Conditions for Making Sodium Hypochlorite (Bleach) for Water

Treatment in a Developing Country While Avoiding Inorganic Disinfection By-Products

Mike Bellamy PhD

Northwest Missouri State University

House of Hope Haiti

bellamy@nwmissouri.edu

General Goal: Identify Water Disinfection Technology to Treat Well Water for Schools and Children’s Homes in Haiti

• Treat up to 1,000 gallons at a time.

• We typically treat well water. Turbidity and concentration of organic molecules are low.

• Residual disinfectant is desirable since water is used to wash food, bathing etc.

• Desired equipment cost is less than a few hundred dollars (USD).

• Easily maintained.

• Eventually be constructed by the end users.

• Be used as a laboratory exercise in the high school.

Some Small-Scale Water Disinfection Options for Developing Countries

• SODIS

• Slow Sand Filtration

• Micro or Ultrafiltration

• Ultraviolet

• Oxidation-Reduction Reactions • Ozone

• Mixed Oxidants (HOCl, OCl-, O3, ClO2 and other oxidants with Cl and O MIOX [1])

• Chlorination (HOCl, OCl-) • Commercial Bleach

• On-Site Generation: Divided Cell

• On-Site Generation: Undivided Cell [1] Bradford ET AL http://cdn2.hubspot.net/hub/312816/file-357588552-pdf/Downloads/technical-downloads/Master_Features_Summary_-_Feb_2011_Parkson.pdf

Pros and Cons of Chlorination

Pros

• Village-scale quantities can be made for little cost.

• Bleach can be made on-site.

• Some on-site generation (OSG) systems can be made by the end users and can be sustainable.

• Residual disinfectant.

• It is fairly easy to test for residual chlorine compared to testing for microorganisms.

Cons

• Inorganic by-products are likely with commercial bleach [2] and possible with OSG bleach.

• Organic molecules in surface water will react with chlorine.

• Taste can be a concern if dosage is not reproducible.

• Chlorination may not be understood and trusted in some settings.

• Chlorination is not effective against all microorganisms related to water and sanitation.

[2] Stanford ET AL Journal AWWA, Vo. 103, No. 6, June 2011, 1-13.

Some Small-Scale OSG Systems: Divided Cells

Organization Unit Price Power Source Notes

Newlife International

www.waterfortheworld.com

$1,050 for basic

system that will

run off a 12-V

battery.*

Basic system runs

off 12-V battery.

AC pump is extra.

Pump could fail. Membrane may

foul. Heat exchanger will need

cleaning. User training is a concern.

Leaking Cl2 gas is a concern.

Free chlorine level in treated water

tested multiple times. By-Product

concentrations likely low.

Waterstep

www.waterstep.org

$1,000 for basic

unit. Price is on

their website.

Basic system runs

off 12-V battery.

AC pump is extra.

The M-100 is very similar to the

system from NewLife.

Miox Brine Pump System

http://www.miox.com/

$7,000*

*Denotes information obtained through phone call.

Some Small-Scale OSG Systems: Undivided Cells Organization Unit Price Power Source Notes

Safe Water International Ministry (SWIM)

http://www.swimforhim.info/

$50 + battery or power supply 12-Volt Batter or

Power Supply

Flow-Through Design. Fast and inexpensive.

Could be made by end-users.

Disinfection by-products are a consideration will

all OSG systems.

Hays Pure Water for all Foundation

http://www.hayspurewater.com/

$227 for CPU. Price is on their

website.

12-V batter. Similar to SWIM unit. CPU connects to plastic

beverage bottles.

WatAyls® (Bulane Product)

http://www.femmesdedemain.fr/fdd_images

/divers/brochure%20WATALYS%20EN_2007.p

df

Could not find price. 12-Volt Power

Supply

Batch (Static) chlorinator similar to the Aqachlor

and Envir-O-Cell2.75.

Aquachlor

http://www.equipmentandsystems.com/

$1,459 for model AC-25.* Includes

power supply.

