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Effluent CBOD5 loading (mt/day) Effluent CBODu loading (mt/day) Effluent NBODu loading (mt/day) Effluent BODu loading (mt/day)

CBOD5 percent removal CBODu percent removal NBODu percent removal BODu percent removal

3,812 9,232 7,093 16,325

835 2,422 1,399-3,821

Total"

Inventory of POTWs 18,303

Population of U.S. (millions) 311.5

Population served (millions) 274.7

Percent of population served 88%

Influent wastewater flow (mgd) 45,329

Unit flow (gpcd) 165

Influent CBOD5 loading (mt/day) 36,892

Influent CBODu loading (mt/day) 44,270

Influent NBOD° loading (mt/day) 23,760

Influent BODu loading (mt/day) 68,030

Effluent CBOD5 loading (mt/day) 4,025

Effluent CBODu loading (mt/day) 10,995

Effluent NBOD° loading (mt/day) 8,611

Effluent BODu loading (mt/day) 19,607

CBODj percent removal 89%

CBODu percent removal 75%

NBODu percent removal 64%

BODu percent removal 71 %

Less than Greater than

Raw Secondary Secondary Secondary On-Site

2016 Projections

910 16,883 25,200 2,337

0 740 13,740 20,509 1,902

0 888 16,489 24,611 2,282

0 477 8,850 13,209 1,225

0 1,365 25,338 37,819 3,507

TABLE 2-12 Continued

Inventory of POTWs Population of U.S. (millions) Population served (millions) Percent of populaton served Influent wastewater flow (mgd) Unit flow (gpcd)

Influent CBOD5 loading (mt/day) Influent CBODu loading (mt/day) Influent NBODu loading (mt/day) Influent BODu loading (mt/day)

Effluent CBOD5 loading (mt/day) Effluent CBODu loading (mt/day) Effluent NBOD° loading (mt/day) Effluent BODu loading (mt/day)

CBODj percent removal CBODu percent removal NBODu percent removal BODu percent removal

Less than Greater than

Total" Raw Secondary Secondary Secondary On-Site

2025 Projections

39,684 47,620 25,558 73,179

4,330 11,827 9,263 21,090

Sources: USEPA (1997) 1996 Clean Water Needs Survey and U.S. Census Bureau Population Projections. Notes: Less than secondary = Primary and ad vanced primary wastewater treatment; Greater than secondary = "Totals only shown for 2025 projections.

Advanced secondary and advanced wastewater treatment.

Figure 2-17 POTW influent and effluent BODu loading and removal efficiency for select years between 1940 and 1996 and 2016 and 2025. Sources: U.S. Public Health Service Municipal Wastewater Inventories, USEPA Clean Water Needs Surveys, and U.S. Census Bureau Population Projections.

Key observations from Figure 2-17 include the following:

• Population growth from 1996 to 2016 will increase influent BODu loading nationwide to 68,030 mt/day, an increase of 45 percent. By 2025, influent loading will be about 73,057 mt/day, a 56 percent increase from 1996.

• In spite of a projected national increase in BODu removal efficiency from 65 to 71 percent by 2016 (a 9 percent increase), it is estimated that the trend of decreasing effluent BODu loadings experienced in the 24-year period from 1968 to 1996 will be reversed. It is predicted that effluent BODu loadings will increase from 16,325 mt/day in 1996 to 19,606 mt/day in 2016, an increase of 20 percent. The effluent BODu loading rate estimated for 2016 is about equal to effluent loading rates that existed in the mid-1970s, only a few years after the CWA was enacted!

• By 2025, the projected effluent BODu loading will be 21,090 mt/day, an increase of 29 percent from 1996. This rate is about equal to effluent loading rates experienced in 1968 (21,280 mt/day), the year when the discharge of oxygen-demanding material from POTWs had reached its historical peak!

• By 2016, when the projected needs for wastewater treatment are expected to be met (USEPA, 1997), the overall BODu removal efficiency of 71 percent and increases in population will result in a 20 percent increase of effluent loads relative to the 1996 loading rate. To maintain an effluent BODu loading rate comparable to 1996 conditions through 2016 (i.e., "running in place"), the national aggregate removal efficiency would have to be increased from 71 to 76 percent. This would need to be accomplished by shifting the projected population served from secondary to advanced secondary and advanced wastewater treatment facilities.

The estimated projections of increasing effluent loading rates of BODu over the next quarter-century underscore the importance of continually investing in improvements to wastewater treatment infrastructure to maintain and improve pollutant removal efficiencies. Without these improvements, many of the environmental successes of the water pollution control efforts over the past three decades may be overwhelmed by the future demand from population growth. The very real risk of losing the environmental gains achieved by federal (Construction Grants Program), state, and local water pollution control efforts under the technology-based and water quality-based effluent limit regulations of the 1972 CWA is also documented by Jobin (1998) and the Water Infrastructure Network (WIN, 2000).

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