Desalination,73 (1989)27-36 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

27

TREATED WASTEWATERS AS A GROWING WATER RESOURCE' FOR AGRICULTURE USE

I.S. Al-Mutaz

Chemical Engineering Department, King Saud University, P.O.Box 800, Riyadh 11421, Saudi Arabia.

ABSTRACT

About 72% of the 1985 Saudi Arabia water consumption was for agriculture

purposes. Wastewater treatment supply only 5% of the 1985 Saudi water balance.

By the year 2000, wastewater would account for over than 20% of the total water

supply.

This paper will discuss the contribution of the treated wastewater as an

important water resource for agriculture uses. The Saudi Arabian case will be

investigated. A breif description of the major wastewater treatment plant in

the country will be presented.

INTRODUCTION

The initial attempts for treatment of municipal wastewater was made in

Paris in 1970. Not till 1875 when hundreds of commercial treatment processes

were available. The United Kingdom started its earlier wastewater reclaimation

programs in 1880-1890. In the United States, wastewater treatment did not

receive much attention up to 1886. By 1933, the reuse of wastewater became a

common practice all over the world. There were about 5786 wastewater treatment

plants in USA only in 1945(I). Great attention has been paid to this growing

source of water. Figure 1 shows the intentional reuse of water.

The reuse of municipal wastewaters for irrigation is the oldest and largest

reuse. Health consideration are minimal for irrigation of non-food crops.

Advance treatment of wastewaters is not strictly required. The advantages of

using treated wastewater for irrigation are(21:

- Low-cost source of water.

- An economical way to dispose of wastewater to prevent pollution and sani-

tary problem.

- An effective use of plant nutrients contained in wastewater.

- Providing additional treatment before being recharged to the ground water

reservoir.

OOll-9164/89/$03,50OElsevier SciencePublishersB.V.

6000

5000

x 1000

d

5 E 3000

CT

kl 2000

e

1000

a

Figure 1: Possible Municipal Wastewater Reuse

ng?Y _,” /’

YVA”’ _//---zc

7-----1 -----r------- I 1975 1980 1985 1990 1995 2000

YecJr

Figure 2: Municipal and Agriculture Water Demand Model

in Saudi Arabia.

29

In the following sections, the benefits of reusing treated wastewater in

Saudi Arabia for agricultural purposes will be discussed.

SAUDI WATER DEMAND SUPPLY

The project water demand in Saudi Arabia is 5724 million m3/day in 1990 and

6523 million m3/day in 2000. Agriculture accounts for more than 80% of the

water consumption. Agriculture consumption rose from less than 2000 million

m3/day in 1980 to 7430 million m3/day in 1985. Figure 2 shows the Saudi demand

model for municipal and agriculture sectors while Table 1 below lists the total

Saudi projected water balance.

Table 1

Projected Water Balance in Saudi Arabia

Water Resourcs 1980

Non-renewable 3450

Renewable 1145

Desalination 63

Urban Waste _-

Water Utilization

Urban and Industry

Rural and Livestock

Irrigated agriculture

Surplus

502

27

1832

2247

Total Resources 4658

Total Utilization 4658

(Million m3/year)

1985 1990

3450 3450

1145 1145

605 794

140 335

828 1211

28 31

1873 2345

2611 2137

5340 5724

5340 5724

2000

3450

1145

1199

730

2279

38

3220

986

6523

6523

Water demand in major Saudi cities is growing in accordance with the vast

population growth and the implementation of industrial projects. The major

source of water supply in the country is underground water. It has two types,

replenished and non-replenishable. Replenishable ground water with an average

age of 10 years has a volume of more than 200 million m3. It is mainly found

in the central part of Saudi Arabia. A proven reserve of 338 billion m3 of

non-renewable subsurface water is estimated which may be formed some 20,000

years ago.

30

Desalination is considered the other alternative for supplying fresh water

in Saudi major cities. The present capacity of desalted seawater in Saudi

Arabia is 1.82 million m3/day (480.5 mgd) with an addition of 307,400 m3/day

(81.14 mgd). This only accounts for some 11% of the total water demand. The

water demand for major Saudi cities is presented in Table 2 below.