12-V power supply. Batch (Static) chlorinator. Run times are in

hours range. Reproducibly produces 6,000 ppm

sodium hypochlorite solutions.

SANILEC®6

Severn Trent De Nora

http://www.severntrentdenora.com/

$3,900* 110 or 220 V to a DC

rectifier.

Makes large batches at 5000 ppm NaClO.

Envir-O-Cell 2.75

http://www.grsolutions.co.za/sodium_hypoc

hlorite_generator.htm

$6,000 at

http://www.alibaba.com/product-

detail/Water-

Treatment_112969061.html

Power Supply Seems to be a batch chlorinator similar to the

Aquachlor product.

*Denotes information obtained through phone call.

Basic Components of Flow-Through OSG Systems

Cl- → Cl2 → HClO→ ClO-→ ClO3

-→ClO4-

The same electrodes used to make hypochlorite (bleach) from a salt solution

are also used to make chlorate.

Industrial Conditions Used for Chlorate Production

• pH ≈ 6 to 7 [5].

• Temperature ≈ 80ᵒC [5].

• Brine concentration ≈ 80 to 120 g/L [5].

• High current density [6].

[5] Chlor-Alkali and Chlorate Technology, Electrochemical Society, Inc. 1999, Edited by Burney et. al. ISBN: 9781566772440.

[6] Rengarajan, V. et. al. Influence Factors in the Electrolytic Production of Sodium Hypochlorite, Bulletin of Electrochemistry, 12 (5-6), May-June 1996, pp 327-328.

Batch Mode Undivided Cell (Hypochlorite Generator)

Stainless Steel Cathode 2 H2O (l) + 2 e- → H2 (g) + 2 OH- (aq)

Anode = DSA 2 Cl- (aq) → Cl2 (g) + 2 e-

Possible Forms of Cl in Solution: Cl2 ↔ HOCl ↔ OCl- ↔ ClO2- ↔ ClO3

- ↔ ClO4-

Na+ and Cl-

e- Flow →

2 Cl- (aq)

Cl2

H2O

H2 (g) + 2 OH- (aq)

Cl2 + OH- (aq) → HOCl + Cl-

HOCl + H2O ↔ OCl- + H3O+

Electrolytic Production of Bleach (Sodium Hypochlorite) (On-Site Generation or OSG)

Desired Reactions

Anode: 2 Cl- → Cl2 (g) + 2 e-

Cathode: 2 H2O → H2 (g) + 2 OH-

Bulk Solution:

Cl2 (g) + OH- → HOCl + Cl-

HOCl + H2O ↔ OCl- + H3O+

Forms of Chlorine vs. pH

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Re

lati

ve C

on

cen

trat

ion

(M

)

pH

[HOCl]

[OCl-]

[Cl-]

[Cl3-]

[Cl2]

Divided Cell (Including Membrane Electrolyser)

Stainless Steel Cathode H2O (l) + 2 e- → H2 (g) + 2 OH- (aq)

Na+ and Cl-

e- Flow →

2 Cl-

Cl2

H2O

H2 (g) + 2 OH- (aq)

DSA Anode 2 Cl- (aq) → Cl2 (g) + 2 e-

Na+

OH-

Simplified Block Diagram of a Divided Cell Water Chlorination System

Water Tank

Cl2 ↔ HOCl ↔ OCl-

Cl2 Gas

Water Pump

Cl2 Gas

Divided Cell

Note that water from the tank passes through a heat exchanger in the reaction chamber.

The Importance of Simple, Convenient Technology in the Developing World

(Below is an e-mail message to the presenter.)

