Document(s) 17 of 19

Abstract

With per capita freshwater availability of around 450 m³, Tunisia is one of the most drought-stressed countries in the Middle East and North Africa (MENA) region. In the MENA region, and indeed worldwide, Tunisia along with Israel, has been recognised as a leader in the area of wastewater reclamation and use. This chapter presents the case of a middle-income country that has pursued a conscious strategy of treated wastewater reuse in agriculture with a fair measure of success. The current status of wastewater treatment and the use of treated wastewater in agricultural irrigation are reviewed. The impacts of water quality are discussed in this context, and the institutional, legal, and economic aspects analysed. The final section presents the lessons learned from the Tunisian experience and the options and hurdles for expanding the scope of treated wastewater use in agriculture. The key findings are that despite strong government support, treated wastewater use in irrigation has faced several constraints, chief among them being problems of social acceptance, agronomic considerations and sanitation, and restrictive regulations that have tended to limit its full potential for development. Further, the multiplicity of agencies and overlapping institutional responsibilities have also tended to limit the potential for expansion. Through its carefully phased approach to treated wastewater use and the concomitant development of a regulatory framework that prohibits untreated wastewater use, Tunisia has significantly mitigated the environmental and public health risks associated with untreated wastewater use elsewhere in the world.

Background

Tunisia is a middle-income country located on the southern rim of the Mediterranean Sea with a population of approximately 10 million that is growing at about 1.8% per annum. Annual per capita income is around US$4,250 (World Development Report, 2002). Tunisia has a semi-arid climate and few renewable natural resources. It occupies 165,000 km² with the Atlas mountain range in the north accounting for 25% of the area. The Central Steppe and Sahel regions make up another 25% and the Southern Sahara region 50%. The annual rainfall varies from 600 mm in the north (400 mm in Tunis) to 100 mm in the southern region. The population is relatively urbanised, with 58% living in urban areas on the northern and eastern coast. Administratively, Tunisia is divided into 23 governorates, 136 counties, and 250 communes.

Water Resources and Quality

The annual total volume of exploitable water resources in Tunisia is about 4670 million cubic metres (MCM) of which about 57% (2,700 MCM) is surface water and the remaining 43% (1970 MCM) groundwater. Tunisia is a drought-stressed country with per capita renewable water availability of 486 m³ – well below the average of 1,200 m³/capita for the Middle East and North Africa (MENA) region. Of the available surface water resources of 2,100 MCM, only about 1,220 MCM are expected to be captured for actual use. Eighteen existing dams, 21 projected dams, and 235 hillside dams are expected to augment the available supply but rapid sedimentation of reservoirs will progressively reduce storage capacity and shorten life. Deep groundwater extraction rates are currently at 73% of annual recharge, and shallow groundwater is at 97% in the coastal and central regions. Excessive groundwater extraction in the coastal regions of Cap Bon, Soukra, and Ariana has resulted in saline intrusion in many areas leading to groundwater being rendered unsuitable for further irrigation. Water quality, especially salinity, is a serious constraint. Only 50% of all water resources have salinity levels lower than 1,500 mg/l and can be used without restrictions. While the surface water has a generally low salinity (with the exception of the tributaries entering the Medjerda river from the south), groundwater resources are badly affected with 84% of all groundwater resources having salinity levels of more than 1,500 mg/l and 30% of the shallow aquifers more than 4,000 mg/l. World Health Organization (WHO) Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture (1989) specifies considerably lower limits for potable water. This saline irrigation water reduces crop yields and requires the installation of costly drainage systems to maintain soil fertility. The effect of salinity on the water balances is an important consideration for Tunisia’s water resource planning (World Bank, 1994). As in most other countries, agriculture accounts for the bulk of water consumption (89%) with domestic use accounting for 8% and industrial use 3%.

Tunisia has also experienced three serious droughts in the last decade that have affected agricultural growth and domestic consumption. With an increasing population, rapid urbanisation, and rise in living standards developing additional water resources is imperative. The last three Five-Year Plans (Government of Tunisia, 1987, 1992, 2002) have emphasised water harvesting and treated wastewater use. Since the severe drought in 1989, the use of treated wastewater in irrigation has been a part of the Government’s overall water resource management strategy. As seen in Table 15.1, treated wastewater use and desalination are both expected to virtually double in the coming years.

