Reclaimed Municipal Wastewater used for the Irrigation of Green ...

JKAU: Mar. Sci., Vol. 19, pp: 121-146 (2008 A.D. / 1429 A.H.)

Reclaimed Municipal Wastewater used for the Irrigation of Green Areas in Jeddah: 1 – Chemical Characteristics Radwan Kh. Al Farawati, Amr Al Maradni, Ali S. Basaham and Mohamed A. El Sayed Faculty of Marine Science, King Abdulaziz University, P.O. Box 80207, 21589 Jeddah, Saudi Arabia Abstract. For a better management of water resources, the municipality of Jeddah uses recycled municipal wastewater for the irrigation of parks and green areas. These places are recreational areas and are frequently visited by the population. A comprehensive study was planned to measure the potential health risk that may result from inadequate water treatment through the examination of the chemical and bacteriological characteristics of the recycled wastewater as well as the soil. In this context, 20 water and soil samples were collected from the most frequently visited sites all over the city. Water samples were analyzed for their content of, between others, nitrogen species (ammonium, nitrite, nitrate, organic nitrogen) phosphorus, dissolved oxygen, dissolved organic carbon, pH and suspended particulate matter. The trace elements Cu, Pb and Cd were also measured In order to achieve the major objective, we looked for the regulations regarding the quality criteria for this particular type of application. In the absence of particular guidelines for the irrigation of parks and green areas with recycled water, the reference criteria applied for unrestricted irrigation were used. Concentrations of TSS, Ammonium, nitrate, total nitrogen and phosphate averaged 65.25, 20.8, 3.4, 24.5 and 6.3 mg l–l, while concentrations of the trace elements Cd, Pb and Cu averaged 0.0003, 0.0044 and 0.009 mg l–1. These results indicate that the concentrations of the analyzed parameters are within the limits fixed for the water reuse for irrigation. The health risk may come from the potential contamination with other chemicals and any eventual bacterial contamination particularly with faecal coliform. Keywords: Wastewater, water reuse, irrigation, green areas, chemical characteristics, health risk.

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122

R.Kh. Al Farawati, et al.

Introduction Managing Water Security by Water Reuse Many factors will challenge water professionals in the new millennium. Growing water scarcity, rapid increase in population, rapid urbanization and megacity development, increasing competition among water users, and growing concerns for health and environmental protection are examples of important issues. Despite improvements in efficiency of water use in many developed countries, the demand for fresh water has continued to climb as the world’s population and economic activity have expanded. According to the International Water Management Institute, (IWMI), by 2025, 1.8 billion people will live in countries or regions with absolute water scarcity. The term “absolute water scarcity” means water availability of less than the 100 m3 / inhabitant / year that is necessary for domestic and industrial use. This water availability level is not sufficient to maintain the current level of per capita food production from irrigated agriculture. The world population is expected to increase dramatically between now and 2020 which will certainly result in the production of huge amounts of wastewater. Many countries throughout the world are approaching, or have already reached, the maximum attainable limits of their water supplies; water reclamation and reuse have almost become necessary for conserving and extending available water supply. Today, most countries in the Middle East and North Africa can be classified as having absolute water scarcity. By 2025, these countries will be joined by Pakistan, South Africa, large parts of India and China and a number of other regions (IWMI). These data suggest that many countries will have to manage water resources more efficiently than they do now if they are to meet their future needs. Water Reuse Practices Water reuse alternatives can be broadly classified into two categories: single type of reuse and dual or multiple (sequential) type of reuse (Hamoda, 2004). The first category includes: (i) agricultural reuse, (ii) urban and landscape reuse, (iii) industrial reuse, (iv) domestic reuse, and (v) groundwater recharge. The second category involves first use of reclaimed water for low-consumptive, high-quality purpose (i.e. industry)

Reclaimed Municipal Wastewater used for the Irrigation of Green Areas in Jeddah:…

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and second use for high-consumptive, lower-quality purpose (i.e. landscape). The feasibility of reusing reclaimed wastewater for these alternatives is dependent upon several factors including water quality requirements of each user, location of user, amount of demand, potential health risks, government regulations, and costs. Reclaimed wastewater is now widely accepted as an alternative source of water for wide variety of applications, including landscape and agricultural irrigation, toilet and urinal flushing, industrial processing, power plant cooling, wetland habitat creation, restoration and maintenance and groundwater recharge. In the Arabian Gulf countries, urban and landscape reuse continues to be a first priority among other reuse alternatives, especially in the large cities. This includes the use of treated municipal wastewater effluents for irrigating grass and shrubs within the urban community such as parks and highways for recreation, beautification and soil stabilization purposes. The second priority is agricultural reuse where the high consumptive demands by agriculture require considerable amounts of treated wastewater. Water reclamation and nonpotable reuse typically require conventional water and wastewater treatment technologies that are already widely practiced and readily available in many countries throughout the world. When discussing a treatment for a reuse system, the overriding concern continues to be whether the quality of the reclaimed water is appropriate for the intended use. Higher level uses such as irrigation of public-access lands require a higher level of wastewater treatment and reliability prior to its use. For example, in urban settings, where there is a high potential for human exposure to reclaimed water used for landscape irrigation, the reclaimed water must be clear, colorless and odorless to ensure that it is aesthetically acceptable to the users and the public at large, as well as to assure minimum health risk. Benefits and Constraints of Reuse of Recycled Water for Irrigation According to some water reuse specialists, benefits to be gained from the retrofit of landscape irrigation to recycled water reuse are numerous and may be greater than the benefits of agricultural irrigation.

