Civil Engineering Reference
In-Depth Information
meet the established process objectives. A process that appears to work on paper may
experience operational difficulties during pilot testing as a result of some unforeseen
water chemistry complication. It is better to identify such problems during pilot testing
than to discover a problem after expensive treatment facilities have been constructed.
Iron and Manganese Treatment Plant Layout
The typical iron and manganese removal plant is a stand-alone facility providing treat-
ment at a well head or for a wellfield. Iron and manganese oxidation and filtration
may occur as a secondary benefit of other treatment processes. Those types of plants
will not be considered here. Iron and manganese treatment plants are simple in design
and layout. A typical plant will consist of a chemical feed system, pressure filters, and
backwash water processing facilities. Gravity filters may be used for iron and man-
ganese removal, depending on the hydraulic conditions at the facility. Pumps for pro-
cess or backwash supply may be required, as well as standby power generation. A
small lab or control room provides the operator a convenient place to monitor plant
performance and prepare regular reports. Iron and manganese removal plants often
operate unstaffed, being controlled instead by a supervisory control and data acquisi-
tion (SCADA) system.
The layout of an iron and manganese plant should account for seasonal variations
in water demand and for projected system growth. It is recommended that a minimum
of two filters be provided in the treatment plant. To minimize the size of the backwash
facilities and to provide flow flexibility, it is recommend that the maximum filter size
be between 400 and 700 gpm (25 and 44 l / s). During the low-demand months of the
winter, filters can be taken off line to reduce operations and maintenance costs and
provide an opportunity for maintenance and repair.
The typical iron and manganese removal treatment plant uses pressure filters. These
types of filters offer the advantage of a flow-through configuration and eliminate the
need to repump. The finished water is pumped through the filters either directly into
the distribution system or into the system storage reservoir. A gravity filtration system,
on the other hand, usually requires a clearwell and pumps to lift the filtered water into
the system, resulting in higher capital costs.
Washwater Recycle
A large volume of water is used during a backwash cycle to clean and restore a filter's
capacity. This volume of water can account for as much as 5 percent of the total water
produced during the filter run. In many instances, this water is wasted to the sanitary
sewer system and lost. The large slug flow can overload the sewer system and cause
problems at the wastewater treatment plant. To alleviate this condition, the treatment
facility can install holding tanks or basins to meter the washwater into the sewer
system; this will reduce the hydraulic loading on the sewer system. The installation
of holding tanks or basins, however, does not reduce the amount of water lost to the
sewer system during every backwash cycle.
Water conservation concerns are driving many utilities to consider washwater re-
cycle for their iron and manganese removal plants. Washwater recycle is the process
of returning the washwater supernatant to the head end of the treatment plant for
reprocessing rather than just dumping it down the sewer. By recycling the water after
settling in a covered tank or basin, the majority of the water is returned to the system
