Statutes, codes, and regulations
Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. ofSubagency 0011 - Water QualityChapter 11 - DESIGN AND CONSTRUCTION STANDARDS FOR SEWERAGE SYSTEMS, TREATMENT WORKS, DISPOSAL SYSTEMS OR OTHER FACILITIES CAPABLE OF CAUSING OR CONTRIBUTING TO POLLUTION AND MOBILE HOME PARK AND CAMPGROUND SEWERAGE AND PUBLIC WATER SUPPLY DISTRIBUTION SYSTEMS
Part B - MUNICIPAL AND DOMESTIC SEWERAGE SYSTEMS, TREATMENT WORKS, AND DISPOSAL SYSTEM
Section 11-19 - Tertiary treatment systems

020-11 Wyo. Code R. § 11-19

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Current through April 27, 2019
Section 11-19 - Tertiary treatment systems

(a) Phosphorus removal.

  • (i) Equipment requirements.
    • (A) Flash mixing. Chemical addition points shall be at points of high turbulence, such as Parshall flumes, hydraulic jumps, or separate mixing basins.
    • (B) Flocculation. Inlet and outlet design shall prevent short circuiting and turbulent destruction of floc. Minimum detention time shall be 20 minutes at the average design flow rate.

      The velocity of flocculated water to settling basins shall be 0.5 to 1.5 fps (0.15 to 0.46 mps). Changes in direction shall be with long radius elbows or curved channels.
    • (C) Chemical feed equipment. Storage shall be provided for at least 14 days of chemical supply. Liquid chemical storage tanks shall have a liquid level indicator, an overflow, and a receiving basin capable of holding 110 percent of the stored volume, or a drain capable of receiving accidental spills or overflows. Liquid chemical storage shall be provided with heat.

(b) Ammonia nitrogen reduction.

  • (i) Activated sludge. Ammonia nitrogen removal by activated sludge processes shall be designed with sludge retention time of at least 15 days and shall provide at least 16 hours of hydraulic detention time. Aeration requirements are described in Section 15.
  • (ii) Attached growth. Rock media trickling filters shall not be used for ammonia reduction. Fabricated media trickling filters used for ammonia shall be designed using a BOD loading of less than 14 lb/1000 cu ft (224 kg/1,000 m3) of media. Rotating biological contactors used for ammonia reduction shall be designed with hydraulic loadings less than 1.0 gpd/sq ft (40.7 L/m2/d) of media surface area. At least four stages shall be provided for ammonia nitrogen removal.
  • (iii) Lagoons. The design of facultative lagoons for ammonia removal shall provide a minimum detention of 180 days. Aerated lagoon systems may be designed for 160 days.

(c) Solids reduction.

  • (i) Filtration.
    • (A) Filtration rate. The maximum hydraulic loading for 24 inch (61 cm) or deeper media is 5 gpm/sq ft (292.5 m3/m2/d) of filter area. Filtration rates for shallower media shall be limited to 3 gpm/sq ft (175 m3/m2d).
    • (B) Backwash requirements. Provide a minimum backwash rate of 20 gpm per square foot (1170 m3/m2/d) of filter bed for 24 inch (61 cm) or deeper media and 12 gpm/square foot (702 m3/m2/d) for shallower media; supply shall be filtered water. A rate of flow regulator on the main backwash line shall be provided. The total backwash water storage capacity shall be adequate for twenty 20 minutes of continuous backwash.

      Air scour or surface wash facilities are required. All surface wash devices shall be provided with a minimum flow rate of 0.5 gpm per sq ft (29.3 m3/m²d) water pressures of 50 psi (3.52 kg/cm2) or greater and use filtered water.
    • (C) Backwash waste handling and treatment. Waste filter backwash shall be collected in a surge tank and recycled to the treatment plant at a rate not to exceed ten percent of the average plant design flow rate. Waste backwash water may be returned to any point upstream of the biological treatment units.
    • (D) Number of units. At least two units shall be provided. With one filter out of service, the remaining filters shall be capable of passing the maximum day design flow rate.
    • (E) Controls. Controls should be provided to remove a filter from service, backwash the filter, and return it to service. Where the control is automatic, there shall also be a means of manually overriding the operating equipment, including each valve essential to filter operation.

      In addition, the following shall be provided:

      • (I) Sampling tap on filter influent and effluent.
      • (II) Indicating and recording loss of head gauge.
      • (III) Flow rate indicating and control.
      • (IV) Means for feeding polymer as a filter aid at a controlled rate to filter influent water when chemically coagulated effluent is being filtered.
  • (ii) Microscreens.
    • (A) Pilot testing. Pilot plant testing on the fluid to be screened or data from other similar applications to demonstrate the suitability of the proposed filter fabric, fabric life, proposed loading rates, and other design criteria shall be provided.
    • (B) Loading rates. Flow equalization facilities shall be included in the design to moderate influent quality and flow variations.