Current Status of Wastewater Treatment

About 70% of the urban population is connected to a sewerage network but among the rural population only 20% are connected. The number of wastewater treatment plants (WWTPs) has gradually risen in the last decade and is expected to reach 83 by 2006 (Table 15.2). Currently, 61 WWTPs are in operation with 9,650 km of wastewater network collecting 178 MCM wastewater, 148 MCM of which are treated and used in agriculture, to water golf courses and for other purposes. Almost 83% is treated in 44 WWTPs by activated sludge, 0.5% is treated in 3 WWTPs by biological filters, 7.6% in 7 plants in natural lagoons, and 8.6% in 7 plants in aerated lagoons (Koundi, 2001). Effluent is treated to the primary and secondary levels.

Table 15.1. Projected water resources in Tunisia – accessible (A) and available (B) (MCM/annum) for different time horizons (1998).

Source: Bahri, 2000.

Table 15.2. Evolution in number of wastewater treatment plants in Tunisia, 1995–2006.

Source: Ministry of Agriculture, 1998.

Treated Wastewater Use in Agriculture

Tunisia has had a cautious and gradual approach to applying treated wastewater in irrigation. Since 1965, wastewater from the Charguia WWTP has been used to irrigate citrus orchards in the Soukra irrigation scheme covering 1,200 ha (now reduced to 600 ha due to urbanisation) north of Tunis in order to safeguard them from saline intrusion caused by the overexploited aquifer. However, it was not until 28 July 1989 with the passage of the Decree 89-1047 setting conditions for the use of treated wastewater for agricultural purposes, that the use of treated wastewater in irrigation really expanded in a controlled manner (Ministry of Agriculture, 1998). This Decree set the conditions for the use of treated wastewater in agriculture. In addition to the institutional aspects, the Decree also specified the modalities for control of quality including the necessary physicochemical parameters, microbiological parameters and the frequency of monitoring (Ministry of Agriculture, 1998). The main legal framework is also contained in the Code des Eaux (Water Code) dating back to 1975. As Table 15.3 shows, use in irrigation and golf courses is predominant. However, only about 35 MCM of treated wastewater is currently used on about 6,500 ha mainly (55%) in the area surrounding Tunis which represents about 20–30% of the volume produced. It is estimated that by 2020 about 20,000–30,000 ha, or about 7–10% of total irrigated area, will be irrigable using treated wastewater (World Bank, 1997; Ministry of Agriculture, 1998).

Table 15.3. Categories of treated wastewater use in Tunisia.

Source: Ministry of Agriculture, 1998.

Effluent Water Quality and Impacts of Treated Wastewater Use

In Tunisia the quality of treated wastewater varies spatially with the lowest salinity found in the northwest (min. 1,000; max. 1,500; average 1,300 mg/l) owing to the good quality of surface water resources and the low level of industrial activity in that region. By contrast, the WWTPs in the south exhibit alarmingly high concentrations of salt due to the salinity of the distribution waters and the presence of important industries that dispose of their wastes in certain stations (min. 2,700; max. 8,900; avg. 4,100 mg/l) (see Table 15.4). This is a major problem for the farmers who express concerns about the long-term impacts on their soils and crops. Around Moknine, the high salinity of the treated wastewater supplied by the National Sanitation Agency [Office National d’ Assainissement] (ONAS) resulted in serious soil degradation. In order to drain the salts from the soil and to provide compensation, the farmers in that area now receive free conventional water from the neighbouring Nebhana dam. A high rate of suspended solids exceeding the norm of 30 mg/l in many cases has also been reported, with associated discoloration of the water. This has also led to complaints about clogging local irrigation systems, and poses a constraint to farmers adopting drip irrigation.

Table 15.4. Average quality of treated wastewater in different regions of Tunisia, 1996.

Source: Calculated from Ministry of Agriculture, 1998.