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Many water reuse project planners would prefer landscape irrigation as an outlet for the recycled they will produce, rather than agricultural irrigation and especially irrigation of food crops. There are several reasons for this (Devaux, 1999). • Most irrigated landscapes are located within or adjacent to cities where effluent water is produced, so transportation costs are reduced. • Recycled water is produced continuously, and, depending on climate, the turf grass may be continuous (i.e. uninterrupted by cultivation, seeding, or harvest, all of which mean stopping irrigation for considerable periods). • Turf grasses absorb relatively large amounts of nitrogen and other nutrients often found in higher quantities in recycled water than in freshwater. This characteristic may greatly decrease the potential of groundwater contamination by use of recycled water. • Depending on recycled water quality, potential health problems arising from the use of recycled water would appear to be less common when water is applied to turf than when it is applied to food crops. • Social-related problems that might develop due to the use of recycled water would have less social and economic impact if they develop where turf is cultivated than if they develop where food crops are grown Geographic Considerations Four of the six Gulf Cooperation Council (GCC) countries, including Qatar, are rated among the 10 most water scarce countries in the world. Kuwait (10 m3 / person / yr), the UAE (58 m3), Qatar (94 m3) and Saudi Arabia (118 m3) rank first, third, fifth and eighth respectively in the world in terms of lowest domestic water availability per capita. Over the last quarter of a century there has been a three- to four-fold increase in population and total water use respectively. According to predictions from the Saudi Arabian Central Department of Statistics, the Kingdom's total population will exceed 29 million by 2010 and rise to 36.4 million ten years later. Taking a baseline consumption of 300 liters per person per day, the resulting demand for water will increase to over 3,000 million m³/year by 2010 and nearly 4,000 million m³/year by 2020.


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Being situated in an arid region, the Kingdom is getting most of its potable water through the highly expensive desalination industry. The need for potable water is increasing paralleling the spectacular increase of the population. In coastal cities such as Jeddah where the population increase rate is much higher than the inland cities, municipalities are facing two crucial water problems. The first is the necessity to increase potable water production to meet the needs, while the second is to manage the discharge of the increasing wastewater in order to protect the marine ecosystem. Having these objectives in view, the municipality of the city of Jeddah directs a part of the treated wastewater for the irrigation of green parks and landscapes. These areas represent recreation sites for the public which means that humans may come in direct contact with possibly contaminated soil and water. Public health may be threatened if water and soil were contaminated with chemicals such as heavy metals and pathogenic bacteria. High concentrations of heavy metals are frequently associated with urban wastewater either in the dissolved or the particulate form. Studies on the sediments of the coastal area of Jeddah have shown the presence of elevated concentrations of heavy metals such as Zn, Cu, Ni, Cr, and Pb in the areas of sewage dumping (El Sayed; 2002a; and Turki et al., 2002). The potential health hazard due to the accumulation trend of heavy metals Cd, Cr, Cu, Zn and Pb was revealed in soils irrigated with sewage. Objectives Not only nothing is known about the quality of the wastewater used in the irrigation of green parks and landscapes in Jeddah neither the quality of the soil itself but also, all our observations indicate that the used water is of very poor quality, smelling very bad and having dark color indicators of high load of solids and organic matter. It seems evident that the issue is of public concern and deserves a particular attention. This research is part of a comprehensive study on the chemical and bacteriological characteristics of the reused water and the irrigated soil; it aims at examination of the physico-chemical characteristics of the reclaimed water used for the irrigation of these sensitive areas.

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Materials and Methods Sample Collection Twenty water (treated municipal wastewater) samples were collected from twenty sampling stations selected to assure a good geographic cover of the city with particular interest given to areas the most frequently visited by the population (Fig. 1).

Fig. 1. Area of study and sampling location, twenty sites were selected representing areas frequently visited by the population.


