Sewage sludgeHeavy metalsCrop productionCropsOrganic matterSoil

Abdelgawad, G.

Al-Zoubi, M. M.

Arslan, A.

Jouzdan, O.

Pejon, N.

Tabbaa, M.

English

Research Papers in Economics

57
Effects of Sewage Sludge on Heavy Metal
Accumulation in Soil and Plants, and on Crop
Productivity in Aleppo Governorate
M.M. Al-Zoubi
1, A. Arslan
1,2,
G. Abdelgawad
2, N. Pejon
1,
M. Tabbaa
1 and O. Jouzdan
2
1General Commission for Scientific
Agricultural Research, Ministry of
Agriculture and Agrarian Reforms,
Douma, Damascus, Syria
2Arab Center for Studies of Arid Zones and
Dry Lands, Douma, Damascus, Syria
Abstract
Although sewage sludge is a good source of nutrients for plant growth, the
presence of heavy metals in sludge can limit its use. We conducted a field
study to evaluate the effects of soil application of sludge on heavy metal
accumulation in soil and plants and on the productivity of wheat, maize
and vetch. There were four treatments: (i) control; (ii) application of inor-
ganic fertilizer according to the recommendation of the Ministry of
Agriculture and Agrarian Reforms (MAAR); (iii) application of sludge equiv-
alent to the MAAR-recommended nitrogen application; (iv) application of
sludge at double the rate used in (iii). The experiment was conducted at
the Kamari Research Station in Aleppo. Analysis of soil before sludge appli-
cation and after harvest reveals significant build up of some heavy metals.
Similarly in crops, heavy metal content increased with the increased appli-
cation rate of sludge. In terms of other parameters, there was significant
increase in organic matter and plant-available soil P levels in sludge-fertil-
ized treatment. There were no significant differences for wheat yield
between the sludge-fertilized treatments (2.66 and 2.86 t ha-1) and mineral-
fertilized treatment (2.93 t ha-1). Maize yield increased significantly in sludge-
fertilized treatments compared to the control (3.88 t ha-1); the highest yield
(6.34 t ha-1) was in the treatment fertilized with double the amount of
sludge. Vetch production also followed a similar pattern. Based on the
results of this study, it is concluded that sludge application to the soil is
effective in improving crop yield. It is unlikely that a single factor in sludge
was responsible for the yield improvement rather a combination of macro
and micronutrients and organic matter supplied by the sludge. The addi-
tion of heavy metals to the soil with the application of sludge was minimal. Sustainable Management of Wastewater for Agriculture 
58
Keywords: sewage sludge, organic matter, heavy metals, wheat, 
maize, vetch, Syria
1 Introduction
Sewage sludge is a good source of micro and macronutrients and organic
matter (OM) for plants. However, unquantified and unscientific application
of sewage sludge can be detrimental to plant growth, animal nutrition,
and human health. Crop responses to sludge application vary by source,
application rate, plant species, soil type, weather conditions, and man-
agement practices (Rabie et al. 1996). Application of sewage sludge can
improve soil structure and increase infiltration rate, aggregate stability, and
soil water holding capacity (Sort and Alcaniz 1999). However, heavy met-
als in sludge can limit its use (Barriquelo et al. 2003), potentially adding high
concentrations of Cd, Cu, Ni, Pb, and Zn to soil can cause serious problems
to plants and their consumers. The Syrian government is establishing
sewage treatment plants in towns and districts, and the annual amount of
solid organic waste from these plants is expected to reach 0.2 million t in
2010. There have been few studies carried out in Syria that address the
implications of sludge application. Based on a field study, we evaluated
the effects of sludge application to soil on heavy metal accumulation in
soil and plants and on the productivity of wheat, maize and vetch.
2  Materials and methods
2.1 Soil  description 
The top 30 cm layer of red soil (Inceptisols) was collected from Kamari
Research Station, Aleppo, Syria, and analyzed for the following: organic
matter, available P according to Olsen et al. (1954); total N using the
Kjeldahl method; organic matter by wet oxidation; available K by extract-
