Controlled Composting of Paper Pulp Sludge Using the Aerated Static Pile Method

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Abstract
The UK paper industry is searching for alternatives to landfilling for the 700,000 tonnes of sludge that is produced every year. This project examines the feasibility of composting paper pulp sludge using the, relatively low cost, aerated static pile method. Recycled paper sludge from the de-inking plants and primary and secondary sludge from the wastewater treatment, mixed with chicken manure and green waste at an 8:2:1 volume ratio, were composted in two 2.2m × 1.5m × 5m piles. The raw material had low heavy metal contamination, meeting European requirements for sludge application to land. The characteristic temperature profile of the ASP using temperature feedback control was observed, with a core temperature drop by day 12. Changes in the compost chemical characteristics and its stability, as assessed by respiration, indicated that the aeration period did not need to extend over two weeks. During this period more than 30 percent of the initial volatile solids content was decomposed, and the respiration rate dropped by more than 80 percent, to 0.8 mg O2/g VS/hr. However, phytotoxicity, as assessed by cress germination, may take some what longer to disappear and subsequent storage of the material without aeration could improve its quality. This suggests a composting strategy of a two weeks aeration phase, and a further four to five weeks maturation.