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RULE §217.182Trickling Filters--General Requirements

  (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.

      (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.

  (1) Covers.

    (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 and removal.

    (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 treatment efficiency.

Source Note: The provisions of this §217.182 adopted to be effective August 28, 2008, 33 TexReg 6843; amended to be effective December 4, 2015, 40 TexReg 8254

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