ing with 1 mol L-1 ammonium acetate (1:5 ratio) and using a flame pho-
tometer. Soil organic matter content was 1.23%, total nitrogen level was
0.06%, available concentrations of P and K were 7.5 and 469 mg kg-1. With
23.3% CaCO3, the soil was calcareous in nature. pH was in the alkaline
range, and EC1:5 was 0.4. Soil texture was 26% sand, 18% silt, and 56% clay.
2.2 Sludge  characteristics
The sludge used in the experiment was sampled and analyzed for physical
and chemical properties. The samples were digested using the wet
method (Walinga et al. 1995) and total N and P were estimated using a
Skalar auto analyzer. Total K was estimated by flame photometer.Inorganic N was extracted using KCl (1:10) and measured using an auto
analyzer. Sludge was digested by HClO4 for micronutrient determinations
and digested with aqua regia to determine heavy metal concentrations
by atomic absorption spectrophotometer. Bulk density of the sludge was
0.86 g cm-3. With pH value of 6.37, the sludge was in acidic in reaction. The
salinity level expressed in terms of EC was 3.38 dS m-1. Other characteristics
of sludge are given in Tables 1 and 2.
Table 1 Physical and chemical characteristics of sewage sludge used in the
study (average of three samples) 
Sludge source Moisture (%) OM (%) Total N (%) K2O (%) P (mg kg-1)
Aleppo wastewater
plant 6.5 40.5 3.70 1.35 132
Table 2 Total concentration of metal ions (mg kg-1) in sewage sludge used in
the study (average of  3 samples)
Sludge source Cd Ni Pb B Cu Fe Mn Mo Zn
Aleppo wastewater 
plant 2.30 78.4 71.6 117 230 2400 159 30 1025
Allowable limits  20 200 800 - 1000 - - 30 3000
2.3  Experimental design and treatments 
A completely randomized complete block design with four replications was
used; plot size was 5 ×10 = 50 m2. There were four treatments: (i) control; (ii)
application of inorganic fertilizer according to the recommendation of the
Ministry of Agriculture and Agrarian Reforms (MAAR); (iii) application of
sludge equivalent to the nitrogen application as recommended by the
MAAR; (iv) application of sludge at the rate double that used in treatment 3.
2.4  Cultivation and fertilization
Wheat, maize, and vetch were cultivated for three seasons during 2004-
2006 in crop rotation. Nitrogen and P were added as per MAAR recom-
mendations. Sludge was added to soil after calculating the required
amount. 
3  Results and discussion
3.1  Effect of sludge on nutrient availability status in soil
There were no significant differences in OM content of soil under wheat
and maize (Table 3) due to good initial OM content in soil (Table 1). After
Effects of Sewage Sludge on Heavy Metal Accumulation in Soil and Plants 
59Sustainable Management of Wastewater for Agriculture 
the third crop in rotation (i.e. vetch), the addition of sludge significantly
enriched soil OM especially in T4 where OM increased significantly over
control (T1). 
Table 3 Total N, available P, and organic matter (OM) in 0-30 cm soil depth
after harvesting wheat, maize, and vetch crops.
Wheat Maize Vetch
OM  Total   Available  OM  Total   Available OM  Total   Available
Treat- N P N P N P 
ment % mg kg-1 % mg kg-1 % mg kg-1
T1 2.1 0.084 b 4.1 c 2.13 0.106 3.96 b 1.65 c 0.018 b 3.48 b
T2 1.9 0.110 a 7.7 a 1.97 0.100 6.89 b 2.23 b 0.03 ab 7.68 a
T3 2.2 0.092 ab 6.3 ab 2.06 0.103 8.33 b 2.49 ab 0.06 a 6.15 a
T4 2.2 0.103 ab 5.2 bc 2.13 0.107 19.10 a 2.90 a 0.04 a 5.73 ab
LSD - 0.023 2.0 - - 8.03 0.45 0.02 2.28
Sludge addition increased total N in soil; in case of wheat rotation, the
total N increased by 23% compared with control (Table 3) because of high
N in sludge (Table 1). Available P in soil was significantly different between
treatments. Previous studies reveal that sludge addition can noticeably
increase total N and available P levels in soils (Hernandes et al. 1991,
Oudeh 2002). 
3.2  Effect of sewage sludge on heavy metal accumulation in soil
There was no significant effect of sludge application on heavy metal (Cd,
Ni, Pb, and Cr) concentrations in soil after wheat harvest, the first crop in
rotation. Cadmium levels were found to higher in post-harvest maize plots
where sludge was applied twice. The concentrations of other metal ions
