Photoionisation: A Superior Odor-Control Technology

All odor control in wastewater treatment, where the odorous compounds are actually broken down, involves some form of oxidation. Traditionally, this comes down to biological and chemical approaches. For biofilters and bioscrubbers this is accomplished by organisms that obtain their energy from exothermic oxidation reactions. For chemical scrubbers, oxidizing agents such as hypochlorite do the oxidizing. There is now a new generation of odor-control technologies that use oxidizing agents created in situ by various physical-chemical processes such as UV light and corona discharge. The main new off-gas treatment technology is called “Photoionisation” or simply “PI”, designed and built by Neutralox GmbH of Germany. It is relatively new in North America, but has been in use in Europe and elsewhere for years and there are now hundreds of installations worldwide, representing the spectrum of odorous situations in the wastewater treatment environment.Basically, the technology uses UV light and a catalyst to breakdown odorous compounds. The UV light creates oxidizing agents (O–2, OH–, O3, activated O2 and other free radicals) that begin to oxidize the odor causing compounds. Compounds not treated here proceed to the catalyst, where they are trapped and broken down by various reactions, including catalysis.There are many advantages to this technology over traditional odor control methods :1) The footprint is small;2) It handles spikes very well;3) Temperature and relative humidity of the air are not issues;4) It can effectively treat very high levels of odorous compounds, especially all of the reduced sulfur compounds, even up to many 100s of ppm of H2S;5) Design odor levels at outlet are usually in the range of 300-500 O.U./m3; however, there are many independent tests below 50 and even 30 O.U./m3.There are now numerous installations in the U.S. either recently installed or in progress. The most detailed U.S. performance data come from the MissoulaWWTP. The City was under an order to clean up their odor issues, and, after piloting the technology, opted for PI units on their two most odorous locations, the Headworks and a TWAS storage tank and dewatering room. The units were installed in December 2012. Compliance testing was implemented after the second month of operation. For a three day period, eight hours per day, H2S (inlet and outlet) levels were checked every hour or so using a Jerome Analyzer. Once a day, a bag sample was taken and sent for odor panel analysis and another for reduced sulfur compounds (H2S, mercaptans, DMS and DMDS) at independent laboratories. Inlet concentrations of H2S varied up to about 10 ppm, and inlet odor levels were over 3,000 O.U. The results show that the odors were handled with ease by the Photoionisation system - consistently providing greater than 99.8% removal of H2S, on average and peak conditions, as well as less than 100 O.U. at outlet. The units continue to perform well, a year and a half after installation, with the original UV lights and catalyst. When considered in conjuction with performance data from Germany, the Middle East and elsewhere over the past 10 years in many very odorous situations, Photoionisation has established itself as a superior odor-control technology.