An Examination of BOD Loadings Before and After the CWA

Chapter 1 introduced the "three-legged stool" approach to assess the success of the CWA's mandate for POTW upgrades to secondary and greater than secondary waste-water treatment. The premise is that each "leg" of the approach must provide cumulative support for the stool to stand up firmly and success to be declared. Chapter 2 presents the results of the first leg. Specifically, this chapter focuses on whether there was a significant reduction in the discharge of oxygen-demanding materials from POTWs to the nation's waterways after implementation of the 1972 CWA.

To help put this analysis into perspective, Chapter 2 begins with a background discussion of the historical consequences of ignoring the wastewater treatment component of the urban water cycle on the aquatic ecosystem (Section A), and then explains how scientists and engineers eventually harnessed the power of decomposers and developed the process now known as secondary treatment (Section B). Section C traces the legislative and regulatory history of the federal role in water pollution control and how the 1972 CWA accelerated the national trend of upgrading POTWs to at least secondary treatment. Section D presents national trends in influent BOD loading (BOD entering POTWs) and effluent BOD loading (BOD discharged from POTWs into surface waters) for select years between 1940 and 1996, as well as effluent loading projections into the twenty-first century.

During the mid-1990s (ca. 1995), pollutant loading from municipal wastewater treatment facilities accounted for only about one-fifth of the estimated total national point and nonpoint source load of BOD discharged to surface waters. Section E presents comparative estimates of the remaining four-fifths of the total national load accounted for by industrial wastewater dischargers, combined sewer overflows (CSOs), and nonpoint (rural and urban) sources. Section F examines the national public and private investment costs associated with water pollution control. Section G provides a summary, conclusions, and a perspective on future trends for municipal wastewater loads.

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