The potential for blending residuals to create valuable products that are publicly accepted is an example of recycling at its best. Previously, much of the research done on reuse of residuals has centered on potential negative effects. Generally, blending of materials has been done in a relatively haphazard fashion. There is a growing understanding that residuals can be deliberately mixed for specific end uses. This is the initial phase of transition from residuals disposal to product development. The XXII Annual Beltsville Symposium focused on the range of factors that need to be taken into account for any co-utilization programme to be successful. The proceedings include research reports as well as reports from the private sector. Potential uses for co-utilization products as well as areas requiring more research are outlined.

Co-utilization or blending of residuals offers a unique opportunity to develop products with particular characteristics that are able to target specific customer needs. The very notion of deliberately blending by-products suggests that the recycling and beneficial reuse industries are taking a quantitative step forward towards developing products rather than simply reusing residuals. At the same time that this step provides unique opportunities, it also presents unique challenges. The science associated with the beneficial use of one product may not apply when that product is mixed with another residual. Blending of materials may alter the chemistry of the components of the mixture. This may offer additional benefits, as in the case of disease suppression in composts, or present unexpected problems, as the use of lime-stabilized biosolids has done in Maryland. This book consists of the proceedings of the Beltsville Symposium. The organizers of the Symposium attempted to structure a meeting that would outline both the potential benefits of co-utilization as well as concerns. The editors have divided the proceedings into sections that describe the practical basis for co-utilization of residuals as well as the potential benefits. Specific considerations are described. Finally, case studies include descriptions of successful operations and data that detail results of research involving co-utilization materials. Blending of materials for specific objectives needs to be the focus of any successful co-utilization effort. The scientific implications of the mix need to be determined before a product can be used properly.