IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Research article
erdFundamental Study on Nitrogen Removal from Paddy
Drainage Using Clinker Ash
HITOSHI YAMAMOTO
Graduate School of Agriculture, Tokyo University of Agriculture, Japan
Email: h1okazaw@nodai.ac.jp

HIROMU OKAZAWA
Faculty o Regional Environment Science, Tokyo University of Agriculture, JapanYUKO OHTAKA
Atsugi City Office, Kanagawa, Japan

YASUSHI TAKEUCHI
Faculty o Regional Environment Science, Tokyo University of Agriculture, JapanYOSHITAKA MURAKAMIFukushima Prefecture, Fukushima, Japan
Received 10 December 2010

Accepted 27 January 2011

Abstract Clinker ash is a kind of coal ash produced by the burning of coal at thermal
power plants. Recycling of clinker ash is highly desirable since most of it goes to landfills
at present. Because of its porous solid, clinker ash has high potential as a means ofpurifying contaminated water. On the other hand, nitrogen outflow by paddy drainage has
become a major problem in Japan. Therefore, this study examines the effectiveness of afiltering system using clinker ash for removing nitrogen from paddy drainage. A column
experiment was conducted in the laboratory to examine the nitrogen removal function ofclinker ash. Four types of filtering materials were prepared as the test samples. TheSample I consisted only of clinker ash; the Sample II and the Sample III were a mixture ofclinker ash and paddy soil in the ratios of 3:1 and 1:3 respectively; and the Sample IV wascomprised of paddy soil only. Each sample was poured into PVC columns (44 mm indiameter; 350 mm in length). A solution prepared with NH4-N at a concentration of 10mg/L and C/N of 12 was fed to the columns at a flow rate of 100 to 200 mL/d for 121
days. During the experiment, the columns were kept saturated at a room temperature of
24.4±1.3℃ and illuminated at 544±192 lux. The study showed that clinker ash has theeffect  of  removing  nitrogen.  However,  it  also  found  that  clinker  ash’s  removal  function  is  compromised when a large amount of paddy soil is mixed with clinker ash. In order toremove nitrogen from paddy drainage by using clinker ash, only a relatively small amountof paddy soil should be mixed with clinker ash.
Keywords nitrogen removal, clinker ash, paddy drainage, filtering system

INTRODUCTION
Water contamination due to agricultural activity is a global issue (Garnier et al., 2010). During
Japan’s rapid economic growth from the 1950s to 1970s, pollution issues relating to watercontamination surfaced across the country. The Water Pollution Law was introduced in 1970 as acountermeasure, and other laws and regulations followed in subsequent years. These days, watercontamination from point sources, such as factories and residential wastewater, has ameliorated
thanks to regulatory efforts; however, nitrogen and phosphorous water contamination arising fromfarmland and other non-point sources is not yet sufficiently resolved (Mishima. 2007).
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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Many studies have reported nitrogen removal efforts on paddy fields, which account for 60%of farmland in Japan (Ichino et al., 1998; Feng et al., 2004). It has also been reported that nitrogen
runoff from paddy fields is related to river water contamination, and paddy fields are thus identified
as a source of water pollution. In particular, discharge of high-concentration nitrogen is noted tooccur in paddy fields immediately after fertilizers are used (Yoshinaga et al., 2007).
Approximately 20% of Japan’s total energy is provided by coal-fired thermal generation. In
2003, thermal generation produced a total of 7,470,000 tons of coal ash, which is roughly
categorized into clinker ash and fly ash. Fly ash constitutes the majority of coal ash and is recycled
as construction material. Although as much as 220,000 tons of clinker ash is generated each year,
most of it ends up in landfills; thus recycling of clinker ash is an important issue to address (JETAet al., 2005). Since the surface of clinker ash has numerous pores of 1-20 μm in diameter (Fig. 1)
and has a large specific surface area, it has good potential as a water purification material.
Nitrogen discharge from paddy drainage divided into seepage, surface runoff, denitrificationand vaporization. Especially, it is easy to take measure regarding with decrease of nitrogenconcentration in seepage and surface water using filtering system. In this study, a column
experiment was conducted using clinker ash as a filtering material in order to illustrate the nitrogen
removal performance of clinker ash when used against paddy field wastewater.
METHODOLOGY
A column experiment was conducted in the laboratory to examine the nitrogen removal function ofclinker ash as shown in Fig. 2. Four types of filtering materials were prepared as test samples.
Table 1 shows characteristics of each filtering material before the experiment. Sample I consisted
only of clinker ash; Sample II and Sample III were a mixture of clinker ash and paddy soil in theratios of 3:1 and 1:3 respectively; and Sample IV consisted of paddy soil only. Mixture samples
were assumed to be degraded by paddy soil.
The coefficient of permeability was 6.23×10-2cm/s in Sample I, and 1.20×10-4cm/s in Sample
IV. A rise in the ratio of paddy soil decreased the coefficient of permeability. While no amount ofnitrogen was detected from Sample I, 181.4×10-5kg/kg was found in Sample IV. The higher theratio of paddy soil was, the greater the amount of nitrogen.

