NR 811.49(1)(i)2.
2. A method for avoiding excessive loss of the filter media during backwashing shall be provided.
NR 811.49(1)(i)3.
3. Air scouring shall be followed by a fluidization wash sufficient to restratify the media.
NR 811.49(1)(i)5.
5. Air scour distribution systems shall normally be placed below the media and supporting bed interface; if placed at the interface the air scour nozzles shall be designed to prevent media from clogging the nozzles or entering the air distribution system.
NR 811.49(1)(i)6.
6. Piping for the air distribution system may not be flexible hose which will collapse when not under air pressure and may not be a relatively soft material which may erode at the orifice opening with the passage of air at high velocity.
NR 811.49(1)(i)7.
7. Air delivery piping may not pass down through the filter media nor may there be any arrangement in the filter design which would allow short circuiting between the applied unfiltered water and the filtered water except if all of the following criteria are met:
NR 811.49(1)(i)7.a.
a. The vertical piping is double wall, welded at top and bottom, schedule 40 stainless steel for the internal pipe and schedule 5 stainless steel for the external pipe.
NR 811.49(1)(i)7.c.
c. An air connection to the double-wall annulus shall be provided including piping with a pressure gauge, regulator, flow switch and ball valve along with an air reservoir and compressor.
NR 811.49(1)(i)7.d.
d. The flow switch shall alarm and trigger filter shutdown if a pressure drop of over 10 psi is detected.
NR 811.49(1)(i)8.
8. The backwash delivery system shall be capable of 15 gallons per minute per square foot of filter surface area; however, when air scour is provided, the backwash rate shall be variable and may not exceed 8 gallons per minute per square foot unless operating experience shows that a higher rate is necessary to remove scoured particles from filter surfaces.
NR 811.49(1)(i)9.
9. The filter underdrains shall be designed to accommodate air scour piping when the piping is installed in the underdrain.
NR 811.49(1)(j)
(j) Appurtenances. The following shall be provided for every filter:
NR 811.49(1)(j)1.
1. Sampling faucets on the individual and combined influent and effluent lines. Combined filter effluent sample faucets shall be located upstream of subsequent treatment processes.
NR 811.49(1)(j)2.
2. Indicating loss-of-head gauge with appropriate cross-connection protection.
NR 811.49(1)(j)3.
3. Indicating flow rate controls. A modified rate controller which limits the rate of filtration to a maximum rate may be used. However, equipment that simply maintains a constant water level on the filters will not be approved unless the rate of flow onto the filter is properly controlled. A pump in each filter effluent line may be used as the limiting factor for the rate of filtration only with approval from the department.
NR 811.49(1)(j)4.
4. For surface water and groundwater under the direct influence of surface water, provisions for filtering to waste with appropriate measures for backflow prevention.
NR 811.49(1)(j)5.
5. For surface water and groundwater under the direct influence of surface water, on-line continuous turbidimeters shall be installed on the effluent from each filter. All turbidimeters shall consistently determine and indicate the turbidity of the water in nephelometric turbidity units (NTUs). Each turbidimeter shall report to a recorder that is designed and operated to allow the operator to accurately determine the turbidity at least every 15 minutes. Turbidimeters on individual filters shall be designed to accurately measure low-range turbidities and trigger an alarm when the effluent level exceeds 0.3 NTU. Access to the filter interior through wall sleeves shall be provided in several locations to allow the installation of sampling lines, pressure sensors and other devices, at different depths in the filter media.
NR 811.49(1)(j)6.
6. A 1 to 1.5-inch pressure hose and rack at the operating floor for washing the filter walls.
NR 811.49(1)(k)
(k) Backwash. Backwashing facilities shall be designed to provide:
NR 811.49(1)(k)1.
1. A minimum rate of 15 gallons per minute per square foot, consistent with water temperatures and specific gravity of the filter media. The department may approve a reduced rate of 10 gallons per minute per square foot for full depth anthracite or granular activated carbon filters, if justification is provided. A reduced rate of backwashing is acceptable when air scouring is provided that meets the requirements of par.
(i).
NR 811.49 Note
Note: A rate of 20 gallons per minute per square foot or a rate necessary to provide for a 50% expansion of the filter bed is recommended.
NR 811.49(1)(k)2.
2. Backwashing by filtered water at the required rate from washwater tanks, a washwater pump from a reservoir or a high service main, or a combination of these.
NR 811.49(1)(k)3.
3. Washwater pumps in duplicate unless an alternate means of obtaining washwater is available.
NR 811.49(1)(k)4.
4. Backwashing of not less than 15 minutes wash of one filter at the design rate of wash.
NR 811.49(1)(k)5.
5. A washwater regulator or valve on the washwater line to obtain the desired rate of filter wash with the washwater valves on the individual filters open wide.
