Environmental Engineering: Fundamentals and Design - Chapter 11

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# Chapter 11 Wastewater Treatment

James R. Mihelcic, David W. Hand and Martin T. Auer

## Wastewater: Backstory

Syracuse, New York. 1851. This recently chartered city, formed from two neighboring villages, was located along the route of the Erie Canal. Shiploads of cargo and immigrants moved west from New York City signaling a period of rapid growth for central New York. The streets were dirt, horsepower was a reality and municipal amenities were, at best, primitive. The outhouse was the sole option for handling sanitary waste. Indoor plumbing was some time off, as a dependable water supply and systems of wastewater conveyance were not yet in place.

The stimulus for construction of municipal facilities came not from concerns over sanitation, but from problems with water in the streets. Much of Syracuse has been developed from marshland and the dirt streets became quagmires of mud during rainy periods. Sewer systems constructed in the second half of the 19th century drained runoff from the streets to one of three local creeks that discharged to Onondaga Lake on the City's north side. In 1894, Syracuse turned to Skaneateles Lake, some 20 miles away, for an abundant, dependable and high quality source of drinking water. With the sewers in place and plenty of water available, indoor plumbing became practical. Wastewater discharged to the sewers flowed into the three creeks and on to Onondaga Lake. These inputs led to worsening water quality and public health concerns focusing on Onondaga Lake's Canal Harbor became a major issue in the mayoral election of 1919. An interceptor sewer system was put in place in 1922, taking the wastewater out of the streams and providing screening and disinfection before discharge to the lake. In 1925, a primary treatment plant was constructed, removing pollutants by gravity settling before discharge to the lake. The Syracuse Metropolitan Treatment Plant (METRO) was built at the south end of Onondaga Lake in 1960. This was a regional facility, providing primary treatment before discharge to the lake. Passage of the Federal Water Pollution Control Act Amendments in 1972 provided funding for major upgrades at METRO, adding secondary (biological) treatment in 1979 and tertiary (phosphorus removal) treatment in 1981. Efforts to improve treatment efficiency continue into the 21st century with investments of more than $450 million for nitrification and advanced phosphorus removal. METRO continues to discharge to Onondaga Lake, providing approximately one-third of the hydrologic input in mid-summer. This is the largest input of treated wastewater to an inland lake among New York State's 607 permitted dischargers.

The timeline for development of a domestic waste treatment strategy in Syracuse and in other cities is mirrored in the layout of a modern wastewater treatment plant. Raw wastewater entering the plant receives screening and then proceeds through primary, secondary and tertiary treatment before disinfection and discharge. As we walk through a modern plant, we are also walking through time and can observe the evolution of technology and attendant improvements in the quality of the water discharged our rivers and lakes.

The defining moment for wastewater treatment in the U.S. was Congress' passage of the Clean Water Act, formally entitled the Federal Water Pollution Control Act Amendments, in 1972. This legislation specified levels of wastewater treatment technology and provided funding to municipalities for its implementation. The Act required that all municipalities upgrade to secondary treatment and authorized $18 billion in support of construction. Federal contributions in the year preceding the Act were $1.25 billion. Industrial dischargers had two options: they could treat their waste in an onsite facility or they could take steps to remove materials that would not be removed at a municipal plant or damage plant processes and then route this pre-treated waste to the municipality. Onsite treatment of industrial waste required that the best treatment practices currently available be applied and, in subsequent years, that the best control technologies economically achievable be utilized.

This and subsequent legislation, coupled with great strides in technology development have led to remarkable improvements in the quality of treated wastewater and in the condition of our nation's waters. But much remains to be done. It is estimated that beneficial uses (e.g. drinking water, recreation, support of wildlife) are impaired in 30-40% of the country's lakes and streams. Today's engineer plays an active role in restoring beneficial use, through involvement in regional planning, storm water management, the design, construction, operation and regulation of treatment facilities and the development of new treatment technologies. Engineers are also looking beyond 'end of pipe' solutions, applying principles of pollution prevention and green engineering to reduce the production of wastes, reducing the burden on treatment facilities and their receiving waters. In this chapter, we will describe the sources and nature of wastewater, the unit operations that provide treatment and the management of residuals, i.e. the materials remaining once water has been cleansed and discharged to the environment.

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