Agriculture Reference
In-Depth Information
rite, 30,000 ppm hydrogen peroxide, 80 ppm peracetic acid, and 100,000 ppm sodium
bicarbonate were all ineffective against F-specifi c coliphage MS2 and Feline calici-
virus (as surrogates to norovirus).
Ozone
Ozone has been used for many years as a disinfectant in water and wastewater treat-
ment. Its fi rst use in water disinfection dated back to 1893 in Oudshourn, Netherlands
(Rice and Farquhar 1982). Currently, more than 200 water and wastewater treatment
plants employ ozone treatments for water supplies in the United States. In 1997, ozone
as an aqueous disinfectant was declared to be generally recognized as safe (GRAS)
for food contact applications (Guzel-Seydim and others 2004). Ozone is cleared by
the FDA for use on raw agricultural commodities (Anonymous 2007d). The primary
advantages of ozone include strong oxidizing capabilities and fast decomposition in
water without leaving any chemical residues. Effi cacy of ozone is not affected by the
solution pH (Graham 1997). Richardson and others (1998) indicated that the by-
products of ozone are less likely to cause deleterious health effects than the by-
products of chlorine treatment. A drawback of ozonated water wash is its sensitivity
to organic loading and potential off-gassing.
Ozone is formed by the excitation of molecular oxygen (O
2
) into atomic oxygen
(O) in an energizing environment that allows the recombination of atoms into O
3
, as
shown in the following reaction:
3
+ →
The half-life of molecular ozone in air is relatively long (approximately 12 hr);
however, the half-life of ozone in aqueous solutions is signifi cantly shorter and
depends on temperature, pH, UV light, initial O
3
concentration, and concentration of
radical scavengers.
Ozone has shown a strong bactericidal effect against a wide spectrum of micro-
organisms, including the chlorine-resistant parasites
Cryptosporidium parvum
and
Giarda lambla
oocysts, both of which have invaded food and water supplies and
caused deaths in recent years (Kim and others 1999a). Exposure to 1 mg/l ozone for
5 min achieved
O
electricity
2
O
2
3
90% inactivation of
Cryptosporidium parvum
oocysts (Korich and
others 1990). In contrast, a nearly 90-min exposure to 80 mg/l of chlorine was required
to achieve the same results. Ozonated water (0.1-0.2 mg/l) was reported to instanta-
neously kill 5 logs
S.
typhimurium and
E. coli
, 3 logs
Pseudomonas aeruginosa
and
Yersinia enterocolitica
and 4.5 log
Candida albicans
and
Zygosaccharomyces bacilli
and 1 log
Aspergillus niger
after 5 min (Restaino and others 1995). Ozone can also
destroy pesticides and chemical residues, such as chlorinated by-products, and convert
nonbiodegradable organic materials into biodegradable forms (Kim and others 1999b).
The primary mode of action of ozone is oxidation. Ozone acts by oxidizing the
outer cell membrane of vegetative bacterial cells, endospores, yeast, and mold spores
(Graham 1997). The oxidation of cell membrane results in a change in cell permeabil-
ity, eventually leading to cell lysis and death (Murray and others 1965). Ozone may
inactivate microorganisms by causing damage to their DNA (Scott 1975).
Ozone is a more effi cient sanitizer than chlorine for inactivating microorganisms
on meat, poultry, eggs, fi sh, fruits, vegetables, and dry fruits (Kim and others 1999b).
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