Grit Removal Processes

MIL-HDBK-1138

Caution: Be aware of the potential for combustible

materials entering with the wastewater. Provide proper

ventilation and equipment to prevent explosive conditions.

Screenings may freeze to the sides and bottom of

containers; prevent this from happening if at all possible.

Grinders may bind because of ice if they are not run often

enough. Consider operating the grinders continually or often

enough to prevent ice buildup. Covering channels with rigid

insulating materials may contain enough heat from the wastewater

within the channel to prevent ice buildup on the grinder. Gear

oil viscosity will be affected by freezing weather. Follow the

manufacturer's recommendations for cold weather maintenance.

Condensation will also occur in the gear boxes of this equipment,

adversely affecting the gear oil. Check the oil routinely (twice

monthly) in the winter.

7.2.2

Grit Removal Processes. Operation of grit-

handling facilities may be very difficult during extremely cold

weather. The grit that is collected and transported will freeze

easily in the equipment used to clean and move it to the holding

container. Temporary enclosures may assist in keeping the

process warm. If this process is to be enclosed, choose the

materials carefully to prevent dangerous or explosive conditions.

Heat-tracing the metal equipment may help prevent ice buildup.

Heat-tracing involves wrapping an electrified wire loop around

the equipment. Running warm water across cleaning areas may also

prevent freezing, depending upon local conditions.

7.2.3

Flow Measurement. Freezing weather conditions may

cause the stilling well of flow measurement devices to freeze.

A solution of mineral oil, or a small amount of antifreeze or a

salt solution, will keep this stilling well liquid. Under low-

flow conditions, some of this antifreeze will drain out and may

need to be replenished periodically. Other remedies are to

enclose the area with rigid insulating board or plywood and to

use a light bulb for heat. Enclosing float wires will prevent

them from freezing.

A layer of frost may coat ultrasonic sensors inside the

cone on the sensor head. Use a thin layer of petroleum jelly on

the face of the detector to prevent this problem. Note that the

sensor should be recalibrated after the jelly is applied.

In systems that have an air bubbler system to measure

the level of water, condensate may become trapped within the air

line and it may freeze. Heat-tracing the air line will prevent

freezing and condensate problems. Dry air will also help prevent

59