11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Wastewater treatment in Alexandria, a developing
country big city on north African coast
O. El-Rayis1*, M. Abbas2 and M. Abdallah2
1
Oceanography Dept., Faculty of Science, Uni versity of Alexandria, Alexandria
Moharrem Bek 21511, Egypt.
2
National Institute of Oceanograph y and fishery, Khayt-bey, Alexandria, Egypt
*Corresponding author, e-mail: [email protected]
ABSTRACT
Alexandria City is the second largest city after Cairo in Egypt and is lying on the southeast
Mediterranean coast. It has about 40 % of the total Egyptian industrial activities and its
population is about 3 million. Two primary treatment plants were erected in 1993 to serve two
third of Alexandria area domestic and industrial wastewaters and to discharge their effluents to a
main basin (area, 6000 acres with mean depth 1 m) of a natural lake called Lake Maryout. The
surplus water from this basin is pumped to the neighboring sea. The present work is a study for
the treatment efficiency of the treatment plants and the impact of these effluents on the lake
water and sediments quality. The results reveal that these plants are currently able to reduce the
organic and total suspended solids (TSS) loads by only less than 48 % of their corresponding
initial loads in the raw wastes at their inlets. In addition, the studied oxygen-consuming
indicating elements (BOD5 and COD) in the outlets are at levels still far beyond those
corresponding permissible levels recommended by the Egyptian Environmental Protection
Agency, EEPAA. In the mean time, the current water quality of Lake Maryout Main Basin,
LMMB, in comparison with that of a neighboring basin (the lake NW basin which does not
receive sewage effluents) revealed deterioration of the LMMB reflected on fish diversity and fish
catches besides intermittent evasion of the malodorous H 2S gas smell from this polluted basin,
lead people to complain. Solutions like diversion of the waste effluents or/and application of
secondary wastewater treatment processes for restoration of the lake are suggested and assessed.
KEYWORDS
Primary treatment plants, treatment efficiency, recipient Lake Maryout, impact on lake water and
sediment quality, lake restoration, Alexandria-Egypt
INTRODUCTION
Alexandria City is the second largest city after Cairo in Egypt and is lying on the southeast
Mediterranean coast. It has about 40 % of the total Egyptian industrial activities and inhabited by
3 million inhabitance in winter and more than 4 million in summer. As Alexandria is the main
summer resort for the Egyptians in general. Before 1993 only one third of the city area (Figure
1) has been served by sewerage system before a preliminary treatment process is done and
discharging to both the neighboring sea (through several short marine outfalls distributed along
the 25 km length of Alexandria coast between El-Mex and Abu-Kir Headland, Figure 1) and to
Lake Maryout. The Lake is lying south of Alexandria City its surface water is always maintained
artificially by pumping, at 2.8 m below sea level. It is the main source of the common favorite
brackish water fish (Tilapia species) for most of Alexandrine people. In the mean time is also a
good nesting ground for many migrating birds and as a place for creation, entertainment and
El-Rayis et al.
1
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
different water sports such as line fishing. This lake dislikes other delta lakes or lagoon in the
region by having no direct connection with the Mediterranean Sea as there is a natural ridge
separating the lake from the sea. Besides it is composed of four separate basins, namely the Main
Basin (proper lake, 6000 acres), Northwest Basin (3000 acres), Fisheries Farm Basin and
Southwest Basin, most of the fish catch comes from the first basin. The average water depth of
the lake is about 1 meter and, as mentioned, the water level is always maintained at about 2.8 m
below sea level using huge pumps. This makes the lake to work as a sink to drain different kinds
of drainage waters from the surrounding lands including sewage before discharging, using the
pumps, into the sea at El-Mex Bay. In 1987 all the sea outfalls have been diverted to the Main
Basin of Lake Maryout as a fast solution to protect Alexandria coasts from sewage pollution. In
July 1993, both the diverted sea sewage outfalls and the sewage and industrial outfalls on the
Lake Main Basin (LMB) have been directed to be primary treated first in two newly erected and
independent sewage treatment plants; (Eastern Treatment Plant, ETP and Western Treatment
Plant, WTP); then discharging them into LMMB. At this stage particularly by the end of 1994
M E D I T E R R A N I A N S E A OFF ALEXANDRIA CITY C O A S T
Abu-Kir
Headland
El-Mex Bay
Omoum
Drain
Position of
the WWTP
Kalaa
Drain
LAKE MARYOUT
MAIN BASIN (LMMB)
1980
After 1995
Figure 1. Map of Alexandria Wastewater System Service Areas: a- the dark area
since 1980 and b- the grey area
served after 1995.