NR 811.49(1)(k)6.
6. A rate-of-flow indicator and totalizer on the main washwater line, located for convenient reading by the operator during the washing process.
NR 811.49(1)(k)7.
7. Backwashing by a method which prevents rapid changes in the backwash water flow.
NR 811.49(1)(k)8.
8. Backwash shall be operator initiated. Backwash systems with automated sequencing shall be operator adjustable.
NR 811.49(1)(k)9.
9. The backwash discharge shall terminate above a collection basin with a free air break. Backwash discharges may not be directly piped to a wastewater collection unless a breather pipe is installed that provides adequate backflow prevention.
NR 811.49(1)(L)
(L) Miscellaneous. Roof drains may not discharge into the filters and basins or the conduits preceding the filters.
NR 811.49(2)
(2)
Slow rate gravity filters. The use of slow rate gravity filters is not allowed without prior engineering studies to demonstrate the adequacy and suitability of this method of filtration for the specific raw water supply. The following standards shall be applied:
NR 811.49(2)(a)
(a) Quality of raw water. Slow rate gravity filtration shall be limited to waters having maximum turbidities of 50 nephelometric turbidity units (NTUs) and maximum color of 30 units; turbidity may not be attributable to colloidal clay. Raw water quality data shall include examinations for algae.
NR 811.49(2)(b)
(b) Structural details and hydraulics. Slow rate gravity filters shall be designed to provide:
NR 811.49(2)(b)1.
1. Not less than 2 filter units. If only 2 units are provided, each shall be capable of meeting the plant design capacity, normally the projected maximum daily demand, at the approved filtration rate. If more than 2 filter units are provided, the filters shall be capable of meeting the plant design capacity at the approved filtration rate with one filter removed from service.
NR 811.49(2)(b)3.
3. Headroom to permit normal movement by operating personnel for scraping and sand removal operations.
NR 811.49(2)(b)5.
5. Filtration to waste and overflow at the maximum filter water level.
NR 811.49(2)(c)
(c) Rates of filtration. The permissible rates of filtration shall be based on the quality of the raw water as determined from experimental data. Proposed rates shall be submitted to the department for approval. The design rate shall be 45 to 150 gallons per day per square foot of sand area. However, the department may approve design rates of 150 to 230 gallons per day per square foot if effectiveness is demonstrated to the satisfaction of the department.
NR 811.49(2)(d)
(d) Underdrains. Each filter unit shall be equipped with a main drain and an adequate number of lateral underdrains to collect the filtered water. The underdrains shall be so spaced that the maximum velocity of the water flow in the lateral underdrain will not exceed 0.75 feet per second. The maximum spacing of the laterals may not exceed 3 feet if pipe laterals are used.
NR 811.49(2)(e)
(e) Filtering material. A minimum depth of 30 inches of filter sand, clean and free of foreign matter, shall be placed on graded gravel layers. The effective size shall be between 0.30 and 0.45 mm, and the uniformity coefficient may not exceed 2.5.
NR 811.49(2)(f)
(f) Filter gravel. The supporting gravel shall conform to the size and depth distribution requirements in sub.
(1) provided for rapid rate gravity filters.
NR 811.49(2)(g)
(g) Depth of water on filter beds. The design shall provide a depth of at least 3 feet of water over the sand. Influent water shall be distributed in a manner which will not scour the sand surfaces.
NR 811.49(2)(h)
(h)
Control appurtenances. Each filter shall be equipped with:
NR 811.49(2)(h)2.
2. An orifice, Venturi meter or other suitable metering device installed on each filter to enable measurement of the rate of filtration.
NR 811.49(2)(h)3.
3. An effluent pipe located at an elevation which will maintain the water level in the filter above the top of the sand.
NR 811.49 History
History: CR 09-073: cr.
Register November 2010 No. 659, eff. 12-1-10; renumbering of (1) (e) made under s.
13.92 (4) (b) 1., Stats.,
Register November 2010 No. 659;
CR 22-074: am. (1) (b), (c), (f) 6. b., (j) 1., cr. (1) (k) 9. Register January 2024 No. 817, eff. 2-1-24. NR 811.495
NR 811.495 Filtration — pressure. A pressure filter may not be used in the filtration of surface water, polluted waters, or following lime-soda softening as provided under s.
NR 811.57. A pressure filter shall meet all of the following requirements:
NR 811.495(1)
(1)
Number. At least 2 filter units or cells shall be provided. Provisions shall be made to meet the plant design capacity at the approved filtration rate with one filter out of service. If only 2 units or cells are provided, each shall be capable of meeting the plant design capacity, normally the projected maximum daily demand.
NR 811.495(2)
(2)
Rate of filtration. The rate of filtration shall not exceed 4 gallons per minute per square foot of filter area except when pilot testing under s.
