1. (a) The report must include a justification for the proposed sludge dewatering units, including design calculations, results from any pilot studies, all assumptions, and appropriate references.
2. (b) The design of a dewatering unit must be based on mass balance principles.

3. (c) General Requirements.

   1. (1) Centrate or Filtrate Recycle.

      1. (A) The drainage from beds and centrate or filtrate from dewatering units must be returned to the head of the facility for treatment.
      2. (B) The design of a treatment unit downstream from a dewatering unit must be based on the organic load from the centrate or filtrate recycle.
   2. (2) Sludge with Industrial Waste Contributions. A dewatering system must be designed to prevent the release of any constituent (such as a free metal, an organic toxin, or a strong reducing or oxidizing compound) that threatens water quality or compliance with the associated wastewater permit.

   3. (3) Redundancy.

      1. (A) A mechanical dewatering system must have at least two units, unless the report justifies adequate storage or an alternative means of sludge handling.
      2. (B) When performance reliability and sludge management are dependent on production of dewatered sludge, the mechanical dewatering units must be able to dewater the average daily sludge flow with the largest unit out of service.

   4. (4) Storage Requirements.

      1. (A) A mechanical dewatering system must have separate storage if the equipment will not operate on a continuous basis and the treatment system has no digesters with built-in short-term storage.
      2. (B) In-line storage of stabilized or unstabilized sludge must not interfere with any treatment unit.
      3. (C) The separate sludge storage from a primary digester must be aerated and mixed to prevent a nuisance odor condition.
   5. (5) Sampling Points. A dewatering system must have sampling stations before and after each dewatering unit and must allow periodic evaluation of the dewatering process.
   6. (6) Maintenance. Each dewatering system unit must have a bypass to allow for maintenance, repair, and replacement.

4. (d) Sludge Conditioning.

   1. (1) An additive addition point must be located in relation to downstream equipment and in relation to the combined effect of other additives.
   2. (2) A dewatering system must provide adequate mixing time for the reaction between an additive and the sludge. Any subsequent handling must eliminate floc shearing.
   3. (3) The report must include a pilot plant or full-size performance data used to determine the characteristics and design dosage of any sludge additive.
   4. (4) The report must justify the in-stream flocculation and coagulation system design by including comparable performance data or pilot plant data.
   5. (5) The report must include whether the mixers require conditioning tanks.
   6. (6) The report must include calculations for a range of detention times.
   7. (7) Solution storage may be smaller than the design volume required for daily dosage if the equipment is not in continuous operation.
   8. (8) A minimum of eight hours storage must be provided, unless the specific chemical or additive selected is adversely affected by storage.
   9. (9) The storage for a batch operation must be adequate for one batch at maximum chemical demand.
   10. (10) The report must justify any storage volume reduction and any other method used to ensure a continuous supply of chemicals through an operating day or batch.

5. (e) Sludge Drying Beds.

   1. (1) The sludge drying beds size must be based on data from a similar facility in the same geographical area with the same influent sludge characteristics.

   2. (2) If such data is unavailable, or if the executive director determines that the data is not appropriate for a proposed facility, the design of sludge drying beds must be based on the following:

      1. (A) Open Beds.

         1. (i) A sludge drying bed system must have at least two beds.
         2. (ii) The report must include the calculation of the minimum surface area for a sludge drying bed using the values in the following figure for an area of the state with less than 45 inches annual average rainfall or annual average relative humidity of less than 50%, as determined by National Weather Service data.
            Attached Graphic
            
         3. (iii) Another method of sludge dewatering is required in lieu of a sludge drying bed in an area of the state that experiences either greater than 45 inches average annual rainfall or annual average relative humidity of 50% or greater, as determined by National Weather Service data.

         4. (iv) A design must:

            1. (I) provide a method of effectively dewatering sludge;
            2. (II) provide a means for accelerated dewatering;
            3. (III) size the sludge drying beds to store accumulated sludge during periods of extended high humidity and rainfall; and
            4. (IV) provide an alternative dewatering method to effectively dewater the sludge during periods of extended high humidity and rainfall.
         5. (v) The report must provide justification for use of innovative or non-conforming sludge drying beds in high rainfall, high relative humidity areas of the state.
      2. (B) Gravel Media Beds. A gravel media bed must be laid in two or more layers. The gravel around the underdrains must be properly graded and must be at least 12 inches deep, extending at least 6.0 inches above the top of the underdrains. The top layer of a gravel media bed must be at least three inches thick and must consist of gravel 1/8 inch to 1/4 inch in size.
      3. (C) Sand Media Beds. A sand media bed must consist of at least 12 inches of sand with a uniformity coefficient of less than 4.0 and an effective grain size of at least 0.3 millimeters (mm) but not more than 75 mm above the top of an underdrain.

      4. (D) Underdrains.

         1. (i) The underdrains must be at least 4.0 inches in diameter and sloped not less than 1.0% to drain.
         2. (ii) The underdrains must be spaced not more than 20 feet apart.
      5. (E) Decanting. A sludge drying bed may have a method of decanting supernatant installed on the perimeter of the bed.

      6. (F) Walls.

         1. (i) The interior walls of a sludge drying bed must be watertight and extend 12 to 24 inches above and at least 6 inches below the bed surface.
         2. (ii) The exterior walls of a sludge drying bed must be watertight and extend 12 to 24 inches above the bed surface or ground elevation, whichever is higher.

      7. (G) Sludge Removal.

         1. (i) A sludge drying bed system must be arranged to facilitate sludge removal.
         2. (ii) The sludge drying beds must have concrete pads for vehicle support tracks on 20 foot centers for all percolation type sludge beds.

      8. (H) Sludge Influent.

         1. (i) A sludge pipe to the beds must terminate at least 12 inches above the surface of the media and be arranged so that the pipe drains to a sump to be pumped to the headworks.
         2. (ii) A sludge discharge point must have a concrete splash plate.

      9. (I) Drying Bed Bottom.

         1. (i) The bottom of a sludge drying bed must consist of a minimum of one foot layer of clayey subsoil having a permeability of less than 10^-7 centimeters per second (cm/sec).
         2. (ii) An impermeable concrete pad must be installed over a liner in locations where the groundwater table is within 4.0 feet of the bottom.
   3. (3) Innovative or Non-Conforming Sludge Drying Beds. The executive director will review any vacuum assisted or other variations to the gravity drying bed concept as innovative and/or nonconforming technologies subject to §217.7(b)(2) of this title (relating to Types of Plans and Specifications Approvals).

   4. (4) Rotary Vacuum Filtration.

      1. (A) Filtration Rate. The report must justify the actual value calculated for the rates of filtering for various types of sludge with proper conditioning, using the following table:
         Attached Graphic
         
      2. (B) Duplicate Equipment. Unless dual trains are provided, the following equipment must be provided in duplicate to allow equipment alternation: feed pump, vacuum pump and filtrate pump. Spare filter fabric must be provided except when metal coils are used.
      3. (C) Filter Equipment. Wetted parts must be constructed of corrosion-resistant material. Drum and agitator assemblies must be equipped with variable-speed drives and provisions must be made for adjusting the liquid level.

      4. (D) Pumps.

         1. (i) A vacuum pump with a capacity of at least 1.5 cubic feet per minute per square foot (cfm/sf) must be provided for metal-covered drums.
         2. (ii) A dry-type vacuum pump must have a vacuum receiver.
         3. (iii) A filtrate pump must have adequate capacity to pump the maximum amount of liquid to be removed from the sludge.
         4. (iv) Each filter must be fed by a separate feed pump to ensure a proper feed rate.

   5. (5) Centrifugal Dewatering.

      1. (A) The report must justify the sizing and design of a centrifugation system. A design must be based on performance data from a similar centrifugation system when available. If no performance data is available, the results of a pilot or full-scale test must be used.
      2. (B) Selection of a material for a scroll must be include consideration of the amount of grit expected in the sludge.
      3. (C) A design must include adequate sludge storage.

      4. (D) Unless dual trains are provided, a centrifugation system must have the following spare equipment, including necessary connecting pipes and electrical controls:

         1. (i) drive motor;
         2. (ii) gear assembly; and
         3. (iii) feed pump.
      5. (E) Each feed pump must have variable speed.
      6. (F) Each centrifuge must have a separate feed system.
      7. (G) Each centrifuge must be equipped for variable scroll speed and pool depth.
      8. (H) Each centrifugation system must have a crane or monorail for equipment removal or maintenance.
      9. (I) Each centrifuge system must have access for adequate and efficient wash down of the interior of the machine.

   6. (6) Plate and Frame Presses.

      1. (A) Sizing.

         1. (i) A design must be based on performance data developed from similar operational characteristics concerning the size of a plate and frame press when available. If no performance data is available, the results of a pilot scale tests or full-scale tests must be used.
         2. (ii) A design may be based on appropriate scale-up factors for full size designs if pilot scale testing is done in lieu of full-scale testing.
         3. (iii) The report must justify the size of a plate and frame press.

      2. (B) Duplicate Equipment and Spare Parts. Unless multiple units are provided, a plate and frame press system must include the following spare equipment:

         1. (i) a duplicate feed pump;
         2. (ii) at least one extra plate for every ten required for startup, but not less than two;
         3. (iii) one complete filter fabric set;
         4. (iv) one closure drive system;
         5. (v) air compressor; and
         6. (vi) one washwater booster pump.

      3. (C) Operational Requirements.

         1. (i) The filter feed pumps must be capable of a combination of initial high flow, low pressure filling, followed by sustained periods of operating at 100 pounds per square inch (psi) to 225 psi.
         2. (ii) A design may specify an integral pressure vessel to produce this initial high volume flow.
         3. (iii) A plate and frame system may use operating pressures less than 225 psi if the report includes actual performance data using similar sludge justifying such a use.
         4. (iv) A design may include provisions for cake breaking to protect or enhance down line processes when necessary.

      4. (D) Maintenance.

         1. (i) A plate and frame system must have a crane or monorail capable of removing the plates.
         2. (ii) A plate and frame system must have a high-pressure water or acid wash system to clean the filter.

   7. (7) Belt Presses.

      1. (A) Sizing.

         1. (i) Actual performance data developed from a facility with similar operational characteristics must be used to size a belt press system. If pilot plant testing is performed in lieu of full-scale testing, appropriate scale-up factors must be used to develop a full-scale design.
         2. (ii) A belt press system must have a duplicate belt press or another method of sludge processing or disposal that has been approved by the executive director if the design flow exceeds 4.0 million gallons per day (mgd).
         3. (iii) The report must include all data used to size a belt press system.

      2. (B) Duplicate Equipment and Spare Parts. Unless multiple units are provided, a belt press system must have the following spare equipment:

         1. (i) a duplicate feed pump;
         2. (ii) washwater booster pumps;
         3. (iii) one complete set of belts;
         4. (iv) one set of bearings for each type of press bearing;
         5. (v) duplicate tensioning;
         6. (vi) tracking sensors;
         7. (vii) one set of wash nozzles;
         8. (viii) one doctor blade; and
         9. (ix) duplicate conditioning or flocculation drive equipment.
      3. (C) Conditioning. The report must include the polymer selection methodology, account for sludge variability, and document the anticipated sludge loading to the press.

      4. (D) Sludge Feed.

         1. (i) The sludge feed must be relatively constant to eliminate difficulties in polymer addition and press operation.
         2. (ii) The report must include the range in feed variability.
         3. (iii) A belt press system may include grinders ahead of a flocculation system.
         4. (iv) The sludge feed must provide a method for uniform sludge dispersion on a belt.
         5. (v) A belt press system must use thickening of the feed sludge unless the report justifies separate thickening or dual purpose thickening.

      5. (E) Filter Press Belts.

         1. (i) A belt must have variable speed.
         2. (ii) A belt press system must have belt tracking and tensioning equipment.
         3. (iii) The report must justify the weave, material, width, and thickness of the belts.

      6. (F) Filter Press Rollers.

         1. (i) The rollers must have a protective finish.
         2. (ii) The maximum roller deflection and operating tension of a belt must be included in the report to justify equipment selection.
         3. (iii) The roller bearings must be watertight and rated for a life of 100,000 hours.

      7. (G) Spray Wash System.

         1. (i) A belt press system must use high-pressure wash water for each belt.
         2. (ii) A design must specify the operating pressure at the point of washwater discharge.
         3. (iii) A spray wash system must allow cleaning without interfering with the system operation.
         4. (iv) The report must justify the nozzle and nozzle cleaning system selection.
         5. (v) A belt press system must have replaceable spray nozzles and spray curtains.

      8. (H) Maintenance Requirements.

         1. (i) A belt press system must have drip trays under the press and under the thickener when gravity belt thickening is employed.
         2. (ii) The side and floor of a belt press must have adequate clearance for maintenance and removal of the dewatered sludge.
         3. (iii) An electrical panel or other material subject to corrosion must be weatherproof or located outside of the press area.
         4. (iv) A doctor blade clearance must be adjustable.

Source Note:The provisions of this §217.250 adopted to be effective August 28, 2008, 33 TexReg 6843.