| (3) The floor of a new trickling filter using stackable
modular or synthetic media must slope toward a drainage channel at
a slope of at least 1% and not more than 5%, based on filter size
and hydraulic loading.
(m) Passive Ventilation.
(1) The effluent channels and effluent pipes of an
underdrain system or a synthetic media support structure must permit
free passage of air.
(2) Any drain, channel, or effluent pipe must have
a cross-sectional area with not more than 50% of the area submerged
at peak flow plus recirculation.
(3) The effluent channels must accommodate the specified
flushing hydraulic dosing intensity and allow the possibility of increased
(4) A passive ventilation system may include an extension
of an underdrain through a trickling filter sidewall, a ventilation
opening through a sidewall, or an effluent discharge conduit designed
as a partially full flow pipe or an open channel.
(5) A vent opening through a trickling filter wall
must include hydraulic closure to allow flooding of a trickling filter
for nuisance organism control.
(6) A passive ventilation design must provide at least
2.5 square feet of ventilating area per 1,000 pounds of primary effluent
BOD5 per day.
(7) An underdrain system for a rock media filter must
provide at least 1.0 square foot of ventilating area for every 250
square feet of the trickling filter basin surface area.
(8) The minimum required ventilating area for a synthetic
media underdrain is the area recommended by the manufacturer. The
manufacturer's recommendations must be included in the engineering
(9) The ventilating area must be equal to the greater
of 1.0 square foot per 175 square feet of synthetic media area or
2.6 square feet per 1,000 cubic feet of media volume.
(n) Forced Ventilation.
(1) Forced ventilation is required for a trickling
filter designed for:
(B) a trickling filter design with a media depth in
excess of 6.0 feet; and
(C) a location where seasonal or diurnal temperatures
do not provide sufficient difference between the ambient air and wastewater
temperatures to sustain passive ventilation of one cubic foot of air
per square foot of trickling filter area per minute.
(2) A design must specify the minimum airflow for forced
ventilation and optimized process performance, and the engineering
report must include all calculations associated with this determination.
(3) The design of a down-flow forced ventilation system
must include a provision for:
(A) the removal of entrained droplets; or
(B) the return of air containing entrained moisture
to the top of a trickling filter; and
(C) a reversible fan or other mechanism to reverse
the airflow when a wide temperature difference between the ambient
air and wastewater creates strong updrafts.
(4) A ventilation fan and the associated controls must
withstand flooding of a trickling filter without sustaining damage.
(5) The following equation and the values in Table
G.3. in Figure: 30 TAC §217.182(n)(5) determine the minimum airflow
rate for forced ventilation.
(1) Cleaning and Sloughing.
(A) A flow distribution device, an underdrain, a channel,
and a pipe must allow for maintenance, flushing, and drainage.
(B) A trickling filter system must hydraulically accommodate
the specified flushing hydraulic dosing intensity and must facilitate
cleaning and rodding of the distributor arms.
(C) A trickling filter system must prevent recirculation
of sloughed biomass in pieces larger than the distributor nozzle openings
or the filter media voids.
(2) Nuisance Organism Control. A trickling filter system
must control nuisance organisms by operation of trickling filters
at proper design dosing intensities, with periodic flushing at higher
(A) Filter Flies.
(i) The structural and hydraulic design of a trickling
filter must enable flooding of the trickling filter for fly control.
(ii) The executive director may approve an alternate
method of fly control for a trickling filter that exceeds 6.0 feet
in height if the effectiveness of the alternate method is verified
at a full-scale installation and documented in the engineering report.
(B) Snails. A trickling filter system must be designed
to prevent sludge accumulation that attracts snails. A trickling filter
system must include a low-velocity, open channel between a trickling
filter and final clarifier for manual removal of snails.
(3) Corrosion Protection. A trickling filter must be
designed to prevent corrosion. Corrosion-resistant materials must
be used for all equipment and for construction of a trickling filter,
including ventilation equipment and covers.
(p) Flow Measurements. A trickling filter system must
include a means to measure the flow to each trickling filter and the
recirculation flow of each trickling filter.
(q) Odor Control. A trickling filter system must use
ventilation and periodic flushing at a higher dosing intensity to
minimize potential odor.
(A) The executive director may require an owner of
a wastewater treatment facility with prior odor complaints to install
a cover over a new or altered trickling filter.
(B) A cover must allow access to the entire top of
the trickling filter media and to the distributor for maintenance
(C) A covered trickling filter must have a forced ventilation
system with a scrubber or an adsorption column for odor control.
(2) Stripping. A trickling filter with an influent
organic strength of BOD5 greater than
200 milligrams per liter must have forced ventilation in a down-flow
mode to minimize odor. Odorous off-gases may be:
(A) recycled through a trickling filter;
(B) used to ventilate a tertiary nitrifying trickling
filter in an up-flow mode;
(C) diffused into an aeration basin; or
(D) treated separately for odor control using a scrubber
or an adsorption column.
(r) Final Clarifiers. The size of the final clarifiers
for a wastewater treatment facility with a trickling filter must ensure
the required effluent total suspended solids removal at the peak flow
with all recirculation pumps in operation.
(s) Report Requirements.
(1) The engineering report must specify the trickling
filter efficiency formula used in the design calculations.
(2) The engineering report must include the operating
data from any existing trickling filter of similar construction and
operation to justify the projected treatment efficiency, kinetic coefficients,
and other design parameters as required in this subchapter.
(3) The engineering report may include more than one
set of applicable design equations to allow crosschecking of predicted