The Strategic Use of Liquid Lime in Sludge Treatment

Lime treatment of wastewater sludge has been in use for over a century. This paper describes the use of ‘Liquid Lime’ and hydrated lime suspensions as a sludge treatment process for the specific purpose of agricultural recycling. The introduction of ‘Liquid Lime’ treatment has enabled South West Water to achieve full compliance with the Sludge (Use in Agriculture) Regulations at a time when the major refurbishment of a number of existing anaerobic digestion installations had been identified to enable the final sludge product to be recycled to land. Initially considered as a shortterm solution to transient problems, liquid lime dosing has been shown to be an efficient method of pathogen reduction and a cost effective alternative sludge treatment process for medium term applications. A comprehensive review of the advantages and potential difficulties to be encountered when introducing liquid lime treatment at existing sludge treatment centres has been undertaken. The findings of the review have provided confidence that liquid lime dosing could be relied upon as a robust sludge treatment process and could play an important role in the company’s sludge strategy. The role that liquid lime sludge treatment has played in the modification of the sludge strategy, and the savings in capital expenditure that have been realised, are discussed.