Evidence of microbial contamination exists and poses a health and sanitary risk to both farmers and consumers. A 1985 study jointly carried out by the Ministries of Agriculture and Public Health evaluated the impact of treated wastewater on crops and human health in the Soukra, Borj Touil, and Djebel Ammar areas. The study revealed 141 cases of gastrointestinal (GI) disease (21% of the surveyed Soukra population). Some of the diseases could be related to treated wastewater use, but the study was not exhaustive enough to clearly identify the sources. In 1990, a study carried out by the regional health and agricultural authorities of Ariana in Borj Touil recommended strict control of wastewater use in the Soukra and Borj Touil regions (UNDP et al., 1992). An ONAS survey carried out in 1992 pointed to a lack of information amongst farmers about wastewater quality, health risks related to wastewater use and impacts on crops and soils. Farmers do not systematically receive health education concerning the risks they incur, nor do they adopt the preventive measures that are advocated by the public health service. The Ministry of Public Health does not have the necessary means or organisation to effectively supervise the use of treated wastewater in irrigation. Implementation of effective disinfection for reclaimed wastewater effluents using maturation ponds or high-rate ponds could reduce the public health risks. This would also eliminate the need for extensive and complex epidemiological studies to assess the health status of populations using treated wastewater for irrigation or living within the irrigated areas (Asano and Mujeriego, 1992).

Water Quality Standards and the Legal Framework

Treated wastewater use in agriculture is regulated by the 1975 Water Code and associated Decree No. 89-1047 (Ministry of Justice and Human Rights, Republic of Tunisia, 1989). The Water Code prohibits use of untreated wastewater in agriculture and restricts the use of reclaimed water for irrigation of any vegetable to be eaten raw. The use of secondary treated effluents for growing all types of crops except vegetables, whether eaten raw or cooked is allowed. Water quality criteria for treated wastewater use in agriculture have been developed using the 1989 WHO Guidelines as the basis and a list of crops that can be irrigated has also been established. According to the 1989 Decree No. 89–1047, treated effluent can only be used to irrigate crops that are not directly consumable. No vegetables can be irrigated with treated wastewater. The main crops irrigated with treated wastewater are: fruit trees including citrus, grapes, olives, peaches, pears, apples, pomegranates, etc. (28.5% by area); fodder including alfalfa, sorghum, clover, etc. (45.3%); industrial crops such as sugarbeet (3.8%); and cereals (22.4%). 57% of the area equipped with irrigation facilities is sprinkler-irrigated and 48% surface irrigated. Water quality standards have also been established for wastewater disposal in receiving waters (seas, lakes and rivers). According to Bahri (2000), monitoring the quality of treated water for a set of physical-chemical parameters once a month, for trace elements once every 6 months, and for helminth eggs every 2 weeks was originally envisaged. However, due to organisational and capacity constraints in the Ministry of Public Health, such monitoring is not systematic. Nonetheless, unlike other countries of the Middle East (e.g. Syria and Egypt), there is no evidence of the widespread use of untreated wastewater in agriculture. Compliance with existing restrictions on cropping patterns is relatively good. This is facilitated by the fact that the bulk of the wastewater (over 50%) originates in the capital Tunis, which is relatively small (population approximately 1 million) allowing the effective enforcement of existing guidelines. In small and medium-sized towns, ONAS is currently developing an indigenous low-cost technology for treatment but coordination with the new Ministry of Agriculture, Environment, and Water Resources, that was formed in 2002 when the Ministries of Agriculture and Environment merged, to determine market demand from farmers is still limited.

Economic and financial aspects of wastewater treatment

ONAS, which is responsible for the collection, treatment, and the disposal of wastewater, faces varying costs of treatment depending on the age and type of the plant, its location, and capacity with a high of US$0.51/m³ (Menzel Bouzelfa WWTP in the northeast; 1995; capacity 2065 m³/day) to a low of US$0.02/m³ (Dar Jerba WWTP in the south; 1972; capacity 1100 m³/day). These costs include the investment,¹ and operations and maintenance (O&M) costs. The average cost of secondary treatment is estimated at US$0.14/m³ but a study commissioned by ONAS in 1996 estimates that this will more than double to US$0.29/m³ in the next 5 years or so, owing to the high costs of new investments (Ministry of Agriculture, 1998).

