22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Characteristics of soil treated with ozone generated by surface discharge
T. Abiru1, F. Mitsugi1, T. Ikegami1 and K. Ebihara2
1
Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, JP-860-8555 Kumamoto,
Japan
2
Environment and Energy Laboratory, 1-4-15, Otemon, JP-810-0074 Fukuoka, Japan
Abstract: We have applied plasma technology to generate ozone. Ozone is expected as an
alternative to agricultural chemicals such as pesticide and nitrogen fertilizer. In this study,
ozone was generated by using the surface discharge injecting into soil directly in a quartz
container. We investigated the influence of ozone treatment on physical properties of soil
by evaluating acidity of soil.
Keywords: ozone treatment, soil, nitrogen nutrient, pH(H 2 O), pH(KCl)
1. Introduction
There are many kinds of studies about plasma with the
development of science technology [1-4].
Plasma
technology is applied in agricultural [5-8] and engineering
field [9-11]. We have proposed to use plasma technology
in agricultural field. Recently, chemical contamination of
agricultural crop, water and soil has become a serious
issue by the overuse of agricultural chemicals. There are
many types of agricultural chemicals such as pesticide
and nitrogen fertilizer. Pesticide has high effect of
sterilization, however, it affects human body because it
remains in agricultural crop, water and soil as residual
toxic substances. Chemicals contained in pesticide
penetrate into the underground, causing groundwater
pollution. Nitrogen fertilizer has been used to advance
the growth of crops. Nitrate nitrogen of nitrogen fertilizer
proceeds acidification of soil, although it proceeds slowly.
The acidification of soil and residual nitrogen oxides in
groundwater have been observed all over the world by the
overuse of nitrogen fertilizer. Therefore, alternatives to
pesticide and nitrogen fertilizer are required from human
health and environmental point of view. We propose the
use of ozone in oxygen plasmas generated by surface
discharge in agricultural applications, expecting the use of
ozone to replace both pesticide and nitrogen fertilizer as
alternative method because ozone can sterilize pathogens
and virus in soil as well as increase nutrient composition
of soil. We considered that ozone treatment affects
physical properties of soil. There are many kinds of
studies on application of ozone in agricultural field. Our
previous study revealed that characteristics of soil such as
inorganic nutrient (NO 3 -, NO 2 -, and NH 4 +), pH(H 2 O)
were influenced after ozone treatment [12-14]. It also
revealed that the value of pH(H 2 O) recovered to the
initial value with time after ozone treatment. In this
study, we measured the acidity of soil. Soil is generally
consisted of soil solution and soil colloid. Acidity was
evaluated by two different methods. One is pH(H 2 O)
showing H+ in soil solution. The another is pH(KCl)
showing H+ in soil solution as well as onto the surface of
soil colloid because H+ which absorbs on soil colloid is
P-III-9-2
replaced by K+. Therefore, pH(KCl) value is lower
compared with pH(H 2 O). The difference between both
values indicates to H+ absorbed onto soil colloids. Ozone
was generated by oxygen plasma using a surface
discharge and injected into andosol in a quartz container
which is rotated by a motor. The concentration of ozone
was 78 g/m3 with the flow rate of oxygen gas of 1.5
L/min. The treatment time was 90 min. We measured the
change of pH(H 2 O) and pH(KCl) after ozone treatment.
2. Experimental Setup
Fig. 1 shows the schematic illustration of the ozone
treatment system for soil. This setup was used mainly for
fundamental study because the use of the quartz container
can avoid ozone consumption into unexpected organic
matters. Ozone was generated by oxygen plasma using a
surface discharge and injected into soil in a quartz
container which is rotated by a motor. The concentration
of ozone was 78 g/m3 with the flow rate of oxygen gas of
1.5 L/min. Exhaust ozone gas was monitored with an
ozone monitor (Iwasaki electric., OZM-700GN). The soil
used for treatment was andosol that was taken from field
for cultivation of crops. The amount of andosol used for
treatment was 100 g. The treatment time was 90 min.