• (a side note.. Name Removed, the man we are working with in Haiti installed a Name Removed unit before we got there. He paid over $1,000 for it and then had to add additional parts. He build an 8’ by 8’ block building with roof, cement floor and locked door to house it. The Haitians had to pump from a well into a 5 gallon bucket and dump that into a 125 gallon tank. It was literally steps away. It took 25 buckets to fill the 125 gallon tank. After 2 weeks they decided it was too much work and discontinued its use. They cut the wires off to use elsewhere. Andy went back and removed the equipment. They are now using the Name Removed with a pastor and distributing chlorine in 4 oz bottles to the community. He also has a brand new unit at his house but sees no application for it since he’s been using the CPUs)

The OSG Equipment from SWIM is an Attractive Option.

Observations

• Equipment costs are low.

• Sodium hypochlorite (bleach) solutions are made rapidly.

• The equipment could potentially be made by the end-users creating independence and sustainability.

• There is no membrane to foul, pump to break, heat exchanger to clean…

Questions:

• What are Safe Combinations of current density, brine concentration, and reaction time?

• Time needed to treat up to 1,000 gallons?

• Can water be treated to reproducible levels of chlorine?

• For all OSG systems: What is a viable source of NaCl that is low enough in bromide ion?

0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6 7 8 9 10 11 12

Free

Ch

lori

ne

(pp

m C

l 2)

Passes Through System

Free Chlorine vs. Passes Through SWIM Unit (Two resistors in curcuit; DPD Method)

Related to Convenience of the System

29 g/L Power Supply

58 g/L Power Supply

29 g/L Battery

58 g/L Battery

88 g/L Battery

Conditions Comparison for Making OCl- in with an Undivided Cell

Controlled Lab Environment

• DSA Anode/Stainless Steel Cathode

• Temperature is kept about room temperature.

• Current density is constant and low compared to that of chlorate production.

• Pure salt is used to make brine. Brine concentration is about 29 g/L.

Developing Country

• DSA Anode/Stainless Steel Cathode.

• Temperature increases fairly linearly with reaction time.

• Current density varies during the reaction and is higher.

• Salt Quality • Processed salt may contain iodide

which will form iodate. • Rock salt may contain bromide

which will form bromate. Will vary with salt source.

Time Needed to Treat 1,000 Gallons

• It takes about 15 minutes to pass 1 liter of a liter 58 g/L through the system seven times. When added to a 1,000-gallon tank the initial concentration of free chlorine would be about 1 ppm.

There is enough salt in the container in the photo to treat nearly 13,000 gallons of water to 1 ppm free chlorine.

Reproducibility of Chlorine Dose.

In field tests we found that we can treat water in Haiti to within about plus or minus 0.2 ppm.

Inorganic By-Product Formation

Chemical Reactions [3]

Electrochemical ClO3- formation at Anode:

12OCl- + 6H2O → 4ClO3- + 12H+ +8Cl- +3O2 + 12e-

Chemical ClO3- Formation in Bulk Solution:

2 HOCl + OCl- → ClO3- + 2H+ + 2 Cl-

Chlorite intermediate (pH 11-13, AWWA)

OCl- + OCl- →ClO2- + Cl-

OCl- + ClO2- → ClO3

- +Cl-

Overall: 3 OCl- + ClO2- →ClO3

- + Cl-

Chemical ClO4- Formation in Bulk Solution

OCl- + ClO3- → Cl- + ClO4

-

Other Possible Electrochemical Conversions

Br- in salt to BrO3-

I- in salt to IO3-

Maximum Contaminant Levels in Drinking Water

ClO2- 1.0 mg/L (Title 40 CFR 141.64)

ClO3- 0.7 mg/L (WHO; unregulated

federally)

ClO4- low μg/L (CA = 6 ppb; MA = 2

ppb; NJ proposed 5 ppb [4] )

BrO3- 10 μg/L (Title 40 CFR 141.64)

IO3- (?)

[3] AWWA and Water Research Foundation Report:

http://www.awwa.org/Portals/0/files/legreg/documents/HypochloriteAssess.pdf

[4] Shah, J. et al. MRWA Today, Spring 2012, 30-33.

