Comparing The Environmental Impact of Disinfection Technologies

In recent years, there have been increasing concerns regarding the carbon footprint of municipal infrastructures. Carbon footprint is a measure of the environmental impact in terms of greenhouse gas (GHG) production in units of carbon dioxide. Although the rise of GHGs is a concern due to its contribution to climate change, other types of impacts can also be included for a more holistic assessment.

Life Cycle Assessment (LCA) is a tool that can effectively be used to investigate the impact of a product in a holistic manner. LCA includes the extraction of raw materials, processing, manufacturing, distribution, use, reuse, maintenance and disposal processes.

The environmental burdens that are usually evaluated include the use of land, energy, water, and other materials and the release of substances to the air, water, and soil.

Comparing Disinfection Alternatives 

Wastewater treatment systems are designed to minimize the environmental impacts of discharging treated wastewater into aquatic or terrestrial ecosystems. Disinfection is one of the most important steps of the wastewater treatment process since it prevents the spread of waterborne diseases to downstream users and the environment.

This fact sheet describes a study of specific environmental impacts caused by the lifecycle of three wastewater disinfection systems:

  1. Chlorine gas
  2. Sodium hypochlorite
  3. Ultraviolet (UV) disinfection.

Results are summarized and allow the comparison of these disinfection systems in terms of the effects on human health and the environment throughout three stages of their life cycle: civil works, operation and disposal.

The majority of the data collected for this study was from the  National Renewable Energy Laboratory and US Environmental Protection Agency.

To compare different disinfection technologies, the functional unit has been established as 20 years of operation. The specifications and assumptions for the disinfection systems of this study can be seen in Table 1.

Table 1. Specifications for LCA Example

Peak Flow 30 million gallons per day (4,732 m3/hr)
Average Flow 15 MGD (2,366 m3/hr)
UVT65% (minimum)
Disinfection Limit200 Fecal Coliform/100ml

The electrical composition in a region can significantly alter the environmental impact of a disinfection system. For the purpose of this study, California’s electrical composition will be used as seen in Figure 1.

A pie chart comparing electrical composition in California
Figure 1. The electrical composition in California, USA. (Source: US EPA, EGRID, 2006)

Civil Works 

Typical materials used in the construction of a disinfection facility are concrete, steel and wood. Concrete production is considered to have a high environmental impact because of its various constituents.

There are many different types of concrete depending on the manufacturer, desired quality and strength. For the purpose of this study, it has been assumed that generic 100% Portland concrete is used for the civil works of the disinfection systems (National Institute of Standards and Technology, 2007).

Operation 

The environmental impact of the operation of a disinfection system has been measured in terms of resource consumption and waste production over a 20-year period.

The following processes have been included for the analysis:

  • Production of chlorine gas and sodium hypochlorite
  • Salt mining and purification
  • Manufacturing of the UV lamps
  • Transportation of chlorine gas, sodium hypochlorite and sulfur dioxide
  • Transportation of the UV lamps
  • Energy consumption at the disinfection site

Disposal

The values of solid waste for the civil works and operation phases included the disposal of concrete and UV lamp components at the end of the life cycle.

Impact Categories

The impact assessment methodology was based on midpoint characterization. The impact categories taken into consideration are summarized in Table 2. Characterization and normalization factors were obtained from the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI).

Table 2. Impact Categories for Life Cycle Assessment

Impact Category Characterization (US EPA)Examples of Data
Ozone Depletionkg CFC-11-eq.CFCs, HCFCs, Halons, CH3Br
Global Warmingkg of CO2 eq.CO2, NO2, CH4, CFCs.
AcidificationH + moles eq.SOx, NOx, HCL, HF, NH4
Eutrophicationkg of N eq.PO4, NO, NO2, NH4
Eco-Toxicitykg 2, 4-dioxane-eq.Toxic chemicals to rodents
Human Health Non-Cancerkg toluene-eq.Toxic chemicals to humans
Human Health Cancerkg benzene-eq.Cancer causing chemicals
Resource Depletionkg of antimony eq.Minerals and fuel used
Land Use (Solid Waste)lbs.Landfills

In this study, the data was normalized relative to the environmental impacts caused by a served population of 50,000 people. This demonstrates the contribution from each of the disinfection systems in each environmental impact category as a fraction of the total emissions in that category.

Normalization gives a dimensionless percentage for each impact category, which allows the results to be aggregated as seen in Figure 2 (De Hass, 2008).

Figure 2. The normalized results for all environmental impact categories show that UV is the most environmentally-friendly option for disinfection.

UV – The Green Solution 

This LCA concluded that UV has the least impact compared to chlorine gas and sodium hypochlorite. The total environmental impact of UV is mostly affected by the electrical grid composition. This makes UV disinfection the most versatile option since its environmental impact is directly related to the electrical energy source.

As sources of electricity become more “green”, UV will inherently have less environmental impact. UV can also be used as a public relations tool to educate residents about the importance of protecting the environment. As a result, many communities have implemented UV disinfection as a safe, non-chemical disinfection technology to protect their water resources and to accomplish long-term sustainability goals.

References: 

De Hass D, Foley J and Barr K. Greenhouse inventories from WWTP’s – The trade off with nutrient removal. Sustainability conference, Maryland, 2008. Water Environment Federation.

Environmental Protection Agency (US EPA). Life Cycle Assessment: Principles and Practice. Scientific Applications International Corporation (SAIC). National Risk Management Research Laboratory. USA. 2006.

Environmental Protection Agency (US EPA). The emissions and generation resource integrated database for 2006 (eGRID2006). Office of Atmospheric Programs, Climate Protection Partnerships Division. April 2007.

National Institute of Standards and Technology. Building for Environmental and Economic Sustainability. US Department of Commerce, 2007

National Renewable Energy Laboratory (NREL). Chlorine/Caustic Soda Production, 2007. U.S. LCI Database Project. U.S. Department of Energy. www.nrel.gov.