Proceedings

High lime doses have become accepted as unnecessary to comply with conventional sludge treatment standards as defined by the new Sludge (Use in Agriculture) Regulations. The results of an Anglian Water Lime Optimisation Project to reduce lime consumption and Operational Expenditure (OPEX) are presented. While a lime dose of 10%(DS) exceeds HACCP requirements, a minimum lime dose of 15% is necessary to ensure ‘stackability’ of cake and stability (inhibition of putrefaction) prior to spreading. Fourteen lime streams were optimised with minor plant modification and lime feed-screw calibration. Preliminary work, calibration and optimisation has been completed. In addition to OPEX savings, the following was achieved: a). A consistent approach to operation of liming plants, b). Pathogen kill well above that required for HACCP, and c). Reliability of limed Biosolids quality. The remaining work encompasses the adoption of lime dose (%DS), rather than endpoint pH, for HACCP control; and training of operators.

KEY WORDS Lime Stabilisation, Sludge, HACCP, Biosolids, Escherichia coli, Pathogen Kill, Agricultural Recycling, OPEX, Ammonia.