The Use Of Blend Lime For Biosolids Stabilisation To Defer Operational Spending

Alkaline stabilisation of biosolids is a well-known process to reduce pathogenic organisms, control odours and increase cake solids. The Mangere WWTP produces an average of 300 wet tonnes of biosolids a day, which requires approximately 25 tonnes of burnt lime to be added on a daily basis. Lime addition increases the pH biosolids to 12 to comply with the resource consent requirements. It also improves the on-site operation with regards to biosolids processing, handling and disposal, by reducing the machinery blockages and increasing the shear strength. Different blends of burnt lime and additives were tested in a laboratory scale to increase shear strength through the additives without impacting the pH. The results of this study were used to carry out a full scale blended lime trial at Mangere WWTP. The blend is a composition of 70% burnt lime and 30% lime kiln dust. Lime kiln dust is a co-product of the burnt lime process. The main objective of the trial was to assess the performance of the blended lime on the full scale process and over a minimum period of 6 months. The operational savings generated by the use of blended lime to replace burnt lime was estimated to be 15% of the budgeted lime consumption. This paper presents the challenges of this full scale trial and operational results obtained through the trial period, and economic benefits.