The ozone dose rate, which is defined as ozone does
weight per unit weight of soil, was 11 %. We measured
physical properties of soil such as inorganic nutrient
(NO 3 -, NO 2 -, and NH 4 +), pH(H 2 O), pH(KCl), amount of
soil DNA, amount of exchangeable bases (Ca2+, K+, Fe2+,
and Al3+), fungi, and amount of nematodes before and
after ozone treatment. Quantities of nitrate, nitrite and
ammonium were evaluated using standard indices of
NO 3 -, NO 2 -, and NH 4 + at mg/kg. Inorganic nutrients and
bases were measured by colorimeter method with test
reagent (Kanto Chemical Co. Inc., Reflrctoquant). After
ozone treatment, we measured both pH(H 2 O) and
pH(KCl) with time. One sample was a solution for
pH(KCl) which the andosol (10 g) had been filtrated by
potassium chloride solution (25 mL). Another sample
was a solution for pH(H 2 O) which the andosol (10 g) had
been filtrated by hyperpure water (25 mL).
1
pH(H2O)(90min)
7.0
Before treatment
6.5
pH(H2O)
6.0
5.5
5.0
4.5
0
1
2
3
4
Time (day)
Fig. 1. Schematic illustration of ozone treatment system
for soil.
3. Results and discussions
We measured physical properties of soil before and
after ozone treatment. In our previous study, inorganic
nutrient in soil increased after ozone treatment, and kept
at a constant value [14]. The pH(H 2 O) decreased after
ozone treatment because organic matters in soil were
decomposed by ozone. However, the pH(H 2 O) value
recovered to the initial value with time [12, 13]. Fig. 2
shows the recovery curve of pH(H 2 O) after ozone
treatment. There are also some studies about sterilizing
effect of ozone in our previous studies. The almost of
high molecular DNA in soil were decomposed and living
bacteria were also sterilized after 11% ozone dose [15].
In this study, we measured H+ ions in soil solution as well
as onto the surface soil colloid by pH(KCl), and H+ ions
in soil solution by pH(H 2 O) after ozone treatment.
Comparing between the recovery properties, as shown in
Table 1, pH(H 2 O) and pH(KCl) decreased from 7.3 to 5.5
and 6.2 to 4.3, that increased 6.0 and 5.2 after 7 days
passed from ozone treatment, respectively, increasing 7.4
and 6.4 after 14 days passed from ozone treatment. The
pH(H 2 O) and pH(KCl) almost recovered to the initial
value. The pH(H 2 O) indicated same recovery curve of
our previous study. The pH(KCl) also indicated same
recovery curve of pH(H 2 O). Both pH(H 2 O) and pH(KCl)
value indicated that amount of H+ ions increased by a
factor of hundred just after ozone treatment. The result
suggested that amount of H+ ions changed only in soil
solution. Subsequently amount of H+ ions decreased by
one hundredth with time. From these results, it was found
that H+ ions don’t migrate from soil solution to soil
colloids.
4. Summary
In this study, influence of ozone treatment on physical
properties of soil was investigated. Ozone was generated
by oxygen plasma using a surface discharge and injected
into soil in a quartz container which is rotated by a motor.
The concentration of ozone was 78 g/m3 with the flow
rate of oxygen gas of 1.5 L/min. The treatment time was
2
Fig. 2. Recovery curve of pH(H 2 O) after ozone treatment.
The dot line shows pH(H 2 O) value before treatment.
Table 1. Changes in pH(H 2 O) and pH(KCl) of soil.
Before
ozone
treatment
Just after ozone
treatment
7 days after
ozone treatment
14 days after
ozone treatment
pH(H 2 O)
pH(KCl)
7.3
6.2
5.5
4.3
6.0
5.2
7.4
6.4
90 min. We measured the change of pH(H 2 O) and
pH(KCl) after ozone treatment. Comparing between the
recovery curves, pH(H 2 O) and pH(KCl) decreased just
after ozone treatment, subsequently recovered to the
initial value. From the change of pH(H 2 O) and pH(KCl)
value, it was found that H+ ions changed only in soil
solution and don’t migrate from soil solution to soil
colloids.
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