NR 110.255(4)(a)4.
4. The system shall consist of at least 2 cells of approximately equal area which can be alternately loaded and rested. Where self-propelled equipment which operates on a continuous basis is installed and division into identifiable cells is impossible, its movement shall be regulated to provide alternate loading and resting of the soil.
NR 110.255 Note
Note: It is recommended that an overland flow cell be rested for at least one third of the total time in the rest/load cycle.
NR 110.255(4)(a)5.
5. The system shall be arranged so that individual cells within the system can be taken out of service for resting without interrupting discharge to the remaining cells.
NR 110.255(4)(a)6.
6. The distribution equipment shall be arranged so that the wastewater will be evenly distributed over the entire area of an overland flow cell and the wastewater travels down the slope in a non-channelized flow.
NR 110.255(4)(a)7.
7. The wastewater distribution equipment shall be located at or near the ground level.
NR 110.255 Note
Note: A pressurized distribution system is recommended for ease of operation.
NR 110.255(4)(a)8.
8. The wastewater distribution system shall be designed to allow for cleaning of the distribution orifices. Flexibility to adjust the flow from individual orifices shall be provided to allow the system to be hydraulically balanced to minimize flow channeling.
NR 110.255(4)(a)9.
9. An impermeable channel shall be provided for collecting runoff from the overland flow fields. The collection system shall be capable of removing the effluent and the rain from a 10-year frequency, 24-hour duration rainfall event with only temporary backing up of water onto the fields.
NR 110.255(4)(a)10.
10. The overland flow fields shall be vegetated with a water tolerant mixed perennial grass cover crop such as reed canary grass, tall fescue and orchard grass. A nurse crop shall be used to establish the perennial grass cover. The grass cover shall be maintained by frequent resting. The crop shall be cut and the cuttings removed at least twice per year to stimulate grass growth and enhance nutrient removal from the system.
NR 110.255(4)(a)11.
11. Winter operation may be allowed as long as the soil surface remains unfrozen. The department may require storage or additional treatment of the runoff during cold weather.
NR 110.255(4)(a)12.
12. An overland flow field may be used when the land surface elevation is at least 5 feet above bedrock.
NR 110.255(4)(a)13.
13. The land surface elevation of an overland flow field shall be no closer than 5 feet to the seasonally high groundwater level. The department may on a case-by-case basis allow this distance to be reduced if the permittee can show, based on hydrogeologic and other relevant site factors, that the groundwater will be adequately protected. If such a variance is approved or if the risk of groundwater contamination is otherwise high, the department may require additional pretreatment of the wastewaters.
NR 110.255(4)(a)14.
14. The hydraulic application rate, expressed as a flow rate per unit width of slope, shall be between .16 gpm/ft and .60 gpm/ft.
NR 110.255(4)(b)
(b) Discharge limitations for overland flow systems. Effluent limitations are as specified in s.
NR 206.08 (4) (b) and applicable surface water limitations.
NR 110.255 History
History: Cr.
Register, November, 1990, No. 419, eff. 12-1-90.
NR 110.26
NR 110.26 Sludge handling, storage and disposal. NR 110.26(1)(1)
Design report. A design report shall be submitted in accordance with s.
NR 110.15 (1). The report shall show calculations used to design the sludge facilities. Design of sludge handling facilities shall consider such factors as the volume of sludge generated, its percent solids and character, the degree of volatile solids reduction, sludge temperature, the degree or extent of mixing to be obtained, the sludge percent solids and characteristics after processing and the size of the installation with appropriate allowances for sludge and supernatant storage and energy requirements whenever such factors are appropriate for the design of the sludge processing facilities.
NR 110.26(2)(a)
(a) Grit removal. When grit removal facilities are not provided, the volume of thickeners, digesters and storage facilities shall be increased to accommodate the additional solids loading.
NR 110.26(2)(b)2.
2. Thickened sludge should have a minimum solids concentration of 5% prior to transmission to the digesters.
NR 110.26(2)(c)
(c) Multiple units. Multiple units shall be provided. A single unit may be allowed, provided an alternate method of sludge processing, emergency storage or ultimate disposal operation exists to insure continuity of service.
NR 110.26(2)(d)1.1. Provisions shall be made for draining, cleaning, inspection, and maintenance of all units.
NR 110.26(2)(d)2.
2. Tank bottoms shall be sloped to drain to a sump pump or withdrawal pipe.
NR 110.26(2)(d)3.
3. Access manholes shall be provided. Covered tanks shall have one side wall entrance large enough to permit the use of mechanical equipment to remove grit and sand.
NR 110.26(2)(e)1.1. The construction of sludge storage facilities shall be required to improve sludge handling capabilities, provide flexibility in operations, and to avoid environmental or public health hazards due to improper disposal techniques.
NR 110.26(2)(e)2.
2. Construction of these facilities will depend upon treatment plant capabilities, land availability, surface and groundwater protection, health factors, municipal sludge management capabilities and other environmental factors.
