Environmental Engineering Reference
In-Depth Information
or cleaned on a time- or flow-controlled cycle. As with the manually
cleaned screen, the area surrounding the mechanically operated screen
must be cleaned frequently to prevent a buildup of materials that can
cause unsafe conditions. As with all mechanical equipment, operator
vigilance is required to ensure proper operation and that proper main-
tenance is performed. Maintenance includes lubricating equipment and
maintaining it in accordance with manufacturer's recommendations or
the plant's operations and maintenance (O&M) manual. Screenings from
mechanically operated bar screens are disposed of in the same manner
as screenings from manually operated screens: landfill disposal, incin-
eration, or being ground into smaller particles for return to the waste-
water flow.
5.3.2.1.1 operational Considerations
Many of the operational problems associated with mechanically
cleaned bar screens are the same as those for manual screens: sep-
tic wastes entering the primary, surge flows after cleaning, excessive
grit in the bar screen channel, or frequent screen clogging. Basically,
the same corrective actions employed for manually operated screens
would be applied for these problems in mechanically operated screens.
In addition to these problems, however, mechanically operated screens
also have others, including the cleaner not operating at all or the rake
not operating even though the motor is. Obviously, these are mechani-
cal problems that could be caused by a jammed cleaning mechanism,
broken chain, broken cable, or broken shear pin. Authorized and fully
trained maintenance operators should be called in to handle these types
of problems.
5.3.1.3 Screening Safety
The screening area is the first location where the operator is
exposed to the wastewater flow. Any toxic, flammable, or explosive gases
present in the wastewater can be released at this point. Operators who
enter enclosed bar screen areas should be equipped with personal air
monitors. Adequate ventilation must be provided.
It is also important to remember that, due to the
grease attached to the screenings, this area of the
plant can be extremely slippery. Routine cleaning
is required to minimize this problem.
Key Point:
Never override any
safety devices on mechanical
equipment. Overrides can result in
dangerous conditions, injuries, and
major mechanical failure.
5.3.1.4 Screenings Removal Calculations
Operators responsible for screenings disposal are typically required
to keep a record of the amount of screenings removed from the wastewa-
ter flow. To keep and maintain accurate screening records, the volume of
screenings withdrawn must be determined. Two methods are commonly
used to calculate the volume of screenings withdrawn:
