Photocatalytic Oxidation & Ultraviolet Irradiation

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A study on the elimination power of AiroCide of ethylene, mold and bad odours inside cold rooms.

The presence of harmful elements that affect stored fresh produce inside cold rooms is a well known problem to the industry. Within these harmful elements, the organic volatile compounds (named VOCs from now on) represent one of the biggest worries. VOCs existence is a consequence of the stored produce own metabolism, and mold spreads through the air in a spore form; and also the ethylene, that although we can include it within the VOCs group, it should be separately considered due to its condition of vegetable hormone and because it is a direct cause of the fresh produce ripening process. There are some technologies available in the market to lessen these problems. The majority of these technologies are based in the use of strong oxidants in order to destroy the compounds, and among them we find the Photocatalytic Oxidation with Titanium Dioxide (TiO2) in conjunction with Ultraviolet Irradiation (UV). In this study, we are presenting the results obtained after a few tests conducted in the SAT 9821, CFM group in Balsapintada, Murcia (Spain) utilising the AiroCide PPT device, in two different cold rooms filled with peppers and melons respectively.

Objectives & Method

Three parameters are to be measured in this study. The ethylene concentration, the count of colony forming units (CFUs), and the presence of VOCs. Ethyle is measured due to its vital role played in the produce ageing processes, direct responsible of cold room shrinkage; the CFUs are measured due to the infection and contamination experienced in stored produce, and finally, VOCs are to be meassured too. These compounds which are usually originated from the stored produce own metabolism, create the strong smells we find when entering any cold room, and we can tell just by the particular smell what kind of product is in store. The VOCs can easily spoil the quality of stored produce when absorved by other fruits or vegetables. The elimination of such VOCs can be used as a guide of the air cleansing efficiency of the AiroCide inside the cold rooms. In order to understand this statement we must explain further what is the oxidating process. To ilustrate this example we can use the ethylene. To be able to oxidise ethylene until we get CO2 y H2O it is necessary to follow certain steps, and these steps will lead to creating byproducts, which can be even more poisonous that the original product. These byproducts, in the case of ethylene, are ethylene oxide, formaldehyde, or methanol, depending on the oxidative characteristics of our medium, but all of them involving sanitary risks. The larger the size of the molecule to destroy, the more difficult the situation becomes, which also increases the possibility of producing more byproducts. Measuring of VOCs allows us to determine if this reducting system actually reduces the levels of VOCs present in the area of study, and also whether byproducts are formed as a result of the oxidation process or not.

Three differentiated methods were used for taking the samples, a constant electrochemical detecting air sampler brand Bioconservación was used in the ethylene case, with a measuring range of 0 and 100 ppm. An average calculation out of five different concentration readings was made in order to estimate the ethylene concentration in the air. For CFUs count, we used a high volume air sampler brand Graseby on petri dishes of SMA culture specifically advised for fungal growth. One rehearsal sampling was performed in each cold room to be able to establish the necessary sampling period of time in order to get significant results. Each sample was taken twice, therefore results are the average calculation of both readings. Finally, VOCs were measured on granular (3 pore range) activated carbon filtering tubes to guarantee the highest range of VOC picking at one single pass. The tubes were later tested through thermal desorption and gas chromatography with mass spectrometer (GCMS) for compound identification.

Conclusions

The AiroCide PPT has proven to efficiently remove ethylene, CFUs and VOCs concentrations in cold storage indoor air as well as that it is applicable to different stored produce.

In addition, AiroCide is a clean device with no harmful effect to the indoor environment where it performs, as the oxidating process happens inside a tightly closed reactor bed kept inside the unit, resulting in a zero emision of byproducts in the process

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