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Analytical Methods Water samples assigned for the analysis of the chemical parameters, nitrogen species, and phosphorus were collected in appropriate polyethylene containers conditioned according to the recommended methods (Aminot and Kerouel, 2004). Dissolved oxygen samples were collected in the traditional oxygen bottles. Dissolved organic carbon and total nitrogen samples were collected in glass bottles previously heated for 4 hours at 400°C. All samples were directly collected in the sampling bottles from the irrigation lines. Samples were kept in ice boxes until returned to the laboratory for further processing and analysis. pH was measured in the field using calibrated pH meter with combined glass electrode, and dissolved oxygen was measured using the Winkler method. Ammonium was determined by the method of Koroleff (1969). Nitrite concentrations are measured using the Griess reaction applied to seawater by Bendschneider and Robinson (1952). Nitrate ions in the – sample were firstly quantitatively reduced to NO2 ions by passage on a cadmium-copper column. The method used for the analysis of nitrite was – – then applied to obtain the concentration of NO2 + NO3 . Reactive phosphate was measured by applying the method of Murphy and Riley (1962). Dissolved Organic Carbon (DOC) was measured using a total organic carbon analyzer TOC-VCPH – Shimadzu applying the non purgeable organic carbon technique (NPOC). Total nitrogen was determined using the TOC analyzer. The filtered water sample is introduced into the combustion tube where it is ignited at 720°C, the organic and inorganic nitrogen in the sample (excepting molecular nitrogen) are oxidized to nitrogen oxide NO. The nitrogen oxide gas is carried by the carrier gas, cooled and de-humidified. The NO is directed to the ozone generator where it is excited and then forwarded to a chemiluminescence gas analyzer where its concentration is measured. A calibration curve is prepared using potassium nitrate. Total nitrogen concentration in the sample represents the sum of the dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON). DON is obtained by subtracting DIN from TN.

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Samples for the analysis of trace elements Cu, Pb and Cd were collected in acid cleaned HDPP bottles. Samples were filtered on Nuclepore acid soaked membranes (0.45 µm pore diameter). Aliquots of the filtered samples were acidified to pH 2 and UV irradiated. Cu, Pb and Cd were measured in the treated samples using the Cathodic Stripping Voltametry technique CSV (Achterberg and Braungardt, 1999) using 8hydroxyquinoline (oxine) as complexing legand. Results and Discussion TSS, DO and pH Results of the analyses of water samples are presented in Table 1 and summarized in Table 2. Table 1. Results of physico-chemical characteristics of water of irrigation collected from 20 stations representing the different green areas frequently visited by the population.

1

O2 mg l–1 3.059

TSS mg l–1 27.3

7.12

POC % 42.5

2

1.61

25.6

7.26

42.0

St. no.

pH

3

2.898

42

7.28

32.9

4

2.737

26.5

7.44

45.9

5

0.805

39.5

7.34

42.9

6

2.576

126

6.72

44.7

7

0.00

641

7.25

40.4

8

0.00

40

6.52

50.2

9

0.00

135.7

6.84

34.1

10

0.00

34

6.88

45.0

11

0.00

21.5

7.37

30.0

12

1.93

10.4

7.47

35.6

13

5.15

20

7.82

35.4

14

2.74

31.5

7.64

29.1

15

7.57

0.8

7.38

14.0

16

8.05

0.75

7.33

15.5

17

3.06

6.6

7.58

30.0

18

7.89

12.2

7.52

22.2

19

4.03

15

7.31

29.0

20

0.00

48.7

7.63

34.1


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Table 2. Statistical values illustrating the variability of the measured parameters around their averages. O2 mg l–1

TSS mg l–1

pH

POC %

2.70

65.25

7.29

34.8

SD

2.68

140.13

0.33

9.9

Lowest

0.00

0.75

6.52

14

Highest

7.89

641

7.64

50

RSD%

99

215

4.5

28.4

Parameter Average

Total suspended solids (TSS) showed considerable variability in the irrigation water. TSS varied between 0.75 and 641 mg l–1 with an average of 65.25 mg l–1. This important variability (RSD 215%) is due to the presence of particularly high values at stations 6, 7 and 9. The following points may explain this variability: 1. Irrigation water comes from different treatment stations that produce water of different quality, 2. The storage time of the irrigation water in the on-site storage tanks is different permitting the advance of the settlement process to advance unequally at the different sites, 3. The storage tanks are not regularly purged; when the water level in the tank is very low the pumping system will bring to the surface water with high charge of TSS. The average TSS concentration for our set of samples is 65 mg l–1. Fourteen samples out of 20 (70%) have concentrations higher than 20 mg l–1. The removal of suspended matter is related to the virus issue. Many pathogens are particulate-associated and that particulate matter can shield both bacteria and viruses from disinfectants such as chlorine and UV radiation. To protect public health and to ensure proper discharge and reuse of effluent, draft standard were set and regulations issued by the Ministry of Agriculture and Water MAW and general standards by the Meteorology and Environmental Protection Administration (MEPA, 1989) now known as Presidency of Meteorology and Environment (PME). These standards fixed the concentration of TSS, for restricted irrigation at 15-20 mg l–1. This value was contested and considered unrealistic (Abu Reziza, 1999).

