| (A) The design of a trickling filter must include a
mechanism to maintain minimum recirculation during periods of low
flow to ensure that the biological growth on the filter media remains
active at all times.
(B) For all trickling filters with continuous recirculation,
the design must include the minimum recirculation rate in the evaluation
of the efficiency of the filter.
(C) Minimum flow to the filters must be equal to or
greater than 1.0 million gallons per day per acre of filter aerial
surface and must ensure the proper operation of the distribution nozzles.
(D) The minimum flow rate for a trickling filter design
using hydraulically driven distributors must keep rotary distributors
turning at the minimum design rotational velocity.
(E) For a wastewater treatment facility designed with
a design flow equal to or greater than 0.4 million gallons per day
and recirculation for BOD5 removal, the
recirculation system must include variable speed pumps and a method
of conveniently measuring the recycle flow rate.
(2) Compensatory Recirculation.
(A) The design of a trickling filter must provide compensatory
recirculation to supplement influent flow if design and flushing dosing
intensities are not achieved solely by the control of distributor
operation.
(B) Controls for the distributor speed and recycle
pumping rate must provide optimum dosing intensity under all anticipated
influent flow conditions.
(3) Process Calculations. The engineering report must:
(A) provide design details about removal of the remaining
organic matter by recirculation;
(B) identify the effect of dilution of the influent
on the rate of diffusion of dissolved organic substrates into the
biofilm; and
(C) identify the effect of reduced influent concentrations
on reaction rates in each section of a filter having first order kinetics.
(4) Recirculation Rate. A recirculation rate may exceed
four times the design flow if calculations to justify the higher rate
are included in the engineering report.
(5) Configuration.
(A) In a wastewater treatment facility with influent
that has constant organic loadings, direct recirculation of unsettled
trickling filter effluent must be used.
(B) A design must ensure that the distributor nozzles
can handle the recirculated sloughed biofilm.
(C) In a wastewater treatment facility with variable
influent organic loadings, effluent must recirculate from a final
clarifier to either a primary clarifier or a trickling filter to equalize
organic loading.
(j) Average Hydraulic Surface Loading.
(1) The engineering report must include calculations
of the maximum, design, and minimum surface loadings on the trickling
filters in terms of million gallons per acre of filter area per day
for the flow expected in the initial year and at full capacity.
(2) The average hydraulic surface loadings of a trickling
filter with crushed rock, slag, or similar media:
(A) must not exceed 40 million gallons per day per
acre based on design flow, except in roughing applications;
(B) must not be less than 1.0 million gallons per day
per acre; and
(C) must be within the ranges specified by the manufacturer.
(k) Underdrain System Design.
(1) A trickling filter must include an underdrain with
semicircular inverts that cover the entire floor of the trickling
filter.
(2) An underdrain must be constructed of vitrified
clay or pre-cast reinforced concrete.
(3) An underdrain constructed of half tile is prohibited.
(4) Underdrain inlet openings must have a gross cross-sectional
area greater than 15% of a trickling filter's surface area.
(5) A modular synthetic media design must be supported
above a trickling filter floor by beams and grating with support and
clearances in accordance with the trickling filter media manufacturer's
recommendations. The manufacturer's recommendations must be included
in the engineering report.
(l) Underdrain Slopes.
(1) An underdrain and trickling filter effluent channel
floor must have a minimum slope of 1%.
(2) An effluent channel must produce a minimum velocity
of 2.0 feet per second at the design flow rate to a trickling filter.
(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
hydraulic loading.
(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
report.
(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:
(A) nitrification;
(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.
Attached Graphic
(o) Maintenance.
(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
dosing intensities.
(A) Filter Flies.
(i) The structural and hydraulic design of a trickling
filter must enable flooding of the trickling filter for fly control.
Cont'd... |