also increased after the harvest of vetch, the final crop in rotation (Table
4). In general, heavy metal accumulation was below allowable levels of
Cd (0.01-2 mg kg-1), Ni (5-500 mg kg-1), Pb (2-200 mg kg-1), and Cr (10-150
mg kg-1) (Adriano 1986).
Table 4 Cadmium (Cd), nickel (Ni), lead (Pb), and chromium (Cr) levels in soil
(mg kg-1) after harvest of wheat, maize, and vetch crops
Treat- Wheat Maize Vetch
ment Cd Ni Pb Cr Cd Ni Pb Cr Cd Ni Pb Cr
T1 0.125 101.7 8.6 104 0.70 b 124.9 7.9 95.7 0.41 59.2 b 3.72 b 58.3 b
T2 0.140 105.7 8.0 104 0.15 a 120.8 4.7 96.2 0.53 75.7 a 3.93 ab 84.7 a
T3 0.135 96.5 8.0 104 0.13 ab 124.2 8.3 93.2 0.60 68.5 ab 4.50 a 85.2 a
T4 0.130 103.5 7.0 103 0.18 a 124.8 10.4 97.0 0.77 65.0 ab 4.13 ab 75.5 a
LSD - - - - 0.07 - - - - 13.2 0.66 13.7
603.3  Effect of sewage sludge on heavy metal accumulation in plants
There was no effect of sludge on metal ion concentrations in wheat and
maize (grain and straw; Table 5). There was an increase of Cd and Cr con-
centrations in both grain and straw of vetch. These results are in agree-
ment with those of Chu and Wong (1987). Heavy metal accumulation in all
the crops was within allowable limits (Cd 0.05-1.2, Ni 0-4, Pb 0.1-30, and Cr
1-5, all mg kg-1; Adriano, 1986).
Table 5 Cadmium (Cd), nickel (Ni), lead (Pb), and chromium (Cr) concentra-
tions (mg kg
-1) in grain and straw of wheat, maize, and vetch
Wheat Maize Vetch
Cd Ni Pb Cr Cd Ni Pb Cr Cd Ni Pb Cr
Grain
T1 0.09 0.8 0.20 0.97 0.06 0.27 5.7 3.8 0.51 b 2.8 0.93 59.2 b
T2 0.09 0.8 0.20 0.95 0.09 0.31 6.3 4.0 0.55 b 2.3 1.07 75.7 a
T3 0.08 0.8 0.20 0.97 0.08 0.16 6.2 3.9 0.61 ab 1.8 1.08 68.5 ab
T4 0.09 0.8 0.20 1.04 0.11 0.15 4.5 3.8 0.79 a 1.7 1.09 65.0 ab
LSD - - - - - - - - 0.21 - - 13.2
Straw
T1 0.18 1.8 0.95 2.10 0.20 0.21 11.1 4.7 0.05 b 3.1 0.29 ab 0.8
T2 0.19 1.2 0.97 2.30 0.21 0.25 11.5 4.7 0.09 ab 3.3 0.23 b 1.1
T3 0.18 1.2 0.98 2.20 0.18 0.18 10.6 3.6 0.12 a 6.6 0.47 a 0.2
T4 0.19 1.3 0.98 2.40 0.21 0.17 12.2 3.8 0.09 ab 6.2 0.40 ab 0.5
LSD - - - - - - - - 0.05 - 0.24 -
3.4 Crop  yield 
There was a significant increase in wheat grain yield from the sludge-fertil-
ized treatments compared with control (Table 6). T4 was the best with sig-
nificant differences to controls and the chemically fertilized treatment.
Similarly for maize grain production, sludge addition was significantly better
than control; with T4 the best, significantly more than control and the
chemically fertilized treatment. For vetch grain production, sludge addition
was significantly better than control. Again, T4 was the best, significantly
more than control and the chemically fertilized treatment. Other studies
have shown high yields after sludge application, because of its contribu-
tion to greater availability of macro and micronutrients in the soil
(Barriquelo et al. 2003).
Table 6 Grain yield (t ha-1) of wheat, maize, and vetch as affected by the
application of chemical fertilizers and sewage sludge application
Treatment Wheat Maize Vetch
T1 2.03 d 1.100 c 9.8 b
T2 2.83 c 1.775 b 9.89 b
T3 3.3 0 b 2.150 b 11.41 b
T4 3.85 a 3.050 a 12.97 a
LSD 0.20 0.450 1.88
61
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Sustainable Management of Wastewater for Agriculture 
62

Effect of sewage sludge amendment on soil aggregation.

Effect of sewage sludge application on growth and mineral composition of maize plant. Congress of recent technologies in agriculture.v1:280-289.

Estimation of available phosphorus in soil by extraction with sodium bicarbonate.

Heavy metal contents of vegetable crops treated with refuse compost and sewage sludge.

Influence of sewage sludge application on crop yields and heavy metal availability.

Influence of two sewage sludge sources on plant growth and nutrient uptake.

Lead behavior in soil treated with contaminated sewage sludge and cultivated with Maize.

Trace elements in the terrestrial environment.

Effects of sewage sludge on heavy metal accumulation in soil and plants and on crop productivity in Aleppo governorate

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Effects of sewage sludge on heavy metal accumulation in soil and plants and on crop productivity in Aleppo governorate

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