The problem of high levels of dissolved solids in Alexandria wastewater system
*Dr. Helalley A.H. Helalley 1, Dr.Samaa M.Z. Abdel Aziz 2
1 Chief of Alexandria wastewater treatment plants sector.
2 Manager of Industrial Wastewater Research Dept.,
Alexandria Sanitary Drainage Company, Alexandria, Egypt
Keywords
TDS, Groundwater, seawater intrusion, seepage, wastewater.
ABSTRACT
The high levels of TDS in the wastewater of Alexandria city, is one of the problems intensified now a days, the concentrations ranged in some treatment plants between (4500-12000 mg/L), which refers to a combination of different factors causing this phenomenon. Which required to study and identify these factors which may include the occurrence of the wastewater networks in areas with salty soil or these areas are below sea level and that causes the increase in the concentration of salts in the groundwater, which is working at its penetration of the networks and wastewater networks that do not take into account the implementation of precautions necessary to prevent leakage and penetration on the high concentration levels in the normal limits for liquid waste received for pumping stations and treatment plants.
The negative effects of increasing the level of dissolved solids than the allowable limits in wastewater (400-600 mg/L) is that the final effluent of the treatment plants does not comply with the allowable limits set forth by Law 48 of the year 1982 regarding the discharge on the water bodies (2000 mg/L).
And this problem became a threat to impede the implementation of the national plan to meet the water deficit of the non-traditional sources and from which the reuse of sewage treatment, estimated at about 0.7 billion cubic meters annually, with the attendant disabilities of reuse of agricultural drainage water because the points of the final discharge of most treatment plants in Alexandria is the agricultural drains.
The problem of increasing dissolved solids in the inlet of the wastewater treatment plants causes also increase in the rates of erosion of the components of the treatment plants. This is accompanied by the problem of the increasing inflows that reaches the treatment plants as a result of penetration of groundwater to the wastewater networks, which led to other problems introduced by the effect on the efficiency of treatment plants and generate regions of low pressure inside the lines, sewage systems and the risk of falling and break down of the areas that the network is passing through.
The objective of this research is to high light on the problem and the possible causes of its occurrence and its different effects on the environment recommendations and possible solutions to reduce them or avoid them.
INTRODUCTION:
The coastal area of the Nile delta is one of the most populated regions in Egypt and contains a variety of development activities. One of the major constraints facing the development is the availability of water requirements for different purposes. (1) Demand of water has steadily increased in Egypt during the last 50 years due to population increase, new land reclamation and urban and industrial development.(2)
Sea water intrusion is the movement of seawater into fresh water aquifers due to natural processes or human activities. It is caused by decreases in groundwater levels or by rises in seawater levels. (1)
Alexandria lies north-west of the Nile delta and stretches along a narrow land strip between the Mediterranean Sea and Lake Maryout. The city extends southwards from the cost to a depth of 2-5 km in the area of Abou Qir to El-Dekhila, to about 30 km near el Amriya and Borg El-Arab. It stretches for 140 km along the Mediterranean sea, from Abou Qir in the east to to sidi krir in the west.(1)
The area is characterized by the irregular hills in the southern parts with an elevation from 0 to more than 40 meters above mean sea level and slopes towards the Mediterranean sea in the northward. The entire drainage systems of the Alexandria flow into the Mediterranean Sea. (Figure (1)).
Figure (1): Location and Topographic Map of Alexandria Governorate.
Some studies indicate that the water level in the Mediterranean Sea has already started increasing with about 5 to 20 cm through the last century. It is expected in these studies that the Mediterranean Sea water level will increase by about 50 to 100 cm through the next century. According to the prediction of these studies, Alexandria will be one of the first cities on the Mediterranean area that will be affected by the increase of the sea water level and therefore will suffer of high saltwater intrusion. (3)
MATERIALS AND METHODS:
Literature survey of studies of Alexandria groundwater levels and salinity, and the history of total dissolved solids in wastewater system in Alexandria was studied. The survey included the laws of effluent reuse and the quality of the secondary treated effluent discharged into water bodies.
A field survey was done by the Industrial wastewater, sludge and reuse sector, the survey included four of the secondary wastewater treatment plants in Alexandria including Agamy (km 21), El-Seiouf, Abis 4th El-Nasriya and El-Maamoura wastewater treatment plants.