      The screening rate shall be selected to be compatible with available pilot plant test results and selected screen aperture, but shall not exceed 1.5 gpm/sq ft (87.8 m3/m2/d) for lagoon effluent or 5 gpm/sq ft (292.5 m3/m2/d) for activated sludge or attached growth effluents based on the maximum hydraulic flow rate applied to the units. The screening rate shall not exceed 0.75 lb/sq ft/day (3.7 kg/ m2/day). The effective screen area shall be considered the submerged screen surface area less the area of screen blocked by structural supports and fasteners.
    • (C) Backwash requirements. The backwash water shall be at least eight gpm/ linear foot (99 Lpm/m) of screen length at 60 psi (4.2 kg/cm2), obtained from microscreened effluent.
    • (D) Controls. Each microscreen unit shall be provided with automatic drum speed controls with provisions for manual override.

(d) Rapid infiltration.

  • (i) Wastewater preapplication requirements. Rapid infiltration shall be preceded by settling or fine screening having 0.6 inch (15.2 mm) or smaller openings.
  • (ii) Hydraulic loading rates.
    • (A) Permeability. Hydraulic capacity of the rapid infiltration site shall be based upon soil permeability, basin infiltration tests, or cylinder infiltrometer tests. Design loading rates based on these tests shall be as follows:

      Field Measurement Annual Loading Rate
      Basin infiltration test 10% of minimum measure rate
      Cylinder infiltrometer 2% of minimum measured rate
      Permeability 5% of conductivity of most restricting soil layer

    • (B) Precipitation. The total hydraulic load to the rapid infiltration basins includes precipitation. The one in ten year precipitation event should be used as the basis for design.
    • (C) Cold weather conditions. The design must recognize that drying rates, oxidation rates, nitrification and denitrification rates all decrease in cold weather. Cold weather loading rates shall be used to determined land requirements or cold weather storage shall be used. Provisions should be made to mow and disc basin surfaces in the fall to prevent ice from freezing the vegetation near the soil surface. Snow fences can be used to keep snow cover on the rapid infiltration basins to insulate the applied wastewater and soil.
  • (iii) Land requirements.
    • (A) Storage. A minimum of fourteen (14) days of storage shall be provided. Where applied sewage will be less than 4° C, 160 days of effluent storage shall be provided.
    • (B) Location. Rapid infiltration basins shall be located more than 500 feet (152 m) from existing habitation.
  • (iv) Basin size. Individual basin size shall not be greater than five (5) acres (2.0 ha). Basin sizing should be based upon a maximum water depth of twelve (12) inches (30.5 cm) in the rapid infiltration basins.
  • (v) Subsurface drainage. The capillary fringe above the groundwater mound shall not be closer than two (2) feet (0.6 m) to the bottom of the infiltration basin. The distance to groundwater shall be at least five (5) feet (1.5 m) below the soil surface within two (2) days following wastewater application.
  • (vi) Groundwater monitoring. Refer to Chapter 3, Section 15, of the regulations.

(e) Intermittent sand filters.

  • (i) Wastewater preapplications treatment requirements. Intermittent sand filters shall be preceded by settling or fine screens having 0.06 inch (1.5 mm) or smaller openings.
  • (ii) Hydraulic loading rates. The maximum application rates shall be limited to:

    Maximum Application Rate
    Source gallons/acre/day (m3/ha/d)
    Primary Effluent 130,000 (1216)
    Secondary Effluent 400,000 (3742)
    Lagoon Effluent 300,000 (2806)

  • (iii) Media. The minimum sand depth shall be twenty-four (24) inches (0.6 m). The sand must be free of cementing materials and clay or loam. The sand should have an effective size of not less than 0.2 mm and not greater than 0.5 mm, and a uniformity coefficient of less than 5.

    Clean graded gravel shall be placed around the under drains and to a depth of at least twelve (12) inches (0.3 m) over the top of the underdrains.
  • (iv) Underdrains. All intermittent sand filters shall be provided with underdrains. Underdrains shall be at least four (4) inches (10.2 cm) in diameter. The under-drain pipe shall have a minimum slope of 5 feet per 1,000 feet (5 m/1,000 m).

    The groundwater shall be at least two (2) feet (0.6 m) below the bottom of the underdrain pipe.
  • (v) Number of units. Three (3) or more filters shall be provided.
  • (vi) Dosing.
    • (A) In each dosage of an intermittent filter, the hydraulic capacity shall permit covering the bed to a depth of two (2) inches (5 cm), within twenty (20) minutes or less.

020-11 Wyo. Code R. § 11-19

Amended, Eff. 6/29/2018.