Current through Register Vol. 56, No. 18, September 16, 2024
(a) For intermittent
sand filters, at least two filter units shall be provided.
(b) Sod and similar coverings over intermittent
sand filters are prohibited.
(c) Loading
requirements for intermittent sand filters are as follows:
1. Organic loading of five-day B.O.D. shall not
exceed 3.8 pounds per 1,000 square feet per day;
2. With acceptable primary treatment of normal
sewage, volumetric loading shall not exceed 2,875 gallons per 1,000 square feet per
day. For stronger sewage the rate of filtration shall be proportionately
lower.
3. For chemical coagulation and
sedimentation the volumetric loading shall not exceed 5,750 gallons per 1,000 square
feet per day.
4. For standard or high
rate trickling filters or activated sludge followed by secondary settling tanks, the
volumetric loading shall not exceed 9,200 gallons per 1,000 square feet per
day.
5. For schools, camps, and
institutions, not having a full-time treatment plant operating staff, volumetric
loading should not exceed 1,150 gallons per 1,000 square feet per day for primary
tank effluent.
(d)
Intermittent sand filter media shall be in conformance with the following:
1. Clean graded gravel shall be placed in at least
three layers over the entire floor of the bed and around the underdrains and to a
depth of at least six inches. Grading for the three layers shall be 1 1/2 inches to
3/4 inch, 3/4 inch to 1/4 inch and 1/4 inch to 1/8 inch.
2. Underdrains shall have maximum spacing not
exceeding six feet and shall be at least four inches in diameter, or of equivalent
area.
3. Pipes shall be laid on a firm
base with open joints with a space of approximately 1/4 inch between ends.
i. A single layer of muslin, cheese cloth, burlap
or other suitable material shall be wrapped around each joint of open joint
underdrains.
ii. Tar paper or other
waterproof material may not be used.
iii. Perforated clay or other approved perforated
pipe may be used for underdrains.
4. Sand with an effective size of 0.3 to 0.6
millimeters and a uniformity coefficient of not more than 3.5 shall be provided to a
depth of at least 30 inches. The sand shall be free from clay, loam or
silt.
(e) Intermittent sand
filter dosing shall be in conformance with the following:
1. A dosing tank or its equivalent with a capacity
to dose each filter at least twice a day shall be provided. Where practical, a
dosing tank or equivalent shall have a maximum detention time of two hours based
upon the design flow.
2. The dosing tank
volume shall be such that each filter bed will be covered to a depth not less than
two nor more than four inches with each dose.
3. Siphons shall have a discharge capacity, at
minimum head, of at least 100 percent in excess of the maximum rate of inflow to the
dosing tank, and at average head, at least one cubic foot per second per 5,000
square feet of each filter bed.
(f) Intermittent sand filter distribution shall be
in conformance with the following:
1. A rotary
distributor may be used if nozzles are adjusted so flow will not erode the sand
bed.
2. Troughs or piping used for
distribution of the settled sewage over the filter surface shall be so located that
the maximum lateral travel distance is not more than ten feet. Provision shall be
made at each discharge port for adjustment of the flow.
3. Splash slabs shall be provided at each point of
discharge.
4. A drain opening from
troughs or discharge piping shall be provided.
(g) The base of the filter shall be either
enclosed with concrete or lined with a material that has a permeability no faster
than 10[LESS THAN]-7 cm[GREATER THAN]/sec.
(h) Rapid sand filter design shall be in
conformance with the following:
1. The use of
rapid sand filters may be considered where treatment beyond secondary treatment is
required and where skilled operational personnel will be present.
2. In general, rates shall not exceed three
gallons per square foot per minute; backwash facilities shall be provided; the sand
bed should not be less than 20 inches in depth; and suitable underdrainage of graded
gravel shall be provided.
3. Operating
head on the filter shall not exceed eight feet.
(i) The use of micro-strainers is acceptable when
additional treatment such as reduction in B.O.D. and suspended solids is required
after secondary treatment and final settling, and will be considered when
accompanied by an engineer's report that contains complete data on the installation
and accompanied by suitable plans.
