Current through Register Vol. 41, No. 3, September 23, 2024
A. Grit removal unit operations facilities
shall be provided for all sewage treatment works with a design capacity of 0.15
million gallons per day or greater and are required for treatment works
receiving sewage from combined sewers or from sewer systems receiving
substantial amounts of grit. Grit removal facilities should be provided at all
sewage treatment works.
1. Grit removal
facilities should be located ahead of pumps and comminuting devices. Coarse bar
racks and other suitable screens should be placed ahead of mechanically cleaned
grit removal facilities.
2.
Treatment works treating wastes from combined sewers shall have at least two
mechanically cleaned grit removal units, with provisions for unit
bypassing.
3. A single manually
cleaned or mechanically cleaned grit removal unit, with a unit bypass, is
acceptable for those sewage treatment works with a design capacity of less than
0.15 million gallons per day and serving separate sanitary sewer
systems.
4. Minimum facilities for
larger treatment works serving separate sanitary sewers shall be at least one
mechanically cleaned unit with a unit bypass.
B. Design. The design of grit removal
facilities shall be based on the requirements of the downstream treatment
units. Local conditions and wastewater characteristics shall be evaluated in
selecting the design size of particle to be removed. Flow turbulence into and
through grit removal basins shall be minimized.
1. Horizontal flow basins shall be designed
so as to provide controlled velocities as close as possible to one foot per
second during average design flow conditions. The detention period shall be
based on the size of particle to be removed. The design should take into
consideration hydraulic inefficiencies and positioning of inlets and
outlets.
2. Aerated chambers shall
be designed to provide a minimum detention time of three minutes at average
flow. An air flow of three to five cubic feet per minute per foot of chamber
length should be maintained. Aerated chambers shall have adequate and flexible
controls for agitation and air supply devices.
3. Other types of degritters will be approved
on a case-by-case basis upon evaluation of satisfactory performance
data.
4. Wherever possible, grit
removal facilities should be located in open areas with easy access. Grit
removal facilities located in deep pits shall be provided with mechanical
equipment for pumping or hoisting grit to ground level. Such pits shall have a
stairway, elevator, or manlift, adequate ventilation, and adequate lighting in
accordance with VOSH requirements.
5. Provisions shall be made for dewatering
each unit. Drain lines shall discharge to points within the system such that
maximum treatment of the contents of the drained unit is provided.
6. The provision of grit washing facilities
shall be a function of the ultimate disposal and transportation methods
provided for the grit. Impervious surfaces with drains shall be provided for
grit handling areas. If grit is to be transported, conveying equipment shall be
designed to avoid loss of material.
Statutory Authority
§ 62.1-44.19 of the Code of Virginia.
