| (ii) a higher concentration is justified by the use
of a sludge thickening unit upstream of a digester.
(B) A diffuser must be designed to minimize clogging.
(C) A diffuser must be removable without dewatering
a tank for inspection, maintenance, and replacement. Removable diffusers
are not required if the wastewater treatment facility is designed
with a redundant basin.
(D) The volatile solids loading rate must be designed
to be at least 100 pounds but not more than 200 pounds of volatile
solids per 1,000 cubic feet per day, unless otherwise justified in
the engineering report.
(E) The dissolved oxygen concentration maintained in
the liquid in an aerobic digester must be at least 0.5 milligrams
per liter.
(F) If mechanical aerators are used, the energy input
for mixing must be at least 0.5 horsepower per 1,000 cubic feet.
(G) If diffused air mixing is used, the energy input
for mixing must be at least 20 standard cubic feet per minute per
1,000 cubic feet of aeration tank.
(H) An aerobic digester must be able to separate and
withdraw solids, or must decant the supernatant.
(u) Heat Stabilization.
(1) The design of a heat treatment system must be based
on the anticipated sludge flow, sludge characteristics, and sludge
concentration.
(2) A heat treatment system must operate continuously
to minimize the additional heat input necessary to start up the system,
unless justified in the engineering report.
(3) A heat treatment system must have multiple units,
unless storage or an alternate stabilization method is available.
(4) A single unit heat treatment system must have a
standby grinder, a fuel pump, an air compressor, and dual sludge pumps.
(5) The engineering report must identify the expected
downtime for maintenance and repair, based on data from a comparable
wastewater treatment facility.
(6) The engineering report must include a design for
adequate storage for process feed and downtime.
(7) A heat treatment system must provide heat stabilization
in a reaction vessel:
(A) at a minimum of 175 degrees Celsius (350 degrees
Fahrenheit) for 40 minutes, but not more than 205 degrees Celsius
(400 degrees Fahrenheit) for 20 minutes and at a pressure of not less
than 250 pounds per square inch, gauge, but not more than 400 pounds
per square inch, gauge; or
(B) provide for pasteurization at temperatures of 30
degrees Celsius (85 degrees Fahrenheit) or more and gauge pressure
of more than 1.0 standard atmosphere (14.7 pounds per square inch)
for a period of at least 25 days.
(8) A heat treatment system must have a sludge grinder
to protect a heat exchanger from damage or clogging caused by rags
or other debris.
(9) A heat treatment system must include an acid wash
or high-pressure water wash system to remove scale from heat exchangers
and reactors.
(10) A decant tank must have a sludge scraper mechanism
and must be covered.
(11) A heat exchanger must be constructed of corrosion-resistant
material.
(12) A heat treatment system must have a continuous
temperature recorder.
(v) Recycle Loads.
(1) The engineering report must identify a method of
treatment for the recycle stream from the heat treatment system.
(2) A recycle stream must not impact effluent quality
or the wastewater treatment facility's treatment processes.
(w) Alkaline Stabilization.
(1) Design Basis.
(A) Alkaline Dosage. The engineering report must include
the calculation of the alkaline dosage required to stabilize sludge
based on the type of sludge, chemical composition of sludge, and the
solids concentration in the sludge. Performance data taken from a
pilot test program or from a comparable wastewater treatment facility
must be used to determine the proper dosage.
(B) Temperature, pH, and Contact Time. An alkaline
stabilization system must uniformly mix an alkaline additive-sludge
mixture to maintain the pH, temperature, and contact time, as specified
in §312.82 of this title (relating to Pathogen Reduction) and §312.83
of this title (relating to Vector Attraction Reduction).
(2) Reliability.
(A) An alkaline stabilization system must have multiple
units, unless storage or an alternate stabilization method is available
to continue operations when a unit is not in service.
(B) A single unit that has adequate storage or an alternate
stabilization method must have a standby conveyance and mixer, a backup
heat source, and dual blowers.
(C) A design must include:
(i) the expected downtime for maintenance and repair
based on data from a comparable wastewater treatment facility; and
(ii) adequate storage for process, feed, and downtime.
(3) Alkaline Stabilization Housing Unit.
(A) A housing unit must meet the requirements in §217.247(r)(1)
of this title (relating to Chemical Pretreatment of Sludge).
(B) A housing unit must have mechanical or air agitation
to ensure uniform discharge from the storage bins.
(4) Feeding Equipment.
(A) The alkaline additive feeding equipment must meet
the requirements of §217.247(r)(1) of this title.
(B) Hydrated lime must be fed as a slurry consisting
of at least 6% calcium hydroxide (Ca(OH)2)
by weight but not more than 18% Ca(OH)2 by
weight, unless otherwise justified in the engineering report.
(C) The engineering report must identify a means for
controlling the feed rate of any other dry additive.
(5) Mixing Equipment.
(A) An additive and sludge blending or mixing vessel
must be large enough to hold the mixture for a minimum of 30 minutes
at the maximum feed rate.
(B) A batch process must maintain a pH greater than
12 standard units in a mixing tank during the blending period.
(C) A continuous flow process must maintain a pH greater
than 12 standard units in an exit pipe.
(D) A continuous flow process must be designed for
a detention time that is the tank volume divided by the volumetric
input flow rate.
(E) A slurry mixture may be mixed with either a diffused
air mixer or a mechanical mixer.
(F) The mixing equipment must maintain an alkaline
slurry mixture in complete suspension.
(G) If using a diffused air mixer, the following requirements
apply:
(i) a coarse bubble diffuser must have a minimum air
supply of 20 standard cubic feet per minute per 1,000 cubic feet (cf)
of tank volume; and
(ii) a mixing tank must be ventilated and include odor
control equipment.
(H) If using a mechanical mixer, the following requirements
apply:
(i) a mechanical mixer must provide at least 5.0 horse
power per 1,000 cf of tank volume but not more than 10 horse power
per 1,000 cf of tank volume; and
(ii) the impellers must minimize debris fouling in
the sludge.
(6) Detention Time. A pasteurization vessel must provide
a minimum detention period of 30 minutes.
(7) External Heat. The engineering report must include
specifications about any supplemental external heat necessary for
sludge stabilization.
|