¹ Capital costs amortised over 45 years with an interest rate of 7%; equipment amortised over 15 years at 7%.

In Tunisia, the price charged by the Commissariat Régional du Développement Agricole (CRDA), the Regional Commissioner for Agricultural Development, for the water supplied for irrigation (conventional and treated wastewater) varies by governorate. Usually the price of water includes the costs of conveyance, O&M, but not of investment. In the northern CRDA of Ariana, generalised irrigation costs are determined by the overall price of O&M, irrespective of whether the specific source is treated wastewater. In 1996, this was estimated at 103 millièmes (mmes)/m³ ~US$0.06/m³ (1 Tunisian Dinar (DT) = 1,000 millièmes; 1 DT = US$0.66).

In the Ben Arous CRDA, the O&M costs of treated wastewater were estimated at 122 mmes/m³ including labour costs (18%), costs of electricity for pumping (68%), and other costs (14%). The estimation of the O&M costs is sensitive to the volume of water pumped and billed. For example, in the Ariana CRDA, the quantity of water pumped in the irrigation perimeter was more than 2.9 MCM. If this volume was in reality properly accounted for, the O&M costs would have been 44 mmes/m³, lower than those actually charged by the CRDA, i.e. 55 mmes/m³. Table 15.5 presents the variation in treated wastewater prices among CRDAs and the differences between the prices charged for treated wastewater and conventional water (Ministry of Agriculture, 1998).

In 1997, a Presidential Decree set the price of treated wastewater at a uniform 20 mmes/m³ or US$0.01/m³ in order to encourage farmers to expand its use. This is a significant subsidy considering the average cost of treated wastewater is estimated at US$0.14/m³, and is expected to rise to US$0.29/m³ in the coming years as new WWTPs come on line. However, the impact of this subsidy in expanding demand has been far lower than expected due to such reasons as poor quality, social acceptance, agronomic considerations, and sanitation. Further, despite the tariff reforms undertaken by the Government, which require the CRDAs to annually raise the price of water by 15% on average, the price of conventional water still remains very low. Where the farmers have a choice between treated wastewater and conventional water, they prefer conventional water because of the crop restrictions on treated wastewater and problems with its quality. For farmers who would not otherwise have had access to irrigation, treated wastewater is the preferred option because it has helped raise their incomes. For example, farmers living on the perimeter of Borj Touil on the northern coast had no access to surface water resources, and groundwater resources there are far too saline for their use

Table 15.5. Comparison of prices [DT/m³ (US$/m³)] for treated wastewater and conventional water in Tunisia prior to the 1997 Government Decree.

Source: Calculated from Ministry of Agriculture, 1998
Note: 1 DT = US$0.66

Institutional and Organisational Structure

Water resources are managed at the national level by the newly-consolidated Ministry of Agriculture, Environment and Water Resources (MAEW) formed by the merger of the Ministry of Environment with the Ministry of Agriculture in September 2002. Its hydraulic works section, the Direction Générale des Grands Barrages et des Grands Travaux Hydrauliques (DGBGTH), is responsible for the construction of major water resources projects. Responsibility for the water supply systems in urban areas and large rural centres is assigned to the Société Nationale d’Exploitation et de Distribution des Eaux (SONEDE), a national water supply authority that is an autonomous public entity under the MAEW. Planning, design, and supervision of small and medium water supplies and irrigation works are the responsibility of the Direction Générale du Génie Rurale (DGGR), a department of the MAEW. Responsibilities for managing investment planning and implementation of projects and agriculture activities are with the Commissariats Régionaux au Développement Agricole (CRDAs). These were created as semiautonomous agencies in each of the country’s governorates to represent the Ministry of Agriculture, now the MAEW. They now manage over 50% of public investment in the agriculture sector. A few water users groups (Associations d’Intérêt Collectifs, AICs) have also been created to handle water distribution e.g. the AIC in Monastir. In 1975, with the assistance of the World Bank, the Government created the ONAS, which is responsible for the sewerage subsector management including the collection, treatment, and disposal of wastewater in urban, industrial, and tourism zones. In 1993, ONAS’s mandate was consolidated under the (then) created Ministry of Environment and Land Use Planning with increased responsibility for sewerage operations. Now ONAS has expanded into an institution responsible for the protection of the aquatic environment, working in close cooperation with the National Environmental Protection Agency (Agence Nationale de Protection de l’Environnement, ANPE, established in 1989), which is charged with developing and enforcing regulations concerning wastewater discharge. The other key ministry involved is the Ministry of Public Health (MPH), which regulates the quality of wastewater used for irrigation and of marketed crops, as well as monitoring water pollution and enforcing control. This Ministry has an important say in pollution control and wastewater use regulations.

