THM Removal – Small THM Removal – Small System ApplicationsSystem Applications

Finger Lakes Conference – Watkins Glen

Thomas F. Clark, P.E.

Monroe County Water Authority

DBP Control EffortsDBP Control Efforts

• MCWA system overview

• DBP reduction water spray system

• Results

• Pembroke tank

Monroe County Water Authority

Shoremont Treatment Plant

145 MGD

MCWA Service Area

MCWA Zones

• MCWA operates 28 separate pressure zones – each are essentially a small supply.

• One or two points of water entry with tankage.

• Each one is a small system….some are quite small demand-wise.

Pembroke New York

• One of these zones is the Pembroke zone.

• MCWA buys water from Erie County Water Authority.

• Just as many systems do, we purchase treated, disinfected water.

• We have no control over the initial water quality that we receive.

Service Area by Supply

Pembroke Booster

Pump Station

Path of Water

ECWA VandeWater

Treatment Plant MCWA Pembroke BPS

•Pembroke service

area

DBP Formation

Town of Pembroke

• Several hamlets and the Village of Corfu constitute the Genesee Water District. MCWA assumed operation of the district in 2003.

• Approx 500 accounts in the district plus another 670 accounts in the Village of Corfu and the Town of Darien, further south along Rte 77.

• Average demand ~ 400,000 gpd

Pembroke BPS

• Pumping distance is approx 26 miles from Buffalo to the BPS in Pembroke.

• Because of travel time, THM levels coming into Pembroke can be problematic during the late summer after Lake Erie water has warmed.

Historic THM Data at Entry Point

Pembroke System

• The water enters our grid and moves 3 ½ miles to the Pembroke tank.

• The tank is 0.5 MG capacity.

• Retention time of water within the tank is 4- 5 days.

Pembroke System

• Upon leaving the tank, water moves another (nearly) 5 miles (about 4 days travel) to our 2594 Main Road DBP sample site.

• THMs at sample point have been higher than our in house goal of 64 ppb during the summer.

Pembroke Grid

Pembroke Pump Station

Pembroke Tank

2954 Main RdEast Pembroke

Autoflush unit

New York State Thruway

To Corfu NY

Town of PembrokeGenesee County, NY

4.5 miles3.5 miles

Pembroke Tank

• 31 ft diameter

• 61 ft tall

• Steel plate construction

• 0.50 MG capacity

• Water spray aeration

added in 2010 due to

high DBP levels

Why Water Spray?

• Chloroform and dichlorobromomethane are two THMs that are relatively volatile.

• One benefit…..increasing water temperature increases Henry’s Law constant and increases THM removal.

• Reports are being prepared by engineers in both this country and in Canada describing removal of THM compounds by either water spray or aeration.

Why Water Spray?

• We have optimized treatment at the plant.

• Localized treatment allows us to zero in on “problem” areas of water in the distribution system.

• The MCWA opted for a water spray at tanks due to the height of the tank and the desire to keep equipment out of the tank.

Pembroke Water Spray

• T

Inflow/Discharge Line

•Tank Outlet

•Tank Inlet Line

Riser Piping

• Sch 80 PVC pipe• 2 inch diameter

Tank Penetration

• Penetration into the hatch- bulk head fitting.

• From 7 to 25 ft in

separation between

spray heads and water surface.

Multi-spray head

• Two were inserted into the top of the tank. Each head is brass costing about $ 300 each.

• To be replaced with stainless steel for longevity.

Spray Heads

Hypo System

• Because of the long travel time to the hamlets at the east end of the season, we also added a sodium hypo disinfection system. This allows us to keep a free residual at the end of the system.

Pembroke Tank

• To assist with moving water faster, we have the option of installing an automatic flush unit at the eastern end of the system.

Pembroke Tank- Autoflushing

• The unit is set to release about 100 gpm for 90 minutes each night.

• This is equivalent to about 1.25 ft of water in the Pembroke tank

Pembroke Water Spray- 2010-2011

• In 2010, Pembroke water spray turned ON July 6.

• Water flow through the aeration unit was 65 gpm.

=>About 4-5 day recirculation rate.

Pembroke Results- 2010

Water spray started July 8

And at 2594 Main Rd

•

Water spray started

July 8thTHM level at monitoring site

drops 12 days later Loss of power to water

spray pump ?

Pembroke Water Spray - 2011

• Pembroke water spray turned ON July 16, 2011.