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The author considered that these standards do not permit quality levels of reclaimed water to be specified on the basis of local site conditions; nor do they take into account the types of application for which the water will be used and asked for more flexibility. However, the American Environmental Agency EPA has fixed the level of TSS for the safe application in controlled irrigation and green areas irrigation at 20 mg l–1 (USEPA, 2004). This standard is applied in different American states. Some states such as California, Atlanta, Georgia, Arizona, Florida and Texas, fix the TSS at a lower level 5-10 mg l–1 (Crook, 2006). Suspended material constitutes a support and a favorable ground for microorganisms. Organic carbon content was analyzed in the suspended particulate matter of the irrigation water (Tables 1&2). Analysis revealed that organic carbon content varied between 14 and 50%. This means that suspended matter rich in organic matter, is a favorable ground for bacterial growth including pathogenic species. Despite the absence of a frank correlation between the total bacterial count (TBC) and the concentration of TSS, it seems that samples with low concentrations have total bacterial count TBC (El Sayed et al., 2007). Dissolved oxygen (DO) showed also great variability (Tables 1&2). Concentration varied between nil and oxygen saturation, with an average of 2.7 mg l–1. 30% of the samples are totally depleted in dissolved oxygen and more than 85% have large oxygen deficiency. DO is one of the critical parameters that measures the oxidation state of the environment. Its concentration in reused water depends on organic content of the untreated sewage, aeration period, residual organic matter in the treated water and the residence period in the storage tanks. Neither in the Saudi regulations nor in the EPA guidelines had we found indications or recommendations for the oxygen content in the wastewater. pH measurements indicate that most of the water used in irrigation has a slightly alkaline character. pH values showed slight geographic variations. Values varied between 6.52 and 7.64 (Tables 1&2). pH values agree with values measured in the untreated sewage water of Al Khumra effluent (El Sayed, 2002b) and are situated inside the range of values fixed by the MAW (MEPA, 1989). Particulate organic carbon POC of the TSS varied between 14 and 50% and averaged 34.8% (Tables 1&2). If we suppose that C represents


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about 50% of the organic matter, this means that about 70% of the TSS is composed of organic matter. These values are slightly lower than the values measured in the untreated sewage which averaged 37.5% and varied between 28.5 and 60% (El Sayed, 2002b). This means that either the particulate organic matter is hardly degradable or no sufficient time is being given to the degradation process to be completed. It is worth mentioning that DO correlates negatively with POC (Fig. 2).

Fig. 2. Relationship between dissolved oxygen and the organic carbon content of TSS (POC).

Nutrient Elements, N, P and C Results of the analyses of the inorganic nitrogen species (NH4+, NO2–, NO3–) and phosphorus are given in Table 3 and a summary statistic is given in Table 4. Nitrogen The two major forms of nitrogen in reclaimed water are typically ammonium and nitrate. The concentrations and forms of nitrogen in the reclaimed water are strongly function of the treatment type. Secondary effluents contains ammonium nitrogen at concentrations up to 20 mg l–1 while denitrified effluents contained primarily nitrogen at concentrations less than 10 mg l–1. Ammonium nitrogen is the major form of oxygen demand in secondary effluents that are not nitrified.

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Table 3. Concentration of dissolved nitrogen and phosphorus (µmol l–1) and the N/P ratio in the wastewater samples. St. no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

NH4+ 203.14 753.66 672.70 513.73 1832.64 401.85 1920.96 1483.77 2163.84 1470.53 3429.70 2958.72 2576.00 1613.31 384.10 369.47 1586.82 426.88 1301.25 3628.49

NO2– 22.92 20.67 30.56 19.37 0.92 22.02 0.83 1.15 0.88 1.08 0.49 3.46 14.13 19.71 60.23 61.12 27.19 37.98 37.30 2.83

NO3– 682.18 563.43 538.14 404.13 13.78 34.08 19.74 0.13 0.23 0.55 0.10 7.01 14.73 366.39 431.48 494.38 522.81 435.02 378.50 2.45

TIN 908.24 1337.76 1241.40 937.23 1847.34 457.95 1941.53 1485.05 2164.95 1472.16 3430.29 2969.19 2604.86 1999.41 875.80 924.97 2136.82 899.88 1717.05 3633.77

PO43– 233.25 257.83 224.72 225.22 284.91 147.47 225.72 137.94 201.15 206.66 273.38 230.74 140.45 138.95 150.48 152.99 153.99 217.70 224.22 221.21

N/P 3.89 5.19 5.52 4.16 6.48 3.11 8.60 10.77 10.76 7.12 12.55 12.87 18.55 14.39 5.82 6.05 13.88 4.13 7.66 16.43

Table 4. Summary statistics of the data presented in table 3, all concentrations are in µmol l–1. Parameter

NH4+

NO2–

NO3–

TIN

PO43–

N/P

Average

1484.58

19.24

245.46

1749.28

202.45

8.90

SD

1053.85

19.04

251.67

882.66

46.92

4.58

Min.

203.14

0.49

0.10

457.95

137.94

3.11

Max.

