Filter Media Replacement

City of Fairborn

Bill Theall

Why Replace?

• More expensive• Increased downtime• Close examination of under drain

• Correct/repair under drain deficiencies

• Perform modifications• Structural repair• Change media type• Disposal of used media• Media no longer meets AWWA specification

• Less expensive• Less downtime• Can be performed in-house

• Worked well for Greene County

• Disposal of cleaning compounds

Can’t we clean them?

Replacing Cleaning

Options:

What’s Our Objective?

1. Thoroughly evaluate and address all needs• Age and type of equipment (30 years old)

• Leaks in underdrain

• Condition of plastic filter nozzles and screen

• Condition of structure of floors and walls (repair leak at filter five wall)

• Surface wash nozzle replacement

• Verify valve operation

• Cleaning

Let’s look at specs…

1. Filter Media• AWWA B100-01

• NSF 60/61 approved materials only

• Quantify and qualify

• Ensure you get what you ordered (allow for 3rd party lab certification)

• If you change to a different type of media you will require EPA approval.

2. Additional considerations for the specs• Material storage/staging (keep media dry)

• Timely completion

• Cover your assets (take pictures)

• Encourage operator input

Our Direction

• Replace filtration media

• Replace surface wash nozzles

• Inspect underdrain

• Teleview effluent header

• Evaluate underdrain piping and grouting

• Determine modifications required to correct backwash deficiencies

Filters 1-4 Underdrain

• 12 inch header DIP (tapped)

• 2 inch plastic laterals

• 1 inch risers

Underdrain piping grouted into floor

• Uneven lengths of laterals cause uneven backwash distribution

• Caused slight upward gradient of filter material from left to right

• Mudballing on the right side corners was common

High initial turbidity breakthrough and longer ripening periods are indicators of fouled media. Turbidity spikes for filters 1-4 are considerably higher than newer filters 5-8.

Plastic strainers (nozzles- with stainless steel screening)

• 1 inch threaded nozzles- all identical- no variation of throat size to vary flows

New Nozzle Flow Calculations

• To avoid costly underdrain replacement

• Complicated calculations are used to determine outflow distribution on multiple port diffusers

• Robert’s filter representatives assisted with flow calculations to determine proper throat sizing for new replacement nozzles

New Nozzles Selected To Balance Backwash Water Distribution

• Manufactured by Orthos Nozzles

• Throat size of 22mm was selected for the longer right side laterals

• Throat size of 16mm was selected for the shorter side laterals

Staging and Verifying the New Filter Materials

• The Media arrives in 2000-pound supersacks

• Media is staged to accommodate ease of installation

• Verification testing of each supersack prior to acceptance and installation

Removing the Old MediaA truck-mounted hydrovac system supplies the

vacuum and storage for media removal

Hoses are installed to convey the material from the filter to the truck

After following confined space entry procedures and verifying air quality testing, contractors can safely enter

the filter cell to vacuum out old material

Now that all the media has been removed, the filter can be thoroughly cleaned through high-pressure washing at 3600 psi. AWWA C-653-97

The old media is easily removed from the truck for disposal.

Flow Testing the Old Nozzles

• Prior to their removal, flow tests performed on the old nozzles verified the uneven backwash distribution

• Noted higher velocities on the shorter-sided laterals

Removing the Old Nozzles• WTP operators removed all old nozzles and performed underdrain and grouting inspection

• Televiewing of the 12 inch header pipe was performed next

• No deficiencies were found in the underdrain manifold piping or grouting

Additional Flow Tests

Flow tests performed with the nozzles removed further indicated uneven backwash distribution. Fountains seen are from nozzle ports located directly on top of the offset 12 inch header.

All flow tests performed verified uneven backwash distribution.

Installing the New Nozzles• The 16mm nozzles (designed to restrict flow) were installed on the 12 inch header and the shorter laterals.

• The 22mm nozzles were installed on the longer laterals.• Flow tests performed following nozzle replacement indicated this modification appeared to successfully balance out backwash distribution.

The new nozzles are easily threaded into the existing 1 inch straight-threaded ports and required no sealant. They seat tight to the floor and are tightened into

place with a 5/8 inch wrench.

Filter Media Configuration

EPA approved filtration media specifications

Installing the New Media

Additional tests performed at the contractor’s expense on the new filter sand and garnet delivered showed this media met AWWA standards.

• Pipes are assembled to convey the media to the filter.

• Plywood is used to protect the floor from pipe vibration.

• Plastic covers were used to protect the filter consoles

• The 3/4 x 3/8 and the 3/8 x 3/16 inch support gravels are pneumatically conveyed to the filter.

• A ¾ inch water supply line is fed into the pneumatic system to limit dust created during this operation.

Support gravel is pneumatically conveyed to the filter. The filter is filled with water to

protect the new filter nozzles.

• The support gravel is backwashed then leveled to the marks previously made on all four walls.

• Water is used for precise leveling.

Each of the subsequent sand and anthracite layers are installed using a pump and eductor box. The filter material in a slurry is conveyed

through piping to the filter.

• Each layer is thoroughly backwashed and skimmed to remove the fines. Each layer of both the quartz sand and garnet required two skimming's to adequately remove the fines.

• Plywood boards should be used to distribute body weight for standing on the sand.

The skimmed fines are bucketed from the filter and removed for disposal.

Supersacks of anthracite are lifted to the eductor box using a forklift. Filter media

should be covered to keep it dry and prevent possible freezing of the material.

• All layers of the finer filtering materials including the anthracite are pumped from the eductor box into the filter as a slurry.

• Skimming can be performed if desired, although most of the fine (low-density) anthracite is removed during backwashing.

Disinfection

• Performed as per AWWA standard C-653-97

• The filter is filled to its maximum level and dosed with sodium hypochlorite to achieve a disinfection residual of 25mg/l throughout the entire bed.

• The chlorine demand experienced was very high (50 mg/l dosage to achieve 25 mg/l residual).

• A minimum 12 hour contact time is required.

• The minimum disinfection residual after the required contact time is 15 mg/l. If less, disinfection should be performed again.

Bacteriological Analysis

• Bacteriological analysis - AWWA C-653-97 section 5

• Two samples should be collected after the disinfection has been successfully completed and the filter thoroughly backwashed.

• Collect samples not less than 30 minutes part - two consecutive coliform negative sample results are required.

• Tested for Coliform in accordance with the latest edition of Standard Methods for the Examination of Water and wastewater.

• If Coliform positive, repeat samples at 24 hours apart until 2 consecutive are negative.

• Record of compliance – bacteriological test report.

Returning the Filter to Service• The filter is started at low flows (less than 2 gpm/sq ft foot) and allowed to ripen while in a filter-to-waste cycle.

• For the first few hours, operators monitored filter effluent for total Fe, Mn and turbidity. All analyses during this period at acceptable levels.

• The filter was returned to normal service and allowed to season overnight at low flows. Analyses performed the following day indicated concentrations of Fe and Mn to BDL, and a turbidity of .04.

• The filter was then returned to service at higher flows, and monitored closely for several days.

Results

• Initial turbidity spikes for these filters are nominal. With short ripening times.

• Turbidities average .025-.035ntu.

• Mn and Fe consistently BDL

• Shorter backwash time required

• Filter media remains level following a backwash, indicating even distribution of backwash water (no more mudballs!).

Filter 2 & 4 initial turbidity post rehab