(a) Ventilation. A nitrifying trickling filter must
include forced ventilation to distribute airflow throughout the underdrain
area. The minimum design airflow rate must be the greater of:
(1) 50 pounds of oxygen provided per pound of oxygen
required at average organic loading, based on stoichiometry; or
(2) 30 pounds of oxygen provided per pound of oxygen
required at peak organic loading, based on stoichiometry.
(b) Temperature. The engineering report must justify
the temperature used in the design equations. A design may include
deep towers or other means to minimize recirculation while providing
a design hydraulic dosing intensity that lessens the effects of temperature
on removal efficiency.
(c) pH. The engineering report must document that the
design recirculation rates are appropriate for dealing with the effects
of pH.
(d) Predation. A nitrifying trickling filter must include
a means for control of biomass predators, such as snails.
(e) Hydraulic Application Rates. A nitrifying trickling
filter must operate at a design dosing intensity of at least 1.47
gallons per minute per square foot and provide operational control
of dosing intensity.
(f) Media. Crossflow synthetic media is required for
a new tertiary nitrification filter or for the nitrifying section
of a new combined nitrification filter.
(g) Tertiary Nitrification Filters. A trickling filter
treating influent that has a fiveday biochemical oxygen demand (BOD_{5 }) to total Kjeldahl nitrogen (TKN) ratio of
equal to or greater than 1.0 and soluble BOD_{5 } of
less than or equal to 12 milligrams per liter (mg/l) is a tertiary
nitrification filter.
(1) Design Justification. The engineering report must
include process design calculations and selection criteria of kinetic
coefficients for a tertiary nitrification trickling filter. The design
calculations and selection criteria must be justified by operating
data from an existing trickling filter of similar construction and
operation.
(2) Media biotowers. A tertiary nitrification trickling
filter design must minimize pH depression due to recirculation. A
tertiary nitrification trickling filter must use either:
(A) a single tower at least 20 feet tall; or
(B) a series of towers less than 20 feet tall. The
design must include provisions to readily switch the operating sequence
of the trickling filters if multiple towers are operated in series.
(h) Combined BOD_{5 } and
Nitrification Filters. A trickling filter intended to perform nitrification
and treating influent having a BOD_{5 } to
TKN ratio of less than 1.0 or soluble BOD_{5 } of
less than 12 mg/l is a combined BOD_{5 } and
nitrification filter.
(1) Design Justification. The engineering report must
justify the projected treatment efficiency and other design parameters
of a combined BOD_{5 } and nitrification
trickling filter by including operating data from any existing trickling
filter of similar construction and operation.
(2) BOD_{5 } Removal Requirements.
A combined BOD_{5 } and nitrification filter
must achieve effluent total BOD_{5 } of less
than 15 mg/l.
(3) Recirculation. A combined BOD_{5 } and
nitrification filter design must enable a high recirculation rate
with turndown capability.