Fig. 1 Photomicrograph of clinker ash
Each sample was poured into a PVC column (44 mm in diameter; 350 mm in length). A test
solution prepared with NH4-N at a concentration of 10 mg/L and C/N of 12 was fed to the columns
at a flow rate of 100 to 200 mL/d for 121 days. The drainage tube was lifted in the column upper
part to make it a saturation state. During the experiment, the columns were kept saturated at theroom temperature of 24.4±1.3 ℃ and illuminated at 544±192 lux. Water samples were taken every© ISERD55IJERD – International Journal of Environmental and Rural Development (2011) 2–1

day for the first 31 days. The sampling interval was then changed to once every 2 days until the 60thday, when it was again changed to once every 4 days until the 121st day.

Fig. 2 Schematic diagram of column experimentParameters used to measure the water quality were total nitrogen (T-N), nitrate nitrogen (NO3N), nitrite nitrogen (NO2-N), and ammonium nitrogen (NH4-N); these were analyzed using
ultraviolet spectrophotometry in accordance with the Japanese Industrial Standards (JIS). Thequantities of nitrogen and carbon were each measured using the CN coder (SUMIGRAPH NCH22F : Sumika Chemical Analysis Service, Ltd.) before and after the column experiment.
RESULTS AND DISCUSSION
Fluctuation of outflow nitrogen concentration as a function of time and cumulative flow
Fig. 3 shows the relationship between the number of days elapsed and the T-N concentration (Cout)in the outflow. Fig. 4 plots the relationship between the cumulative flow of the solution and the Coutin the outflow. The volume of the solution passing through during the experiment period of 121
days varied from sample to sample, due to the differences in the coefficient of permeability.
Samples I and II recorded the lowest nitrogen concentrations at 2.21 mg/L (1st day: 0.42 L)
and 3.24 mg/L (5th day: 1.27 L) respectively. From then on the concentration rose gradually,stabilizing at approximately 7 mg/L. Samples I and II both recorded lower concentrations ofnitrogen than that in the incoming solution throughout the experiment period, consistently
demonstrating the presence of a water purification mechanism.
Table 1 Physical and chemical properties of samples
SampleProportion
CA: soilSoil
textureCoefficient
permeability(cm/s)

Dry
density(g/cm3)

Voidratio

T-C(x10-5kg/kg)

T-N(x10-5kg/kg)

C/N
ratio

Sample I

1:0

S

6.23x10-2

0.94

1.34

441.1

0.0

ND

Sample II

3:1

LS

1.50x10-2

0.96

1.34

620.1

31.0

20.0

Sample III

1:3

CL

3.17x10-4

0.99

1.50

1259.6128.5

9.8

Sample IV

0:1

LiC

1.20x10-4

1.03

1.55

1497.0181.4

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1Samples III and IV, on the other hand, recorded the highest nitrogen concentrations, at 67.40
mg/L (3rd day: 0.25 L) and 98.72 mg/L (3rd day: 0.20 L), respectively. The concentrations gradually
decreased, with Sample III stabilizing at 11 mg/L and Sample IV at 16 mg/L. These values werehigher than those in the inflow, evidencing that Samples III and IV had no nitrogen cleansing effect.
The above results demonstrate that the ratio of clinker ash and paddy soil is related to theperformance of the mixture as filtering material.
Nitrogen balance in each column
The nitrogen balance in each column during the 121 days was calculated by using Eq. (1) and (2):Lout  Lin  SD  SP

