Replacing Gas Chlorine with Onsite Sodium Hypochlorite Generation

Tim Geraghty, P.E.

Division Manager Alliance Water Resources, Inc.

Replacing Gas Chlorine with Onsite Sodium Hypochlorite



Generation

Goal: help other utility managers decide if changing disinfectants would be worth considering

     What made us consider a change What options we considered Costs & benefits Design Construction

Background

    Most water treatment facilities use chlorine as their primary disinfectant Chlorine use became widespread in the early 1900’s Chlorine has a proven track record Chlorine gas is a highly hazardous chemical

Background

  St. Charles County, MO Water Treatment Plant has successfully used chlorine gas in 1-ton containers as a disinfectant since 1941 Plant capacity  8 MGD average  22 MGD peak

Water Treatment Plant,

St. Charles County, MO 1940 2013 They don’t build ‘em like they used to

Water Treatment Plant

1940 Not much has changed 2013

Background

  2005 - Water District purchased the treatment plant 2012 - Water District completed an overall WTP assessment  Reviewed existing condition of the plant facilities & equipment  Reviewed plant processes  Developed and prioritized a capital improvement plan



Background

Results of the plant assessment  Electrical/efficiency upgrades

$1.4M

 Filter upgrades

$2.3M

 Booster pump station replacement

$4.0M

 Replacement of the gas chlorine feed system

$2.5M

 Lime, ammonia and fluoride system improvements

$0.9M

 Total

$9.7M

Why consider changing from chlorine gas?

  Need to update existing chemical processes, controls and equipment due to age Safety  Employees  People in the surrounding community  Environment

Why consider changing from chlorine gas?

1997 – one ton container split 25 miles away in Kirkwood, Missouri 2012 – one ton container leaking 10 miles away in Chesterfield, Missouri

Why consider changing from chlorine gas?

2002 – leaking 1” hose connected to 90-ton railcar 50 miles away in Festus, Missouri 48,000 pounds released - 63 people injured Pictures from US Chemical Safety & Hazard Investigation Board Report, 2003

Why change?

Federal OSHA Safety Regulations

(TOSHA requirements may be more stringent) EMPLOYEES

OSHA Process Safety Management (

29 CFR 1910.119

)   Respirators – fit testing, medical baselines and periodic evaluations Hot Work     Coordination with LEPC Management of Change Chlorine Institute Pamphlet 65 for PPE Chlorine Institute Pamphlet 155 for water and wastewater operators   Confined Space Contractor Safety & Record Keeping   Training Record keeping, record keeping, record keeping

Why change?

Federal Safety Regulations - EPA

PEOPLE IN THE SURROUNDING COMMUNITY

  Estimating offsite receptors Hazard reviews US EPA Risk Management (

Act

)

in section 112(r) of the Clean Air

   Operating procedures Compliance Audits  Worst case release scenario  Mechanical integrity Employee participation  Coordinating with LEPC  Alternative release scenarios  Communication with the Public  Offsite consequence analysis  Regular re-submittals

Why change? Protect the Environment



Water Plant



Missouri Conservation Department Wildlife Area

  

US Army Training Area University Research Area (added political pressure from regulators)



To decide if a disinfectant change was worthwhile, we reviewed our goals and other disinfectants

Review of Alternatives Water Quality Considerations

Requirements for disinfection

  Groundwater Rule

4-log removal of viruses



Chlorine contact time

 

Effects of chlorination on pH

Distribution system bacteria re growth potential  THM’s/HAA’s   Nitrate formation Chlorite formation

Review of Alternatives Selection Criteria

Criteria

 Safety  Life Cycle Costs  

Capital O&M labor

 

Power Chemicals



Waste treatment/hauling

 Chemical & power cost stability  Chemical strength stability  Chemical availability

Review of Alternatives Selection Criteria

Criteria

 Need for additional treatment  Level of automation  Permitting issues  Space requirements  Operational flexibility, familiarity & simplicity  Equipment reliability

Review of Alternatives

     

Gas chlorine Ozone Ultraviolet (UV) Light Chlorine dioxide Hypochlorite

  Calcium hypochlorite Sodium hypochlorite  Onsite hypochlorite generation  Bulk deliveries

Combinations of the above

Review of Alternatives



Gas Chlorine in 1-ton containers (current practice)

 Advantages – low capital and operating cost, simple operation, low maintenance  Disadvantages – hazardous and toxic chemical, potential of leaks & high level of regulation

Review of Alternatives



Gas Chlorine in 150-pound cylinders

 Advantages – low capital and operating cost, simple operation, low maintenance  Disadvantages – hazardous and toxic chemical, potential of leaks & high level of regulation  Switching to smaller cylinders would reduce the quantity released during a major leak, but more changeovers & handling would be required

Review of Alternatives



Ozone

 Expensive   Additional disinfectant needed for maintaining residual in distribution  Often used to eliminate a specific contaminant

Ultraviolet (UV) Light

 Additional disinfectant needed for maintaining residual in distribution  Often used to eliminate a specific contaminant

Review of Alternatives



Chlorine dioxide

 Strong disinfectant  Stops THM formation  May require additional treatment for chlorite  Often used for pre-treatment – not as the lone disinfectant

Review of Alternatives



Bulk Sodium Hypochlorite (typically 12.5% solution)

 Advantages – Low capital cost, generally safer than chlorine gas  Disadvantages – High operating cost, degradation, corrosive health hazard

Review of Alternatives



Generated Sodium Hypochlorite (0.8% solution)

 Advantages – no storage of highly hazardous chemicals, consistent product concentration  Disadvantages – High capital cost, hydrogen gas byproduct, short product storage time

Review of Alternatives Process Schematic Bulk hypochlorite components Onsite hypochlorite generation components

Hazardous to Environment, Users, and Community Chlorine Gas Bulk Sodium Hypochlorite (11 - 15%) NFPA Rating Health = 4 Flammability = 0 Instability = 0 Oxidizer 4 0 OX 0 NFPA Rating Health = 2 Flammability = 0 Instability = 1 Oxidizer 2 0 OX 1 Health = Lethal Short Term Exposure = Burns, Chest Pain, Emotional Disturbances, Lung Damage, Death Physical Hazards = Containers may rupture or explode.

