Section 58.01.16.490 - FACILITY AND DESIGN STANDARDS FOR MUNICIPAL WASTEWATER TREATMENT OR DISPOSAL FACILITIES: BIOLOGICAL TREATMENTIf biological treatment is used, the process shall be determined in the preliminary engineering report. The choice shall be based on influent characteristics and effluent requirements.
01.Trickling Filters. a. General. Trickling filters shall be preceded by effective settling tanks equipped with scum and grease collecting devices or other suitable pretreatment facilities.b. Hydraulics. The flow will be uniformly distributed across the surface of the media. The piping system, including dosing equipment and distributor, shall be designed to provide capacity for the design peak hour flow, including recirculation.c. Media.i. Quality. The media shall be appropriate for the wastewater and shall be of sufficient strength to support itself under design loading and build up of biomass.ii. Depth. Trickling filter media shall have a minimum depth of six (6) feet above the underdrains.d. Underdrainage System.i. Arrangement. Underdrains shall be provided and the underdrainage system shall cover the entire floor of the filter. Inlet openings into the underdrains shall have an unsubmerged gross combined area equal to at least fifteen (15) percent of the surface area of the filter.ii. Ventilation. The underdrainage system, effluent channels, and effluent pipe shall be designed to permit free passage of air.e. Special Features. i. Maintenance. All distribution devices, underdrains, channels, and pipes shall be installed so that they may be properly maintained, flushed or drained.ii. Winter Protection. Covers shall be provided to maintain operation and treatment efficiencies when climatic conditions are expected to result in problems due to cold temperatures.iii. Recirculation. The piping system shall be designed for recirculation as required to achieve the design efficiency. The recirculation rate shall be variable and subject to plant operator control at the range of 0.5:1 up to 4:1 (ratio of recirculation rate versus design average flow). A minimum of two (2) recirculation pumps shall be provided.f. Rotary Distributor Seals. Mercury seals shall not be permitted.g. Unit Sizing. Required volumes of filter media shall be based upon pilot testing with the particular wastewater or any of the various empirical design equations that have been verified through actual full scale experience. Such calculations must be submitted to the Department if pilot testing is not utilized. Trickling filter sizing design shall consider peak organic load conditions including the oxygen demands due to solids and process recycle flows.02.Activated Sludge. a. Aeration. i. Capacities and Permissible Loadings. The size of the aeration tank for any particular adaptation of the process shall be determined by full scale experience, pilot plant studies, or rational calculations based mainly on solids retention time, food to microorganism ratio, and mixed liquor suspended solids levels. Other factors, such as size of treatment plant, diurnal load variations, and degree of treatment required, shall also be considered. In addition, temperature, alkalinity, pH, and reactor dissolved oxygen shall be considered when designing for nitrification. Calculations shall be submitted to the Department in the preliminary engineering report to justify the basis for design of aeration tank capacity.ii. Arrangement of Aeration Tanks.(1) Dimensions. The dimensions of each aeration tank or return sludge reaeration tank shall be such as to maintain effective mixing and utilization of air. An exception is that horizontally mixed aeration tanks shall have a depth of not less than five point five (5.5) feet.(2) Number of Units. Total aeration tank volume plus redundancy requirements shall be divided among two (2) or more equal units, capable of independent operation.(3) Inlets and Outlets. (a) Controls. Inlets and outlets for each aeration tank unit shall be designed to control flow to any unit with reasonable accuracy and to maintain reasonably constant liquid level. The properties of the system shall permit the design peak day flow to be treated with any single aeration tank unit out of service. The properties of the system shall permit the design peak hour hydraulic flow to be carried with any single aeration tank unit out of service.(b) Conduits. Channels and pipes carrying liquids with solids in suspension shall be designed to be self-cleansing.(c) Scum and Foam Control. Aeration tanks shall be designed to include adequate control or removal of scum and foam.(4) Freeboard. All aeration tanks should have a freeboard of not less than eighteen (18) inches.iii. Aeration Equipment. (1) General. Oxygen requirements generally depend on maximum diurnal organic loading, degree of treatment, and level of suspended solids concentration to be maintained in the aeration tank mixed liquor. Aeration equipment shall be capable of maintaining a minimum of two point zero (2.0) mg/L of dissolved oxygen in the mixed liquor at all times and provide thorough mixing of the mixed liquor (for a horizontally mixed aeration tank system, an average velocity of one (1) foot per second must be maintained). In the absence of experimentally determined values, the design oxygen requirements for all activated sludge processes shall be 1.1 lb 02 per lb of design peak hour BOD5 applied to the aeration tanks, with the exception of the extended aeration process, for which the value shall be one point five (1.5) to include endogenous respiration requirements.(a) Where nitrification is required or will occur, the oxygen requirement for oxidizing ammonia must be added to the above requirement for carbonaceous BOD5 removal and endogenous respiration requirements. The nitrogenous oxygen demand (NOD) shall be taken as four point six (4.6) times the diurnal peak hour total Kjeldahl nitrogen content of the aeration tank influent. In addition, the oxygen demands due to recycle flows must be considered due to the high concentrations of BOD5 and total Kjeldahl nitrogen associated with such flows.(b) Meet maximum oxygen demand and maintain process performance with the largest unit out of service. Provide for varying the amount of oxygen transferred in proportion to the load demand on the plant.(2) Diffused Air Systems. Air requirements including, but not limited to, process air, channel aeration, aerobic digestion, and miscellaneous plant air shall be submitted to the Department in the preliminary engineering report. Blowers shall be provided in multiple units, so arranged and in such capacities as to meet the maximum air demand with the single largest unit out of service. The design shall also provide for varying the volume of air delivered in proportion to the load demand of the plant. Aeration equipment shall be easily adjustable in increments and shall maintain solids suspension within these limits.