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Effects of Irrigation with Disposed Produced Petroleum Water on the
Soil and Plants at Khartoum Refinery, Sudan
Asma A. M. Makeen1*, Mohamed M. A. Elnour2
and Nawal K. N. Al Amin3
1
Faculty of Agriculture, University of Al-Zaeim Alazhari, Khartoum North, Sudan
2
Faculty of Forestry, University of Khartoum, Shambat, Sudan
3
Faculty of Forestry and Range Science, Sudan University for Science and
Technology, Khartoum, Sudan
ABSTRACT
This study aimed to assess the effect of irrigation interval with disposed produced
petroleum water (DPPW) on the soil and vegetation cover at Khartoum Refinery
Company (KRC). Thirty-six soil samples (at depths of 0-30, 30-60 and 60-90 cm) were
taken from tree plantation blocks. The treatments were P0 (none irrigated, as a control)
and P1 and P2 were irrigated for four and eight years, respectively, and were analyzed for
pH, cation exchange capacity (CEC), total soluble Na+, Ca++, Mg++ and Cl-. Twenty-one
samples of tree leaves were collected from P0, P1 and P2 and analyzed for Na, Ca and
Mg. The results showed that at the soil surface (0-30 cm) no differences within and
between blocks in pH that was about 7.0 where the CEC of P0 and P2 have lower content
compared to P1. Application of the DPPW increased the soluble Na+ of P1 and P2
compared to P0 (2.2, 0.46 and 0.04 Meq/L respectively), and the same trend was shown
by soluble Ca++ (74.5, 18 and 2.5), and Mg++ (3.0, 2.5 and1.0). Cl- content increased as
irrigation interval increased (4.5, 104.5 and 30.0 Meq/L for P0, P1 and P2, respectively).
Systematic decrease of all soil chemical content with depths was shown for P0, P1 and
P2. For the plant, there was an increase in Na as irrigation interval increased (50.67,
516.67 and 723.33 for Po, P1 and P2 respectively), whereas Ca and Mg increased in P1
compared to P2 and P0. The risk of accumulation of soluble salts is expected to occur
with time, therefore, specific treatments to decrease the salts content of DPPW are
crucial.
Key words: Soil; vegetation; disposed produced petroleum water
* Corresponding author: Email: asmamakeen@gmail.com
INTRODUCTION
Substantial amount of produced water in USA can be generated from oil
production and industries, and most of it is re-injected; however, a portion of the waste
stream could be re-used for specific purposes such as agricultural and industrial use
(Sullivan et al., 2004). This is by some estimates the largest single waste stream in the
USA (Allen and Rosselot, 1994). It usually contains large amounts of dissolved salts,
hydrocarbons, trace heavy metals, organic compounds and small quantities of dissolved
organic components, suspended oil (non-polar), and solids (sand, silt). Two thirds of the
produced water is recycled by injecting it into the oil wells to maintain the pressure of oil
reservoirs, an estimated 35% of produced water requires disposal means, because it
cannot be recycled (Willum et al., 2007). Most of produced waters are more saline than
seawater, (Cline, 1998). For each barrel (bbl) of oil produced, an average of 10 barrels of
water is produced for an annual total of about 3 billion tons. The environmental impact of
the oil industry includes the land use, waste management, groundwater and air pollution
from the production and refining processes, such discharging of produced water can
pollute surface and underground water and soil, (Razi et al., 2009). Produced water is
conventionally treated through different physical, chemical, and biological methods to be
re-used for specific purposes such as agricultural and industrial. In many countries,
produced water is managed by re-pumping it back to the well-head. This however, is not
practised in Sudan, probably, due to the high cost of such operation.
Khartoum Refinery Company (KRC) is a one of the two major refineries in
Sudan. It was originally designed to process 50,000 barrels of crude oil per day.
However, due to the increasing demand for petroleum products, especially diesel, the
shareholders of the refinery have decided to increase the processing capacity of KRC to
100,000 barrels/day. The plant consists of several units producing 2.2587 metric tons per
hour, ranging from gasoline to liquefied gas, in addition to a substantial amount of water
as a major waste by-product. The amount of waste water is estimated to be about 20
million m3 / annum. Basically the waste water accumulates in open ponds to evaporate
after preliminary pre-treatment. The KRC is equipped with three evaporation ponds for
discharging waste water. Each pond is 650 m x 420 m x 2.2 m of length, width and depth,
respectively. The ponds are underlined with plastic sheets to insure seepage prevention.
The total evaporation surface area is estimated to be 800,000 m3 with an estimated
evaporation of about 6800 m3/day, with daily excess water of 4200 m3.
Each of the waste water treatment ponds is designed to neutralize alkalis and
acids, and skimming thereafter the oil from the water. This waste passes through
biochemical unit for further treatment to cater for removal of other polluting materials.
This treated wastewater thence is used to irrigate Eucalyptus camaldulensis forest trees
on an area of 300 feddans (1 feddan = 0.42 ha) starting 2004 followed by a second
plantation of the same species in 2008.