served
two third of Alexandria becomes served with sewerage and the sewage influents are substantially
increased. The positions of the two treatment plants and the disposing sites on the LMMB after
1993 are also shown in Figure 1. Actually the treated effluent from the ETP reaches the lake
indirectly through an agricultural open drain (about 7 km in length) called Kalaa Drain. While
the effluent of the other plant WTP is disposed directly into LMMB at its northwest side.
The ETP receives the whole sanitary wastes of the eastern Districts of the city from Gleem and
Hadara to Abu-Qir (with an average discharge rate 377,000 m 3/d). The treated wastes are then
discharged to Kalaa Drain via El-Moheet Drain before reaching to LMMB, Figure 1. The other
plant WTP, receives the effluents of old (Figure 2) three outfalls of Moharem Bek industrial
complex, Ghait El-Enab and Kabbary collected from the city center and part of the western
districts (with average discharge rate about 222,000 m 3/d). The treated effluent is directly disposed
into LMMB but at its northwestern side. The municipal wastewater received by the two treatments
plants is composed of water used for residential, commercial, industrial and public purposes, as
well as ground water that has infiltered into the sewera ge system. In each plant the following
treatment processes are made: (i) bar screening, (ii) grit chambers and (iii) settling tanks. Primary
treatment is usually accomplished by sedimentation. The wastewater passes through a large tank
under relatively quiescent conditions. If the detention time is long enough then suspended
2
Wastewater treatment in Alexandria
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
materials having a sp.gr. greater than water sink to the bottom, forming a sludge, while those with
a lower sp. gr. will rise to the surface forming a floating scum. The resulting wastewater has a
reduced BOD5 and suspended solids load. The treatment efficiency of the two plants was studied
here besides studying the current levels of water and sediment quality parameters of the recipient
LMMB and comparing with (1) their corresponding levels in a neighboring basin (the lake
Maryout NW Basin), which does not receive effluents from the two treatment plants, and with (2)
the water quality criteria required by the Egyptian EPAA (48/1982) Law.
METHODS
Indeed, the present study represents one of the most recent and compreh ensive studies made on
the treatment efficiency of Alexandria city municipal and industrial wastes for the newly erected
two treatment plants. Water samples were collected from the inlets and outlets of the two
treatment plants and from the recipient LMMB and from its drain system, Figure 2. Entails
results on the physico-chemical characteristics of the waters i.e. total suspended solids (TSS),
chlorophyll-a, transparency (STD), chlorosity (Cl v) DO, BOD, COD5, H2S, plant nutrient (N and
P compounds) and some heavy metals like Fe, Mn, Zn, Cu and Cd) were obtained. Sediment
samples were collected from LMMB and subjected to analysis of organic P (OP), Organic-N
(ON), Organic-C (OC) and the same heavy metals. All the analyses were commenced according
to the methods mentioned in the Standard Methods for Examination of Water and Wastewater
(APHA, 1995).
