Even though a primitive box toilet is said to have been invented in 1596, the first patent for a flush toilet was issued in 1775, and it was another century or so before sewerage systems were widely in use in cities of Western Europe and North America. Wastewater had previously simply been discharged, without treatment, into nearby waterways. Stench and repeated cholera outbreaks were common in London, and the early solution of an “interceptor” along the River Thames only managed to move the problem downstream from the city.
As a part of the solution, in the late 1800s a series of “sewage farms” had been established to receive the discharges from city sewers and the resulting sludge and wastewater was used for crop growth. The development of technology to produce “clarified effluents” that could be directly discharged into bodies of water eliminated further need for such sewage farms.
A book, Use of Reclaimed Water and Sludge in Food Crop Production, published in 1996 by the National Academies Press, makes for some fascinating reading, and details both the history and the potential as well as the practice and problems associated with reclaiming some of the benefits of municipal wastewater for agricultural irrigation and the use of sewage sludge for soil improvement and crop fertilization. It has broad recommendations for governmental entities and well as public utilities and the food production and processing.
In the United States alone, municipal wastewater treatment plants served approximately 75% of the population by 1995, according to the data cited, treating an estimated 182 gallons of wastewater (blackwater from toilets and greywater from other household and business use) per capita per day.
These modern municipal wastewater treatment plants remove pollutants that are classified into five categories:
- Organic matter (measured as biochemical oxygen demand – BOD)
- Disease-causing microorganisms (pathogens)
- Nutrients (nitrogen and phosphorus)
- Toxic contaminants (both organic and inorganic), and
- Dissolved minerals
Authorities originally attempted to manage the volume of wastewater as well as the type of pollutants that made their way into the sewers to protect the infrastructure and the health of sanitation workers and the environmental impact. Subsequent efforts have evolved to intensify the removal and/or treatment of toxic contaminants and pathogens, and to reclaim some of the beneficial effects of the organic matter contained in the sludge.
Great strides have been made in both areas. At BTL, our liners facilitate the containment of sewage and sludge. Additionally, our tarps and covers are in use at wastewater treatment facilities throughout the country and have aided management efforts while continuing to improve the ability of such facilities to remove impurities and infectious, disease-causing organisms.
As this resource book notes: “With more than one hundred years of continuous development, municipal wastewater treatment technology [in use today] can achieve almost any degree of treatment and removal of impurities desired. The conventional municipal wastewater treatment system consists of a series of processes, through which pollutants are removed, step by step, from the water and are concentrated into the solid fraction or sludge.”
Examples of Beneficial Reuse
Communities from coast to coast and from north to south have instituted programs that make treated water and fertilizer available for a fee to large-scale commercial users, as well as educational programs that highlighted the technical ability to produce clear, safe and usable water as an end product at highly sophisticated wastewater treatment plants.
Just as one example, wastewater from Bakersfield, California has been used for irrigation since 1912. At that time, it was raw sewage; in the mid-1990s, reclaimed water from three treatment plant irrigated more than 5,000 acres of corn, alfalfa, cotton, barley and sugar beet with primary and secondary effluents. Tallahassee, Florida has used treated effluent since 1966 to irrigate city-owned farmland.
By the early 1970s, forward-thinking communities throughout the United States used wastewater treatment plant effluents for municipal irrigation of median strips, city-owned golf-courses and walking trails, open space, and public landscaping. In some communities, the treated water was also used for public education and informational purposes, to educate citizens about the need for better programs to preserve resources and the environment. One resourceful north Dallas suburb at the time even led school classes on tours of the community’s water treatment facility, creating quite a stir by offering coffee and lemonade made with purified and treated reclaimed water! It was a memorable tour!
A decade and a half later, in 1987, a seven-year demonstration study was concluded in Castroville, California that used a secondary biological treating that included coagulation, filtration and disinfection to show that the final effluent met California’s quality standard for food crops intended to be consumed raw. The results concluded that “no pathogenic organisms [were detected] in the treated effluent,” and that soil permeability was not adversely affected. Nor was there any adverse effect on crop yield, quality or shelf life.
In semi-arid Western states, it was concluded that such use of treatment wastewater effluents is of major beneficial impact for irrigation, and that the quality range of such effluents is well within accepted crop irrigation standards.
On the other hand, the economic viability of such efforts is not as clear, because the bulk of sewage created in this country is not in areas of high agricultural production. So, as safe and viable as it may be to reuse liquid effluent and treated sludge for agricultural production, it is not likely to become a major application for either liquid or solid treated waste.
Sewage Sludge or Biosolids
A new term – Biosolids – is now used by the wastewater treatment industry to describe sewage sludge that has been sufficiently treated to stabilize and reduce pathogens so that is of sufficient quality to be used for land application. That distinguishes it from raw sewage sludge or from compacted sludge that still is loaded with environmental pollutants.
It also helps to distinguish sewage sludge from industrial sludge because it emphasizes that it is produced through biological processes. According to wastewater treatment officials, it is not used to mislead the public, but rather as a scientific term to refer to treated sewage sludge that is deemed to be safe to use for other purposes, including as fertilizer for agriculture, horticulture and landscaping.
Sewage, also known as municipal wastewater, refers to water that is used in urban and suburban homes and businesses for washing, bathing and flushing toilets. It may also includer water from some industrial sources, but that water generally must be pre-treated to remove toxic chemicals and other pollutants before it is released into a sewer system.