This research assessed the effect of irrigation time with treated produced
petroleum water (TPPW) on the soil and plants within the vicinity of Khartoum Refinery
in Al Gaily area.
MATERIALS AND METHODS
This research was conducted at KRC, 70 kilometres north to Khartoum,12 km
from eastern bank of the River Nile and 25 Km North-East of Al Gaily city. The study
area is a semi-rocky-desert land with two valleys, on both side of the refinery, flowing
directly to the river Nile. The area is currently an arid desert scrub with sparse natural
vegetation. The annual rainfall ranges between 0.0 to 200 mm with an annual average
temperature of 29o C. The established forest plantations were surveyed first, where three
blocks were identified and used to collect data on soil and plants. These were: block (P4)
and block (P8) which have been irrigated with TPPW for 4 and 8 years respectively, and
block (P0) as anon irrigated control. In 2011, 36 soil samples were taken from each block
at depths 0-30, 30-60, and 60-90 cm. These soil samples were analyzed for: pH, cation
exchange capacity (CEC) and soluble cations of Na+, Ca++, Mg++ and Cl-. Soil samples
were prepared and analyzed in the Laboratory of Faculty of Agriculture at University of
Khartoum according to a method described by (Richards, 1969). A pH meter with glass
electrode was used to determine pH and the EC at 25oC. An extraction of soil solution
was prepared, thence a Flame Photometer (410 Sherwood) was used to measure Na. Cl
was determined by AgNo3 titration. Calcium and Magnesium were measured by Atomic
Absorption using Spectrometer – Spectra AA220 Varian.
For plant leaf analysis, 21 samples of leaves were collected from trees in the three
blocks and their foliar chemicals composition was assessed in the Chemistry Laboratory
in the Faculty of Science at University of Khartoum. Flame Photometer (410 Sherwood)
was used to measure Na and Ca while Mg and heavy metals were assessed using Atomic
Absorption (Spectrometer – spectra AA220 Varian).
RESULTS AND DISCUSSION
The soil pH trend showed an increase with depths in the blocks (P4 and P8)
irrigated with DPPW and in the control block (P0). The soil pH attained higher values of
7.7 and 7.9 for P4 and P8, respectively, particularly at depth 60-90 cm, compared to 7.4
in control (P0) (Fig. 1). According to (Thompson et al., 1982), the soil pH was nearly to
be neutral in control block (P0) and ranged from slightly alkaline to medium alkaline in
P4 and P8 respectively. The soil pH in P4 and P8 matches with the pH of water in the last
pond. The treated waste water in the three ponds was assessed according to the standard
methods for the Examination of water and waste water following (Franson et al., 1998),
and compared with the standards of guidelines of the quality of water used for irrigation
according to (Ayers et al.,1985), (table 1). However, temperature and sunlight beside the
presence of Algae in the ponds might have led to an increase in pH values in the last
pond, as reported by (Faris, 2003). The soluble minerals; Na, Ca, Cl and Mg, which were
originally very low and almost constant with depths (Fig. 2) did not show systematic
trend upon irrigation. The soluble sodium content of the soil increased with increase of
duration of irrigation compared to control (Fig. 2a). In P4 soluble sodium content attained
very high level (34 meq/L) at depth 0-30cm, and then decreased with depth. In blocks
kept under irrigation for 8 years (P8), the soluble sodium seems to be leached as the
values were low compared to irrigation for 4 years (P4) but with high values reaching
twofold of control block (P0). High soluble calcium content (45 Meq/L) was reported in
P4 at (0-30cm) of soil depth then decreased to 33 and 25 Meq/L, respectively, with
depths of 30-60cm and 60-90cm. In blocks under irrigation for 8 years (P8), soluble
calcium and CL contents were low compared to values from blocks under irrigation for 4
years (P4) but still higher than in control blocks (P0) (Fig. 2b and fig. 2c). Ca contents
were 10 Meq/L at depth 0-30 cm, 7.5 Meq/L at 30-60 cm and 5 Meq/L for 60-90 cm. The
decreasing pattern of soluble sodium and chloride contents indicate that salts are mainly
of sodium chloride; (Fig.2a and Fig.2c). The Magnesium (Mg), although affected by
irrigation and reported higher values compared to non-irrigated soil behaved differently.
It increased at 30-60 cm and then decreased at 60-90cm of soil depth (Fig. 2d). The
cation exchange capacity showed different trends (Fig. 3). It increased at soil depth 0-30
cm with the increase of duration of irrigation giving 15, 24 and 35 meq/100g for P0, P8
and P4, respectively. The highest CEC was obtained at soil depth 0-30cm for all blocks
and it keeps increasing in the original soil but after irrigation for 4 and 8 years it
decreased with depth.
Table.1. Average parameters of disposed produced water in the last treatments
stabilization ponds in Khartoum Refinery.
