Part 1: What are the Most Common Disinfection Methods?

Top 5 Essential Considerations for Selecting the Right Geomembrane for Your Disinfection System

Part 1: What are the Most Common Disinfection Methods?

Geomembranes play a significant role in the water and wastewater industry. That industry is broad and large, and important to public health and the environment. This post will provide an overview of water/wastewater disinfection processes, and top considerations in geomembrane selection in those applications.

In the early 1900’s, cities began disinfecting drinking water supplies to kill bacteria, viruses and other microorganisms that were attributed to health outbreaks such as cholera. It was 
decades later when the process was implemented for wastewater discharges. Disinfection is typically the last treatment process prior to releasing the water for consumption (potable), or for discharge or reuse (wastewater). Chlorine and Chlorine derivatives have been, and still are, the dominant disinfection chemicals used in both the clean and dirty water sides of the industry. A survey of disinfection practices by the Water Pollution Control Federation (WPCF, now the Water Environment Federation, WEF), in 1979, reported that Chlorine, primarily Chlorine gas, was the dominant chemical used. Some sources indicate that 2/3 of wastewater treatment plants still use Chlorine. Similarly, a limited American Waters Works Association (AWWA) survey in 2017 indicated almost all disinfection at water treatment plants used Chlorine.      

While Chlorine continues to be a highly effective and economical disinfector, it can create Disinfection Byproducts (DBP’s) when contacting organics. These are halogenated compounds, including Trihalomethanes, and are of concern in both drinking water and wastewater disinfection. One of the ways to control DBP production is to closely control Chlorine dose rate and residence time. Geomembranes are a vital tool to aid in disinfection control not only with Chlorine, but with all disinfection systems to control contact time and residence time in contact chambers, clearwells and storage tanks. One of the attributes of Chlorine is that it can maintain a residual after disinfection. This is desirable with drinking water so that a residual, assuring disinfection, exists in the distribution system up to the point of consumption. It is also good practice to have a low level of residual active disinfectant in water reuse impoundments. On the other hand, what is not desirable is releasing residual Chlorine to surface water. 

There are today however various options for disinfection processes and chemicals:

Processes
Chemical Oxidation
UV
Nanofiltration

• Chlorine
  • Gas
  • Sodium Hypochlorite
  • Chloramines
  • Chlorine Dioxide
  • Calcium Hypochlorite
• Peracetic Acid
• Ozone
• Potassium Permanganate
• Iodine
• Bromine
• Ferrate

Peracetic Acid (PAA) and UV Disinfection have been growing in popularity for treated wastewater disinfection in recent years. Ozone and UV are used as alternative disinfectants for potable water. These chemicals, like all disinfection alternatives, have advantages and disadvantages. Peracetic Acid for example, is an organic that adds Chemical Oxygen Demand (COD) to the waste stream, but as a non-halogenated compound, harmful DBP concerns are minimal. Some geomembranes may have compatibility issues, even at low concentrations such as those used for disinfection. The XR-5 geomembrane has been tested with PAA at 15% concentration (standard commercial concentration) and has proven compatible for long term, high concentration use, alleviating concerns at much lower concentrations for disinfection. 

Once the disinfection process/chemical has been selected, where are geomembranes used and what is the criteria for performance? The next post in this series will outline the applications, requirements and the process to evaluate geomembranes for proper selection.

XR-3 PW Geomembrane Baffle Curtains, 
Finished Water Storage Tank. First Utility District, Knoxville, TN  USA