Chlorination


Chlorine treatments are currently the most commonly used method for treating zebra mussel biofouling. Chlorine is a popular method of controlling zebra mussel populations as it is very cost-effective. The use of chlorine also has many other advantages, as it is toxic at low concentrations but quickly loses toxicity with bioaccumulation. Chlorine also works in most raw water systems. The chlorination of mussels can be provided by a variety of chlorine compounds, including chlorine dioxide gas, sodium chlorite, as well as sodium, potassium and calcium hypochlorites[1] .

How Chlorine Works

Chlorine treatments control mussels through the effects of oxidation. In the presence of water, chlorine or hypochlorite reacts to form hypochlorous acid [HOCl]. [HOCl] then undergoes partial dissociation, producing hypochlorite [OCl-] and hydrogen ions [H+].

Cl2 + H2O --> HOCl + HCl

HOCl --> H+ + OCl-

With the hypochlorous acid and hypochlorite ions, upfree available chlorine (FAC) is formed, which has a toxic effect on mussels.
Hypochlorous acid is the main oxidant that attacks cell structures. [HOCl] is a strong oxidizing agent and has a biocidal effect. The acid kills the mussels by diffusing through cell walls, damaging the cell membrane and disrupting enzyme activity and ion regulation [2] . The reaction targets the lipids in the cell walls and destroys the sensitive cell components inside the cells, the cell becomes oxidized and is killed [3] .

Furthermore, it is thought that the oxidizing biocide can also cause mussel mortality through asphyxiation and the prevention of glycolysis with prolonged periods of exposure[4] . Chlorine can also cause weakening of the byssal thread attachments, and the toxicity of chlorine to zebra mussels is a function of exposure time, chlorine concentration, and the quantity of chlorine compounds formed in water following treatment[5] .


Disadvantages

Although chlorination is an effective method for treating mussels, there are also some disadvantages. When chlorine is used in pipelines and not applied carefully and selectively, the chlorine could be ejected into open ecosystems, becoming very deadly to surrounding wildlife. The storage and transportation of chlorine is another hazard as chlorine requires special handling, due to chlorine's corrosive properties.

Chlorine is less effective in alkaline water, where a higher pH results in a higher rate of dissociation of [HOCl] into hypochlorite [OCl-] and hydrogen ions [H+] [6] . One of the major disadvantages of using chlorination is that mussels respond to the chlorine by closing their valves and avoiding the toxic effects for up to 3 weeks[7] . This poses problems, as prolonged dosing periods are needed to ensure that the chlorine is able to penetrate into the mussels and kill them. Furthermore, when chlorine reacts with organic compounds and the mussel bodies in water, potentially carcinogenic substances such as trihalomethanes (THMs) and dioxins are formed[8] . These THM's are toxic to humans and other organisms, and therefore chlorine doses are high restricted in water treatment plants.


Possible Nanotechnology Applications

Some species of seaweed produce vanadium haloperoxidases (V-HPOs), which catalyze the oxidation of naturally occurring halides, such as bromide or chloride, into their corresponding hypohalous acid, using hydrogen peroxide[9] . This would enable the creation of a coating which would constantly produce HOBr or HOCl from components occurring naturally. However, production of V-HPOs is expensive to scale up. As an alternative, vanadium pentoxide nanowires mimic the V-HPOs in their ability to catalyse the reaction between halides such as bromide or chloride and hydrogen peroxide [10] . These nanowires are already used as an inexpensive catalyst material, and as such would be easier to use in coatings designed to prevent marine biofouling. By coating surfaces prone to zebra mussel colonization with these nanoparticles, companies would be able to inject more environmentally benign chemicals such as chloride or bromide salts, which would be converted to hypochlorite and hypobromite at the locations that they are needed most.
Vanadium Peroxidase.png
Mechanism of Vanadium Pentoxide Catalyst

  1. ^ Sprecher, S. L., & Getsinger, K. D. (2000). Zebra Mussel Chemical Control Guide (No. ERDC/EL-TR-00-1). ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS ENGINEER RESEARCH AND DEVELOPMENT CENTER.Retrieved From: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA375208
  2. ^ Claudi, R., & Mackie, G. (1993). Practical Manual for the Monitoring and Control of Macrofouling Mollusks in Fresh Water Sys. CRC.
  3. ^ Buecker, B., & Post, R. (1998). Control biofouling in evaporative cooling systems. Chemical Engineering Progress, 94(9), 45-45. Retrieved from http://ezproxy.lib.ucalgary.ca:2048/login?url=http://search.proquest.com/docview/221549697?accountid=9838
  4. ^ Van Benschoten, J. E., Jensen, J. N., Lewis, D., & Brady, T. J. (1993). Chemical Oxidants for Controlling Zebra Mussels(Dreissena polymorpha): A Synthesis of Recent Laboratory and Field Studies. IN: Zebra Mussels: Biology, Impacts, and Control. Lewis Publishers, Boca Raton, FL. 1993. p 599-619.
  5. ^ Claudi, R., & Mackie, G. (1993). Practical Manual for the Monitoring and Control of Macrofouling Mollusks in Fresh Water Sys. CRC.
  6. ^ Buecker, B., & Post, R. (1998). Control biofouling in evaporative cooling systems. Chemical Engineering Progress, 94(9), 45-45. Retrieved from http://ezproxy.lib.ucalgary.ca:2048/login?url=http://search.proquest.com/docview/221549697?accountid=9838
  7. ^ Claudi, R., & Mackie, G. (1993). Practical Manual for the Monitoring and Control of Macrofouling Mollusks in Fresh Water Sys. CRC.
  8. ^ Claudi, R., & Mackie, G. (1993). Practical Manual for the Monitoring and Control of Macrofouling Mollusks in Fresh Water Sys. CRC.
  9. ^ Wever, Ron, et al. "Brominating activity of the seaweed Ascophyllum nodosum: impact on the biosphere." Environmental science & technology 25.3 (1991): 446-449
    Retrieved From: http://pubs.acs.org/doi/pdf/10.1021/es00015a010
  10. ^ Tremel, W. (2012). Vanadium pentoxide nanoparticles mimic vanadium haloperoxidases and thwart biofilm formation.
    Retrieved From: http://www.niok.eu/en/wp-content/files/nnano201291.pdf