Parameter
Average of treated waste water in Standard
water
for
Ponds 3
irrigation
o
7.6
6.5 – 8.0
PH at 25 C
o
888
0.7 – 3.0 ds/m
EC at 25 C
450 – 2000 mg/l
TDS% (w/v) 0.06
NA
TSS% (w/v) 0.07
0.02
NA
OC% (w/v)
0.04
NA
CO3 (g/l)
0.72
1.5 – 8.5 me/l
HCO3 (g/l)
49 mg/l
NH4% (w/v) 0.19
100
3 – 9 me/l
Na (ppm)
28
Ca (ppm)
7.33
Mg (ppm)
1
ND
< 0.041 mg/l
Zn (ppm)
ND
< 0.050 mg/l
Pb (ppm)
ND
< 0.001 mg/l
Cd (ppm)
ND Not Determined
8
7.9
7.8
7.7
7.6
7.5
7.4
pH
1
7.3
7.2
7.1
7
0 - 30 cm
P0= non irrigated
30 - 60 cm
soil depth
P4=irrigated for 4 years
60 - 90 cm
P8=irrigated for 8years
Fig.1: The soil pH trend as function of irrigation duration at
KRC forestry project
50
45
40
Ca Meq/L
35
30
25
20
15
10
5
0
0 - 30 cm
30 - 60 cm
soil depth
60 - 90 cm
P0= non irrigated
P4= irrigated for 4 years
Fig. 2b: The soil Soluble Calcium as
function of irrigation duration
atKRCforestry project
70
60
cl Meq/L
50
40
30
20
10
0
0 - 30 cm
30 - 60 cm
60 - 90 cm
soil depth
P0= non irrigated
P4= irrigated for 4 years
fig. 2c: The soil Chlore as function of
irrigation duration at KRC forestry
project
6
5
Mg Meq/L
4
3
2
1
0
0 - 30 cm
30 - 60 cm
60 - 90 cm
soil dept
P0= non irrigated
P4= irrigated for 4 years
Fig.2d: Magnesium as function of
irrigation duration at KRC forestry
project
40
35
CEC (meq/100g)
30
25
20
15
10
5
0
0 - 30 cm
30 - 60 cm
60 - 90 cm
soil depth
P0=non Irrigated
P4=
P8
Fig.3: Cation Exchange Capacity (CEC) as function of irrigation duration
at Algaily forestry project:
The Cation exchange capacity is an important component of soil fertility, or at
least of potential soil fertility as reported by (Miller et al. 1975 cited by Thompson et
al., 1982). This finding indicates that there was a decrease in soil fertility in soil after
being irrigated with DPPW for 4 and 8 years in blocks P4 and P8, respectively. As for
soluble Ca and Na, the highest contents were found in the surface soil (0-30cm) of the
blocks irrigated for 4 years (Fig. 2a and fig. 2b). The Mg remarkably shows different
pattern, being highest at soil depth 30-60cm (Fig. 2d). This deviation is likely associated
with the total clay content where solubility of Mg increases with the increase of clay
content. From the survey some trees in blocks P4 were lodged and this could be due to
accumulation of soluble sodium and chlore (Fig. 2a and 2d). Increases of sodium
chloride (Nacl) tends to bind fine soil particles to form a stable soil structural aggregates
(falls aggregates), which upon wetting become fragile and unstable to withstand
collapsed structure and this situation leads to incidence of lodging of trees. Figure 4
shows there was a relation of mineral contents of Na, Ca and Mg in the plant with the
minerals in the soil within the treatment blocks P4 and P8. There was an increases in the
up take by the plant with the increase in magnesium content in soil (Fig.4-a). Sodium
content and Calcium content for both soil and plant were decreased in blocks under
irrigation with produced water (Fig.4-b and 4-c).
16
Leaf (Mg/L)
15
14
13
y = 0.1875x2 - 0.7745x + 12.713
R² = 0.9156
12
11
10
0.5
2.5
3
4
Soil (meq/L )
Fig. 4a: Magnesium content
100
80
60
y = -11.5x2 + 51.5x + 26
R² = 0.4962
Na in leaf
40
20
0
0.46
0.711
0.961
2.154
Na in soil
Ca in leaf
Fig. 4b: Soduim content
450
400
350
300
250
200
150
100
50
0
y = -100x2 + 500x - 200
R² = 1
2.5
15.5
Ca in soil
18
74.5
Fig. 4c: Calcium content
Fig. 4: The impact of using TPPW on soluble salts content of the soil and
its up take by the plant
CONCLUSIONS AND RECOMINDATIONS
Irrigation of forest plantations with DPPW produced an increase of soil pH with
depth and an increase of soluble sodium to very high levels (34meq/l). Levels of soluble
salts have similar trends in soil and plants. Leaves shedding of trees were associated with
accumulation of minerals as due to continuous irrigation with DPPW for four years.
Continuous irrigation with DPPW for 8 years has resulted in leaching of soluble salts;
Na, Ca, Mg and Cl in the soil. The study calls for multidisciplinary approaches involving
all concerned stakeholders to cater for the effects of exposures to chemicals in DPPW and
to develop risk-based corrective actions using apt methods to decrease salts in irrigation
water.
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