Page 95 - Water and Wastewater Engineering Design Principles and Practice

2-38 WATER AND WASTEWATER ENGINEERING

TABLE 2-18
American Water Works Association water quality goals
Contaminant Goal, mg/L a
Turbidity < 0.1 turbidity units (TU)
Color < 3 color units
Odor None
Taste None objectionable
Aluminum < 0.05
Copper < 0.2
Iron < 0.05
Manganese < 0.01
Total dissolved solids (TDS) 200.0
Zinc < 1.0
Hardness 80.0

a
All quantities are mg/L except those for which units are given.
in plant sizing include: (1) number and size of process units, and (2) number and size of ancillary
structures. The layout should include: (1) provision for expansion, (2) connection to the transpor-
tation net, (3) connection to the water distribution system, and (4) residuals handling system.

Number and Size of Process Units
To ensure the provision of water to the public water supply, in general, a minimum of two units
is provided for redundancy. When only two units are provided, each shall be capable of meeting
the plant design capacity. Normally, the design capacity is set at the projected maximum daily
demand for the end of the design period. The size of the units is specified so that the plant can
meet the design capacity with one unit out of service (GLUMRB, 2003). Consideration should
also be given to the efficiency/effectiveness of the process units with the low demand at start up
of the facility.

Number and Size of Ancillary Units
The ancillary units include: administration building, laboratory space, storage tanks, mechanical
building for pumping facilities, roads, and parking. The size of these facilities is a function of the
size of the plant. In small to medium sized facilities, particularly in cold climates and when land
is expensive, administration, laboratory, pumping and storage are housed in one building.
The storage tanks include those for chemicals, treated water, and in some instances fuel.
Space for storage of chemical residuals must also be provided.

Plant Layout
When space is not a constraint, a linear layout generally allows the maximum flexibility for
expansion. Redundancy is enhanced if the units are interconnected in such a way that the flow
through the plant can be shuttled from one treatment train to another. Because chemicals must be
delivered to the plant, connection to the transportation net becomes an integral part of the layout.