NR 811.44 or full-scale testing as approved by the department has demonstrated adequate contaminant removal rates at the higher filtration rates, as determined by the department.
NR 811.495(4)
(4)
Design details. A filter shall be designed to provide for all of the following:
NR 811.495(4)(a)
(a) Loss of head gauges on the inlet and outlet pipes of each filter.
NR 811.495(4)(b)
(b) An easily readable meter of flow indicator on each battery of filters.
NR 811.495 Note
Note: A flow indicator is recommended for each filtering unit.
NR 811.495(4)(c)
(c) Piping that allows filtration and backwashing of each filter individually.
NR 811.495(4)(d)
(d) Minimum side wall shell height of 5 feet. A reduction in side wall height may be approved by the department when proprietary filter bottoms permit reduction of the gravel depth.
NR 811.495(4)(e)
(e) The top of the wash water collectors to be at least 18 inches above the surface of the media.
NR 811.495(4)(f)
(f) The underdrain system to efficiently collect the filtered water and to uniformly distribute the backwash water at a rate not less than 15 gallons per minute per square foot of filter area.
NR 811.495(4)(g)
(g) Backwash flow indicators and controls that are easily readable while operating the control valves.
NR 811.495(4)(h)
(h) An air release valve on the highest point of each filter cell. The discharge line from the relief valve shall be metal and terminate downward facing with a 24-mesh corrosion resistant screen, at least 24 inches above the floor.
NR 811.495(4)(i)
(i) An accessible manhole to facilitate inspection and repairs for each filter cell.
NR 811.495 History
History: CR 22-074: cr. Register January 2024 No. 817, eff. 2-1-24; correction in (2) made under s. 35.17, Stats., Register January 2024 No. 817. NR 811.50
NR 811.50 Filtration — membrane. Membrane technologies have a wide range of applications from the use of lower pressure membranes for removal of surface water contaminants such as
Giardia Lamblia and
Cryptosporidium to the use of reverse osmosis for desalination, inorganic compound removal, and radionuclide removal. The following specific requirements shall be met:
NR 811.50(1)
(1)
Treatment objectives. The selection of the specific membrane process shall be matched to the desired treatment objectives. The department shall be contacted to determine inactivation/removal credits for the specific membrane and treatment objective membranes to be used in treatment of surface water or groundwater under the direct influence of surface water.
NR 811.50(2)
(2)
Water quality considerations. A review of historical source raw water quality data, including turbidity or particle counts or both, seasonal changes, organic loading, microbial activity, and temperature differentials as well as other inorganic and physical parameters shall be conducted. The data shall be used to determine feasibility and cost of the system and the degree of pre-treatment. Design considerations and membrane selection at this phase shall also address the issue of target removal efficiencies and system recovery versus acceptable transmembrane pressure differentials. On surface water supplies, pre-screening or cartridge filtration may be required. The source water temperature shall be considered when establishing the design flux of the membrane under consideration and the number of treatment units to be installed. Seasonal variation of design flow rates may be based on documented lower demand during colder weather.
NR 811.50(3)
(3)
Pilot testing. Prior to initiating the design of a membrane treatment facility, pilot testing under s.
NR 811.44 shall be conducted. The pilot plant study shall be designed to identify the best membrane to use, need for pre- treatment, type of post- treatment, cold and warm water flux, backwash optimization, chemical cleaning optimization, fouling potential, operating and transmembrane pressure, integrity testing procedures, bypass ratio, amount of reject water, system recovery, process efficiency, particulate or organism removal efficiencies, and other design and monitoring considerations, each when applicable. The duration of the pilot testing shall be 9 to 12 months for microfiltration and ultrafiltration and 2 to 7 months for reverse osmosis and nanofiltration. The pilot testing shall be operated for a minimum of 3 clean in-place cycles unless an alternate operation schedule is approved by the department. The general protocol and sampling schedule shall follow the U.S. Environmental Protection Agency Membrane Filtration Guidance Manual, EPA 815-R-06-009, November 2005 Table 6.2, which is incorporated by reference, unless the department approves an alternative sampling schedule.
NR 811.50 Note
Note: U.S. Environmental Protection Agency Membrane Filtration Guidance Manual, EPA 815-R-06-009 is the U.S. Environmental Protection Agency guidance for membrane filtration published on November 5, 2005. A copy of the U.S. Environmental Protection Agency standard is available for inspection at the Legislative Reference Bureau and may be obtained from the U.S. Environmental Protection Agency,
https://www.epa.gov.
NR 811.50(4)
(4)
Challenge Testing. Membranes treating surface waters or groundwater under the direct influence of a surface water shall be challenge tested to establish a product specific maximum
Cryptosporidium and
Giardia Lamblia log removal credit. Challenge testing shall meet the requirements of s.
NR 810.45 (2).