Health = Intense or continued exposure could cause temporary incapacitation or residual injury.

Instability = Can become unstable at elevated temperatures and pressures.

Environmentally Benign 0.45% Generated FAC or 0.8% Generated FAC NFPA Rating Health = 1 1 0 Flammability = 0 Instability = 0 0 NFPA Rating Health = 1 NaCl (SALT) Flammability = 0 Instability = 0 1 0 0 Health = Exposure may cause mild irritation Instability = Normally stable, even under fire conditions.

Health = Exposure may cause mild irritation Instability = Normally stable, even under fire conditions.

Review of Alternatives

Comparison Chlorine Gas

(add scrubber & other controls)

Capital Cost

$900,000

Annual O&M

$50,000

Hazard Potential*

highly hazardous gas

Ozone

High

UV

High

Bulk Sodium Hypochlorite

$650,000

Generated Sodium Hypochlorite

$1,900,000 High High $160,000 $100,000 limited low highly corrosive liquid hydrogen gas by-product

Of these alternatives, only gas chlorine requires PSM & RMP programs

Review of Alternatives

Cost savings due to eliminating PSM training and administration

 60 training hours annually for operators & maintenance staff   200 hours annually for contractor training 100 hours annually for administration per year   training reports, maintenance reports, PSM Manual updates, PSM and RMP annual SOP certifications, periodic resubmission of PSM and RMP documentation, internal compliance audits, testing of chlorine sensors, …

$10,000 - $15,000 per year

Review of Alternatives

 UV and Ozone were ruled out - high costs

+

additional need for residual disinfectant  For the two hypochlorite alternatives, onsite generation preferred because of lower O&M 

Chosen Alternative: Onsite Generation of Sodium Hypochlorite because of reduced safety concerns; estimated additional cost of treated water less than $0.04 per 1,000 gallons (<1% of user rate)

Design Considerations First step – choose a hypochlorite generator manufacturer

 Equipment varies by manufacturer  Major considerations   Safety considerations Ease of operation/number of components    Equipment footprint Life cycle costs Availability

Design Considerations Choosing a hypochlorite generator manufacturer

The cost of materials varies by manufacturer but one pound of chlorine is generated by roughly:  15 gallons soft water (at 15-40 gpm and about 60 psi)   3 pounds salt 2 kilowatt-hours

Design Considerations – Site Visits

 Designers and operators visited several installations of various manufacturers

Design Considerations Efficiency & Complexity

   Indoor Equipment (generators, blowers, power and control panels) Room arrangement/ available space  HVAC requirements & equipment heat loss Outdoor Equipment (tanks & accessories)  Sunshades

Design Considerations Sodium Hypochlorite Storage Tanks

  Storage time Degradation (esp. for 12.5%)

Sodium Hypochlorite Metering Pumps

  Based on each feed point’s chlorine demand Sized for both 12.5% and 0.8% solution

Design Considerations Standby Options

   Standby generator Provisions for bulk delivery Plant Shutdown (generally available at this location September through May)

Capital Costs



Equipment Bids

 ChlorTec (two 750 ppd units)$ 536,500  MIOX (three 500 ppd units) $ 572,980  PSI (two 800 ppd units) $ 619,500 

Construction Bids (includes equipment)

 Engineer’s final estimate  Low of 5 bids: KCI Construction $2,041,000

$2,213,500

Chosen Alternative - MIOX

  Simplicity / fewest components Smallest footprint / able to fit most equipment in the existing building

Design Considerations for Chosen Alternative System Control Panel Inputs

   Water hardness Brine tank level Storage Tank Level

System Components

   Brine pump Generators/rectifiers Hydrogen dilution blowers  Sodium hypochlorite storage tank level

Chosen Alternative - MIOX



Construction

Construction Sequence

      Site work Install outdoor hypochlorite tanks Install new process piping and metering pumps Place bulk hypochlorite (12.5%) system in operation Remove existing gas chlorine piping and equipment Install hypochlorite generators in the space vacated by the gas chlorine system

Construction

Schedule and current progress

  Site work completed (relocated storm & sanitary sewers) Bulk tanks, piping, water softeners, pumps and dilution panel installed

Construction

Schedule and current progress

   SOP’s written and operators trained in bulk chemical feed process Bulk chemical (12.5%) and tanks being put in operation next week Remaining work to be completed by

July 2013

 Remove existing gas chlorination system  Install hypochlorite generation and other equipment inside the building and start-up

Key Points

 Ultimately, the Water District Board decided that increasing the level of safety was worth the additional capital and O&M costs  Our chosen disinfection alternative was not the lowest cost alternative  The chosen manufacturer’s equipment was not the lowest cost alternative  Involving the operators in the decision making was critical and strongly influenced the decision  The operators (and probably their spouses) can’t wait for the workplace to be safer

For More Information

Tim Geraghty, P.E.

Division Manager

Alliance Water Resources 100 Water Drive O’Fallon, MO 63368 636-561-3737 x101 [email protected] www.alliancewater.com

Special Thanks to Black & Veatch and Parkson Disinfection for technical information they provided for the presentation