Iron and Manganese Removal - Public Water Systems - page 441

CHAPTER 14
Iron and Manganese Removal
INTRODUCTION
Water containing iron and manganese is visually objectionable to consumers because
precipitation of these metals causes the water to turn a rusty-looking yellow-brown or
black. It can stain plumbing fixtures and laundry, and when used for irrigation, can
stain buildings and concrete surfaces. It can also produce objectionable tastes and other
aesthetic problems.
The presence of iron and manganese may also lead to the growth of microorganisms
in a water distribution system. Slime layers several centimeters thick have been ob-
served in distribution pipelines. These accumulations—which consist of hydrous iron,
manganese oxides, and bacteria—reduce pipeline capacity, require higher chlorine dos-
ages, and deplete dissolved oxygen (DO) levels. Sloughing or resuspension of this
material by high pipeline velocities during hydrant flushing or peak demand periods
causes high turbidities and leads to complaints of rusty or black water. Taste-and-odor
complaints can be expected if the biological slime decomposes prior to arriving at the
customer tap. Discussions of bacteria associated with the presence of iron and man-
ganese can be found in Water Quality and Treatment and Standard Methods. 1,2
The presence of iron and manganese in a water system has not been linked to
health problems and is not regulated on these grounds. Thus, removal of iron and
manganese has not received the attention and funding given to other treatment pro-
cesses. In the absence of both a strong consumer demand for low iron and manganese
levels at the tap and a willingness to pay for construction of treatment facilities, water
systems have operated with elevated levels of these metals for extended periods of
time. Some consumers deal with the iron and manganese problem at their homes by
installing ion exchange water softeners or by changing the way they use the water for
washing, cooking, and irrigation.
Water containing less than 0.1 mg / L of iron and 0.05 mg / L of manganese is not
objectionable to the average customer; however, some industries may require lower
levels of these metals. An American Water Works Association (AWWA) task group
suggested limits of 0.05 mg / L for iron and 0.01 mg / L for manganese for an ''ideal''
quality water for public use. 3 The U.S. Environmental Protection Agency (USEPA)
has established secondary maximum contaminant levels (SMCLs) for iron and man-
ganese at 0.3 mg / L and 0.05 mg / L, respectively. Although regulations and suggested
limits in Europe allow small concentrations of iron and manganese in drinking water,
the goal there is to try to achieve nondetectable iron and manganese concentrations in
the drinking water delivered to the customer.
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