NR 811.50(5)
(5)
Pretreatment. Pretreatment shall be as follows:
NR 811.50(5)(a)
(a) Microfiltration and ultrafiltration. Pretreatment shall be designed to remove suspended solids and large particulate matter. The pretreatment may consist of a screen or strainer with a 200 to 500 micron rating. Chemicals used for pretreatment shall be certified for compliance with ANSI/NSF Standard 60.
NR 811.50(5)(b)
(b) Reverse osmosis and nanofiltration. Pretreatment shall be provided where appropriate for turbidity reduction, iron or manganese removal, stabilization of the water to prevent scale formation, microbial control, chlorine removal for certain membrane types, and pH adjustment. At a minimum, cartridge filters shall be provided for the protection of the reverse osmosis or nanofiltration membranes against particulate matter.
NR 811.50(6)
(6)
Membrane materials. Two types of membranes may be used for reverse osmosis and nanofiltration. These are cellulose acetate based and polyamide composites. Microfiltration and ultrafiltration membranes may be organic polymers such as: cellulose acetate, polysulfones, polyamides, polypropylene, polycarbonates or polyvinylidene. The physical configurations may include: hollow fiber, spiral wound or tubular. Membrane materials shall be compatible with any pre-oxidants.
NR 811.50(7)
(7)
Useful life of membranes. The life expectancy of a particular membrane under consideration shall be evaluated during the pilot study or from other relevant available data.
NR 811.50(8)
(8)
Backwashing. Automated periodic backwashing shall be provided for microfiltration and ultrafiltration on a timed basis or once a target transmembrane pressure differential or a high resistance have been reached. Back flushing volumes may range from 5% to 15% of the permeate flow depending upon the frequency of flushing or cleaning and the degree of fouling. The back flushing volumes shall be considered in the treatment system sizing and the capacity of the raw water source. For systems using pressurized air, the compressors shall utilize food grade oil and filters shall be provided to prevent oil from reaching the membranes. Chemically enhanced backwash systems shall be protected from cross connections and shall be followed by a regular backwash. Backwash wastes shall be disposed of in accordance with subch.
XII.
NR 811.50(9)
(9)
Membrane cleaning. A means shall be provided to allow for periodically cleaning the membrane. Cleaning shall include a soak type cleaning and may also include more frequent maintenance cleans. The cleaning process shall protect the raw and finished water from contamination. Cleaning chemicals, frequency and procedure should follow membrane manufacturer's guidelines. Some cleaning solutions require heated water. Cleaning chemicals shall be NSF/ANSI Standard 60 certified. Membrane cleaning shall be initiated by the operator. Waste streams from chemical cleaning shall be discharged to the sanitary sewer. Adequate space shall be provided for different or additional chemicals which may be required to adequately clean the membranes in the future.
NR 811.50(10)
(10)
Membrane integrity testing. A means shall be provided to conduct direct and indirect integrity testing to routinely evaluate membrane and housing integrity and overall filtration performance. Direct integrity testing may include pressure and vacuum decay tests for microfiltration and ultrafiltration and marker-based tests for nanofiltration and reverse osmosis. The direct testing method shall allow for conducting tests at least once per day and may be required 3 times per day. Indirect monitoring options may include particle counters or turbidity monitors or both and shall allow for testing continuously. The testing methodology shall be approved by the department during startup procedures.
NR 811.50(11)
(11)
Monitoring. Equipment shall be provided to monitor water quality, flow rates, and water pressure.
NR 811.50(11)(a)
(a) Water quality. Sampling taps shall be provided to allow monitoring of water quality from the source water, from the water after any pretreatment, from the filtrate of each membrane unit, from the combined filtrate of all membranes, from the backwash, and prior to the entry to any clearwell.
NR 811.50(11)(b)
(b) Flow monitoring. Water meters shall be provided to allow flow measurement from the source water, from the filtrate of each unit, from the combined filtrate of all units, from the backwash source, from any recirculation line, and from any waste line.
NR 811.50(11)(c)
(c) Pressure monitoring. Pressure gauges shall be provided prior to the membrane units, after each membrane unit, and on the combined effluent of all membrane units.
NR 811.50(11)(d)
(d) Additional monitoring. Additional monitoring points shall be provided as necessary to satisfy integrity testing requirements and operational reporting requirements of sub.
(10) and s.
NR 810.07.
NR 811.50(12)
(12)
Cross connection control. Cross connection control considerations shall be incorporated into the system design, particularly with regard to chemical feeds and waste piping used for membrane cleaning, waste stream and concentrate. Protection may include block and bleed valves on the chemical cleaning lines and air gaps on the drain lines.
NR 811.50(13)
(13)
Redundancy of critical components. Redundancy of critical control components including but not limited to pumps, valves, air supply, chemical feed equipment and computers shall be provided.