3628.49

61.12

682.18

3633.77

284.91

18.55

Ammonium nitrogen showed wide variations. It varied between 203 and 3628 µmol l–1 with an average concentration of 1485 µmol l–1 (Tables 3&4). This value is comparable to the average concentration measured in the untreated sewage 1259 µmol l–1 (El Sayed, 2002a). The highest values were measured at stations 9, 12 and 20. Ammonium nitrogen represents the major part of the total inorganic nitrogen (TIN). It represents between 22 and almost 100% and averages 76.7% (Table 5).


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This value is also comparable to that measured by El Sayed (2002b) in the raw sewage (92%). Ammonium is the first nitrogen species of the mineralization of the organic matter. Ammonium nitrogen is not eliminated in the secondary treated effluents. In the presence of oxygen, ammonium is firstly oxidized to nitrite and its ultimate oxidation state is nitrate. This process is controlled by the availability of oxygen. Figure 3 shows the relationship between ammonium and DO; the two parameters are inversely correlated, the higher the concentration of ammonium the lower is the concentration of DO. Table 5. Participation (%) of the different inorganic nitrogen species in the TIN. –

–

St. no.

NH4+

NO2

NO3

1

22.37

2.52

75.11

2

56.34

1.55

42.12

3

54.19

2.46

43.35

4

54.81

2.07

43.12

5

99.2

0.05

0.75

6

87.75

4.81

7.44

7

98.94

0.04

1.02

8

99.91

0.08

0.01

9

99.95

0.04

0.01

10

99.89

0.07

0.04

11

99.98

0.01

0

12

99.65

0.12

0.24

13

98.89

0.54

0.57

14

80.69

0.99

18.33

15

43.86

6.88

49.27

16

39.94

6.61

53.45

17

74.26

1.27

24.47

18

47.44

4.22

48.34

19

75.78

2.17

22.04

20

99.85

0.08

0.07

Average

76.69

1.83

21.49

SD

25.65

2.2

24.08

Min.

22.37

0.01

0

Max.

99.98

6.88

75.11

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Fig. 3. A scatter diagram representing the relationship between DO and NH4+.

Nitrite–N follows ammonium nitrogen in the ascending series of the oxidation states of nitrogen. Nitrite concentrations averaged 19.24 µmol l–1 and varied between 0.5 and 61.1 µmol l–1. Intersite variability (Table 4) is very high, RSD attains 100%. Despite its presence in relatively high concentrations, nitrite-N represents only an average of 1.8% of the TIN. These results are in good agreement with the values published for the Al Khomra effluent (El Sayed, 2002b), where Nitrite-N concentrations averaged 22.5 µmol l–1 and varied between 1.1 and 63.4 µmol l–1. In the same effluent nitrite contributed 1.7% of the TIN. Nitrite appears to be negatively correlated to ammonium (Fig. 4), which may indicate that nitrite is mainly the product of the oxidation of ammonium-N. These assumptions are supported by the positive correlation between nitrite and DO concentrations (Fig. 5).

Fig. 4. Relationship between ammonium and nitrite distribution.


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Fig. 5. Relationship between DO and nitrite.

Generally, nitrate is the second nitrogen constituent in sewage effluents. In our study, NO3-N comes in the second in importance place after ammonium-N. Its contribution to the total inorganic nitrogen TIN varied between almost nil to an exceptional value of 75% and averaged 21.5% (Table 5). This contribution is significantly larger than the value of about 5% measured by El Sayed (2002b) in the almost untreated sewage of Al Khomrah effluent. It is worth mentioning that nitrate concentrations in the irrigation water were very high (Table 3) and showed very wide intersite variability (Table 4). Nitrate also appeared to be negatively correlated with ammonium (Fig. 6) which means that at least part of it is contributed by the oxidation of ammonium. The dispersion of the points may indicate that nitrate may have different sources and may reflect the temporal variability at the origin.

Fig. 6. A scatter diagram illustrating the reverse association between ammonium and nitrate.

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Regulations regarding the application of reused water in irrigation stipulate a maximum nitrate concentration of about 10 mg l–1 (MEPA, 1989). This value was never measured in our samples, which means that the application of this water in the irrigation of green areas does not represent any direct threat. Concentrations of organic nitrogen (ON) are obtained by subtracting the TIN concentration from the concentration of the TN. This nitrogen component constitutes about one fifth of the total nitrogen pool (Table 6), however, its participation may attain more than 50% in some particular cases (stations 4 & 8). Sixty percent of the samples have organic nitrogen fairly below 20% of the TN. Table 6. Concentration of TN, ON, %of ON in the TN dissolved organic carbon (DOC). St. no.

