Environ. Sci. Technol. 1997, 31, 3198-3203
Corrosion in Drinking Water Distribution Systems: A Major Contributor of Copper and Lead to Wastewaters and Effluents R . A . I S A A C , * ,† L . G I L , † A. N. COOPERMAN,‡ K. HULME,‡ B. EDDY,‡ M. RUIZ,‡ K. JACOBSON,† C. LARSON,† AND O. C. PANCORBO‡ Massachusetts Department of Environmental Protection, Division of Watershed Management, 627 Main Street, Worcester, Massachusetts 01608, and Senator William X. Wall Experiment Station, 37 Shattuck Street, Lawrence, Massachusetts 01843
Corrosion, even in water supply systems with treatment to reduce it, can be a major contributor of copper and lead to both treated municipal (publicly owned treatment works, POTW) wastewater effluents and biosolids. Lead and copper concentrations were measured at several points in the water/wastewater systems of four Massachusetts municipalities. Domestic wastewater was found to contain concentrations of lead and copper significantly higher (p < 0.05) than those in source waters. For each facility, the median concentration of Cu in domestic wastewater was a substantial fraction of the median concentration found in the influent to the POTWs with ratios of 0.36, 0.41, 0.65, and 1.25 for Gardner, New Bedford, Fall River, and Clinton, respectively. The values for lead, in the same order, were 0.28, 0.19, 0.17, and 0.69 (this last ratio based on mean values). Data from the study indicate that minimizing influent concentrations of Cu and Pb to POTWs is an important control factor since the finding of constant removal efficiency for these two constituents means that the higher their concentrations in the influent, the higher they will be in the effluent. These observations strongly support the concern that corrosive drinking water contributes substantially to exceeding, at a minimum, water quality criteria for copper, where dilution of wastewater effluents is low. In turn, this argues for corrosion reduction efforts in water supply systems and the means by which such controls are effected to consider impacts on wastewater as well, which generally is not now done.
Introduction While corrosion and its control in drinking water distribution systems has been studied for many years (see, e.g., the extensive review in ref 1), the critical role that this corrosion plays in contributing copper and lead to wastewaters and treated effluents is presented only to a limited extent and then only in the general literature (e.g., refs 2 and 3). As the traditional pollutantssbiochemical oxygen demand (BOD), suspended solids (SS), and bacteriasfrom point sources have * Corresponding author phone: 508-767-2876; fax: 508-791-4131; e-mail:
[email protected]. † Division of Watershed Management. ‡ Senator William X. Wall Experiment Station.
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been controlled by the construction and/or upgrading of wastewater treatment plants, attention is being focused on the second tier of pollutantssparticularly toxicity in general and specific contributors such as metals. Of special concern for publicly owned (wastewater) treatment works (POTWs) are lead and coppersespecially the latter, which often exceeds water quality criteria for discharges with little dilution available. This is a prominent concern for discharges in those parts of the United States that have soft waters such as the Northeast and parts of the Midwest. While industrial sources of constituents like copper and lead have been the subject of both categorical and local controls, concentrations of these constituents often still exceed permit limits. A major potential source that has not been considered to any great degree thus far is corrosion in water supply distribution systems. The Lead and Copper Rule (4) promulgated by the EPA for drinking water allows lead and copper concentrations to be many times that of the aquatic life criteria. In the case of copper, the factors are 72 and 108, respectively, for the acute and chronic aquatic life criteria at 100 mg/L CaCO3 hardness. For lead at the same hardness, only the chronic criterion is exceeded; the factor is greater than 4. Thus, for these elements, human health is more tolerant of higher concentrations than are many aquatic organisms. It is important, therefore, to consider the contribution of certain metals from the water supply system when addressing unacceptable concentrations of those metals in the corresponding wastewater effluent. Over the years, public health, aesthetics, and structural integrity of water lines have been the primary concerns in the potable water industry. In 1985, the American Water Works Association (AWWA) in cooperation with the water suppliers group in Germany published a major review of the concerns about, chemistry of, and control of corrosion in potable water systems (1). The document notes that concerns about lead from service pipes appeared as early as the beginning of the nineteenth century. Copper piping came into use primarily after World War II, and the concerns about its corrosion focus more on aesthetics, although human health effects do occur at high concentrations (5). Also, it has been found that the material composing the fixturessespecially new onessin a household often are the dominant source of copper, lead, and zinc in tap water as reported in an extensive assessment of six water supplies and distribution systems in Illinois (6). While traditional parameters such as the Langlier Index are used to assess the corrosivity of water, empirical studies indicate a low predictive value even for this well-known measure, which better indicates the likelihood of precipitation when positive than corrosion when negative (7). Piron (7) found that in over 1000 tests of drinking water, the Langlier Index was a poor predictor of the water’s corrosivity based on laboratory tests. This observation is reinforced by Edwards et al. (8). While a multitude of water quality factors, including alkalinity, chloride, carbon dioxide, oxygen, and calcium concentrations all have an impact on the corrosivity of water, pH may be the single most important factor with basic waters being less corrosive than those that are acidic. The most reliable means and perhaps the only adequate method to determine how corrosive a water is may be through standardized laboratory tests. The EPA (9) notes that “...relatively little field and laboratory research has been conducted contrasting alternative approaches or presenting results before and after such (corrosion control) programs were implemented”. This same paper cites limited earlier work that found corrosion control efforts reduced lead concentrations in one system by about 75%, while in other systems the
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1997 American Chemical Society
FIGURE 1. Copper concentrations (µg/L) at selected locations in the water/wastewater systems of the four communities: (A) Gardner, (B) Clinton, (C) Fall River, and (D) New Bedford). The locations were: drinking water source (SOURCE), finished drinking water (FIN.), domestic wastewater (DOM.) POTW influent (INF.), and POTW effluent (EFF.). Box plots display the 10th, 25th, 50th, 75th, and 90th percentiles as solid lines and the mean as a dashed line. Symbols indicate 5th and 95th percentiles. For each community, data from different sampling locations that do not share a letter are significantly different at p < 0.05. reduction of copper was 65-85% and that of zinc was 4570%. The results for a specific system tend to be unpredictable, but should fall into the ranges cited. This publication further notes that, among other potential benefits, corrosion control programs can reduce metal loadings to wastewater treatment plants. In another publication (10), the EPA reports that metal concentrations even in well-controlled experiments using pipe loops cut from the same length exhibit a high variances50% or more in the case of lead, for instance. The AWWA surveyed several hundred water suppliers in 1992 about the results of their sampling for the Lead and Copper Rule and the characteristics of their water’s quality. In analyzing the data, Dodrill and Edwards (11) found that alkalinity and pH were the two most important factors affecting corrosion as measured by the 90th percentile concentrations of lead and copper in standing water samples from taps. Increasing alkalinity in waters with