(3) Mechanical Aeration Systems. (a) Oxygen Transfer Performance. The mechanism and drive unit shall be designed for the expected conditions in the aeration tank in terms of the power performance. Certified testing shall be provided to verify mechanical aerator performance. Refer to applicable provisions of Subsection 490.02. In the absence of specific design information, the oxygen requirements shall be calculated for mechanical aeration systems using a transfer rate not to exceed two (2) pounds of oxygen per horsepower per hour in clean water under standard test conditions. Design transfer efficiencies shall be included in the specifications.(b) Design Requirements. Motors, gear housing, bearings, grease fittings, etc., shall be easily accessible and protected from inundation and spray as necessary for proper functioning of the unit.(c) Winter Protection. Where extended cold weather conditions occur, the aerator mechanism and associated structure shall be protected from freezing due to splashing. Due to high heat loss, subsequent treatment units shall be protected from freezing.b. Non-Aerated Tanks or Zones. Non-aerated tanks or zones within aeration tanks shall have mixing equipment adequate to fully mix the contents. Provide calculations in the preliminary engineering report for sizing of this equipment.c. Return Sludge Equipment. i. Return Sludge Rate. The return sludge rate of withdrawal from the final settling tank is a function of the concentration of suspended solids in the mixed liquor entering it, the sludge volume index of these solids, and the length of time these solids are retained in the settling tank. The rate of sludge return shall be varied by means of adjustable weirs, variable speed pumps, or timers (small plants) to pump sludge.ii. Return Sludge Pumps. If a consolidated return sludge pump facility is used, the maximum return sludge capacity shall be obtained with the largest pump out of service. If individual sludge pumps are used at each settling basin, the pumps shall be designed to facilitate their rapid removal and replacement with a standby unit stored at the treatment plant site. If air lifts are used for returning sludge from each settling tank hopper, no standby unit will be required provided the design of the air lifts facilitate their rapid and easy cleaning and provided other suitable standby measures are made available. Air lifts should be at least three (3) inches in diameter.iii. Return Sludge Piping. Discharge piping should be at least four (4) inches in diameter and shall be designed to maintain a velocity of not less than two (2) feet per second when return sludge facilities are operating at normal return sludge rates. Suitable devices for observing, sampling, and controlling return activated sludge flow from each settling tank hopper shall be provided.iv. Waste Sludge Facilities. Means for observing, measuring, sampling, and controlling waste activated sludge flow shall be provided.d. Sequencing Batch Reactors. The fill and draw mode of the activated sludge process commonly termed the Sequencing Batch Reactor may be used in Idaho. The design must be based on experience at other facilities and shall meet the applicable requirements under Sections 450, 470 and 490, except as modified in Subsection 490.02.d.i. through 490.02.d.xi. Continuity and reliability of treatment equal to that of the continuous flow through modes of the activated sludge process shall be provided. i. At least two (2) tanks shall be provided.ii. The decantable volume and decanter capacity of the sequencing batch reactor system with the largest basin out of service shall be sized to pass at least seventy-five (75) percent of the design maximum day flow without changing cycle times. A decantable volume of at least four (4) hours with the largest basin out of service based on one hundred (100) percent of the design maximum day flow is permissible.iii. System reliability with any single tank unit out of service and the instantaneous delivery of flow shall be evaluated in the design of decanter weirs and approach velocities.iv. Reactor design shall provide for scum removal and prevent overflow of settled solids.v. An adequate zone of separation between the sludge blanket and the decanter(s) shall be maintained throughout the decant phase. Decanters which draw the treated effluent from near the water surface throughout the decant phase are recommended.vi. Solids management to accommodate basin dewatering shall be considered.vii. The blowers shall be provided in multiple units, so arranged and in such capacities as to meet the maximum air demand in the oxic portions of the fill/react and react phases of the cycle with the single largest unit out of service. See Subsection 490.02.viii. Mechanical mixing independent of aeration shall be provided for all systems where biological phosphorus removal or denitrification is required.ix. Flow paced composite sampling equipment and continuous turbidity metering for separately monitoring the effluent quality from each basin may be required by the regulatory agency. All twenty-four (24) hour effluent quality composite samples for compliance reporting or monitoring plant operations shall be flow-paced and include samples collected at the beginning and end of each decant phase.x. A programmable logic controller (PLC) shall be provided. Multiple PLCs shall be provided as necessary to assure rapid process recovery or minimize the deterioration of effluent quality from the failure of a single controller. An uninterruptible power supply with electrical surge protection shall be provided for each PLC to retain program memory (i.e., process control program, last-known set points and measured process/equipment status, etc.) through a power loss. A hard-wired backup for manual override shall be provided in addition to automatic process control. Both automatic and manual controls shall allow independent operation of each tank. In addition, a fail-safe control allowing at least twenty (20) minutes of settling between the react and decant phases shall be provided. The fail-safe control shall not be adjusted by the operator.xi. A sufficient quantity of spare parts shall be on hand. Consideration shall be given to parts with a low mean time between failure such as electrical relays and solid state electronics.03.Other Biological Systems. a. General. Biological treatment processes not included in these rules shall be considered in accordance with Subsection 450.03.b. Membrane Bioreactors. Details for Membrane Bioreactor (MBR) plants shall be submitted and approved in the preliminary engineering report. In addition to the requirements of Section 411, details shall include plant layout, calculations for hydraulic capacity and air required, membrane technology considered and membrane type and model selected, results from similar type MBR plants already in operation, and anticipated sludge production.Idaho Admin. Code r. 58.01.16.490