Heavy Media to Buoyant Media Clarifier Conversions

Enhance Plant Operations Significantly

Hyatt Regency

Buffalo, NY

September 22, 2016

Demands of Drinking Water Systems

• Water treatment systems are being reconfigured to:

– become more efficient allowing them to produce as much water as possible,

– optimize chemical usage,

– minimize waste handling costs and

– reduce downtime for clarifier flushing and filter backwashing

Plant Configurations discussed

• Use 'high rate” media clarifiers prior to filtration

• Treat surface water

• “High-rate” with hydraulic loading rate greater than 5 gpm/sq ft.

• Can be in steel tanks or concrete basins.

• Flow from 150 gpm to 2 MGD/basin typically

Focus on Type of Plant Design

• Typically to remove turbidity and pathogens from surface water with low-to-moderate turbidity.

• Simple flow path

– Raw water dosed typically coagulants (and optional polymer) and flows into the bottom of the clarifier.

– Upflow clarifier media captures coagulated solids until it reaches a terminal head loss and initiates cleaning.

– Collected solids flushed away to waste.

Clarifier is cleaned

• The flushing process uses both raw water and air to scour

• Releases solids by expanding the bed and scouring particles.

• Changes in influent water quality can cause the clarifier to clean more or less frequently

Couple of Options

• Buoyant clarifier media (light)

• Non-buoyant clarifier media (heavy)

Buoyant Media

• Buoyant media SG < 1.0.

• Statically, the media rests or floats against a top screen.

• Dynamically, the top screen holds the media in place, neutralizing the forces that act in the direction of flow.

• As raw water flows through buoyant bed, the adsorption clarifier flocculates and adsorbs the floc onto the surfaces of the media grains.

• Also traps and stores floc in the “pores” between the grains of the bed.

Light Media Clarifier in Package Plant

Heavy Media

• Non-buoyant clarifier media SG > 1.0

• Statically, media sits on a bottom screen or other supporting device.

• Dynamically, the media is held in place by gravity.

• It will remain in place as long as the downward gravitational force acting on it exceeds or equals the upward drag and buoyancy forces acting on it.

• Heavy media clarifiers flocculate solids and remove them by one or more similar mechanisms, and they too store floc in the pores of their media beds.

Heavy Media Clarifier in Packaged Plant

Developed Headloss

• In both systems, removed solids offer additional resistance to the flow or raw water, increasing the headloss across the bed as the clarifier run progresses.

• This “developed headloss” must be added to the clean bed headloss to determine the total headloss across the media bed at any given time during the progress of the process.

Two Case Studies

GEORGE R. SWEENEY WATER TREATMENT PLANT

• Located at the Beaver Run Reservoir in Bell Township. The Beaver Run Reservoir was constructed in 1952 and then enlarged in 1962. It has a present capacity of 11 billion gallons, and a safe yield of 45 million gallons of water per day.

George Sweeney Background

• Facility went on line in July 1997.

• Rated capacity of 24 MGD.

• Sought to increase its NET water production

• Needed to operate closer to design flow than it had been.

• Seven heavy media clarifier and filter basins at this plant

• Required a tremendous amount of water to flush the clarifiers and frequently backwash the filters

Plant Problems

• Each clarifiers takes 45 mins to flush

• To flush all of the basins; it took upwards of 10 million gallons

• One filter was being backwashed about every 6 hours.

• Limited storage for flush and backwash waste

• The time for flushing and backwashing was a huge loss in production.

• A lot of media was lost by excessive cleaning

• Lost media reduced the solids holding capacity of the clarifier bed.

Sweeney WTP’s Thought Process

• Superintendent reported they had rebuilt and serviced all the filters, raw water pumps and high service pumps.

• Felt the biggest obstacle was the original clarifiers with heavy non-buoyant media which have never performed as they wanted.

• They had a lot of confidence in the buoyant clarifier conversions done at the Huntsville WTP as well as the success of the AC in western PA at many of the

existing installations.

HUNTSVILLE, PA. WATER TREATMENT PLANT

• WTP is operated by Pennsylvania American Water.

• Water is supplied from a 25 foot deep Huntsville Reservoir which is a reserve

• Exhibiting a seasonal algae plume in the summer.

• The facility was originally constructed with four concrete heavy media upflow clarifiers feeding four filter media beds.

What Huntsville did

• Clarifiers were modified to use buoyant media in 2007

• While clarifier flush duration did not change, all clarifiers had improved reductions solids removal all across the retrofitted clarifiers.

• As clarifier solids removal efficiency improved, filter runs were increased from a typical 40 hours to over 100 hours.

• The end result for the facility was a 40% increase in capacity and a 50% reduction of filter waste water.

Sweeney’s Approach

• They sequentially replaced one clarifier at a time, except the last two basins wee done together as the converted units met the water demand.

• Then assuming all goes well move forward to have all seven basins installed by the end of CY-2015.

• The driver being that the Sweeney Plant had a contract to provide water to the neighboring town in March/April 2016.

Results-Solids Removal

• According to the plant operator, the new adsorption clarifiers are operating extremely well.

• Effluent water samples taken off the heavy media clarifiers during a flush were showing solids content of about 50 NTU in the waste stream. Samples taken from the new adsorption clarifiers were running about 250 NTU. This indicated, there was a 500% increase in solids capture with the new adsorption clarifier.

• The clarifier run time is about 16 hours between flushes.

Results-Waste Production

• New clarifiers require only about 1/3 the amount of water of the older units to flush.

• Filter run times with the old units was about 40-60 hrs before backwashing.

• The filter run time using the new buoyant media clarifiers increased two fold, backwashing at 95 hrs, as required by PA-DEP not to exceed 100 hrs, and at

that time not even reaching terminal headloss.

Results of Rehabilitation

Before After

Results-Extras

• For the old plant configuration, they lost a lot of clarifier media in the equalization basins, requiring periodic cleaning and had to add more to the clarifiers periodically.

• Now the new Adsorption Clarifiers with buoyant media have eliminated that problem.

• For chemical usage and they reported the PACl dosage went from 4.5-5.0 mg/l to 2-3 mg/l which is pretty much a 50% reduction in chemical usage.

Kuddo’s to:

• Gibson-Thomas Engineering who worked to develop a set of plans, specifications, construction sequence and performance monitoring to convert the adsorption clarifier with buoyant media within the timeframe to meet the additional contracted water demand.

• Municipal Authority Westmoreland County, PA

• Advanced Controls, Inc.

• Installing Contractor: Wm. T. Spaeder

Differences of Clarifier Media

• Non-Buoyant Media

• Heavy (handling)

• Possible media loss

• Unrestrained bed

• Limited headloss capability

• Clarifier operates a lower headloss

• Buoyant Media

• Lightweight

• No media loss in waste-trough

• Restrained bed

• Higher head-loss capability

Summary

• Clarifier buoyant media affects:

– Solids removal effectiveness.

– Waste volume produced.

– Chemical dose and costs.

– Overall plant performance.

– Filter backwash frequency.

Heavy Media to Buoyant Media Clarifier Conversions

Enhance Plant Operations Significantly

Rich Ross

rross@westech-inc.com

443-255-5973