Treatment Systems

A continuous laboratory-scale O3 gas treatment system (Figure 18.8) has been used for decontamination of fruits and vegetables [66]. This system includes a corona discharge ozone generator (Clear Water Tech, Inc., San Luis Obispo, CA), a 10 l Irvine Plexiglass treatment chamber with a stainless steel shelf, a humidifier, a diaphragm vacuum pump, a thermo-hydro recorder, an ozone neutralization unit, and a continuous ozone monitor (model 450H, Advanced Pollution Instrumentation, Inc., San Diego, CA). Ozone gas from the generator is first humidified by flowing it through water in a 125 ml gas-washing bottle. The gas then continuously passes through the treatment chamber.

Thormn-hvnrn motor

03 gas generator

Neutralization

Thormn-hvnrn motor

03 gas generator

Neutralization

Humidifier

FIGURE 18.8 Schematic of a continuous laboratory ozone gas treatment system for decontamination of fruits and vegetables.

Humidifier

FIGURE 18.8 Schematic of a continuous laboratory ozone gas treatment system for decontamination of fruits and vegetables.

Meanwhile, the gas in the chamber is circulated by the pump. The ozone gas is finally neutralized by passing through a solution of reducing agents, such as sodium sulfite. The concentration of ozone gas is continuously monitored using a high-concentration ozone monitor. The concentration of ozone in the air can be recorded as mg/l or ppm. One mg/l ozone gas is approximately equivalent to 467 ppm in volume under standard conditions (0°C, 1 atm) and 509 ppm under normal conditions (25°C, 1 atm).

Ozone concentration can be measured using the indigo colorimetric method, which has been approved by the Committee on Standard Methods for the Examination of Water and Wastewater in 1988 [70]. For in-line monitoring gaseous ozone, a UV spectrophotometric method can be used [12], such as continuous monitors manufactured by Advanced Pollution Instrumentation, Inc. (San Diego, CA) and IN USA (Needham, MA).

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