Low Profile Gravity Sand Filter
PART 1 – GENERAL
1.1 Scope: The work covered in this section includes furnishing all labor, material, equipment and incidents to install complete and ready for operation, a gravity sand filter device as shown on drawings and as specified herein.
1.2 APPLICABLE PUBLICATIONS: The publications listed below form a part of this specification to the extent referenced. The publications are referred to in the text by the basic designation only.
American National Standards Institute (ANSI) Publication:
Pipe Flanges and Flanged Fittings, Class 25, 125, 250 and 800
American Society for Testing and Materials (ASTM) Publications:
A-240 304L Stainless Steel Plate
A-249 Stainless Tubing
A-276 304L Stainless Rounds, Squares, Flats
American Welding Society (AWS) Publications:
D1.1-84 Structural Welding Code, Steel
A5.1 Mild Steel Arc-Welding Electrodes
Standard Welding Terms and Definitions
Standard Welding Symbols
Steel Structures Painting Council (SSPC) Publication:
American Institute of Steel Construction (AISC) Steel Construction Manual, 8th Edition
1.3.1 Contracting officer will review and approve all submittals.
1.3.2. Submit the following before fabrication
126.96.36.199 Shop Drawings: Shop drawings for gravity sand filter and accessory equipment including principle dimensions and location of fittings. Data shall include weight and distribution of weight with the unit empty and filled with water.
188.8.131.52 Test results, signed by the manufacturer, which indicate the gravity sand filter is capable of handling specified effluent concentration, pH, fluid temperature and concentration of suspended solids.
184.108.40.206 Provide calculations of gravity sand filter loading rate at the design flow rate.
1.3.3 Submit the following after fabrication:
- That the unit was hydraulically leak tested for a period of at least 12 hours before further surface preparation.
1.4 MANUFACTURER’S SERVICE REPRESENTATIVE’S REPORT AND CERTIFICATE: Submit service representative’s complete signed report of results of the inspection, operation, adjustment, and tests. Report shall include detailed descriptions of points inspected, tests and adjustments made, quantitative results obtained if such are specified, and suggestions for precautions to be taken to ensure proper maintenance. Include the manufacturer’s certificate that equipment conforms to specified requirements and is ready for permanent operation and that nothing in installation will render manufacturer’s warranty null and void.
1.5 DELIVERY, STORAGE, AND HANDLING MATERIALS:
1.5.1 Delivery and Storage: Inspect materials delivered to site for damage; unload and store with minimum handling. Store materials on site in enclosures or under protective coverings. Protect materials not suitable for outdoor storage to prevent damage during periods of inclement weather, including subfreezing temperatures, precipitation, and high winds. Store materials susceptible to deterioration by direct sunlight under cover and avoid damage due to high temperatures. Do not store materials on ground. Store and protect materials according to manufacturer recommendations.
1.5.2 Handling: Handle gravity sand filter in such a manner as to ensure delivery to final location in sound, undamaged condition. Take special care not to damage interior and exterior surfaces of the gravity sand filter. Make satisfactory repairs to damaged material(s) at no cost. Carry and do not drag materials. Handle gravity sand filter according to manufacturers information.
1.6 QUALITY ASSURANCE:
1.6.1 Inspection: Examine each component of gravity sand filter for compliance with requirements specified. Redesign or modification of equipment to comply with specified requirements, or necessary redesign or modification following failure to meet specified requirements, shall receive particular attention for adequacy and suitability. This element of inspection shall encompass visual examinations and dimensional measurements. Noncompliance with specified requirements, or presence of one or more defects preventing or lessening maximum efficiency of gravity sand filter operation, shall constitute cause for rejection.
1.7 WELDER QUALIFICATIONS:
1.7.1 Welders shall be previously qualified by passing the tests prescribed in the AWS Standard Qualification Procedure, or by passing such other tests as the Engineer may accept.
1.7.2 Welders shall have been tested within the past twenty four months and their qualifications shall be considered as remaining in effect unless the welder is not engaged in a given process of welding for a period exceeding six months.
PART 2 – CONTINUOUS CLEANING GRAVITY SAND FILTER DESIGN CRITERIA AND MANUFACTURING SPECIFICATIONS
2.1 CONTINUOUS CLEANING GRAVITY SAND FILTER – APPLICATIONS & PERFORMANCE
2.1.1 Applications: The filter shall consist of a bottom fed filter vessel * internal diameter. The height of the filter vessel shall not exceed * . The filter shall rely on no screens to filter or wash the filter media.
The gravity sand filter shall be used to filter entrained suspended solids from a wastewater stream having a flow rate of * gallons per minute. Water entering the distribution cone has previously been conditioned to destabilize micro colloidal suspended solids. As the water stream collects under the distribution cone and, when full, flows out and up through the media bed, after exiting the media bed, the clean effluent rises and overflows an effluent weir then is discharged through effluent nozzle.