Samples were collected and analyzed for the levels of TDS in both the influent and Effluent of the treatment plants to determine the salinity levels entering the treatment plants and the amount of dissolved solids in wastewater supposed to be reused and its possibility to be reused.
Levels of TDS were investigated in the groundwater around the treatment plants to determine its levels. Industries located within the zones of each wastewater treatment plant were also surveyed to determine the levels of TDS in their wastewater reaching the treatment plants to determine the possible source of salinity that could be reaching the treatment plants and to determine the actual source of wastewater salinity.
RESULTS AND DISCUSSION:
Drinking tap water is the first source of water forming wastewater. The TDS levels in the drinking water are around 500 mg/L which is within the acceptable limits for drinking water. Generally, this value is increased as it is used by humans and other uses and turns to municipal wastewater which varies as shown in Table (1).
Table (1): Municipal Wastewater Characterization
Contaminant
Unit
Weak
Medium
Strong
TDS
mg/L
250
500
850
In Alexandria, wastewater may exceed the strong levels as most of the main sewers and collectors of sewage are below the groundwater table and close to the coastal area which could easily infiltrate the fresh water during seepage to the sewers resulting in increasing salt water intrusion in the aquifer. Saline water intrusion could be monitored by installing a number of observation wells for determining the amount of fresh water available for development. (3)
The analysis of collected samples indicated that there were no industries producing wastewater with high levels of TDS, where the TDS of different collected samples ranged between 353-815.(4) The history of TDS data in most of Alexandria wastewater treatment plants ranged between 172-625 mg/L.
The permitted levels of TDS in the Egyptian Law for secondary effluent reuse is up to 2000 mg/L, the value of permitted TDS levels in treated effluent discharged to drains is also 2000 mg/L.
The 4th Nariya TP:
The data collected from manholes reaching the 4th Nasriya TP showed increasing levels of TDS along the sewer lines reaching the treatment plants ranging between 353-7280 mg/L, and most of the manholes had TDS values 3000-4000 mg/L indicating invasion of saline groundwater into the sewer system before reaching the TP.(4) The data of Inlet and outlet wastewater to the TP is represented in Table (2).
Table (2): Average monthly TDS levels at El-Nasriya TP during 2012.
Treatment Plant
TDS in Influent (mg/L)
TDS in Effluent (mg/L)
Minimum
Maximum
Aver.
Minimum
Maximum
Aver.
January
6440
7470
7016
7017
7350
7175
February
7390
7920
7680
6160
7340
7215
March
6360
8930
8140
7550
7870
7692
Data showed the high levels of TDS entering the TP which is obvious that its source is from the manholes suffering from intrusion of saline water through the sewer lines. This phenomenon has been continuously impacting the TP and increased to a severe limit which reach to 8140 in the influent of March 2012 with a range between 6360-8930 mg/L. The continuous flow of high TDS into the TP affected the different components of the TP which resulted in failure of the treatment system.
El-Seiouf TP:
The average concentration of TDS in El-Seiouf TP influent was 4500 mg/L in 2010, by the time the area has been heavily inhabited resulting in high flow of domestic wastewater into the system which resulted in dilution of the water entering the TP, thus diluting the TDS concentrations. And temporary reaction of colloidal matter which resulted in cementing the base of the manholes and reduced the groundwater infiltration into the sewerage pipelines. As well as, there has been some non-proper treatment for the groundwater infiltration in most of the manholes. This lead to decrease in levels of TDS as shown in Table (3), which is still out of the allowable range permitted by the Law 48 for year 1982 (2000 mg/L). The location of both 4th Nasriya and El-Seiouf TPs from Google earth are shown in Figure (2).
Table (3): Average monthly TDS levels at El-Seiouf TP during 2012.
Treatment Plant
TDS in Influent (mg/L)
TDS in Effluent (mg/L)
Minimum
Maximum
Aver.
Minimum
Maximum
Aver.
January
1990
2420
2205
2050
2270
2160
February
2170
2650
2410
2150
2370
2260
March
1450
2840
2145
1920
3132
2526
April
1570
2530
2050
2030
2380
2205
May
1340
2080
1710
2090
2560
2325
June
1620
2770
2195
2050
3220
2635
July
1050
2820
1935
2070
2720
2395
August
1450
2570
2010
1770
2210
1990
September
1550
2930
2240
1670
2200
1935
October
1530
2910
2220
2100
2510
2305
4th Nasriya secondary TP
El-Seiouf secondary TP
Figure (2): Location of El-Seiouf and 4th Nasriya TPs.
