Environmental Engineering Reference
In-Depth Information
5.3.2.1 Comminution
The
comminutor
is the most common shredding device used in
wastewater treatment. In this device, all of the wastewater flow passes
through the grinder assembly. The grinder consists of a screen or slot-
ted basket, a rotating or oscillating cutter, and a stationary cutter. Solids
pass through the screen and are chopped or shredded between the two
cutters. The comminutor will not remove solids that are too large to fit
through the slots, and it will not remove floating objects. These materi-
als must be removed manually. Maintenance requirements for comminu-
tors include aligning, sharpening and replacing cutters, and corrective
and preventive maintenance performed in accordance with the plant's
O&M manual.
5.3.2.1.1 operational Considerations
Common operational problems associated with comminutors
include output containing coarse solids. When this occurs, it is usually
a sign that the cutters are dull or misaligned. If the system does not
operate at all, the unit is clogged or jammed, a shear pin or coupling
is broken, or electrical power is shut off. If the unit stalls or jams fre-
quently, this usually indicates cutter misalignment, excessive debris in
the influent, or dull cutters.
Note:
Only qualified maintenance operators should perform mainte-
nance of shredding equipment.
5.3.2.2 Barminution
In barminution, the
barminutor
uses a bar screen to collect solids,
which are then shredded and passed through the bar screen for removal
at a later process. In operation, the cutter alignment and sharpness of
each device are critical factors in effective operation. Cutters must be
sharpened or replaced and alignment must be checked in accordance
with the manufacturer's recommendations. Solids that are not shred-
ded must be removed daily, stored in closed containers and disposed of
by burial or incineration. Barminutor operational problems are similar
to those listed for comminutors. Preventive and corrective maintenance
as well as lubrication must be performed by qualified personnel and in
accordance with the plant's O&M manual. Because of its higher mainte-
nance requirements, the barminutor is less frequently used.
5.3.3 grit removal
The purpose of grit removal is to remove the heavy inorganic solids
that could cause excessive mechanical wear. Grit is heavier than inor-
ganic solids and includes, sand, gravel, clay, egg shells, coffee grounds,
metal filings, seeds, and other similar materials. Several processes or
devices are used for grit removal. All of the processes are based on the
