10    WASTEWATER EFFLUENT TOXICITY CONTROL:
A PRACTICAL APPROACH
Paul S. Dickens, Senior Environmental Engineer
Paul M. Cannon, Environmental Systems Management Advisor
MEMC Electronic Materials, Inc.
Spartanburg, South Carolina 29304
INTRODUCTION
Section 101(a) of the 1972 Clean Water Act' established the goal of restoring and maintaining the
chemical, physical, and biological integrity of the waters of the United States. Section 101(a)(3) of the
Act specifically prohibits the "discharge of toxic pollutants in toxic amounts." Amendments to the
Clean Water Act in 19872 added Section 304(1). Section 304(1) requires that the Environmental
Protection Agency (EPA) and state regulatory agencies adopt water quality standards for specific
"toxic" chemicals. The EPA and states must also develop "individual control strategies" for point
sources of toxic pollutant discharge. As a result, much regulatory and industry effort in the 1990s is
directed toward whole effluent toxicity (WET) testing and methods for water quality-based toxics
control.3"5
This paper discusses WET testing and wastewater effluent toxicity control. It includes requirements
for water quality protection and biomonitoring under the Clean Water Act. A wastewater outfall
diffuser is a practical method for compliance with effluent toxicity limits at many industrial plants.
WATER QUALITY PROTECTION
The goals of the Clean Water Act are achieved with a three-part regulatory approach. This
approach involves technology-based wastewater treatment standards; physical and chemical water
quality standards; and biological monitoring of wastewater effluents, oceans, lakes, and streams. The
relationship between these components of water quality protection are illustrated in Figure 1.
Historically, the EPA and states rely on technology-based treatment standards to control point-
source wastewater discharges from industry. These treatment standards target control of conventional, non-conventional, and toxic pollutants associated with particular industry groups. Conventional water pollutants are pH, oxygen demanding materials, fecal coliform bacteria, and suspended
solids. Non-conventional water pollutants include ammonia, phosphorus, chlorine, color, and other
pollutants that degrade water resource value through secondary effects such as eutrophication. Toxic
pollutants include heavy metals, pesticides, and synthetic organic compounds.
Water quality standards target protection of human health, aquatic organisms, and water resource
value by specifying maximum allowable concentrations of conventional, non-conventional, and toxic
pollutants in oceans, lakes, and streams. Under the Clean Water Act, each state must designate use
categories for its surface waters and assign water quality standards appropriate to protect each
designated use. The state water quality standards must include numeric limits for specific toxic
pollutants as well as "narrative" standards prohibiting toxic conditions in general. The narrative
standards require that wastewater effluents produce no "acute toxicity" in the receiving stream or
wastewater mixing zone. No "chronic toxicity" is allowed in the receiving stream beyond the wastewater mixing zone. The wastewater mixing zone is that portion of receiving stream in which a
wastewater effluent is mixed and diluted with the full volume of the stream. State water quality
standards may limit the size and type of wastewater mixing zone.
"Toxicity" is a characteristic of a substance (or group of substances) that causes adverse effects in
organisms.6 Adverse effects are mortality and those effects that limit an organism's ability to reproduce and otherwise survive in nature. Toxicity is identified through biological monitoring and testing.
"Acute toxicity" refers to short-term adverse biological effects on test organisms, typically mortality.
"Chronic toxicity" refers to long-term adverse effects on test organisms including mortality, reproductive failure, mutation, and teratogenicity.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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