Chlorination in all of its forms — gas, liquid, or solid — has been the primary way for treatment plants to disinfect the treated wastewater. The treatment plants that use gas chlorination must face federal regulatory oversight in the form of a Risk Management Program (RMP). Liquid chlorine plants trade in the regulatory oversight for a more expensive and less effective product. While chlorine in its solid form is good for small treatment facilities known as package plants (named for their mobility). However, ultraviolet (UV) technology is rapidly altering the landscape of disinfection throughout the industry.
Why UV Disinfection?
Though chlorine is widely accepted as a primary disinfection for more than a century, the limitation of chlorine disinfection is increasingly intolerable. The National Small Flows Clearinghouse (NSFC) at West Virginia University (WVU) released a fact sheet on chlorine disinfection that outlines the disadvantages of chlorine as[i]:
Even small doses of chlorine are toxic to aquatic life, and there are no long-term studies of the effect of dechlorinated effluents to the ecology. Reuse applications, where the treated wastewater effluent is used as irrigation or service water, can impact aquatic life with chlorinated effluent. The upstream condition of the treatment plant plays an important role of how much chlorine dosage must be added for disinfection. The chlorine demand increases if the secondary effluent is nutrient-rich with ammonia or nitrites, leading to more chlorine usage to get the same level of disinfection.
The alternative disinfection system is UV irradiation, which is considered one of the three mature methods of disinfection along with chlorine and ozone[ii]. These methods are mature because they have existed for a considerable amount of time[iii]. UV use has increased due to its high efficacy against chlorine-resistant protazoae cryptosporidium and giardia and the prevention of toxic chlorine byproducts in aquatic life[iv].
The UV Experience And Growth
The effects of UV disinfection occur when the system transfers electromagnetic energy from a mercury lamp to the genetic material of an organism, i.e. deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)[v]. The wavelength (nm) to effectively inactivate microorganisms is between 250 to 270 nm with an ideal lamp temperature between 95 and 122 degrees Fahrenheit[vi]. This can be accomplished through low-pressure lamps or medium-pressure lamps (for large facilities).
In the early 1900s, UV disinfection was dismissed in favor of chlorine use because of the high operational cost and maintenance problems. However, in recent years UV systems have become cheaper due to technological advancements[vii]. The EPA states the total cost of UV disinfection — including power consumption, supplies, and miscellaneous equipment repairs — can be competitive with chlorination when the dechlorination step is included[viii].
In light of these technological advances, UV has been rising in popularity and is clawing its way to challenge chlorination. In a September 2013 article on the growth of UV, market analyst Frost & Sullivan project the global demand for UV systems will raise the market to an expected $2.96 billion. This spike is over several industrial sectors with a dependence on clean water, including medical, power, and food and beverage[ix]. In the same article, the author quotes a manufacturer as noting that North America is experiencing about 5-percent growth in the UV disinfection market[x].
There are non-financial benefits that also account for the growth of UV disinfection, such as disinfection without adding chemicals, no new creations of toxic chemicals such as trihalomethanes (THMs), and no change in taste or odor. Furthermore, there is no RMP needed for facilities that use UV, because there is no regulated chemical in the process. UV systems can easily be retrofitted to existing chlorine contact chambers (CCC). However, the gas chlorine facility must de-register the RMP through the federal EPA system.
Photo credit: http://water.me.vccs.edu/courses/ENV110/clipart/UV.jpg
How To De-Register Your Gas Chlorine System
The RMP program was revamped to an electronic system in 2009, so deregulating the gas chlorine system has become easier today than in the past. The RMP regulations can be found 40 CFR Part 68.190(c):
Photo credit: EPA March 2014 Section 68.190(c)
Additional Resources For UV Disinfection And Training
Resources for UV disinfection vary from manufactures and governmental sources. The EPA has a UV Disinfection Guidance Manual: Final Long Term 2 Enhanced Surface Water Treatment Rule. The National Water Research Institute and Water Research Foundation have a joint guidance manual for UV Disinfection for Drinking Water and Water Reuse 3rd Edition. There is a Best Practice Manual from Manitoba Water Stewardship, Canada beginning in section 5.6 for UV disinfection. An additional source is the International UV Association (IUVA) based in Washington, D.C. I will be participating in a webinar series with the IUVA entitled Facility Management of UV Disinfection Systems at Wastewater Plants from June 25, 2014 to August 20, 2014.
Oliver, B. G., & Carey, J. H. (1976). Ultraviolet Disinfection: An Alternative to Chlorination. Water Pollution Control Federation, 2619-2624.
Powell, J. (2013, September 16). Municipal Disinfection Market Grows as UV Segment Expands. Retrieved from TPOMag.com: http://www.tpomag.com/online_exclusives/2013/09/municipal_disinfection_market_grows_as_uv_segment_expands
Solomon, C., Casey, P., Mackne, C., & Lake, A. (1998). Chlorine Disinfection. Retrieved from National Small Flows Clearinghouse at West Virginia University: http://www.nesc.wvu.edu/pdf/ww/publications/eti/chl_dis_gen.pdf
US Environmental Protection Agency. (1999, September). Wastewater Technology Fact Sheet Ultraviolet Disinfection. Retrieved from EPA.gov: http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_uv.pdf
Von Aken, B., & Lin, L.-S. (2011). Effects of the disinfection agents chlorine, UV irradiation, silver ions, and TiO2 nanoparticles/near UV on DNA molecules. Water Science & Technology, 1226-1232.
Water Environment Research Foundation. (2009). Disinfection of Wastewater Effluent: Comparison of Alternative Technologies. Alexandria, VA: Water Environmental Research Foundation.
[i] (Solomon, Casey, Mackne, & Lake, 1998)
[ii] (Water Environment Research Foundation, 2009)
[iii] (Water Environment Research Foundation, 2009)
[iv] (Von Aken & Lin, 2011)
[v] (US Environmental Protection Agency, 1999)
[vi] (US Environmental Protection Agency, 1999)
[vii] (Oliver & Carey, 1976)
[viii] (US Environmental Protection Agency, 1999)
[ix] (Powell, 2013)