NR 110.26(3)(a)
(a) Flow measurement. Devices for measuring flow to and from sludge digestion facilities shall be provided.
NR 110.26(3)(b)
(b) Ventilation. All enclosures which are connected with sludge digestors, or which contain sludge or gas piping or equipment shall be provided with forced ventilation in accordance with s.
NR 110.14 (3) (b). The piping gallery for digesters may not be connected to other passages unless a tightly fitting self-closing door is provided at connecting passageways.
NR 110.26(3)(c)
(c) Safety. Nonsparking tools, rubber soled shoes, safety harness, gas detectors for inflammable and toxic gases and at least 2 self-contained respiratory units should be provided for emergency use whenever inflammable and toxic gases may be present.
NR 110.26(3)(d)
(d) Supernatant withdrawal. Sludge thickeners and aerobic digestors shall be designed for effective separation and withdrawal of supernatant and for effective collection and removal of scum and grease.
NR 110.26(3)(e)1.1. Provisions shall be made for sampling at each supernatant draw-off level and for collecting sludge samples for analysis. Sampling pipes shall be at least 4 centimeters (11/2 inches) in diameter and shall terminate in a suitably-sized sink or basin.
NR 110.26(3)(e)2.
2. Unless sampling facilities are otherwise provided, quick-closing sampling valves shall be installed at the sludge pumps. The size of valve and piping shall be at least 4 centimeters (1
1/
2 inches).
NR 110.26(4)(a)1.1. Sludge pumping systems shall be designed to handle the expected range of sludge flows.
NR 110.26(4)(a)3.
3. Pumps with demonstrated solids handling capability shall be provided for handling raw and processed sludge.
NR 110.26(4)(a)4.
4. A minimum positive head of 60 centimeters (2 feet) shall be provided at the suction side of centrifugal-type pumps and is desirable for all types of sludge pumps. Maximum suction lifts may not exceed 3.0 meters (10 feet) for plunger pumps.
NR 110.26(4)(b)1.1. Sludge withdrawal piping shall have a minimum diameter of 20 centimeters (8 inches) for gravity withdrawal and 15 centimeters (6 inches) for pump suction and discharge lines. The department may approve the use of glass lined pipe which is at least 10 centimeters (4 inches) in diameter. Where withdrawal is by gravity, the available head on the discharge pipe shall be sufficient to maintain a minimum velocity of 90 centimeters (3 feet) per second.
NR 110.26(4)(b)2.
2. Gravity piping shall be laid on uniform grade and alignment. The slope on gravity discharge piping may not be less than 3%.
NR 110.26(4)(b)3.
3. Provisions shall be made for draining, flushing and cleaning sludge piping.
NR 110.26(4)(b)4.
4. Air relief valves shall be provided at high points in pressure sludge lines.
NR 110.26(4)(b)5.
5. Special consideration shall be given to the corrosion resistance and continuing stability of pipes and supports located inside the digestion tank.
NR 110.26(5)(a)1.1. Anaerobic digesters which will also serve as supernatant separation tanks shall have a minimum side water depth of 6 meters (20 feet).
NR 110.26(5)(a)2.
2. Multiple sludge inlets and draw-offs shall be provided. Multiple recirculation suction and discharge points to facilitate flexible operations and effective mixing of the digester contents shall be provided unless adequate mixing facilities are provided within the digester. One sludge inlet shall discharge above the liquid level and be located at approximately the center of the tank to assist in scum breakup. Raw sludge inlet discharge points shall be so located as to minimize short circuiting to the supernatant draw-off. Sludge withdrawal for disposal shall be from the bottom of the tank. The pipe shall be interconnected with the recirculation piping to increase flexibility in mixing tank contents.
NR 110.26(5)(b)1.1. The total digestion tank capacity shall be calculated based upon the factors indicated in sub.
(1). If such calculations are not done, the following minimum requirements shall be met:
NR 110.26(5)(b)1.b.
b. Completely mixed digestion systems shall provide for intimate and effective mixing to prevent stratification and to assure homogeneity of digester content. The maximum system loading shall be 1.28 kilograms per cubic meter per day (80 pounds of volatile solids per 1,000 cubic feet of volume per day) in the digester;
NR 110.26(5)(b)1.c.
c. The maximum system loading for moderately mixed digestion systems in which mixing is accomplished only by circulating sludge through an external heat exchanger shall be 0.64 kilograms per cubic meter per day (40 pounds of volatile solids per 1,000 cubic feet of volume per day) in the digester; and
NR 110.26(5)(b)1.d.
d. The loading rates indicated in subd.
1. a.,
b., and
c. assume that the raw sludge is derived from ordinary domestic wastewater. The loading may be modified upward or downward depending upon the degree of mixing provided. Where mixing is accomplished by other methods, loading rates may be approved on the basis of information submitted justifying the design.
NR 110.26(5)(c)
(c) Temperature. Heating equipment shall have the ability to maintain digestion temperature in the range of 33
° to 38
°C (90
° to 100
°F).