RESULTS AND DISCUSSION
The results of the water quality parameters BOD, COD and TSS in the different effluents and the
relevant organic loads are presented in Table 1. It shows that there is a considerable decrease in
the values of the oxygen-consuming waste parameters BOD 5 and COD in addition to TSS in the
out-flowing waters from the plants with respect to their corresponding values in the untreated
wastewaters at the inlets. In the WTP, the reduction in the outlet BOD 5, COD and TSS levels
reached values 50.5, 28.1 and 50.2 % respectively of their correspondin g in the inlet raw
wastewater. The calculated organic load to the lake from this source currentl y represents about
50 % of that in the inflowing untreated raw wastewater to the plant. On the other hand, in the
ETP the respective parameters in its outlets reached values 34.3, 13.1 and 47.7 % of their
corresponding initial values in inlet untreated influents.
Table 2, shows a comparison between the level of the studied parameters in the out flowing
waters from the two treatment plants and their corresponding recommended permissible levels
(according to the Egyptian Law 4/1994 in any discharged wastes to a natural water body in the
country). From the table it is obvious that the current discharges from the two Alexandria’s
treatment plants are having BOD 5, COD and TSS at levels at least 2.5 times higher than the
permissible limits of the Law 4/1994. This means that either more advanced treatment techniques
(like secondary treatment processes) for the current primarily treated effluents are urgently
needed to reach such permissible limits before discharging the wastes to Lake Maryout. Or the
current effluents from the treatment plants must be diverted or diluted enough prior disposing
into this natural lake.
Impact on the receiving Main Basin of Lake Maryout
The impact of the wastewater effluents from the ETP disposed indirectly to the southeast side of
the lake via Kalaa Drain (at Station K-3, Figure 2) and directly from the WTP at the lake
northwest side can be easily traced from examination of the following figures (from 3 to 6).
El-Rayis et al.
3
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Table 1. Mean level of the studied water quality parameters in the inlet and outlet effluents of
each of the waste treatment plants in Alexandria and its treatment efficiency.
Plant Source
BOD
Load
COD
Load
TSS Load
mg O 2 /L
ETP
WTP
ton BOD/d
Inlet
338.4
127.6
Outlet
222.2
83.7
Efficiency %
34.4
Inlet
654.1
145.2
Outlet
323.4
71.8
Efficiency %
50.5
ETP= East Treatment Plant
mg O/L
ton/d
mg/d
ton/d
730.5
275.4
287 108.2
634.9
239.3
150
56.5
- 13.1
47.8
1765.5
391.9
592
131.4
1268.5
281.6
295
65.5
28.1
50.2
WTP = West Treatment Plant
Table 2. A comparison between the levels of each of the BOD and COD (oxygen-consuming
wastes) and total suspended solids (TSS) parameters with the corresponding recommended
permissible level by EEAA (Law 4/1994)
Parameter
BOD (mg O 2 /L)
Site
Present study
ETP outlet
222
WTP outlet
323
COD (mg O 2 /L)
ETP outlet
635
WTP outlet
1269
TSS (mg O2 /L)
ETP outlet
150
WTP outlet
295
* EEAA= Egyptian Environmental Agency Affairs.
WTP
Permissible Level EEAA*
60
100
60
K3
LMB
NW Bas in
Sewage Contaminated
Agricultural Kalaa Drain
Agricultural Omoum Drain
SW B asin
Old Sources
Figure 2. Map of Lake Maryout Main Basin (LMMB) showing the location of the sampling
stations and position of the three old sources at its northeast side.