Table 2

Water Demand of Major Saudi Cities

(Thousand m3/year)

Year Riyadh Jeddah Mekkah

1975 I47 54 33

1980 205 120 80

1985 270 180 100

1990 315 210 130

2000 420 280 170

THE WASTEWATER TREATMENT SOLUTION

The growing agriculture water demand in Saudi Arabia is due to the recent

attention the government has paid toward agriculture activities. Saudi Arabia

now attains sulf-sufficiency of national wheat production. Surplus wheat being

exported to Europe and nearby countries. The annual wheat production was

141,732 tons in 1980. It was increased to 2,048,OOO tons in 1985, about 1350%

increase. Besides wheat, other products like barlely, tomatoes, squash,

eggplant, okra, carrets, onions and cucumber were planted in Saudi Arabia. .The

total cultivated areas of the winter crops was 3,080,428 Donums in 1982 which

increased to 7,105,632 Oonums in 1985 representing an increase rate of 131%.

This vast agriculture water requirements can be obtained from the treated

wastewater specially for non-food products. The expected municipal wastewaters

from different Saudi cities is shown in Table 3. Small fraction of these

waters is now treated in Riyadh, Jeddah and Madina.

31

Table 3

Available Wastewaters in Saudi Arabia

(Thousand m3/day)

City 1990 2000

Riyadh 292 456

Jeddah 271 441

Mecca 112 184

Madina 61 101

Taif 51 75

Dammam 65 122

Other cities 270 583

Total 1123 1962

Riyadh wastewater treatment plant is the first large plant in operation in

the country since 1972. It was designed for a 40,000 m3/day capacity on average

which expanded later on to 80,000 m3/day in 1980 and then to 200,000 m3/day in

1982. The maximum plant capacity is 370,000 m3/day. This rapid expansion is

due to the fast growth of the city. Riyadh population was about 665,000 in

1974. Now it approaches one million and expected to be about two millions in

the year 2000.

These are other small wastewater treatment plants in Riyadh in certain

housing areas solely for landscape irregation purposes inside the housing

complexes. These includes the following:

- Ministry of Foreign Affairs Housing (MFA) with a capacity of 1,135 m3/day.

- Diplomatic Quarter with a capacity of 9,000 m3/day.

- Kharj Road sewage treatment plant with an initial capacity of 172,800m3/day

- King Saud University Housing with an ultimate capacity of 10,000 m3/day.

The quality of Riyadh wastewaters is displayed on Table 4. Generally, the

raw water quality and the required quality of the produced treated water play

an important role in process selection and in combination of processes. Figure

3 shows the possible treatment processes for each wastewater contamanents.

Figure 3: Typical

Wastewater Treatment

Processes

33

Table 4

Typical Composition of Riyadh Wastewater, mg/L

Constituent -

Concentration

Influent Effluent

Total dissolved solids

Suspended solids

Settleable solids (mL/l)

BOD5, 200C

COD

Ammonia - nitrogen

Nitrates as nitrogen

Phosphates

Chlorides

Alkalinity

Grease

Temperature, oC

Free available chlorine

Total chlorine residual

PH

Dissolved oxygen

Alkyl benzene sulfonates

Total coliforn

1300

250

3

200

450

25

10

190

200

100

29

0

0

7.3

0

12-20

Millions/mL

1100

35

ND

30

90

25

-1

10

210

190

10

27

0.8

"4.0

7.4

5

-5

50-lOO/lOO mL

Historically, Riyadh wastewater treatment plant was essentially built to

satisfy the Riyadh oil refinery with three grades of waters; (1) utility water

for hose station and fire fighting, (2) process water crude oil desalting pro-

cess and cooling water, (3) boiler feedwater, the highest grade water. The

balance was decided to be made available for agricultural irrigation at Dirab

and Dariyah, small villages near Riyadh. About 92,000 m3/day are pumped to

Dirab and 70,400 m3/day to Dariyadh.