A slip stream of effluent is used to continuously wash the “dirty” sand, then taken by hydraulic means or by pumping back to be reprocessed through the initial clarifier. The “dirty” sand shall be lifted via air lift pump from the bottom of the media bed up through the media bed to the sand cleaning chamber. The sand lift mechanisms shall be internal to the tank and shall be the shortest most direct route through the media bed. External sand lift mechanisms that inherently plug shall not be accepted. The filtration media shall be of one uniform size. Multiple sized media is not acceptable.
2.1.2 Performance: The total peak flow capacity of the filter shall be * gallons per minute. The filter shall possess a surface area of at least * square feet. The entire surface area, less the sand lift tube, shall be available for filtration at all times; no portion shall be reserved for or be involved in backwashes. The filter shall be capable of removing suspended solids from the clarifier effluent containing approximately 40 mg/l suspended solids. The filter shall produce a filtrate of 10 mg/l or less of suspended solids at peak flow.
2.2 CONTINUOUS CLEANING GRAVITY SAND FILTER – Manufacturing specification
2.2.1 Filter Vessel: The filter vessel shall be constructed of 304L stainless steel full sheet construction, patchwork construction is not acceptable. All internals shall be constructed of Type 304L stainless steel. The cone of the filter vessel shall be constructed of 3/16″ stainless steel and shall be formed at an angle of 120° to the cylinder wall. The filter vessel shall be supported and anchored to the ground. The filter vessel shall be fitted as follows:
220.127.116.11 Clean-out Nozzle: A six inch (6″), 150# drill pattern, drain nozzle shall be welded to the filter vessel near the filter bottom. A 1″ NPT coupling in the blind flange shall be fitted with a removable internal strainer to facilitate draining the filter vessel without losing filter media. The blind flange will have no strainer and may be used to remove sand.
18.104.22.168 Effluent Weir: A type 304 stainless steel stationary effluent weir shall be welded to the filter vessel wall to distribute water to the effluent nozzle. The weir shall be located to assure adequate differential head between the effluent and reject weirs and to establish freeboard.
22.214.171.124 Reject Weir: The weir shall be a type PVC sluice gate. Reject flow shall be adjustable by placing different width PVC plates into a channel to achieve the desired differential head between the effluent and the reject weir.
126.96.36.199 Reject Nozzle: The reject nozzle shall have a diameter of * inches and shall be 150# ANSI drill pattern.
188.8.131.52 Effluent Nozzle: The effluent nozzle shall have a * inch diameter. 150# ANSI drill pattern.
184.108.40.206 Cover: Each filter shall be supplied with a cover and 4″ diameter vent.
2.2.2 Air Lift Manifold: The filter vessel shall have at least * airlift assemblies internally mounted in the filter vessel and each attached directly to its respective sand cleaning chamber.
220.127.116.11 Each manifold shall have only one air injector to lift and scrub the sand from the bottom of the sand bed to the sand cleaning chamber. The injector shall be constructed to permit acid washing with hydrochloric acid for carbonate removal. The sand lift pipe, injectors and injector dispersion screen shall be constructed of Hastalloy “C”, Teflon or PVC.
18.104.22.168 The vertical portion of the sand lift mechanism shall be constructed of schedule 80 PVC pipe, Teflon or Hastalloy “C” to assure maximum life of the component and shall pass through the sand bed.
22.214.171.124 The sand shall be transported straight-up through the lift pipe to the sand wash chamber. Each sand wash chamber shall be open on the top to permit visual verification of sand movement. Each airlift mechanism shall consume * scf/m of air at 15-25 psi. The sand lift system will turnover the filter bed 3 or more times per day.
2.2.3 Sand Cleaning Chamber: The sand cleaning chamber shall be constructed of type 304 stainless steel or abrasion resistant Teflon.
126.96.36.199 It shall be fabricated to have an opening in the floor to permit the sand to fall through the bottom of the chamber.
188.8.131.52 It shall have guides to house the segmented PVC reject weir.
184.108.40.206 A top splash baffle shall be installed to deflect and contain the “dirty” wash water from contaminating the filtered water.
220.127.116.11 It shall also have a dynamic ring separator system to clean the sand as it returns to the top of the filter bed. The ring separator steps shall cause the descending sand to strike the adjacent ring before dropping to the next level. The cross sectional area of the ring separator shall be sized assuring sufficient velocity of rising water to transport contaminants into the wash chamber and out the reject nozzle.
2.2.4 Filter Media: The filter bed shall consist of a single media which shall contain * ton(s). The resulting bed depth will be 40 inches (1 m).
18.104.22.168 The filter media shall as a minimum meet AWWA B100-89, standard for filtering material.
22.214.171.124 The filter material shall consist of coarse aggregate in which a high proportion of the particles are rounded and tend toward a generally spherical shape.