Where the highest concentration of BOD 5, COD, NH4 and dissolved inorganic P (DIP) and H2S
(of CLv values < 1,000 mg/l, Figure 4a) can be found in the lake waters in front of these sources
with a general decrease in the concentration with increasing distance away from the source. In
the mean time there is relatively less polluted (but it is more saline, its Cl v is > 1,000 mg/l,
Figure 4a) and more aerated water mass intruded between the two polluted water types and its
source is from the southwest side of LMMB from a breach in the dyke separating this lake basin
at that side from the course of the agricultural Omoum Drain (Figure 2). This has led to
occurrence of an anticlockwise water circulation in this basin of the lake. Such situation makes
4
Wastewater treatment in Alexandria
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
the basin to be occupied mainly with highly polluted water type on the east and less polluted
water one on the west in this basin. These two water types can be easily seen from examining
Figure 4b. This figure shows the level of BOD, NH 4, DIP and H2S in each of these two distinct
waters in the LMMB and in the waters of the reference basin (LMNWB). The level of these
pollutants is extremely low in the last basin confirming how the LMMB is impacted with the
wastewater effluents. Such impact has also reflected on the fish catch (Figure 4c) which has
sharply declined from values as high as 14,000 tons/y (of several different fish species) to
about3,000 tones/y at present (of less diversify fish species) causing a big social problem to the
local fishermen and their families. Add to this the problem of the evasion of malodorous H 2S gas
(a)
(c)
31.17
Oxygen consuming materials
19
18
Plant
17
31.16
16
15
31.17
WTP
31.16
31.15
Kalaa Drain
31.14
BOD
31.13
nutrients
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
31.15
14
13
12
31.14
11
10
9
31.13
8
NHNH4
7
4
6
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.93
5
3.10
31.17
2.90
2.70
31.16
2.50
2.30
31.15
2.10
31.14
1.90
1.70
31.12
31.13
29.87
29.88
29.89
29.90
29.91
29.92
1.50
DIP
DIP
29.93
1.30
31.12
(b)
29.87
(d)
29.88
29.89
29.90
29.91
29.92
29.93
1.10
31.17
5.5
5.0
31.16
4.5
4.0
31.17
3.5
31.15
3.0
180
170
31.16
2.5
31.14
2.0
160
140
31.15
130
1.0
Dis. Oxygen
DO
31.12
29.87
1.5
DO
31.13
150
29.88
29.89
29.90
29.91
29.92
29.93
120
110
31.14
31.17
100
90
COD
31.13
31.16
80
70
31.15
60
31.14
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.93
H2S
31.13
31.12
29.87
29.88
29.89
29.90
29.91
29.92
0.5
0.0
-0.5
26
24
22
20
18
16
14
12
10
8
6
4
2
0
29.93
Figure 3. Horizontal distribution of (a) BOD 5, (b) COD, (c) Plant nutrients NH4 and dissolved
inorganic P (DIP), and (d) DO and H2S, in the surface water of LMMB.
El-Rayis et al.
5
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
(a)
31.17
1300
1250
1200
1150
1100
1050
1000
950
900
850
800
750
700
650
600
550
31.16
________
31.15
Kalaa Drain
31.14
East Side
31.13
NW - Basin
______
West Side
Omoum Drain
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.93
(b)
50
45
BOD
mgO2/l
40
mg2/L
O
35
30
25
(c)
Annual fish catch, Ton
Concentration (mg/L)
Concentration (mg/L)
20
15
10
5
0
E.side
W.side
NW
B OD
12
DO & H2S
mg/l
10
O2
8
6
H2S
4
2
0
E. side
W. side
DO
NW
H2S
16
NH4 & DIP
mg/l
14
12
10
8
6
4
2
0
E. side
W. side
NW
NH4
DIP
16000
14000
12000
Fish
Catch
10000
8000
6000
4000
(Tons /year)
2000
0
75
80
Ye a rs
85
90
95
H2S
9
8
7
8
7
6
6
5
5
4
4
3
3
DO
2
1
H
2
S (mg/L)
DO (mg/L)
70
mg/l
2
1
0
0
62
78
Ye a rs
87
91
DO
92
96
H2S
Figure 4. (a) Horizontal distribution of chlorosity (mg/l) in the surface water of LMMB. (b)
Mean level of BOD, DO and H 2S, and NH4 and DIP (mg/l) in the eastern and western sides of
the LMMB and in the reference NW Basin of Lake Maryout, and (c) The yearly change in the
level of fish catch (tons/y) and each of DO and H 2S (mg/l) in LMMB.
particularly from the southeast part of LMMB lead to people complaints.
