Ozone systems

Market areas of interest to manufaeturers of ozone systems, aetual uses defined as those whieh have been in operation for some time and not ineluding "pilot" studies, arise in the following eategories odor eontrol (sewage treatment and industrial), industrial ehemieals synthesis, industrial water and wastewater treatment, and drinking water disinfeetion. 

A typical ozone system consists of 100 g/hr at a concentration of 1.0 percent to 1.5 percent in air fed to the bottom of bleach collection tanks through ceramic spargers (pore size of approximately 100 t). The system contains air compression and drying equipment, automatic control features, and a flat-plate, air-cooled ozone generator. Regeneration of bleach wastes totaling about 10,000 gallons a year, and recovery of other chemicals can also be cost effective. 

Ozonation systems are comprised of four main parts, including a gas-preparation unit, an electrical power unit, an ozone generator, and a contactor which includes an off-gas treatment stage. Ancillary equipment includes instruments and controls, safety equipment and equipment housing, and structural supports. The four major components of the ozonation process are illustrated in Figure 8. 

Favorable operational economics and good management practices require high levels of control of the ozonation system. Depending on the specific process of ozone applications, plant size, and design philosophy, the control system may be simple or complex. The trend in Europe is toward highly sophisticated and centralized control. 

The vendor states that the E-Process is a modular system, and only the modules needed for a specific operation are used. If, for example, for microflocculation, the vendor recommends using the E-O (ozone) system, followed by the E-P (applied magnetic field) system, and the E-G (gravity separation) system. Treatment of other waste streams may require different systems or the use of systems in a different order. 

The discussion of full-scale ozonation systems for waste waters in the following sections is grouped according to the main removal goal of the application, analogous to that used in drinking water ozonation systems. 

The most frequently used contactors in full-scale waste water ozonation systems are bubble column reactors equipped with diffusers or venturi injectors, mostly operated in a reactor-in-series counter-current continuous mode. Many full-scale ozone reactors are operated at elevated pressure (2-6 barabs) in order to achieve a high ozone mass transfer rate, which in turn increases the process efficiency. 

Full-scale ozonation systems have been used to treat waste waters, such as landfill leachates, as well as waste waters from the textile, pharmaceutical and chemical industries (FTGAWA, 1997 Bohme, 1999). The main pollutants associated with these waters are refractory organics, which can be characterized as (Masten and Davies, 1994) ... 

The most frequent operational problems in waste water ozonation systems are foaming and the formation and precipitation of calcium oxalate, calcium carbonates and ferrous hydroxide (Fe(OH)3) which may easily clog the reactor, piping and valves and also damage the pumps. 

According to Bohme (1999) 32 full-scale ozonation systems are located at landfill treatment sites in Germany. However, no such system was sold abroad by German producers. The comparatively widespread application in Germany may be mainly due to the early... 

Considering the investment and operation costs, ozonation still is not a cheap technology. Although safe operation is no longer a problem, ozonation systems require considerable... 

In summary, an ozonation system from a customer s viewpoint has to meet the following technical and economical requirements ... 

The preceding disussion has given an overview of which goals can be achieved with an ozonation system. The following chapters in this book can provide an understanding on how to design and operate an ozonation system to achieve these goals efficiently. 

Much experimental work has been carried out on ozonation in drinking, waste and process water treatment. And since there is still much to be learned about the mechanisms of ozonation, and many possibilities of utilizing its oxidizing potential many experiments will be carried out in the future. Not only researchers but also designers, manufacturers and users of ozonation systems will continue to do bench-scale testing because ozonation is so system dependent. Most full-scale applications have to be tried out bench-scale for each system considered. That means that there is a need for not only fundamental information about the mechanisms of ozonation, but also information on how to set-up experiments so that they produce results that can be interpreted and extrapolated. 

Since ozone is a very strong oxidant, all materials in contact with this gas have to be highly corrosion resistant. This has to be considered for all components in the ozone system including the ozone generator as well as all instruments (Figure 2-1, Table 2-1). 

The type of feed gas used, air or oxygen, determines the achievable ozone gas concentration and the gas preparation requirements. The higher the oxygen content, the higher the ozone concentration possible. Ambient air contains 02 in about 21 vol % (at STP) and is thus a cheap and ubiquitous resource for ozone production. Its main use and advantage is in applications where large mass flows are required at comparatively low ozone gas concentrations, e. g. in drinking water ozonation systems. 

Method 2 basically addresses the same advantages as Method 1, with the additional consideration that the same favorable reaction rates found in batch ozonation systems can be achieved in a continuous-flow tube reactor (Sunder and Hempel, 1996 Levenspiel, 1972). More work is necessary to see how effective such reactors are for higher loaded (waste) waters, where gaseous ozone must be continuously dosed. 

Ultraviolet (uv) light has also been used to sterilize the water in aquaculture systems. The effectiveness of uv decreases with the thickness of the water column being treated, so the water is usually flowed past uv lights as a thin film (alternatively, the water may flow through a tube a few cm in diameter that is surrounded by uv lights). Uv systems require more routine maintenance than ozone systems. Uv bulbs lose their power with time and need... 

Combined process constant (k) and radical rate constant (kr) for UV /ozone system. (Data from Benitez, F.J. et al., Chemosphere, 41,1271-1277, 2000.)... 

It is not clear why this linear NO system is so unreactive. While analytic Xa was shown to reproduce accurately the dynamics of the ozone system, perhaps it is the problem in this system. We are looking at these same dynamics using the GGA, which unfortunately requires more than a factor of two increase in computer time. 

The addition of hydrogen peroxide to the ozonation system provides a better result [42]. The process, called Perozone, combines the direct and indirect ozone oxidation of organic compounds. H202 initiates O3 decomposition by... 

Figure 5. Change in the energy of the ethylene+ozone system by the pathway of non-coordinated addition (1) in the singlet and (2) triplet states and (3) change in the y value in the former case UB3LYP calculations.

In the ozone systems, PbOi 37 and Pb02 are identified as deposits on the catalyst. 

Graham, R.A., Johnston, H.S. (1978) The photochemistry of the nitrate radical and the kinetics of the nitrogen pentoxide-ozone system. J. Phys. Chem. 82, 254. 

Table I. Aerosol Production from Selected Hydrocarbon—Ozone Systems ...

---