| (a) The engineering report must include a justification
for the proposed sludge dewatering units, including design calculations,
results from any pilot studies, all assumptions, and appropriate references.
(b) The design of a dewatering unit must be based on
mass balance principles.
(c) General Requirements.
(1) Centrate or Filtrate Recycle.
(A) The drainage from beds and centrate or filtrate
from dewatering units must be returned to the headworks of the wastewater
treatment facility for treatment.
(B) The design of a treatment unit downstream from
a dewatering unit must be based on the organic load from the centrate
or filtrate recycle.
(2) Sludge with Industrial Waste Contributions. A dewatering
system must prevent the release of any constituent (such as a free
metal, an organic toxin, or a strong reducing or oxidizing compound)
that adversely impacts human health, safety, or welfare, water quality,
or compliance with the associated wastewater permit.
(3) Redundancy.
(A) A mechanical dewatering system must have at least
two dewatering units, unless the engineering report justifies adequate
storage or an alternative means of sludge handling.
(B) Mechanical dewatering units must be able to dewater
the average daily sludge flow with the largest dewatering unit out
of service.
(4) Storage Requirements.
(A) A mechanical dewatering system must have separate
storage if the equipment will not operate on a continuous basis and
the wastewater treatment facility has no digesters with built-in short-term
storage.
(B) In-line storage of stabilized or unstabilized sludge
must not interfere with any treatment unit.
(C) The separate sludge storage from a primary digester
must be aerated and mixed to prevent nuisance odor conditions.
(5) Sampling Points. A dewatering system must have
sampling stations before and after each dewatering unit and must allow
periodic evaluation of the dewatering process.
(6) Maintenance. Each dewatering system unit must have
a bypass to allow for maintenance, repair, and replacement. The engineer
must specify where the bypass flow will be routed in the engineering
report.
(d) Sludge Conditioning.
(1) The design and location of a chemical addition
point must consider interactions of the chemical with other chemicals
and processes used in the wastewater treatment facility.
(2) A dewatering system must provide adequate mixing
time for the reaction between an additive and the sludge. Any subsequent
handling must eliminate floc shearing.
(3) The engineering report must include a pilot plant
or full-size performance data used to determine the characteristics
and design dosage of any sludge additive.
(4) The engineering report must justify the in-stream
flocculation and coagulation system design by including comparable
performance data or pilot plant data.
(5) The engineering report must include whether the
mixers require conditioning tanks.
(6) The engineering report must include calculations
for a range of detention times.
(7) Solution storage capacity, at maximum chemical
demand, must be based on:
(A) the amount of chemical needed per shift for continuous
processes; or
(B) the amount of chemical needed for a full batch
for intermittent and batch processes.
(8) Solution storage capacity may be reduced if the
specific chemical or additive selected is adversely affected by storage.
(9) The engineering report must justify any storage
volume reduction and any other method used to ensure a continuous
supply of chemicals by accounting for chemical use through a full
operating day or a full batch.
(e) Sludge Drying Beds.
(1) The size of sludge drying beds must be based on
data from a similar wastewater treatment facility in the same geographical
area with the same influent sludge characteristics.
(2) If the data required by paragraph (1) of this subsection
is not available, or if the executive director determines that the
data is not appropriate for a proposed wastewater treatment facility,
the design of sludge drying beds must be based on the following:
(A) Open Beds.
(i) A sludge drying bed system must have at least two
sludge drying beds.
(ii) The engineering report must include the calculation
of the minimum surface area for a sludge drying bed using the values
in the following figure for an area of the state with less than 45
inches annual average rainfall or less than 50% annual average relative
humidity, as determined by data from the nearest National Oceanic
and Atmospheric Administration's weather station that has at least
ten years of data. The entire period of record for the weather station
must be used.
Attached Graphic
(iii) Another method of sludge dewatering is required
in lieu of a sludge drying bed in an area of the state that experiences
either 45 or more inches of average annual rainfall or 50% or greater
annual average relative humidity, as determined by data from the nearest
National Oceanic and Atmospheric Administration's weather station
that has at least ten years of data. The entire period of record for
the weather station must be used.
(iv) A sludge drying bed system must:
(I) dewater sludge during normal operations;
(II) provide accelerated sludge dewatering during abnormally
wet conditions;
(III) store accumulated sludge during periods of extended
high humidity and rainfall;
(IV) use an alternative dewatering method to dewater
the sludge during periods of extended high humidity and rainfall;
and
(V) prevent the unauthorized discharge of solids from
the sludge drying beds.
(v) The engineering report must justify the use of
innovative or non-conforming sludge drying beds in high rainfall,
high relative humidity areas of the state, as described in clause
(iii) of this subparagraph.
(B) Gravel Media Beds. A gravel media bed must be laid
in two or more layers. The gravel around the underdrains must be properly
sized to allow drainage. The gravel around the underdrains must be
at least 12 inches deep, extending at least 6.0 inches above the top
of the underdrains. The top layer of a gravel media bed must be at
least 3.0 inches thick and must consist of gravel 1/8 inch to 1/4
inch in size.
(C) Sand Media Beds. A sand media bed must consist
of at least 12 inches of sand with a uniformity coefficient of less
than 4.0 and an effective grain size of at least 0.3 millimeters but
not more than 75 millimeters above the top of the underdrain.
(D) Underdrains.
(i) The underdrains must be at least 4.0 inches in
diameter and a slope of at least 1.0% to the drain.
(ii) The underdrains must not be spaced more than 20
feet apart.
(iii) The engineering report must specify where the
flow from the underdrains will be routed.
(E) Decanting. A sludge drying bed may have a method
of decanting supernatant installed on the perimeter of the bed. The
decanted liquid from a sludge drying bed must be returned to the headworks
of the wastewater treatment facility or to the beginning of the secondary
treatment process.
(F) Walls.
(i) The interior walls of a sludge drying bed must
be watertight and extend 12 inches to 24 inches above and at least
6 inches below the bed surface.
(ii) The exterior walls of a sludge drying bed must
be watertight and extend 12 inches to 24 inches above the bed surface
or ground elevation, whichever is higher.
(G) Sludge Removal.
(i) A sludge drying bed system must be arranged to
facilitate sludge removal.
(ii) The sludge drying beds must have concrete pads
for vehicle support tracks on 20 foot centers for all percolation
type sludge beds.
(H) Sludge Influent.
(i) A sludge pipe to the sludge drying beds must terminate
at least 12 inches above the surface of the media and be arranged
so that the pipe drains to a sump that pumps to the headworks of the
wastewater treatment facility or the influent lift station.
(ii) A sludge discharge point must have a concrete
splash plate.
(I) Drying Bed Bottom.
(i) The bottom of a sludge drying bed must consist
of a layer of clayey subsoil having a thickness of a least 1.0 foot
and a permeability of less than 1 × 10-7 centimeters
per second.
Cont'd... |