6
Wastewater treatment in Alexandria
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Table 3 describes the current trophic status of each of LMMB and the NW Basin based on
standard trophic scale (Wetzel, 2001), where the first basin is in hypereutrophic condition while
the other is in a better healthy condition, mesotrophic state.
Table 3. Transparency (STD), nutrient level and biomass (Chl-a) of natural lakes at each
trophic category (Wetzel, 2001) in comparison to those for Lake Maryout
Trophic
Category
Annual mean
Chlorophyll
3
(mg/m )
Chlorophyll
maxim a
3
(mg/m )
4.0
1.0
2.5
12.0
6.0
<90
Oligotrophic
10.0
2.5
8.0
6.0
3.0
<80
Mesotrophic
10-35
2.5-8
8-25
6 -3
3 -1.5
40-89
Eutrotrophic
35 -100
8-25
25-75
3 -1.5
1.5 -0.7
40-0
Hypereutrophic
100.0
25.0
75.0
1.5
LMB (mean)
3480
49.5
154.5
0.34
NW Basin
350
6.6
14.3
Ultra-oligotrophic
Mean total
Phosphorus
3
(mg/m )
Annual mean
STD
(m)
0.56
STD
minima
0.7
0.1
0.5
Minimum
oxygen
(% sat)
10-0
<< 10
110
Examining Figure 5, one can note that the LMMB pollution distribution pattern has been
reflected on the bottom sediments too where the highest values of OC, ON and OP were
characterizing the sediments in vicinity of the current and old land based sources (the three old
sources which were lying at the north side of the lake before the erection of the WTP, Figure 2).
The current ones are off Kalaa Drain at Station K-3) at the southeast side and off the outlet of the
WTP itself at the NW side of the basin. This same pattern is applicable too to a certain extent for
the metals Cu, Zn and Cd. Manganese is remarkably accumulated in the far southwest sediments
lying under well aerated waters of Omoum Drain origin reflecting its precipitation there mostly
as Mn oxi-hydroxides. While Fe shows more accumulation in the sediments in front of the outlet
of Kalaa Drain. They are mostly sapropetic sediments, the accumulation there are most probably
as Fe- sulphides. So the spoiled sediments contaminated with the priority metal pollutants Cu, Cd
and Zn are lying in front of the old and the new land based sources and these are the ones need to
be dredged as part of a restoration plan of LMMB.
Regarding level of concentrations of the dissolved priority metals pollutants (Cd, Cu and Zn) in
the waters of LMMB are present at respective concentrations (1.2-2.0, <8 and <38 ug/l) which
are relatively far below their corresponding permissible levels (3, 34 and 306 u g/) recommended
by UNEP (1985) and USA-EPA (1992) for clean river and lakes. So the lake water at present has
no metal pollution problem. The lake is currently suffering mainly from the high load of the
oxygen consuming wastes and need solution for this problem before irreversible damage is
reached.
Suggested solutions for Lake Maryout pollution problem
Diversion of both ETP and WTP away from the LMMB
Tables 4 and 5, show how the reduction in the concentration and in the load values of the oxygen
consuming wastes besides TSS and plant nutrients reaches to an acceptable level by the EEPAA
El-Rayis et al.
7
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
when the diversion of the wastewater effluents of the two treatment plants is carried out.
31.17
31.17
31.16
31.16
31.15
31.15
31.14
31.14
31.13
31.13
OC %
31.12
29.87
29.88
29.89
29.90
29.91
29.92
IP %
31.12
29.93
29.87
31.17
31.17
31.16
31.16
31.15
31.15
31.14
31.14
31.13
29.88
29.89
29.90
29.91
29.92
29.93
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
31.13
OP %
ON %
31.12
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.93
29.87
29.88
29.89
29.90
29.91
29.92
29.93
Figure 5. Horizontal distribution of OC, IP, OP and ON in the bottom sediments of LMMB.
