PURPOSE: This rule specifies the minimum standards for the design of biological treatment that is part of wastewater collection and treatment systems. This rule is to be used with rules 10 CSR 20-8.110 through 10 CSR 20- 8.210. It does not address all aspects of design, and the design engineer may refer to other appropriate reference materials so long as these minimum standards set forth in this rule are met.

Editor’s Note: The secretary of state has determined that the publication of this rule in its entirety would be unduly cumbersome or expensive. The entire text of the material referenced has been filed with the secretary of state. This material may be found at the Office of the Secretary of State or at the headquarters of the agency and is available to any interested person at a cost established by state law.

1. (1) Applicability. Wastewater systems that utilize biological treatment shall be designed based on criteria contained in this rule, published standards, applicable federal and state requirements, standard textbooks, current technical literature, and applicable safety standards. In the event of any conflict between the above criteria, the requirement in this rule shall prevail.

   1. (A) This rule shall not apply to treatment units covered in 10 CSR 20-8.300.
   2. (B) This rule shall not apply to treatment units covered in 10 CSR 20-8.500.

2. (2) Septic Tanks.

   1. (A) A septic tank must have a minimum capacity of at least one thousand (1,000) gallons.
   2. (B) The septic tank shall be baffled.

3. (3) Recirculating Media Filters.

   1. (A) Location. Recirculating media filters shall be located in accordance with the minimum separation distances at 10 CSR 20- 8.140(2)(C)(2).
   2. (B) Filter Bed. A minimum of two (2) filter beds and a diversion box are required for all design flows.
   3. (C) Dosing. Both timer and float switch controls are required; timers are the primary method of operation and the float switch control is a back-up.

   4. (D) Loading. Hydraulic loading rate shall—

      1. 1. Follow the manufacturer’s recom-

mendation for synthetic media filters; and

1. 2. Not exceed three and one-half gallons

per day per square foot (3.5 gpd/sqft) for sand or rock filters.

1. (E) Media Characteristics. The media is any of a number of physical structures whose sole purpose is to provide a surface to support biological growth. Commonly used media includes rock, gravel, and sand of various sizes, textile media, and peat. Finely crushed limestone, dolomite, slag, any clay, limestone, or appreciable amounts of organic material is not acceptable.

   1. 1. Rock, sand, and gravel media, when

used shall–

1. A. Be a total of at least thirty-three

inches (33”) deep; and

1. B. Have at least twenty-four inches

(24”) of fine filtering media.

1. (4) Trickling Filters.

   1. (A) General. Trickling filters may be used for treatment of wastewater amenable to treatment by aerobic biologic processes.

   2. (B) Media.

      1. 1. Media depth shall—

         1. A. Be a minimum depth of five feet

(5') above the underdrains for rock filter media;

1. B. Be a minimum depth of ten feet

(10') for manufactured filter media to provide adequate contact time with the wastewater; and

1. C. Be no more than ten feet (10') for

rock filter media.

1. 2. Size and grading of rock and similar

media shall—

1. A. Contain no more than five percent

(5%) by weight of pieces whose longest dimension is three (3) times the least dimension;

1. B. Be free from thin elongated and

flat pieces, dust, clay, sand, or fine material; and

1. C. Conform to the following size and

grading as shown in Table 180-1, included herein, when mechanically graded over vibrating screen with square openings.

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1. 3. Manufactured and synthetic media

material shall—

1. A. Be used in accordance with all

manufacturer’s recommendations;

1. B. Be insoluble in wastewater and

resistant to flaking, spalling, ultraviolet degradation, disintegration, erosion, aging, common acids and alkalis, organic compounds, and biological attack;

1. C. Be evaluated to determine the suit-

ability based on experience with an installation treating wastewater under similar hydraulic and organic loading conditions (include a relevant case history involving the use of the synthetic media);

1. D. Have a structure able to support

the synthetic media, water flowing through or trapped in voids, and the maximum anticipated thickness of the wetted biofilm;

1. E. Support the maintenance activities,

unless a separate provision is made for maintenance access to the entire top of the trickling filter media and to the distributor; and

1. F. Be placed with the edges matched

as nearly as possible to provide consistent hydraulic conditions within the trickling filter.

1. (C) Underdrainage System.

   1. 1. Hydraulic capacity. The underdrains

shall be designed with—

1. A. Slopes of at least one percent

(1%);

1. B. Effluent channels that produce a

minimum velocity of two feet per second (2 fps) at average daily rate of application to the filter;

1. C. Underdrainage system, effluent

channels, and effluent pipe that permit free passage of air;

1. D. Drains, channels, and pipe so that

not more than fifty percent (50%) of their cross section area will be submerged under the design peak hydraulic loading, including proposed or possible future or recirculated flows.

