MATERIALS AND EQUIPMENT (cont.)

bottom or mechanical sludge collector should be

allowed as a Contractor's option. However, of the

various types of mechanical sludge collectors,

rotating sludge collectors appear to be available

for plants of 1.31 L/s 30,000 GPD and above;

chain-and-flight, 1.75 L/s 40,000 GPD and above;

traveling reciprocating type, 0.66 L/s 15,000 GPD

and above.

**************************************************************************

NOTE: Delete "(if used)" for extended aeration type

of 4.38 L/s 100,000 GPD capacity and above; for step

aeration type 3.0 L/s 67,500 GPD capacity and above;

and all complete mixing type plants.

**************************************************************************

NOTE: Delete reference to comminutor when not

required for plant. For plants of 1.09 L/s 25,000

GPD capacity and below, the comminutor and bar

screen unit may be omitted, and in lieu thereof, a

screening basket provided in the aeration tank. For

installations in which all sewage has passed through

a comminutor and bar screen upstream of the plant, a

comminutor and bar screen unit need not be provided

as a part of the plant equipment.

**************************************************************************

NOTE: Delete reference either to chlorinator or to

hypochlorinator. Hypochlorinator should be

specified for all plants 4.38 L/s 100,000 GPD

capacity and below. Chlorinator should be specified

for all plants 6.57 L/s 150,000 GPD capacity and

above. Between 4.38 L/s and 6.57 L/s 100,000 GPD

and 150,000 GPD capacity either is suitable.

Selection should be made on basis of existing

station or base practices, local availability, and

comparative costs.

**************************************************************************

NOTE: Delete last sentence when concrete plant only

is required. This specification is structured for

steel plant only, concrete plant only, or steel or

concrete plant at the Contractor's option. Among

the factors to be considered are initial cost,

maintenance costs, life expectancy, and possible

need for relocation during period of useful life.

Steel plant is generally more economical in first

cost than concrete plant; however, maintenance costs

may be higher. Concrete plant would have a higher

life expectancy in highly corrosive soils. Small

steel plants are suitable for relocation. Concrete

plant is considered as plant having outer walls of

concrete regardless of material used for interior

walls or partitions. Steel plants are considered as

plants having outer walls of steel and bottom of

SECTION 11375N

Page 26