El-Maamoura TP:
The average concentration of TDS in El-Maamoura TP influent located East of Alexandria during 2009 was ranging between 6900-7300 mg/L, by the time the area has been heavily inhabited resulting in high flow of domestic wastewater into the system which resulted in dilution of the water entering the TP, thus diluting the TDS concentrations. And temporary reaction of colloidal matter which resulted in cementing the base of the manholes and reduced the groundwater infiltration into the sewerage pipelines. As well as, there has been some non-proper treatment for the groundwater infiltration in most of the manholes. This lead to decrease in levels of TDS, which is still out of the allowable range permitted by the Law 48 for year 1982 (2000 mg/L). Data in Tables (4),(5) show that TDS levels in Maamoura is more than TDS level in El-Nasriya, this is mainly related to the source of wastewater is coming from the lower areas in Alexandria.(5) The location of El-Maamoura TP from Google earth is shown in Figure (3).
Table (4): Average monthly TDS levels at El-Maamora TP during 2009.
Treatment Plant
TDS in Influent (mg/L)
TDS in Effluent (mg/L)
Minimum
Maximum
Aver.
Minimum
Maximum
Aver.
June
5248
9392
7324
5447
11978
9182
July
5632
10321
6977
6375
9190
7911
August
5289
7950
6605
5609
8697
7196
September
5039
8066
6712
5932
8290
6868
October
4869
10177
7350
6287
11206
7990
November
5588
8165
6948
6482
8882
7533
Table (5): Average monthly TDS levels at El-Maamora TP during 2012.
Treatment Plant
TDS in Influent (mg/L)
TDS in Effluent (mg/L)
Minimum
Maximum
Aver.
Minimum
Maximum
Aver.
September
2247
3698
3011
2247
3698
3011
El-Seiouf secondary TP
4th Maamora secondary TP
Figure (3): Location of El-Maamoura TP.
El-Agamy TP
In west of Alexandria, the condition didn't differ where groundwater in Agamy area was found to be at depths ranging between 0.45-0.7 m, TDS was analyzed in these waters and was found to be 49110 mg/L. Thus, affecting the wastewater TDS levels in the area where increasing to 3362 mg/L in average as shown in table (), which is still out of the allowable range permitted by the Law 48 for year 1982 (2000 mg/L). Location of El-Agamy TP located by Google Earth is shown in Figure (4).
Table (6): Average monthly TDS levels at El-Agamy TP during 2012.
Treatment Plant
TDS in Influent (mg/L)
TDS in Effluent (mg/L)
Minimum
Maximum
Aver.
Minimum
Maximum
Aver.
July
2380
4830
3362
1054
3500
2204
Agamy km 21secondary TP
Figure (4): Location of El-Agamy km 21 TP.
Literature showed that the TPs are located within high to moderate groundwater vulnerability which agreed with the above results. High groundwater vulnerability covers the whole coastal zone and part of middle area of the governorate which are characterized by very high to high permeable soil, shallow depth to groundwater and relatively fresh groundwater, while Moderate groundwater vulnerability covers the middle part of the study and the eastern part of the coastal zone area. Where these areas are characterized by high to moderate permeable soil, relatively shallow depth to groundwater and low saline brackish groundwater, as shown in figure (5). (1)
Figure (5): Groundwater vulnerability in Alexandria governorate.
The above results agree with the fact that saline water intrusion is the invasion of fresh surface water or groundwater by saltwater that contains more than 1000 mg/L of dissolved solids. Since groundwater systems in coastal areas are in contact with saline water, one of the major problems is the saltwater intrusion. The withdrawal of fresh groundwater for water supply and other uses can cause the saline water that underlies the coastal aquifers to intrude into the fresher parts of the aquifers. Seepage of groundwater into the sewerage systems constructed under the water table level is representing a kind of groundwater withdrawals and result in saline water intrusion.(3)
Another reason for saline water intrusion is the rise of the sea level due to the climatic changes and increasing temperature around the world and especially in the northern and southern poles of the earth and melting of the snow there. (3)
Saltwater intrusion refers to the replacement of fresh water in coastal aquifers by saltwater due to the motion of a saltwater body into the freshwater aquifer (Figure (6)). Saltwater intrusion reduces the available fresh groundwater resources in coastal aquifers. (3)
Figure (6): Schematic representation of saltwater intrusion.