2011 Data

Reduced system demand

resulting in increase in THMsWater spray ON

July 16

Water Temperatures

• Within the tank, the water temperatures were:– 2010 average 65 degrees F

max 70 degrees F

– 2011 average 67 degrees F

max 72 degrees F

THM RemovalData Summary

• In our water, 63 % of our THMs are chloroform………28 % is dichlorobromomethane.

• The majority of THMs removed has been chloroform and dichlorobromomethane.

THM Removal Data Summary

• In 2010, our removal percentage within the tank was 43 %.

• In 2011, our removal percentage within the tank was 42 %.

THM Removal

• The THM reduction at the compliance site(s) will depend on the amount of water entering into the system from the treated tank.

• If only half the water at a compliance site is from a treated tank where you are getting 40 % THM removal, you may only see a 15 – 20 % reduction in THM levels.

Cost of Treatment- Pembroke Water Spray

• A 7 ½ Hp pump

• Assuming $ 0.15/kw-hr

• 85 % efficiency

• Cost for four months of operation, 24 hrs/day = $ 1920 ($ 16/day)

Pembroke Tank

• Major components include 7 ½ Hp pump, PVC pipe, two multi-head water spray nozzles

• Total cost of components was approximately $ 7,000.

Cost of Treatment- Pembroke Tank

• Capital Cost : $ 7,000

Includes pump and VFD, piping and spray nozzles

• Operational:

$1920 electrical ($16/day)

• Based on water delivered to East Pembroke, water spray cost was $ 0.10/1000 gal

Water Rates- Pembroke

• 15 cents per day for a ¾ inch meter

• Commodity charge of $ 3.97/1000 gallons

Aeration – NYS Regulatory Aeration – NYS Regulatory ImpactImpact

• NYS Air Quality Standards – 201-3.3

• Item 27- Trivial Activities

• Air stripping processes used on public water supply systems are “trivial and exempt from permitting requirements.”

2013 Activities

• Check removal efficiency at 50 degrees F and 68 degrees F

• Check removal efficiency at 25, 50, 75 and 100 % motor speed.

Other MCWA DBP Removal Sites

Pavilion Tank

Pavilion Tank

• 320,000 gallon tank

• 170 scfm rotary vane compressor and diffuser manifold

• The air line is tapped into the base wall of the tank

Mumford Tank

• 300,000 gallon storage tank

• 75 gpm water spray

Recommendations to Others

• Design electrical services with sufficient capability to operate small pumps if DBP problems are encountered or anticipated …especially in remote parts of the system.

• Power loss alarms to detect loss of power to the pump. (Not a pressure alarm.)

Recommendations to Others

• Make sure the penetration into the tank is done in a sanitary manner.

• If discharge lines are disconnected for the winter, secure openings.

• Water main design – don’t over size.

Recommendations to Others

• If “in house” fabrication isn’t possible, there are manufactured units which have proven effective in THM removal.

• A Medora Spray THM Removal System is one such system.  The design is a 3 part system - mixing, stripping and ventilating. 

Recommendations to Others

THM Removal Proven Results, Fall 2012• Average result across seven systems: 51%

reduction• Design goal 40-50% TTHM reduction

•43%•Red.

•37%•Red.

•62%•Red.

•29%•Red.

•68%•Red.

•68%•Red.

•Notes: 1) All are lab test results shown except CA1 and CA2 which are from an oral report by operator Dec 20, 2012• 2) Results shown are utilizing the floating spray nozzle system design, except OK1 which is the fixed nozzle system

design

•48%•Red.

New Supply?

• Is a properly protected, drilled well possible?

• True groundwater should not have any significant concentration of DBP precursors. THM generation should be minimal.

• A well can be run seasonally to modify water treated by the “parent” utility or the purchasing utility.

Flushing to minimize DBPs

• Your only option may be to what store owners do……periodically flush and release stale, off-quality water (produce) from your system.

Flushing to minimize DBPs

• Routine flushing will improve water quality, increase your demand and will reduce detention time in the system.

Flushing to minimize DBPs

• As an example….consider a 1 mile stretch of 8 inch main. This length of pipe will hold 13,800 gallons of water.

• If you were to flush at 200 gpm, it would take a little over one hour to replace all the water in the main.

• The cost?

Flushing to minimize DBPs

• If water costs $ 3.50/1000 gallons, then you would have lost $ 48 worth of water.

• This regulation is going to cost no matter what !!!!!!

Thank You

Dave Ryan

Question

• Does anyone here purchase untreated rock salt for use in their softening plant? If so, please see me.

Question

• Does anyone here need to purchase Calgon (powdered) carbon, WPH ? If so, please see me. We have some discounted for sale.