126.96.36.199 The filter media (silica sand) shall consist of hard, durable, and dense grains of predominantly siliceous material and shall possess sufficient strength and hardness to resist degradation during handling and use meeting the following specifications:
- Hardness (Moh) 6.5-7.0
- Silica Content >95%
- Acid Solubility (15% HCI) <5%
- Specific Gravity <2.5
- Porosity >45%
- Roundness (API) >0.6
- Sphericity (API) >0.6
188.8.131.52 The silica sand shall be free of clay, dust, and micaceous and organic matter.
184.108.40.206 The filter media shall have an effective size of 1.2 mm with a uniformity coefficient of 1.5 or less.
2.3 CONTROL PANEL
2.3.1 Filter Controls: The filter controls shall be housed in a NEMA 4 enclosure. Controls requiring operator adjustment shall be surface mounted. Control panel shall be mounted integral to the filter.
2.3.2 Pneumatic Controls: The pneumatic controls shall provide automatic dual air flow with initial high flow to initiate the sand lift and secondary low flow to continue the sand lift.
220.127.116.11 The stainless steel pressure gauge shall be panel mounted with a 2-½ inch face and a range of 0-60 psi.
18.104.22.168 A flowmeter for each sand lift mechanism, shall be of the variable area type with a stainless steel indicator. The meter shall have a metering valve with a range of 0 to 100 scf/h.
22.214.171.124 Flow into the pneumatic panel shall be directed through a filter and regulator.
2.4 LADDER AND PLATFORM
2.4.1 Ladder: Filter shall be equipped with stainless steel ladder in compliance with the appropriate OSHA requirements.
2.4.2 Platform: Filter shall be equipped with galvanized grating located on top of the filter for purposes of observation and maintenance. In addition, handrails will be provided around the top circumference of the vessel.
2.5.1 All structural and tank steel stresses shall be within the allowable limits shown in the Steel Construction Manual of the American Institute of Steel Construction, Eighth Edition.
2.5.2 The unit to be structurally designed for installation in Seismic Zone * in accordance with 1985 Uniform Building Code.
2.6.1 All seal welds shall be visually checked for continuity, pinholes, and voids.
2.6.2 The entire unit shall be shop-hydrostatically tested. Documentation of hydrostatic test shall be provided.
2.7 SURFACE PREPARATION
2.7.1 Surface Preparation: The stainless steel surfaces must be dry and clean in accordance with the following requirements. Remove all grease, oils and contaminants as outlined in SSPC SP1. Remove all weld splatter and grind burrs on cut edges and rough welds smooth. Blast clean all surfaces after fabrication in accordance with SSPC SP6 with profile depth of .5-1.0 mils to produce a uniform surface color.
PART 3 – DELIVERY, STORAGE AND HANDLING MATERIALS
3.1 Delivery and Storage: Inspect materials delivered to site for damage; unload and store with minimum handling. Store materials on-site in enclosures or under protective coverings. Protect materials not suitable for outdoor storage to prevent damage during periods of inclement weather, including subfreezing temperatures, precipitation and high winds. Store material susceptible to deterioration by direct sunlight under cover and avoid damage due to high temperatures. Do not store materials directly on ground. If special precautions are required, prominently and legibly stencil instruction for such precautions on outside of equipment or its crating. Store and protect materials according to manufacturers recommendations.
3.2 Handling: Handle gravity sand filter in such a manner as to ensure delivery to final location in sound, undamaged condition. Take special care not to damage interior and exterior surfaces of gravity sand filter and associated supports and pipe coatings or linings. Make satisfactory repairs to damaged material(s) at no cost. Carry and do not drag materials. Handle gravity sand filter according to manufacturers information.
PART 4 – EXECUTION
4.1 Installation: Gravity sand filter to be installed as indicated and as recommended by the manufacturer. Equipment delivered to the site in advance of installation to be stored per the manufacturer’s requirements. Make all connections as required to make gravity sand filter fully operational. Do not weld tank surfaces, interior or exterior, unless authorized by manufacturer. Unauthorized welds will void manufacturers warranty.
4.2 Field Inspection Services: Examine each component of gravity sand filter for compliance with requirements specified. Redesign or modification of equipment to comply with specified requirements, or necessary redesign or modification following failure to meet specified requirements, shall receive particular attention for adequacy and suitability. This element of inspection shall encompass visual examinations and dimensional measurements. Noncompliance with specified requirements, or presence of one or more defects preventing or lessening maximum efficiency of gravity sand filter operation, shall constitute cause for rejection.
4.3 Start-Up Testing: Manufacturer’s field representative shall inspect and test unit and certify that the installation has been performed in accordance with manufacturer’s recommendations and that the system is ready for operation by others. Inspection shall consider, but not be limited to, the following:
- Soundness (without cracked or otherwise damaged parts).
- Completeness in all details, as specified.
- Correctness of settling alignment, set points and relative arrangement of each component.
- Confirm that the unit is level within ¼” side to side and end to end.
- Inspect unit for leakage and that everything is operating as specified.
PART 5 – SUGGESTED MANUFACTURER:
The gravity sand filter shall be model number # * manufactured by:
Hoffland Environmental, Inc.
10391 Silver Springs Road
Conroe, Texas 77303
(936) 856-4515 phone / (936) 856-4589 fax
*Model Number *
*Check following chart for alternates.