Figure 6-13 Long-term trends (1900-2000) of effluent total nitrogen loads by municipal wastewater facilities in the Middle and Lower Hudson basins. Source: Hetling et al., 2001. Presented at the NYWEA conference, February, 2001.
Lower Hudson River basins. During the 1940s and 1950s, effluent flow ranged from 1,250 to 1,344 mgd with about 30 percent from raw, 24 to 38 percent from primary plants, and 30 to 45 percent from secondary facilities. Increasing per capita consumption of water (150 gpcd in 1965 to 170 gpcd in 1985) and a small increase in population served resulted in a steady increase in effluent flow from 1,250 mgd in the early 1960s to 1,900 mgd by 1990. With the upgrade of the Coney Island plant to full secondary in 1994, effluent flow from less than secondary plants has been almost completely abated in the Hudson-Raritan estuary; the Newton Creek plant is expected to be upgraded to secondary by 2007 (Schwartz and Porter, 1994). Declines in population served from 1990 to 2000 and a New York City water conservation program then resulted in a decline of total effluent flow to 1,600 mgd by 2000. Effluent flow from municipal wastewater facilities in the Middle Hudson basin accounted for about 8 percent of the total effluent flow in 1900, 5 percent in the 1940s and 1950s, and 15 percent by 1990-2000.
With the same per capita loading rate (0.18 lb per capita per day) used to estimate effluent loads for BOD5 and TSS (Hetling et al., 2001), the long-term trends for BOD5 (Figure 6-11) and TSS (Figure 6-12) loads for the Middle and Lower Hudson basins are quite similar. The small differences in the estimated effluent loads are dependent on the BOD5 and TSS removal efficiency assigned to primary (15 percent BOD5 and 50 percent TSS removal) and secondary (85 percent BOD5 and 85 percent TSS removal) treatment plants (Hetling et al., 2001). Following a steadily increasing trend similar to that shown for effluent flow and population served, BOD5 and TSS loads from raw discharges to the Middle and Lower Hudson basins increased from 273 metric tons per day (mt/day) in 1900 to a peak load of 554 mt/day by 1932. With the construction of primary treatment plants in the late 1920s and 1930s and upgrades to secondary during the 1940s, 1950s, and 1960s, untreated BOD5 and TSS effluent loads declined by 80 percent from the peak of 554 mt/day in 1932 to 112 mt/day in 1970. The combined raw, primary, and secondary loads declined from 600 mt/day in 1932 to 400 mt/day by 1970. The steady increase in BOD5 loading from 1900 to 1932 is attributed to population growth (Figure 6-5) and an expanding urban sewage collection system (Figure 6-7), while the reduction in loads from the 1930s to the 1950s is attributed to the construction of three primary treatment plants during the 1930s. After the mid-1960s, the decline in total TSS and BOD5 effluent loading to 103 mt/day by 2000 was driven by upgrades to full secondary treatment and the elimination of raw sewage discharges from the west side of Manhattan (North River plant) and Brooklyn (Red Hook plant) with the construction of advanced primary plants in 1986-1987 and eventual upgrades to full secondary in 1988-1991. Effluent loads of BOD5 and TSS from municipal wastewater facilities in the Middle Hudson basin accounted for about 10 percent of the total BOD5 and TSS effluent load in 1900, 10 to 25 percent in the 1950s and 1960s, 15 percent during the 1980s, and 10 to 14 percent by 1990-2000.
Following a steadily increasing trend similar to that shown for effluent flow and population served, TN loads (Figure 6-13) from raw sewage discharges to the Middle and Lower Hudson basins increased from 54 mt/day in 1900 to a peak loading rate of 124 mt/day by 1938. With the construction of primary treatment plants in the late 1920s and 1930s and subsequent upgrades to secondary treatment during the 1940s,
1950s, and 1960s, effluent TN loads declined by only 15 percent from the peak of 124 mt/day in 1938 to 105 mt/day during the early 1960s. After enactment of the CWA in 1972, and the required upgrades of water pollution control plants in the Middle Hudson and the Lower Hudson metropolitan region to full secondary treatment, effluent loads of TN declined from 125 mt/day in 1970 by only ~ 22 percent to 97 mt/day by 1999. Full secondary plants, although not specifically designed for the removal of nitrogen, typically can achieve about 40 percent removal of TN (see Table 2-17). Note, however, that New York City wastewater treatment plant removals for TN are only about 20 percent or less, primarily due to weak influent (O'Shea and Brosnan, 2000). Effluent loads of TN from municipal wastewater facilities discharging to the Middle Hudson accounted for about 9 percent of the total TN effluent load in 1900, 7 to 14 percent in the 1940s and 1950s, 18 to 22 percent during the 1970s and 1980s, and 18 percent by the 1990s.
Following a steadily increasing trend similar to that shown for effluent flow and population served, TP loads (Figure 6-14) from raw sewage discharges to the Middle and Lower Hudson basins increased by 150 percent from 6 mt/day in 1900 to a loading rate of 15 mt/day by 1938. Even with the construction of primary treatment plants in the late 1920s and 1930s, and subsequent upgrades to secondary treatment from the 1940s through the 1960s, effluent TP loads continued to increase to 14.5 mt/day by 1950, with a rapid increase over the next two decades to a peak of 36 mt/day by 1970. Effluent loads of TP increased from 1938 to 1970 even as raw sewage discharges
Figure 6-14 Long-term trends (1900- 2000) of effluent total phosphorus loads by municipal wastewater facilities in the Middle and Lower Hudson basins. Source: Hetling et al., 2001. Presented at the NYWEA conference, February, 2001.
were eliminated and water pollution control plants were upgraded to primary and secondary treatment for three reasons: (1) population served and influent wastewater flow increased; (2) removal efficiency of TP for both primary and secondary plants is only ~ 30 percent; and (3) influent concentration of TP steadily increased from ~ 2 mg P/L to a peak of ~10 mg P/L in 1973 after the introduction of phosphorus-based detergents in 1945 (Hetling and Jaworski, 1995). After state legislative bans of phosphorus-based detergents in 1973 reduced influent levels of TP to ~ 3 mg P/L by the mid-1990s (Hetling and Jaworski, 1995), and after water pollution control plants in the Middle Hudson and the Lower Hudson metropolitan region were upgraded to full secondary treatment, effluent loads of TP declined sharply by 63 percent from the peak of 36 mt/day in 1971 to only 13.7 mt/day by 2000. Since the removal efficiency of 30 percent for phosphorus is similar for both primary and secondary treatment, the decline in effluent loading of TP has resulted from the ban on phosphorus-based detergents (Clark et al., 1992; Hetling and Jaworski, 1995).
The long-term trend (1880-1980) of historical loading of copper and lead to New York Harbor (Figure 6-15) reflects increasing urbanization and uncontrolled wastewater discharges from industrial activity in the metropolitan region from 1880 through 1970 (Rod et al., 1989). The reduction in loading of these metals after 1970, resulting from the industrial pretreatment program, corrosion controls, and effluent controls on industrial discharges, corresponds to a decrease in sediment levels of copper and lead in the Hudson estuary (Valette-Silver, 1993) (Figure 6-16). Studies con-
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