| (v) An aeration system may use non-metallic pipes only
in the aeration basin, but the pipes must be a minimum of 4.0 feet
below the average water surface elevation in the aeration basin.
(c) Mechanical Aeration Systems.
(1) Required Airflow - Equipment and Site Specific
Values. The airflow requirements for a mechanical aeration system
must be calculated in accordance with subparagraphs (A) and (B) of
this paragraph.
(A) Clean Water Oxygen Transfer Efficiency.
(i) The engineering report must include the clean water
oxygen transfer efficiency rate for the mechanical equipment.
(ii) The clean water oxygen transfer efficiency must
not exceed 2.0 pounds of oxygen per horsepower-hour unless justified
by full scale performance data. Full scale performance data must be
developed by an accredited testing laboratory or a licensed professional
engineer. Data developed by a professional engineer must be sealed
by the engineer. Full scale performance tests must follow the oxygen
transfer testing methodology described in the most current version
of the ASCE publication, A Standard for the
Measurement of Oxygen Transfer in Clean Water.
(iii) A technology with a proposed clean water oxygen
transfer efficiency in excess of 2.0 pounds of oxygen per horsepower-hour
is innovative technology and subject to the requirements of §217.7(b)(2)
of this title (relating to Types of Plans and Specifications Approvals).
(B) Wastewater Oxygen Transfer Efficiency.
(i) The engineering report must include the actual
wastewater oxygen transfer efficiency and data to justify the actual
wastewater oxygen transfer efficiency.
(ii) If a wastewater treatment facility will receive
more than 10% industrial wastewater by volume, all mechanical aeration
equipment must be sized based on a wastewater oxygen transfer efficiency
of no more than 0.65 times the clean water oxygen transfer efficiency.
(2) Mixing Requirements.
(A) A mechanical aeration device must provide mixing
to prevent mixed liquor suspended solids (MLSS) deposits under any
flow condition.
(B) A mechanical aeration device must be capable of
re-suspending the MLSS after a shutdown period.
(C) Mechanical aeration devices with a channel or basin
layout must have a minimum of 100 horsepower per million gallons of
aeration basin volume or 0.75 horsepower per thousand cubic feet of
aeration basin volume.
(3) Mechanical Components.
(A) Process Reliability.
(i) Each aeration basin must include a minimum of two
mechanical aeration devices.
(ii) A mechanical aeration device must meet the maximum
design requirements for oxygen transfer with the largest single unit
out of service.
(iii) A mechanical aeration device must either automatically
restart after a power outage, or have a telemetry system or an auto-dialer
with battery backup to notify an operator of any outage.
(B) Operation and maintenance.
(i) A mechanical aeration device must have two-speed
or variable-speed drive units, unless another means of varying the
output is provided.
(ii) To vary the output, a mechanical aeration device
may use single-speed drive units with timer-controlled operation if
the device also includes an independent means of mixing.
(iii) A wastewater treatment facility must be designed
such that an operator is able to perform routine maintenance on the
aeration equipment without coming into contact with wastewater.
(iv) Each bearing, drive motor, or gear reducer must
be accessible to an operator for maintenance and must be equipped
with a splash prevention device. A splash prevention device must be
designed to protect the operator from contact with wastewater and
to prevent wastewater from escaping the basin.
(v) Each gear reducer must have a drainage system to
prevent operator contact with mixed liquor.
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