| (4) A manometer design must specify all safety devices
that are needed for a manometer pipe system and must list the safety
items in the engineering report.
(p) Gas Piping. The gas piping for an anaerobic digester
must be equipped with gauges that measure the following in inches:
(1) the pressure of the main pipe;
(2) the pressure to gas-utilization equipment; and
(3) the pressure to waste burners.
(q) Digestion Temperature Control.
(1) Passive Temperature Control.
(A) A digester must be constructed above the shallowest
groundwater table, including any perched water tables.
(B) A digester must be insulated to minimize heat loss.
(2) Heating Facilities.
(A) The sludge must be heated by circulating the sludge
through an external heater.
(B) A piping system must allow for the preheating of
feed sludge before introduction to the digesters, unless effective
mixing is provided within a digester.
(C) A pipe and valve layout must facilitate cleaning.
(D) The size of a heat exchanger sludge pipe must be
based on the heat transfer requirements.
(3) Heating Capacity.
(A) A digester system must have the heating capacity
to maintain the temperature required for sludge stabilization established
in subsection (j)(3) of this section.
(B) A digester system must be able to use an alternate
source of fuel and must have an alternate source of fuel available
for emergency use.
(4) Mixing. A digester system must have equipment to
mix the sludge.
(5) Location of a Sludge Heating Device. A sludge heating
device with an open flame must be located above grade and in an area
separate from gas production and any storage area.
(r) Supernatant Withdrawal.
(1) Pipe Size. The minimum diameter for a supernatant
pipe is 6.0 inches.
(2) Withdrawal Arrangements.
(A) The supernatant pipes must be arranged to allow
withdrawal from three or more levels in a tank.
(B) A supernatant selector must have at least two draw-off
levels located in the digester's supernatant zone, in addition to
an unvalved emergency supernatant draw-off pipe.
(C) A supernatant withdrawal system must have a positive,
unvalved, vented emergency overflow. The engineer must specify where
overflow is routed in the engineering report.
(D) A supernatant withdrawal level design must be based
on a fixed cover digester design.
(E) Supernatant withdrawal must be by means of interchangeable
extensions at the discharge end of a withdrawal pipe.
(F) A supernatant piping system must have high-pressure
backwash equipment.
(3) Sampling.
(A) A supernatant pipe must have sampling points at
each supernatant draw-off level.
(B) The minimum diameter for a sampling pipe is 1.5
inches.
(4) Supernatant Handling.
(A) The engineering report must include how the treatment
units are designed to handle shock organic loads associated with digester
supernatant.
(B) Supernatant liquor from an anaerobic digester must
either be returned directly to the headworks of the wastewater treatment
facility for treatment, or may be chemically treated before being
returned to the headworks for treatment. Any other method of treating
supernatant liquor must be approved in writing by the executive director.
(C) If treating the supernatant liquor with lime, each
of the following requirements must be met:
(i) Lime must be applied to obtain a pH of at least
11.5 standard units.
(ii) A lime feeder must be capable of feeding 2,000
milligrams per liter of hydrated lime or its equivalent.
(iii) Lime must be mixed with the supernatant liquor
by a rapid mixer or by agitation with air in a mixing chamber.
(iv) After adequate mixing, the solids must be allowed
to settle.
(D) A supernatant liquor treatment system may be either
a batch or a continuous process.
(i) A batch process may have both the mixing and the
settling processes in the same tank.
(ii) A sedimentation tank for a batch process must
have the capacity to hold at least 36 hours of supernatant liquor
at design flow, but not less than 1.5 gallons per capita based on
the design population of the service area.
(iii) A sedimentation tank for a continuous process
must have a detention time of not less than 8.0 hours.
(E) The solids from the supernatant liquor treatment
must be returned to a digester or conveyed to a sludge handling unit.
(F) The clarified supernatant liquor must be returned
to the headworks of the wastewater treatment facility in accordance
with §217.242 of this title (relating to Control of Sludge and
Supernatant Volumes).
(s) Anaerobic Digester Covers.
(1) An uncovered anaerobic digester is prohibited.
(2) The sludge and supernatant withdrawal pipes for
a single-stage or a first-stage digester with a fixed cover must be
arranged to minimize the possibility of air being drawn into a gas
chamber above the liquid in a digester.
(3) A digester cover must include a gas chamber.
(4) A digester cover must be gas tight. The specifications
must include a test of each digester cover for gas leakage.
(5) A digester cover must be equipped with an air vent
with a flame trap, a vacuum breaker, and a pressure relief valve.
(t) Aerobic Sludge Digestion. This subsection applies
to the stabilization by aerobic digestion of waste sludge to Class
B biosolids, as defined in Chapter 312 of this title (relating to
Sludge Use, Disposal, and Transportation).
(1) Solids Management. The engineering report must
include a solids management plan.
(2) Detention Time. The design temperature of an aerobic
digester system must be based on the average of the lowest consecutive
seven-day water temperature from an aerobic digester at a wastewater
treatment facility located within 50 miles of the proposed site.
(3) Mass Balance Requirements. Mass balance calculations
must be included in the engineering report. The mass balance calculations
must take into account design sludge age, wastestream concentration,
operational hours, operational volume in the tanks, decant or dewatering
volumes and characteristics, time needed for decanting or dewatering,
and the volume needed for storage and sampling.
(4) Single Stage. Single stage aerobic digestion consists
of utilizing one tank operating in continuous-mode-no-supernatant
removal, continuous-mode-feeding-batch removal, or other mode detailed
in a solids management plan.
(A) The size of an aerobic digester must be based on
the minimum total detention time for the water temperature in the
table located in subparagraph (B) of this paragraph based on Chapter
312 of this title and 40 Code of Federal Regulations Part 503.
(B) The digester size must be sufficient to provide
both the detention time in the following table and to provide for
the mass load received by the unit:
Attached Graphic
(5) Multiple Stage. Multiple stage aerobic digestion
consists of two or more completely mixed digesters operating in series.
(6) Field Data.
(A) Any increase in flow or organic loading, or any
change in process requires new testing and verification of time and
temperature operating parameters.
(B) An expansion of an existing wastewater treatment
facility may be designed and operated according to previously established
time and temperature operating parameters.
(C) The executive director may re-rate a wastewater
treatment facility under Subchapter B of this chapter (relating to
Wastewater Treatment Facility Design Requirements), if an owner requests
a re-rating and submits sufficient supporting data.
(7) Design Requirements.
(A) The maximum solids concentration used to calculate
the total detention time for an aerobic digester that concentrates
the waste sludge only in a digester tank must be 2.0% solids concentration,
unless:
(i) supporting data is submitted in the engineering
report to increase the solids concentration to 3.0%; or
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