Temperature and Chlorate Formation

2 HOCl + OCl- → ClO3- + 2H+ + 2 Cl-

𝑅𝑎𝑡𝑒 𝐶ℎ𝑙𝑜𝑟𝑎𝑡𝑒 = 𝑘 𝐻𝑂𝐶𝑙 2 𝑂𝐶𝑙−

OCl- + ClO3- → Cl- + ClO4

-

𝑅𝑎𝑡𝑒 𝑃𝑒𝑟𝑐ℎ𝑙𝑜𝑟𝑎𝑡𝑒 = 𝑘 𝑂𝐶𝑙− 1 𝐶𝑙𝑂3

− 1

Rate equations are from reference 3.

Rate constants increase exponentially according to the Arrhenius equation.

𝑘 = 𝐴𝑒−𝐸𝑎

𝑅𝑇

0

20

40

60

80

100

120

15 20 25 30 35 40 45 50

Rat

e C

on

stan

t (x

10

-3 M

-2S-

1)

Temperature (ᵒC)

Experimentally-Measured Rate Constants for the Decomposition of

Free Chlorine from Gordon et. al. [7].

[7] Adam, L.C., Fabian, I. Suzuki, K., Gordon, G., Hypochlorous Acid Decomposition in the pH 5-8 Region, Inorg. Chem. 1992, 31, 3534-3541.

Temperature Increases with NaCl Concentration and Reaction Time

20

25

30

35

40

45

50

55

60

65

70

0 5 10

Tem

pe

ratu

re (

◦C)

Passes Through SWIM OSG System

Temperature vs. Passes thru SWIM OSG PS = 13.8-Volt DC Power Supply Battery = 12-volt Marine Battery

29 g/L NaCl PS

58 g/L NaCl PS

88 g/L NaCl PS

88 g/L NaClBattery

29 g/L NaClBattery

58 g/L NaClBattery

0

10

20

30

40

50

60

70

80

90

100

15 20 25 30 35 40 45 50

Rat

e C

on

stan

t (x

10

-3 M

-2S-

1 )

Temperature (ᵒC)

Experimentally-Measured Rate Constants for the Decomposition of Free Chlorine [7].

Current Efficiency

50

55

60

65

70

75

80

1 2 3 4 5 6 7 8 9 10 11 12

Cu

rren

t Ef

fici

ency

(%

)

Passes Through System

Current Efficiency for Production of Hypochlorite with Marine Battery

29 g/L Battery

88 g/L Battery

58 g/L Battery

55

60

65

70

75

80

85

1 2 3 4 5 6 7 8 9 10 11 12

Current Efficiency for Production of Hypochlorite with Power Supply

29 g/L PS

58 g/L PS

Temperature Can be Controlled in a Flow-Through Undivided Cell by:

•Limiting reaction time.

•Keeping brine concentration reasonably low.

•Placing the reaction solution in an ice bath for about 30 seconds between runs.

•Adding heat exchanger.

On-Going Research

• Set pH to 7.

• Let temperature rise.

• Vary salt concentration.

• Vary current density by using the two common power sources.

• Measure concentrations of ClO3-

and ClO4- versus reaction time.

• Can we have low concentrations of by-products without controlling temperature?

• What is the maximum salt concentration and reaction time that we should use?

Bromate Formation is a Concern with OSG Hypochlorite

By-Product Formation

• Bromide ion in salt is converted to bromate. Bromate is limited to 10 ppb.

• We can purchase iodized food-grade salt in Haiti. Is iodate safe?

On-Going Research

• Bring back rock salt samples from places where OSG hypochlorite is used.

• Do we need to establish a distribution network of food grade salt that has not been iodized?

Conclusions

A flow-through OSG system like that supplied by SWIM is a promising technology to chlorinate water in Haiti and other

developing counties.

By the summer of 2015 we hope to publish recommended reaction conditions for using the SWIM flow-through OSG system.

We plan to incorporate the chemical principles and use of the unit into the curriculum of our high school in Williamson, Haiti next fall.