31.17
31.17
31.16
31.16
31.15
31.15
31.14
31.14
0.75
0.70
< 0.40
0.65
0.60
0.55
0.50
Fe
31.13
0.45
Mn
31.13
0.40
0.35
0.30
Mn (mg/g)
Fe (mg/g)
31.12
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.87
29.93
31.17
31.17
31.16
31.16
31.15
31.15
31.14
31.14
Cu
31.13
29.89
29.90
29.91
29.92
12.0
11.5
11.0
10.5
10.0
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
< 6
Cd
Cd (ug/g)
Cu (mg/g)
< 0.1
29.93
31.13
31.12
31.12
29.87
29.88
29.88
29.89
29.90
29.91
29.92
29.87
29.93
29.88
29.89
29.90
29.91
29.92
29.93
31.17
0.55
31.16
0.50
0.45
0.40
31.15
0.35
0.30
31.14
0.25
31.13
Zn
< 0.2
0.20
0.15
0.10
Zn (mg/g)
31.12
29.87
29.88
29.89
29.90
29.91
29.92
29.93
Figure 6. Horizontal distribution of Fe, Mn, Cu, Cd and Zn in the bottom sediments of the LMB.
Application of secondary treatment processes for the waste effluents
Table 6 shows that according to ACS (1998) how the approximate cumulative waste removal
efficiencies of secondary treatment process, in percent, can be achieved. The efficiency for
removal of the oxygen consuming wastes and TSS in the secondary treatment processes reaches
values as high as 90 % while for TN and TP reach values of 50 and 30 % respectivel y.
8
Wastewater treatment in Alexandria
11th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008
Table 4. The deduced concentrations (mg/l) of each of the BOD, COD, TSS, TN and TP in
water discharge from Kalaa Drain (at Station K-3) to LMMB after diversion of ETP and WTP.
Parameter
The expected concentration at K-3
Permissible level according to EEPAA
BOD 5
35
60
COD
57
80
TSS
39
50
TN
15
TP
1
Table 5. Expected load (ton/d) and times of reduction of BOD5, COD, TSS, TN and TP reaching
LMMB from Kalaa Drain before (a) and after (b) diversion of ETP and WTP effluents.
Parameter
Load in tons/day
Total
times of reduction
Reduction percent
(a)
(b)
ETP+WTP
in load
BOD5
59.3
9.9
131.1
13.2
92.4
COD
75.0
16.3
356.6
21.8
95.4
TSS
67.0
10.9
132.7
12.2
91.7
TN
32.7
4.2
49.1
11.7
91.4
TP
2.9
0.34
4.1
12.0
91.7
CONCLUSIONS
The removal of most of the oxygen consuming matter by either of the two suggested solutions
will lead the lake to become well aerated and soon or later regain its health and fame as a good
fertile lake with high production of fresh- and brackish-water fish.
Dredging the spoiled sediments certainly will accelerate the restoration rate of this vital lake to a
great extent.
Table 6. Approximate cumulative waste removal efficiencies of various sewage treatment
procedures, in percent, according to ACS (1969)
Parameter
Primary
Primary + secondary
Treatment %
treatment %
BOD 5
35
90
COD
30
80
TSS
60
90
TN
20
50
TP
10
30
________________________________________________________________________ ______
REFERENCES
ACS (American Chemical Society) 1969. “Cleaning Our Environment: The chemical Basis for Action”ACS.
Washington.
APHA(1995). Standard Methods for the Examination of Water and Wastewater. 19th edn, American Public Health
Association/American Water Works Association/Water Environment Federation, Washington DC,
UNEP (1985). Cadmium, lead and tin in the environment, Regional Seas. Reports and Studies, No56 ..p6.
US-EPA. Environmental Protection Agency (1992). Water quality standards: Establishmen t of numeric criteria for
priority pollutants. 40 CRF, part 131.
Wetzel R. G. (2001).Limnology. Lake and River Ecosystem. Academic Press. Pp 1108.
El-Rayis et al.
9