Sediments within both natural (freshwater and saltwater) environments and engineered facilities play significant environmental, economic, and public health roles in society. The majority of priority pollutants including heavy metals and organic contaminants (such as PAHs) are associated with sediment particles. The beneficial use impairment of many aquatic environments, including every area of concern as defined within Remedial Action Plans of the Great Lakes basin of North America and elsewhere internationally, is related to contaminated sediments. These beneficial use impairments include swimming, boating, fishing, esthetics, odor, and benthic community impacts. Substantial sums of money are invested each year in the remediation of contaminated sites in an attempt to increase beneficial uses. Within engineered systems such as drinking water and wastewater treatment facilities, the removal of solids is the key aspect of treatment and, as such, here too significant sums of money are invested to provide the most efficient operating system possible.

Within both natural and engineered systems, when sediment issues are in question it is inevitable that flocculation will be a dominant process that will contribute to, or control the issue. This is because the majority of cohesive sediments within natural systems are transported and eroded within a flocculated state and the floc is the model form of solids for most engineered systems. Given that the structure of a floc will influence its physical (transport), chemical (uptake and transformation of contaminants), and biological (community dynamics and biochemical activities) behavior, it is not surprising that flocculation plays a dominant role in influencing the environmental, economic, and public health impacts of sediments. While this is widely accepted, there is still a fundamental lack of knowledge related to many aspects of the flocculation process and the resultant floc and as such our abilities to manage water resources are impaired.

Through the sharing of information between researchers of different disciplines and environments, the workshop has contributed to improving our knowledge of the greater flocculation process and impact within the freshwater, saltwater, and engineered systems. The workshop has demonstrated the strengths and weaknesses within floc research in the three environments and has pointed to the need for continued collaboration between researchers. Of particular note is that cross-environment multidisciplinary studies would be of great benefit in ascertaining the universality of flocculation processes and impacts. Presently such cross-environment studies are very limited in scope. Continued development of new and innovative methods which can be effectively used between environments will be essential to the advancement of flocculation research.

The contributors to the Workshop on Flocculation in Natural and Engineered Systems have provided herein some integral elements to advancing our understanding of flocculation processes; however, the work has only just begun. By integrating resources, expertise, and ideas, researchers will continue to advance our knowledge in this vitally important environmental, economic, and public health issue.

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