NR 110.26(5)(d)1.1. All portions of the gas system, including the space above the tank liquor, storage facilities and piping shall be so designed that under normal operating conditions, including sludge withdrawal, the gas will be maintained under positive pressure. All enclosed areas where any gas leakage might occur shall be ventilated.
NR 110.26(5)(d)2.
2. Safety facilities shall be included where gas is produced. Pressure and vacuum relief valves and flame traps, together with automatic safety shut off valves, shall be provided. Waterseal equipment may not be installed. Gas compressors with gas safety equipment should be housed in a separate room with an exterior entrance.
NR 110.26(5)(d)3.
3. The diameter of gas piping shall be based on the volume of gas which will be generated. Gas piping shall slope to condensate traps. The use of float-controlled condensate traps is prohibited.
NR 110.26(5)(d)4.
4. Gas burning boilers, engines and other units using gas as a fuel shall be located in ventilated rooms, preferably at ground level and shall be isolated in accordance with the provisions of chs.
SPS 361 to
365. Gas lines to these units shall be provided with suitable flame traps.
NR 110.26(5)(d)5.
5. Electrical fixtures and controls in enclosed places where gas may accumulate shall comply with the national electrical code requirements for class 1, group D, division 2 locations.
NR 110.26(5)(d)6.
6. Waste gas burners shall be readily accessible and shall be located at least 7.6 meters (25 feet) away from any plant structure if placed at ground level. Waste gas burners may be located on the roof of the control building if sufficiently removed from the tank. All waste gas burners shall be equipped with automatic ignition, such as a pilot light or a device using a photoelectric cell sensor. Consideration should be given to the use of natural or propane gas to insure reliability of the pilot light. If the waste gas burner is in a remote location, the department may approve the discharge of gas to the atmosphere through a return-bend screened vent terminating at least 3 meters (10 feet) above the walking surface, provided the assembly incorporates a flame trap.
NR 110.26(5)(d)7.
7. A gas meter with by-pass shall be provided to meter total gas production. Additional gas meters may be required to measure gas usage.
NR 110.26(5)(e)1.1. Whenever possible, digestion tanks shall be constructed above groundwater level. Digestion tanks shall be insulated to minimize heat loss.
NR 110.26(5)(e)2.
2. Piping shall be designed to provide for the heating of feed sludge before introduction to the digesters. Heat exchanger sludge piping shall be sized for heat transfer requirements.
NR 110.26(5)(e)3.
3. Sufficient heating capacity shall be provided to consistently maintain the design sludge temperature. Where digestion tank gas is used for other purposes, an auxiliary fuel supply shall be provided.
NR 110.26(5)(e)4.
4. Consideration should be given to equipping hot water internal heating controls with an automatic mixing valve to temper the boiler water with return water so that the inlet water to the heat jacket can be maintained between 49
° to 55
°C (120
° to 130
°F) to prevent excessive caking or encrustation of sludge on the heat jacket. Manual controls shall also be provided.
NR 110.26(5)(e)5.
5. The boiler shall be provided with automatic controls to maintain the boiler temperature at approximately 82
°C (180
°F). Automatic controls shall also be provided to shut off the main gas supply in the event of pilot burner or electrical failure, low boiler water level or excessive temperature.
NR 110.26(5)(e)6.
6. Thermometers shall be provided to show temperatures of the sludge, hot water feed, hot water return and boiler water.
NR 110.26(5)(f)1.1. Supernatant piping shall be 15 centimeters (6 inches) in diameter, or larger.
NR 110.26(5)(f)2.
2. Piping shall be arranged so that withdrawal can be made from 3 or more levels in the tank. A positive unvalved vented overflow shall be provided.
NR 110.26(5)(f)3.
3. If a supernatant selector is provided, provisions shall be made for at least one other draw-off level located in the supernatant zone of the tank in addition to a positive unvalved vented overflow pipe. High pressure backwash facilities shall be provided.
NR 110.26(6)(a)1.1. Aerobic digesters shall be designed to provide effective air mixing, reduction of organic matter, supernatant separation and sludge concentration.
NR 110.26(6)(a)2.
2. The digester detention time may be calculated based upon the factors indicated in subd.
1. If such calculations are not done, the following minimum requirements shall be met:
NR 110.26(6)(a)2.a.
a. A minimum of 15 days detention time shall be provided for waste activated sludge and 20 days for primary sludge or a combination of primary and waste activated sludge. Where sludge temperature is lower than 10
°C (50
°F), additional time shall be provided; and
NR 110.26(6)(a)2.b.
b. The volatile suspended solids loading may not exceed 1.60 kilograms per cubic meter per day (100 pounds per 1,000 cubic feet per day) in the digestion unit. Lower loading rates may be necessary depending on temperature, type of sludge and other factors.
NR 110.26(6)(a)3.
3. The aeration system for aerobic digesters shall be capable of meeting the oxygen requirements of par.
(b), or the mixing requirements of par.
(c), whichever is greater.