1. (D) Forced Ventilation.

   1. 1. Forced ventilation for a trickling fil-

ter is required when—

1. A. Designed for nitrification;
2. B. Designed with a media depth in

excess of six feet (6’); or

1. C. Designed where seasonal or diur-

nal temperatures do not provide sufficient difference between the ambient air and wastewater temperatures to sustain passive ventilation.

1. 2. Minimum design airflow rate to nitri-

fy using a trickling filter shall be the greater of—

1. A. Fifty pounds (50 lbs) of oxygen

provided per pound of oxygen demand at average organic loading, based on stoichiometry; or

1. B. Thirty pounds (30 lbs) of oxygen

provided per pound of oxygen demand at peak organic loading, based on stoichiometry.

1. (5) Activated Sludge.

   1. (A) Basin lining. If using a synthetic liner, it shall be a minimum of thirty millimeters (30 mm) thick.
   2. (B) Tank dimensions. Horizontally mixed aeration tanks shall have a depth of not less than five and a half feet (5.5').
   3. (C) High purity oxygen, when used and enclosed. An enclosed high purity oxygen exhaust system shall be provided to collect and vent the reactor off-gases.

2. (6) Sequencing Batch Reactor (SBR).

   1. (A) General. The minimum total basin volume shall be equal to the design daily influent flow volume and either upstream in-line or off-line storage is necessary to minimize influent flow during settling and decanting.
   2. (B) Design. A minimum of two (2) reactor basins shall be installed.

3. (7) Membrane Bioreactor (MBR).

   1. (A) General.

      1. 1. For wastewater treatment plants with

a flow equal to or greater than one hundred thousand gallons per day (100,000 gpd), the MBR process must be designed with a minimum of two (2) membrane trains capable of treating the daily average flow with one (1) membrane cassette out of service.

1. 2. Design flux criteria must be satisfied

with one (1) membrane module out-of-service (e.g., for external clean in place, recovery cleaning, repair). For purposes of these criteria, a membrane module is the smallest membrane unit capable of separate removal from the tank while maintaining operation of other membrane units in the same tank.

1. 3. Membranes placed in the aeration

basin(s) rather than a separate membrane tank shall have—

1. A. Individual modules and individual

diffusers that can be removed separately for maintenance and repair; and

1. B. Aeration basin(s) volume sized for

complete nitrification.

1. (B) Preliminary Treatment. Each system shall—

   1. 1. Be consistent with the membrane

manufacturer recommendations;

1. 2. Comply with 10 CSR 20-8.150(6) for

grit removal;

1. 3. Provide oil and grease removal when

the levels in the influent may cause damage to the membranes;

1. 4. Provide a fine screen and high water

alarm, designed to treat peak hourly flow. Coarse screens followed by fine screens may be used in larger facilities to minimize the complications of fine screening; and

1. 5. Comply with 10 CSR 20-8.150(4)(B)

for reliability.

1. (C) Aeration. The aeration blowers must provide adequate air for membrane scour and process demands.

2. (D) Redundancy. The facility shall have at least one (1) of the following:

   1. 1. The ability to run in full pro-

grammable logic control (PLC) or standby power mode in case of an automatic control failure;

1. 2. An operational battery backup PLC if

manual control is not possible; or

1. 3. Sufficient standby power generating

capabilities to provide continuous flow through the membranes during a power outage (e.g., preliminary screening, process aeration, recycle/RAS/permeate pumps, air scour, vacuum pumps) or an adequate method to handle flow for an indefinite period (e.g., private control of influent combined with contingency methods).

1. (E) Operations and Maintenance. The MBR design shall—

   1. 1. Include provisions to monitor mem-

brane integrity;

1. 2. Provide on-line continuous turbidity

monitoring of filtrate or an equivalent for operational control and indirect membrane integrity monitoring for a treatment plant with design average flow greater than or equal to one hundred thousand gallons per day (100,000 gpd); and

1. 3. Include provisions to remove mem-

brane cassette for cleaning considering the membrane cassette wet weight plus additional weight of the solids accumulated on the membranes.

1. (8) Moving Bed Bioreactor (MBBR). A MBBR secondary treatment system shall provide upstream preliminary treatment units capable of—

   1. (A) Screening to reduce pass-through and suspended solids;
   2. (B) Grit removal; and
   3. (C) Oil and grease removal.

AUTHORITY: section 644.026, RSMo 2016.* Original rule filed Aug. 10, 1978, effective March 11, 1979. Amended: Filed June 15, 2018, effective Feb. 28, 2019.

*Original authority: 644.026, RSMo 1972, amended 1973, 1987, 1993. 10 CSR 20-8