Harvey H. Harper, Ph.D., P.E. and Jeffrey L. Herr, P.E.
Environmental Research & Design, Inc.
3419 Trentwood Blvd., Suite 102; Orlando, FL
Phone: (407) 855-9465; Fax: (407) 826-0419; email: email@example.com
Eric H. Livingston
Florida Department of Environmental Protection
Bureau of Water Resource Protection/Nonpoint Source Management
Twin Towers Office Building - MS 3570
2600 Blair Stone Road; Tallahassee, FL
Phone: (850) 921-9915; Fax: (850) 921-5655; email: LIVINGSTON_E@dep.state.fl.us
Since at least Roman times, salts of aluminum have been added to drinking water and surface water to reduce
turbidity and improve appearance.
Aluminum sulfate, Al
, commonly called alum, has been used
extensively as a flocculating agent in the treatment of wastewater for over 100 years.
In 1970, Jernelov was
apparently the first to use alum to remove phosphorus from the water column of a lake in a whole-lake alum
application conducted as part of a lake restoration project on Lake Langsjon in Sweden.
The first U.S. lake to be
treated with a whole-lake alum application was Horseshoe Lake in Wisconsin which received a surface application
of 2.6 mg Al/liter in May 1970.
Twelve years later, phosphorus concentrations were still below the pre-treatment
level (Garrison and Knauer, 1984).
The addition of alum to water results in the production of chemical precipitates which remove pollutants by two
Removal of suspended solids, algae, phosphorus, heavy metals and bacteria occurs primarily
by enmeshment and adsorption onto aluminum hydroxide precipitate according to the following net reaction:
Removal of additional dissolved phosphorus occurs as a result of direct formation of AlPO
The aluminum hydroxide precipitate, Al(OH)
, is a gelatinous floc which attracts and adsorbs colloidal particles
onto the growing floc, thus clarifying the water.
Phosphorus removal or entrapment can occur by several
mechanisms, depending on the solution pH. Inorganic phosphorus is also effectively removed by adsorption to the
Removal of particulate phosphorus is most effective in the pH range of 6-8 where maximum floc
occurs (Cooke and Kennedy, 1981).
At higher pH values, OH
begins to compete with phosphate ions for
aluminum ions, and aluminum hydroxide-phosphate complexes begin to form.
At lower pH values and higher
inorganic phosphorus concentrations, the formation of aluminum phosphate (AlPO
) is favored.
In 1985, a lake restoration project was initiated at Lake Ella, a shallow, 13.3 ac hypereutrophic lake in Tallahassee,
Florida, which receives untreated stormwater runoff from approximately 163 ac of highly impervious urban
Initially, conventional stormwater treatment technologies, such as retention basins, exfiltration
trenches and filter systems, were considered for reducing available stormwater loadings to Lake Ella in an effort to
improve water quality within the lake.