Defining Biosolids Stability

Abstract

The test methods, criteria, and approaches used for stability assessment of biosolids produced by composting, alkaline stabilization, heat drying, and digestion technologies have been reviewed in a recently completed study sponsored by the Water Environment Research Foundation (WERF) and are summarized in this paper. It was concluded that no one method is suitable for assessing stability for all types of biosolids. Stability assessment depends on the process used to manufacture the product, and intended use of the biosolids. A matrix based on use and technology was developed as an approach for biosolids stability assessment. A table was presented that summarizes the current state of practice. Tests were recommended as the most useful methods of stability assessment, at the present time, for each of the stabilization technologies examined. While there is an increasing recognition of the importance of stability assessment for beneficial use of biosolids, there is a lag in the practical use of stability assessment. Research needs were presented for further implementation of biosolids stability assessment.