TN µmol l–1

ON µmol l–1

ON %

DOC mg l–1

1

1117

209

18.71

26.19

2

1825

487

26.68

33.47

3

1892

651

34.41

36.23

4

1963

1026

52.27

37.27

5

2672

825

30.88

10.37

6

862

404

46.86

29.63

7

2905

963

33.15

17.17

8

3275

1790

54.66

67.16

9

2494

329

13.19

12.89

10

2660

1188

44.66

34.78

11

3995

565

14.14

11.93

12

3323

354

10.65

9.06

13

2977

372

12.50

8.89

14

2280

281

12.32

8.49

15

986

110

11.16

3.49

16

965

40

4.15

3.16

17

2173

36

1.66

8.07

18

993

93

9.37

5.00

19

1792

75

4.19

6.26

20

3688

54

1.46

10.85

Average

2241.8

492.6

21.8

19.0

SD

954.9

464.1

17.3

16.4


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The results presented here show that the concentration of the individual species of nitrogen as well as the total nitrogen does not represent any direct threat to the health of the public that may come in contact with this water; concentrations are within the safe limits. However, nitrogen at these high concentrations may represent threat for the population and the environment if we consider the following points: 1) A considerable part of the water of irrigation will migrate in the ground and will join at any moment the ground water. This water, if pumped and used for potable purpose, it will represent a direct threat to pregnant women and very young children, 2) Ultimately, the ground water will reach the coastal area and mix with the coastal water resulting in the enrichment of this water with nitrogen which is considered as the limiting element for the marine primary productivity (Owens et al., 1989; Falkowski, 1997; Codispoti, 1997). The coastal waters off Jeddah are suffering episodic eutrophication while some regions are permanently showing signs of eutrophication evidenced by the permanent presence of algal mats. Phosphorus Phosphate concentrations varied geographically within narrow limits compared to all the preceding variables (Table 3&4). This fact could be attributed to the buffering action of the suspended matter; phosphate ions are known to have a great tendency to be fixed on the surface of the suspended particles. Phosphate concentrations are relatively high and varied between 138 and 285 µmol l–1 with an average of 202 µmol l–1. These values are considerably higher than those measures in the Khomrah effluent (El Sayed, 2002b); the average concentration in the Al Khomrah effluent is three times lower. We believe that this difference could be, once again, attributed to the buffering action of the suspended solids. The Al Khomrah effluent contained higher concentrations of suspended solids; all the samples had concentrations higher than 50 mg l–1, while the suspended matter concentrations in almost all the irrigation water samples were centered on 20 mg l–1.

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Phosphate concentrations varied proportionally to the variation of the TN (Fig. 7). The N/P atomic ratio varied between 3 and about 18, and averaged 8.9. N/P in the almost untreated sewage averaged about 16 which correspond to the ratio in the natural human secretions (El Sayed, 2002b). We cannot attribute this decrease to the loss of nitrogen through a probable denitrification process but rather to a significant phosphate concentration increase. The increase of phosphate concentration may be attributed to phosphate desorption from the particulate matter and/or mineralization of organic phosphorus.

Fig. 7. Relationship between TN and phosphate.

Carbon Dissolved organic carbon DOC concentrations in the filtered water samples varied between 3 and 67 mg 1–1 having an average of 19 mg l–1 (Table 7). Geographic distribution shows that stations 1-4, 6, 8 and 11 have relatively high concentrations. All these stations are situated at the northern part of the city and may receive their water from the same treatment station. However, excepting 2 samples where concentrations are higher than 50 mg l–1, all concentrations are below the maximum allowable level (Table 7). Organic carbon and nitrogen are highly correlated (Fig. 8), this implies that the OC/ON ratio varies within small limits.

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Fig. 8. Relationship between DOC and ON.

Water Quality and Regulations Table 8 shows the maximum permissible limit for the concentration of nitrogen and phosphorus in the reused water for irrigation according to the regulations in Saudi Arabia, Jordan and the United States. It appears clearly that concentrations are within the acceptable levels. However, it should be précised that the Saudi regulations do not present any guidelines for the application of wastewater to the public parks and that we considered that it is legitimate, due to direct exposure of the humans, to consider that the quality criteria imposed for the wastewater reuse for irrigation should be applied for this application. Table 8. Comparison of average levels of the physic-chemical parameters in irrigation water samples to maximum allowable levels for water reuse in irrigation. Country/parameter

TSS –1

mg l

65.25

2.7

mg l Average values for this study Saudi Arabiaa*

10

Jordanb

50

Water Environmental Federation (WEF)c USEPAd,e (for Florida) a

DO

8

–1

NH4+-N mg l

NO3–-N

–1

mg l

20.8

–1

3.4

Total N mg l

24.5

10 >2

10

45

–1

45

1

Phosphate mg l

–1

6.3

7.2 9

1**

6-9

15

6-9 5

10 b

mg l

pH

–1

19

2

5

TOC

5 c

d

MEPA, MAW (1989) for unrestricted irrigation, Government of Jordan (2003), WEF (1998), USEPA e (2004), Crook (2006). *It is not stated whether these standards apply for urban landscape irrigation, **direct discharge into coastal water.

140


Trace Elements Municipal wastewater may contain trace elements such as Cd, Pb and Cu at high concentrations. These elements may accumulate, through surface interactions, in the soil resulting in elevated concentrations. Direct exposure of humans to water or soil containing these elements may represent a health hazard. Concentrations of Cd, Pb and Cu in irrigation water, their average levels and associated statistical values as well are given in Tables 9&10. Table 9. Concentration of dissolved Cd, Pb and Cu (nM) in wastewater samples. St. no.

