1986 and Brooklyn's Red Hook WTP in 1987 as advanced primary facilities eliminated the discharge of 5.3 m3 s-1 of raw sewage into the lower Hudson River and lower East River (Brosnan and O'Shea, 1996a).
Driven by the regulatory controls of the 1972 CWA and an aggressive New York State program, public works officials throughout the region embarked upon programs to upgrade all WTPs to full secondary levels of treatment (that is, 85 percent removal of BOD5 and TSS) during the 1970s and 1980s. From 1979 to 1994, eight of the nine WTPs in New York City in our study area were upgraded to full secondary treatment, with the Red Hook and
North River plants upgraded to full secondary in 1989 and 1991, respectively. WTPs in the rest of New York and New Jersey were also upgraded to secondary treatment at this time. Planning for upgrading of the Newton Creekplant on the lower East River to full secondary treatment is ongoing. As a result of the regulatory requirements of the 1972 CWA and the availability of significant Federal and state construction grants, the population served by secondary treatment plants has increased from 1.8 million in the late 1930s to 8.6 million by 1990 in the lower Hudson basin. A similar change is seen in the middle Hudson basin where the population served by secondary increased slowly during the 1960s to
0.25 million by 1970. After the 1972 CWA and an establishment of a significant state construction grantprogram, the populationserved by secondary plants in the middle Hudson increased to 1.5 million by 1999.
Wastewater effluent flow. Following the long-term trend in population served by sewers, effluent flow from municipal facilities in the middle and lower Hudson basins increased steadily over the course of the twentieth century (Fig. 23.3d). At the turn of the century, a total of 18 m3 s-1 of untreated sewage was discharged to the Hudson River. Increases in population and increasing per capita consumption of water resulted in a steady increase in effluent flow to 83 m3 s-1 by 1990. Declines in population served from 1990-2000 and a New York City water conservation program then resulted in a decline of total effluent flow to 70 m3 s-1 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.
BOD5 and TSS loads. With the same per capita loading rate (81.6 grams/capita per day) used to estimate effluent loads for BOD5 and TSS, the trends for BOD5 (Fig. 23.3b) and TSS (Fig. 23.3e) are quite similar. The small differences in the estimated effluent loads are dependent on the BOD5 and TSS removal efficiency assigned to primary and secondary treatment plants (Hetling et al., 2003). Following a steadily increasing trend similar to that shown for effluent flow and population served, total BOD5 and TSS loads from raw sewage discharges to the middle and lower Hudson basins increased from 273 mt d-1 in 1900 to a peak loading rate of 600 mt d-1 by the early 1930s. 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 BOD5 and TSS loads gradually declined by more than 50 percent from that to approximately 400 mt d-1 in 1970. After enactment of the CWA in 1972, and the upgrades of WTPs in the middle and the lower Hudson to full secondary treatment, effluent loads of BOD5 and TSS continued to decline to approximately 1 mt d-1 by 1999. 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 1900,10-25 percent in the 1950s-1960s, 15 percent during the 1980s and 10-14 percent by 1990-2000.
Total Nitrogen (TN) loads. Total Nitrogen (TN) loads from raw sewage discharges to the middle and lower Hudson basins increased from 60 mt/d in 1900 to a peak loading rate of almost 125 mt/d by 1938 (Fig. 23.3c). With the construction of primary WTPs in the late 1920s and 1930s and subsequent upgrades to secondary treatment during the 1940s, 1950s, and 1960s, effluent TN loads by 1970 were virtually unchanged from 1938. After upgrades to full secondary treatment, effluent loads to the estuary declinedby32 percent to approximately 85 mt/d by the mid-1980s. Full secondary plants, although not specifically designed for the removal of nitrogen, typically can achieve about 40 percent removal of TN (Hetling et al., 2003). Note however, that New York City WTP removals are approximately 20 percent or less, primarily due to weak (that is, diluted) influent (O'Shea and Brosnan, 2000). TN loads in the lower Hudson increased in the early 1990s due to the Ocean Dumping Ban Act of 1988. This act required several municipalities in New York and New Jersey to cease ocean disposal of sewage biosolids. To facilitate land-based management of biosolids, the biosolids were dewatered and the nitrogen-rich centrate was discharged to several WTPs, and ultimately to area waterways. Implementation of nitrogen removal technologies at some WTPs have reduced nitrogen loads back to pre-biosolids centrate levels (O'Shea and Brosnan, 2000). Effluent loads of TN from municipal waste-water facilities discharging to the middle Hudson accounted for about 9 percent of the combined TN effluent load in 1900,7-14 percent from the 1940s-1950s, 18-22 percent from the 1970s-1980s, and 18 percent by the 1990s.
Total Phosphorus (TP) loads. Total Phosphorus (TP) loads from raw sewage discharges to the middle and lower Hudson basins increased by 117 percent from 6 mt/d to 13 mt/dby the late 1930s (Fig. 23.3f). 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 a peak of 36 mt d-1 by 1970. Effluent loads of TP increased from 1938 to 1970 even as raw sewage discharges were eliminated and WTPs were upgraded to primary and secondary treatment for three key reasons: (1) population served andinfluentwastewaterflowincreased; (2) removal efficiency of TP for both primary and secondary plants is only 30 percent; and (3) influent concentration of TP steadily increased after the introduction of phosphorus-based detergents in 1945 (Hetling et al., 2003). After state legislative bans of phosphorus-based detergents in 1973 and the required upgrades of WTPs to full secondary treatment, effluent loads of TP declined sharply by 61 percent to approximately 14 mt/d 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 primarily from the ban on phosphorus-based detergents (Clark et al., 1992; Hetling et al., 2003). The slight increase in TP loads to the lower river reflects in part the addition by New York City in late 1992 of a phosphate-based buffer to inhibit corrosion of copper distribution pipes (O'Shea and Brosnan, 2000).
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