(1)

SP  Psoil  Pvac

(2)

Where Lout is nitrogen discharge (mg), Lin is nitrogen supply (mg), SD is nitrogen discharge
from soil (mg), SP is nitrogen removed (mg), Psoil is nitrogen adsorbed (mg), and Pvac is microbial
decomposition of nitrogen compounds (mg), obtained by a subtraction based on (2).

Fig. 3 Relationship between days lapsed and Cout

Fig. 4 Relationship between cumulative flow and Cout
Table 2 shows the nitrogen balance in each column. The ratios of effluence (Lout /Lin) ofSamples I and II were respectively 0.74 and 0.64. This illustrates that when the nitrogen solution
passes through a column containing a larger proportion of clinker ash, the concentration decreases
by 26 to 36%. The values of Psoil and Pvac in Sample I were 43 mg and 17 mg, while those inSample II were 69 mg and 10 mg. From these it is inferred that nitrogen adsorption and microbial
decomposition occurred in Samples I and II.
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Table 2 Nitrogen balance
SampleLout(mg)

Lin(mg)SD(mg)SP(mg)

Psoil(mg)

Pvac(mg)

Ratio ofeffluence
Lout/Lin (-)

Sample I

169

229

060

43

170.74

Sample II

145

224

080

69

100.64

Sample III

183

135

83

35

035

1.36

Sample IV

19577

165

47

047

2.52

Samples III and IV, on the other hand, recorded ratios of effluence of 1.36 and 2.52
respectively, demonstrating that nitrogen in the columns was released into the outflow. SD valuesof Samples III and IV were respectively 83 mg and 165 mg; it is assumed that nitrogen in thepaddy soil in the column was discharged.
CONCLUSION
The column experiment confirmed that nitrogen is removed by nitrogen adsorption of clinker ash
and microbial decomposition. It was further demonstrated that when the ratio of paddy soil toclinker ash rises in the mixture, the nitrogen removal mechanism fails to materialize, and thenitrogen contained in paddy soil is discharged. Thus, it is necessary to pay close attention to themixture ratio between clinker ash and paddy soil when developing a water purification systemusing clinker ash.
ACKNOWLEDGEMENTS
This research was supported by the Ministry of Education, Culture, Sports, Science andTechnology (MEXT), Japan and Grant in Aid for young Scientists (B), 22780223, 2010. The
authors are grateful for the columns experiment assistance provided by students of the Laboratoryof Hydro-structure Engineering, Tokyo University of Agriculture, Japan.
REFERENCES
Feng, Y.W., Yoshinaga, I., Shiratani, E., Hitomi, T. and Hasebe, H. (2004) Characteristics and behavior ofnutrients in a paddy field area equipped with a recycling irrigation system. Agricultural Water
Management, 68, 47-60.
Garnier, M., Recanatesi, F., Ripa, M.N. and Leone A. (2010) Agricultural nitrate monitoring in a lake basinin Central Italy: a further step ahead towards an integrated nutrient management aimed at controlling
water pollution. Environmental Monitoring and Assessment, 170, 273-286.
Japan Environmental Technology Association, Japan fly ash association (2005) Coal Ash Handbook, (inJapanese).
Ichino, M. and Kasuya, M. (1998) Nitrogen removal in paddy fields: An option for water quality
improvement in rivers. Ecological Engineering, 10, 159-164.
Mishima, S., Taniguchi, S., Kohyama, K. and Komada, M. (2007) Relationship between nitrogen andphosphate surplus from agricultural production and river water quality in two types of production
structure. Soil Science and Plant Nutrition, 53, 318-327.
Yoshinaga, I., Miura, A., Hamada, K. and Shiratani, E. (2007) Runoff nitrogen from a large size paddy field
during a crop period. Agricultural Water Management, 87, 217-222.

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