that the regulatory target for acrylamide monomer is being met.