Digested sewage sludge: characterization of a residual and modeling for its disposal in the ocean off Southern California
Creators: name: Faisst, William Karl
Publisher: name: California Institute of Technology
Year: 1976

description: Sewage sludge is a concentration of the residues that our modern municipal and industrial society discharges to the sewerage system. The sludge solids are removed from the sewage flow by sedimentation and then partially stabilized by biological digestion. Typical digested sludges are 95 to 98 percent water, with the majority of their potential environmental contaminates such as trace metals associated with the two to five percent solids fraction. This particulate matter has usually been characterized only for such gross constituents as total solids, total trace metals, and pesticides. 

For this work, the sludge particle system was approached on a much more detailed level. There is strong evidence that the particles in digested sludge may cause serious deleterious effects when discharged near the productive surface waters of the ocean. Such effects include disruption of light penetration into the water column. This can drastically reduce photosynthesis, the primary productivity in the ocean. Sludge particles discharged to the ocean are heavier than the surrounding water and tend to settle. They may "blanket" the bottom, interfering with the normal life cycles of bottom-dwelling organisms. The digested sludge, only partially stabilized by treatment processes before discharge, may also drastically alter the chemistry of the sediments where it settles. 

The very fine material in the sludge does not settle easily and may be carried many kilometers by the prevailing ocean currents. The trace metals and other components incorporated into the particles are also then carried great distances. Since many marine organisms such as bivalves and zooplankton are filter feeders, the presence of sludge-particulate matter of the right size in the water column may lead to uptake of sludge contaminants in the food chain.
description: © 1976 Environmental Quality Laboratory. California Institute of Technology. 

Sewage sludge, the liquid-solids suspension resulting from the sedimentation phase of wastewater treatment, contains a substantial portion of the waste materials that enter the sewers, but only represents one or two percent of the total plant flow by volume. The sludge is thus a concentration of the municipal and industrial residues that are captured by the treatment processes rather than being dispersed along with the effluent in the environment. The quantities of sludge produced increase as the effectiveness of wastewater treatment is improved. Recent public laws have mandated a general upgrading of wastewater treatment facilities. The resulting sludge must be treated and disposed of, hopefully in the most economical and environmentally sound method available. 

This document reports on research on digested sewage sludge and modeling of sludge disposal done under the joint auspices of the Department of Environmental Engineering Science and the Environmental Quality Laboratory of the California Institute of Technology. This work is part of an ongoing effort in the area of residuals management that includes basic laboratory research, conceptual engineering modeling, and economic analysis of important environmental problems. In the laboratory investigations, the specific characteristics of a particular problem area, such as sewage sludge treatment and disposal, are identified. Engineering modeling efforts then draw on laboratory work in order to propose feasible alternatives which can be compared on a basis of both potential environmental impacts and economic viability. The end results of all efforts should be a solid framework of facts and alternatives for use by the decision-makers who must select the actual plan.
 
This work was submitted as a thesis under the title Digested Sludge: Delineation and Modeling for Ocean Disposal, in partial fulfillment for the degree of Doctor of Philosophy at the California Institute of Technology, May, 1976. 

Financial support for this work was generously provided by the people of the United States through the Environmental Protection Agency (Research Grant R80069-03-l and Research Contract 68-03-0434) and by the Environmental Quality Laboratory from Ford Foundation and other gift funds. 

The author wishes to thank Professors Jack E. McKee, James J. Morgan, and Norman H. Brooks for their help and advice throughout this research. This manuscript was expertly prepared by Ms. Pat Rankin and Ms. Pat McCall; their help and encouragement is greatly appreciated.
description: Submitted - EQLReport13.pdf