Comparison of UV vs. Sodium Hypochlorite
Wastewater Applications
Non-Economic Parameters
Parameters
Sodium Hypochlorite (NaOCl)
UV
Residual Toxicity
Toxic to aquatic life.
Non-toxic – UV disinfection does not add
anything to the water, other than light. As a
result, the surrounding environment is not
harmed in any way.
Disinfection By-products
(DBPs)
Yes – Same carcinogenic DBPs as
chlorine gas. DBPs are not removed or
reduced with dechlorination.
None
Corrosive
Yes – extremely corrosive
None
Community Safety Risks
Low – Due to a limited shelf life, NaOCl
requires frequent transportation and
delivery.
None – Poses no safety threat to the
surrounding community.
Operator Safety Risks
Moderate – Due to corrosive properties,
must be handled and stored with caution.
Low – UV module must be turned off if
worker lifts module out of the channel to
prevent exposure to UV light.
Treatment Performance
Cryptosporidium and Giardia are virtually
unaffected. In the past decade, these
pathogens have caused disease outbreaks
affecting hundreds of thousands of people.
UV disinfection is highly effective against
a wide variety of pathogens, including
chlorine-resistant organisms such as
Cryptosporidium and Giardia.
Changing Regulations
Regulations are becoming increasingly
stringent in order to limit the amount of
chemicals and disinfection by-products
in the water. As a result, the operation
of chemical-based treatment systems
will continue to become more costly and
complex.
UV is well suited to meet current and future
regulations. The process is safe, simple and
does not add chemicals to the water.
Residual Removal Required
Yes – Depending on regional regulations.
Long-term effects of discharging
dechlorinated compounds into the
environment are unknown.
No
SUMMARY
Hypochlorite has some significant
environmental concerns associated with
DBPs and residual toxicity. Hypochlorite is
not safeguarded against a future tightening
of regulations.
UV does not add anything to the water,
other than light. UV does not create DBPs
and is also safe and easy for Operators
to maintain.
References:
EPA. September 1999. “Chlorine Disinfection.” Wastewater Technology Fact Sheet.
Rudd, T. and L. M. Hopkinson. December 1989. “Comparison of Disinfection Techniques for Sewage and Sewage Effluents.”
Journal of International Water and Environmental Management. vol. 3. pp. 612–618.
Comparison of UV vs. Sodium Hypochlorite
Wastewater Applications
Cost Analysis
WWTP with Existing Hypochlorite Disinfection
ITEM
SODIUM HYPOCHLORITE
& DECHLORINATION
ULTRAVIOLET
Capital Costs
$0
$234,000
Annual Costs
$70,000
$14,163
ITEM
Annual O&M Costs
SODIUM HYPOCHLORITE
$802,900
ULTRAVIOLET
$162,900
Net Present Value
$802,900
$396,400
Capital on
Costs
Return
Investment (Yrs)
$0
Annual Costs
$70,000
Present Value of
& DECHLORINATION
4.9
Design Flow: 10 MGD
Average Flow: 2.9 MGD
Service Life: 20 years
Internal Rate of Return: 6.0%
Design Criteria: 65% UVT
with 25% over design for
State Redundancy Requirement
$234,000
$14,163
Present
Value of Value Cost Comparison
Table
1: Present
Annual
O&M
Costs
$802,900
$162,900
Converting to UV
will save the WWTP
more than $55,000 in annual
O&M costs.
($0.09
ITEM/Kw was used for power costs)
SODIUM HYPOCHLORITE
ULTRAVIOLET
Net Present Value
$802,900
& DECHLORINATION
Return on Investment (Yrs)
4.9
Capitalwith
CostsExisting Hypochlorite
$0
WWTP
Disinfection
Annual Costs
$396,400
$571,000
$133,267
$43,000
ITEM
Annual O&M Costs
SODIUM HYPOCHLORITE
$1,528,900
ULTRAVIOLET
$493,200
Net Present Value
$1,528,900
$1,064,200
Capital on
Costs
Return
Investment (Yrs)
$0
Annual Costs
$133,267
$43,000
Present Value of
Annual O&M Costs
$1,528,900
$493,200
Net Present Value
$1,528,900
$1,064,200
Present Value of
Return on Investment (Yrs)
& DECHLORINATION
8.2
$571,000
8.2
Table 2: Present Value Cost Comparison
Converting to UV will save the WWTP more than $90,000 in annual O&M costs.
($0.09 /Kw was used for power costs)
Design Flow: 35 MGD
Average Flow: 10 MGD
Service Life: 20 years
Internal Rate of Return: 6.0%
Design Criteria: 65% UVT
with 25% over design for
State Redundancy Requirement