The hydrochemical data indicated that the groundwater of the coastal aquifer, northwestern Nile Delta is meteoric in origin and is mixed with marine water. The coastal plain aquifer is recognized to be at high risk of increasing salinization. The salinity of the groundwater as a total dissolved solid (TDS) ranges from 1,288 to 4,907 mg/L with an average of 3,155 mg/L. The groundwater is slightly alkaline with pH's ranging from 7.01 to 8.2. The electric conductivity (EC) of the groundwater ranges from 1,900 to 9,790 μS/cm with an average of 4,620 μS/cm. It is directly related to TDS and the geographical position of each well. The high values of salinity, pH and EC indicate seawater intrusion.(2)
The hydrochemical data of the coastal aquifer indicated that the TDS varies from 1,288 to 4,907 mg/L with an average of 3,155 mg/L (Table 1). The water table ranges from 7 to 25 m. The coastal aquifer is generally brackish (>3,000 mg/L). The central area has a type of groundwater that is relatively less brackish (<2,000 mg/L) due to seepage of the Nile water from Maryout Canal. The TDS are not clearly affected by changing in water depths due to shallowness of the wells. (2) This ensures the possibility of increasing TDS in sewerage wastewater which agrees with the results of this study.
CONCLUSION:
The impact of infiltration of saline groundwater into the sewers will lead to:
- Raw wastewater entering the TP does not reflect the actual parameters of domestic wastewater on which the treatment plant was designed.
- Increase of amounts of mixed raw and groundwater wastewater entering the treatment plants.
- Decreasing the treatment efficiency as a result of increase of the hydraulic load entering the treatment plant.
- The treated wastewater will not meet the requirements for reuse as a result of increase in TDS levels in the effluent.
- The saline wastewater enhances the corrosion reaction in metal components of the wastewater treatment plant, then causing the TP to fail, as the condition in 4th Abis Nasriya treatment plant since March 2012.
RECOMMENDATIONS:
Wastewater system should be protected from the possible intrusion of saline water and increasing its levels, by isolating sewer lines, manholes and pump stations to minimize the effect of rise in sea water level, to ensure decreasing dissolved solids levels in wastewater system. Thus, to minimize the effect on the final quality of wastewater effluent that could be possibly reused in Alexandria to overcome decreased River Nile water level, and deficiency in rainwater amounts.
Further research should be done to determine the actual reason for increasing TDS in groundwater in the study areas now and historically, also to determine the ultimate design for sewer lines in areas with high levels of groundwater including precautions and type of sewer pipelines materials.
REFERENCES:
(1) "Assessment of groundwater potential in Alexandria", November 2009.
(2) SALINIZATION OF THE GROUNDWATER IN THE COASTAL SHALLOW AQUIFER, NORTHWESTERN NILE DELTA, EGYPT. S. A. Atta, A. M. Sharaky, A. S. El Hassanein and K. M. A. Khallaf.
(3) "New strategies for wastewater management and reuse in Alexandria in 2037", October 2010.
(4) 4th Abis El-Nasriya secondary wastewater treatment plant report on Reasons of high TDS levels in the TP.
(5) Impact of Sea Level Rise on the Arab Region, Mohamed El Raey
(6) Environmental Management of Groundwater in Egypt via Artificial Recharge Extending the Practice to Soil Aquifer Treatment (SAT), International Journal of Environment and Sustainability ISSN 1927-9566 | Vol. 1 No. 3, pp. 66-82 (2012).
(7) Vertical and Horizontal Simulation of Seawater Intrusion in the Nile Delta Aquifer, First International Conference on Saltwater Intrusion and Coastal Aquifers. Monitoring, Modeling, and Management. Essaouira, Morocco, April 23.25, 2001.
ACKNOWLEDGEMENT
We would like to appreciate the valuable effort and support provided by Chemist Reda Anwar Awad, Eng. Samiha Khalaf, Eng. Manal Galal, Chemist Albeer Milad, Dr. Hossam El-Sherbiny, Eng. Samir El-Sheikh, Chemist. Nasser Saber, Eng. Shadia Yehia and Eng. Mona Khodeir in providing the necessary information and data.