The Riyadh wastewater treatment plant incorporates preliminary, primary,

secondary and chlorination treatment. It has a high rate trickling filter

system with random fill plastic media, followed by two aerated lagoons and

chlorination. Sludge treatment is by anaerobic digesters followed by drying on

sand drying beds. The latest plant expansion will has tertiary treatment. The

secondary treatment is done by an activated sludge system with nitrification -

denitrification process. The tertiary treatment consists of sand filtration

and chlorination. Table 4 also shows the composition of the treated wastewater

effluent from Riyadh sewage treatment plant. The proposed Saudi standards for

wastewater effluents as well as the FAO and USA EPA quality quidlelines for

unrestricted irrigation are shown in Table 5(S).

Generally, the physical and chemical characteristics of Riyadh treated

wastewater are within the standards required for unristricted irrigation. It

must be mentioned that the effluent analysis of Table 4 was before the opera-

tion of the tertiary treatment of the recent plant expa"sion. With regard to

nitrates and phosphate, K. Al-Dhowalia et al(4) had found high concentrations

of these components. However, these constituents are essential plant nutrients

and contribute to plant growth.

Finally, from sanitary viewpoint no crops which come in contact with sewage

should be irrigate with treated wastewater. Also no crops that eaten raw or

that do not have skin to be removed before eating are allowed to be cultivated

on a sewage farm. In Dariyah and Dirab, wheat, fodder, date palms and some

vegetable are grown.

CONCLUSIONS

Saudi Arabia is planning for establishing wastewater treatment facilities

in major cities. These facilities mainly use tertiary processes that have

biological systems and disinfection equipments. The treated wastewaters are

solely used for irrigation purposes.

Water demand in irrigation in Saudi Arabia accounts for 80% of the total

demand. If this partially satisfied by the treated wastewater, a considerable

saving in water demand would be accomplished. Wastewater treatment plants pro-

vide both suitable irrigiation water and safe environment as well as supplying

essential plant nutrients.

35

Table 5

Water Quality Standards for Unrestricted Irrigation

Parameter

Maximum contaminant level (MCL), mg/L

Proposed EPA - Saudi FAO Agricultural Landscaping

Standards

BOD

TSS

Aluminium

Arsenic

Beryllium

Boron

Cadmium

Chromium

Cobalt

Copper

Cyanide

Fluoride

Iron

Lead

Lithium

Manganese

Mercury

Molybdenum

Nickel

Selenium

Vanadium

Zinc

pH in units

Oil and Grease

Phenol

Fecal coliform

Turbidity

Chloride

Sulfate

Nitrogen

10

10

5

0.1

0.1

0.7

0.01

0.1

0.05

0.4

0.05

2.0

5.0

0.1

2.5

0.2

0.001

0.01

0.2

0.02

0.1

4.0

6.0-8.4

Absent

0.002

MPN 2.2/10OmL

2.2 NTU

280

10

Sodium adsorption ratio - 8-18

5.0

0.1

0.1

0.75

0.01

0.1

0.05

0.2

5.0

0.1

0.1

20

15

5.0

0.1

0.1

0.01

0.1

0.05

0.2

0.01

0.1

0.05

0.2

1.0 1.0 2.0

5.0 5.0 5.0

5.0 5.0 5.0

2.5 2.5 2.5

0.2 0.2 0.2

0.01

0.2

0.02

0.2

2.0

0.01

0.2

0.02

0.1

2.0

MPN 1000/100mL

0.01

0.2

0.02

0.1

2.0

6.0-9.0

Nil

50

MPN 2.2/100mL

100-200

200-400

36

REFERENCES

1. G. Tchobanoglous, "Wastewater Engineering: Treatment, Disposal, Reuse",

Tata McGraw-Hill, New Delhi, 1984.

2. H.I. Shuval, "Water Renovation and Reuse", Academic Press, New York, 1977.

3. N.K. Shammas, and A.M. El-Rehaili, "Tertiary Filtration of Wastewater for

Use in Irrigation", The Symposium on the Effect of Water Quality on the

Human Health and Agriculture in The G.C.C. States Al-Khobar, Saudi Arabia,

October, 1986.

4. K. Al-Dhowalin, D.R. Rowe and A. Whitehead, "Utilization of Riyadh Treated

Wastewater", The symposium on the Effect of Water Quality on the Human

Health and Agriculture in The G.C.C. States, Al-Khobar, Saudi Arabia,

October, 1986.