Incubation-derived calcium carbonate equivalence of papermill boiler ashes derived from sludge and wood sources

The burning of a papermill sludge and wood mixture and landspreading the resulting ash is a potential means of disposal of papermill sludge without the use of valuable landfill space. This study evaluated the effectiveness of ashes derived from a mixture of papermill sludge and wood sources to act as an alternative liming agent. The calcium carbonate equivalence of the material was determined using a 91-day laboratory incubation test with three mineral soils and one organic horizon soil. Application rates of soil-incorporated sludge-ash ranged from 2.30 to 32.2 g per kg soil. Soil pH increased linearly with increasing sludge-ash application rate. The calcium carbonate equivalence of the material varied temporally and the average value ranged from 19% to 28%. The fraction of total P, K and Mg added with the sludge-ash and extracted from the ash-amended soils using an NH4OAc based soil test method were 2.6, 3.8 and 17.6%, respectively. The low soil test extractability of ash-derived plant nutrients suggests that this material would provide only a modest increase in plant available nutrient levels in landspread fields.