Cd

Pb

Cu

1

2.97

2.02

91.5

2

2.68

2.51

70.54

3

1.05

6.61

233.7

4

2.94

6.26

25.24

5

3.21

4.66

153.6

6

1.51

3.59

287.87

7

0.8

0.42

57.99

8

1.2

31.09

921.5

9

1.69

3.75

416.85

10

0.37

0.86

146.2

11

0.41

0.51

129.74

12

0.7

0.88

7.125

13

0.42

4.8

34.78

14

1.29

3.99

54.71

15

2.2

84.76

75.76

16

1.02

211.33

5.68

17

1.99

11.08

8.89

18

0.4

38.1

42.56

19

15.18

2.71

15.83

20

1.24

4.66

82.92


141

Table 10. Statistical values showing the range of variabilityof the dissolved trace elements (nM). Cd

Pb

Cu

Average

2.16

21.23

143.15

Min.

0.37

0.42

5.68

Max.

15.18

211.33

921.5

S.D.

3.20

48.98

211.36

Presence of Cd in the water samples may indicate the presence of wastewater of industrial origin. Cd concentrations varied between 0.4 and 15.18 nmol l–1 (45×10–6 - 17×10–4 mg l–1) with an average of 2.16 nmol l–1, highest values are present in samples representing the northern zone of the city. Lead is present in all the samples. The presence of lead may result from either mixing with industrial wastes or it may come from vehicle’s exhaust that may be washed out and mix with the sewage in the collection network. Lead concentrations varied between 0.42 and 211 nmol l–1 with an average of 21.23 nmol l–1 (93×10–6-44×10–3 mg l–1). Lead concentrations were lower than 10 nmol l–1 (2×10–4 mg l–1) in 80% of the samples. The highest Lead values were measured at stations covering the southern part of the city. Copper is the most abundant trace element in the irrigation water. It is present at highly variable concentrations. The highest concentration (921.5 nmol 1–1/56.6×10–3 mg l–1) was measured at station 8 while the lowest one (5.68 nmol l–1/361×10–6 mg l–1) was recorded at station 16. The average copper concentration (143.15 nmol l–1/ 9.1×10–3 mg l–1) is about seven times higher than that of lead and about 66 fold that of Cd. No correlation was found between any of the three elements and the others. This is not surprising since their presence is determined by their chemistry and the characteristics of the medium. For example, lead is known for its great affinity to the solid particles; in a medium such as the wastewater where suspended solids are abundant a great part of lead will leave the solution and fix on the surface of the particles. The extent of

142


this process will depend on the nature of the particles and the pH of the solution. Cd has also high affinity to solid particles; however it forms highly stable chloro-complexes. If chlorination is practiced for the disinfection of the wastewater, Cd will tend to stay in solution rather to form surface complexes. Copper has a very high affinity to the dissolved organic matter. In seawater, copper-organic complexes account for more than 99% of the total dissolved copper (Van Den Berg, 1984; Seritti et al., 1986; El Sayed and Aminot, 2000, Al Farawati and El Sayed, 2005). In this organic rich medium, which is the wastewater, it is expected that copper concentrations will be enhanced by the formation of stable organo-copper complexes. Examination of the relationship between dissolved copper concentrations and the concentrations of TOC and DON reveal the existence of a fairly good agreement between the three parameters (Fig. 9).

Fig. 9. Relationship between dissolved copper and organic nitrogen ON and dissolved organic carbon DOC.

Average concentrations of trace elements were compared to reference levels fixed in the Saudi regulations and references used in Jordan and those fixed by the EPA (Table 11). It is clear that concentrations in the irrigation wastewater of the measured trace elements are largely below the limits fixed in the regulations and; the application of this water in irrigation does not represent any health hazard for the humans. However, the continuous application may result in the


143

progressive accumulation of these elements in the soil to levels that may represent a real health risk. Table 11. Comparison of average levels of Cd, Pb and Cu (mgl–1) in irrigation water samples to maximum allowable levels for water reuse in irrigation. Reference / element Irrigation water Saudi Arabia Jordan

a

b

c

EPA a

b

Cd mgl–1

Pb mg–1

Cu mgl–1

0.0003

0.0044

0.009

0.01

0.10

0.40

0.01

0.10

0.20

0.01

5.0

0.2

c

MEPA (1989), Government of Jordan (2003), U.S. Environmental Protection Agency (2004).

Conclusion Analysis of the treated municipal wastewater of Jeddah city, collected at different geographic locations showed that the concentrations of the elements nitrogen, phosphorus and carbon as well as the trace elements lead and cadmium are below the limits fixed for the use of these waters for agricultural irrigation. No regulations are fixed by the municipality for the reuse of the reclaimed municipal waters for the irrigation of the green areas and public parks. However, this does not mean that the use of these waters is completely safe; a complementary study should be done to investigate the bacterial contamination of the water and soil particularly with the pathogenic bacteria. Water and soil should also be analysed for other chemical contaminants that represent an important health hazard such as aromatic and chlorinated hydrocarbons. Acknowledgements This research has been financially supported by the Deanship of Scientific Research, King Abdulaziz University, Grant No. 255/27H. References Abu-Reziza, O.S. (1999) Modification of the standard of wastewater reuse in Saudi Arabia, Water Res., 33: 2601-2608. Achterberg, E.A. and Braungardt, C. (1999) Stripping voltametry for the determination of trace metals speciation and in-situ measurement of trace metal distribution in marine waters, Anal. Chem. Acta., 400: 381-397.

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Al Farawati, R.Kh. and El Sayed, M.A. (2005) Copper Speciation in the Coastal Water of the Red Sea Using Cathodic Stripping Voltametry, Report KACST, p. 58. Aminot, A. and Kerouel, R. (2004) Hydrologie des Ecosystems Marins, Parameters et Analyses, Ifremer, Brest France, 336 p. Bendschneider, K. and Robinson, R.J. (1952) A new spectrophotometric method for the determination of nitrite in seawater, J. Mar. Res., 11, 87-96. Codispoti, L.A. (1997) The limits to growth, Nature, 187: 237-238 Crook, J. (2006) Over view water reuse, Retrieved: 01, 18, 2007, from http:/www.gadnr.org/DocumentsOverviewWaterReuseJimCrook.pdf. Deveaux, I. (1999) Devaux, I., 1999. Intérêt et Limites de la Mise en Place d’un Suivi Sanitaire dans le Cadre de la Réutilisation des Eaux Usées Traitées de l’Agglomération Clermontoise. PhD thesis; Université Grenoble I ; Grenoble ; France. El Sayed, M.A., Niaz, G.R., Basaham, A.S. and Ghanem, Kh.M. (2007) Study on Chemical and Bacteriological Contamination of Green Areas and Landscapes, in Jeddah, Irrigated with Treated Sewage, KAU, IRC, grant 255/427, 86 p. El Sayed, M.A. (2002a) Factors controlling the distribution and behavior of organic carbon and trace elements in a heavily sewage polluted coastal environment, JKAU: Mar. Sci., 13: 2146 El Sayed, M.A. (2002b) Nitrogen and phosphorus in the effluent of a sewage treatment station on the eastern Red Sea coast: daily cycle, flux and impact on the coastal area, Internat. J. Environm. Stud., 59: 73-94. El Sayed, M.A. and Aminot, A. (2000) C18 Sep-Pak extractable dissolved organic copper related to hydrochemistry in the North-west Mediterranean, Estuar. Coast. Shelf Sci., 50: 835-842. Falkowski, P.G. (1997) Evolution of the nitrogen cycle and its influence on the biological sequestration of the CO2 in the ocean, Nature, 387: 273-275. Government of Jordan. (2003) Technical Regulation for Reclaimed Domestic Wastewater. JS893/2002, Jordan Institution for Standards and Meterology, Amman, Jordan. Hamoda, M.F. (2004) Water strategies and potential of water reuse in the south Mediterranean countries, Desalination, 165: 31-41. IWMI (2000) Global water scarcity study, Retrieved: 01,25, 2007, from http://www.jwmi.cgiar.org/home/wsmap.htm. MEPA (1989) Environmental Protection Standards (General Standards) Doc. No 1409-01. Meteorology and Environmental Protection Administration, Ministry of Defence and Aviation, KSA. Murphy, J. and Riley, J.P. (1962) A modified single solution method for the determination of phosphate in natural waters, Anal. Chim. Acta, 27: 31-36. Owens, N.J.P., Rees, A.P., Woodward, E.M.S. and Mantoura, R.F.C. (1989) Size fractionanted primary production and nitrogen assimilation in the northwest Mediterranean Sea during January 1989, Water Pollut. Rep., 13: 126-135. Seritti, A., Pellegrini, D., Morelli, E., Brghigiani, C. and Ferrara, R. (1986) Copper complexing capacity of phytoplanktonic cell exudates, Mar. Chem., 18: 351-357. Turki, A. J., El Sayed, M.A., Basaham, A.S. and Farawati, R.K. (2002) Study on the Distribution, Dispersion and Mode of Association of Some Organic and Inorganic Pollutants in a Coastal Lagoon Receiving Sewage Disposal, KAU, SRC, Grant No. 253/421, 123 p. U.S. Environmental Protection Agency (USPMA) (2004) Guidelines for Water Reuse, 274 p. Van Den Berg, C.M.G. (1984) Determination of complexing capacity and conditional stability constants of complexes of copper Cu (II) in seawater by cathodic stripping voltametry of copper-catechol complexes, Mar. Chem., 14: 201-212. Water Environment Federation (WEF), Alexandria, VA, USA (1998) Using Reclaimed Water to Augment Potable Water Resources, 347 p.


145

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