Lessons Learned and the Road Ahead

The results and experience gained in Tunisia on treated wastewater use place Tunisia among the leading countries in the Mediterranean area in the field of treated wastewater use in irrigation. It is one of the few countries where treated wastewater use has been made an integral part of environmental pollution control and water management strategies. The knowledge and experience gained by researchers in the Institut National de Recherche Génie Rural, Eaux, et Forêts (INRGREF) should provide excellent guidance to other countries in arid and semi-arid regions in defining the different irrigation uses for reclaimed wastewater, quality requirements for specific uses, the treatment levels best suited to each use, and the most adequate management options available for implementing current and proposed projects. Through its planned and cautious approach together with a well-developed regulatory framework, Tunisia has significantly mitigated the environmental and public health risks associated with untreated wastewater use elsewhere in the world. As a middle-income country, Tunisia also has the benefit of an affluent, well-educated population that has helped to practically eliminate untreated wastewater use. This has not meant that wastewater use in Tunisia is without its constraints. The following important lessons have been learned from Tunisia’s implementation of a conscious strategy of treated wastewater use over the decades.

Institutional

There is a multiplicity of agencies that are currently involved in treated wastewater use with often conflicting objectives and overlapping responsibilities. The lack of co-ordination has resulted in a mismatch in the supply and demand. ONAS generates treated wastewater according to its prerogatives and the established quality standards, but not necessarily to match the quality and quantity demands of the primary users – the farmers. On the other hand, the CRDAs representing farmers’ interests would like to obtain treated wastewater as needed during the cropping season at certain times, in certain volumes, and of a quality appropriate for crops Currently there is no single agency with responsibility for treated wastewater reuse (regulation and enforcement of standards and procedures, management, etc.). A possibility for increased coordination among different stakeholders would be the creation of an executive commission with representatives from the key ministries and agencies. This commission would be tasked with implementing the national strategy for treated wastewater use including supervision, coordination, control and establishment of new use initiatives, education programmes etc. Due to Government concerns about rising public expenditures in the civil services, implementation of this recommendation in the near future is unlikely, unless the wastewater commission were to be created by drawing from the staff of existing agencies.

Technical

Firstly, in order to be able to better match demand and supply, the development of associated infrastructure especially inter-seasonal storage facilities needs to be emphasised. Farmers are willing to pay more if they can be assured of a timely and reliable quantity and quality of water supply. With the growth in the number of WWTPs, ONAS has to work with MAEW, CRDAs, and farmer representatives to determine technical and management solutions that are mutually satisfactory. Secondly, with the Government’s push towards water-saving technologies on a national scale, effective filtration systems need to be devised to enable the use of treated wastewater in micro-irrigation systems such as drip irrigation without clogging.

Social/agronomic

Farmers are still reluctant to use treated wastewater and do not possess the necessary training to use it for agricultural irrigation in a safe and hygienic manner. For the farmers who do use treated wastewater, there is little evidence to suggest that chemical fertiliser use has decreased, a process that is likely to result in over-fertilisation and aquifer contamination in the long term. This points to the need to strengthen agriculture and irrigation extension services so that farmers are appropriately trained. Extension agents themselves need to be better equipped to respond to farmers’ needs and concerns.

Public outreach and education programmes are also essential if greater social acceptance of treated wastewater is to be generated. The use of treated wastewater effluents is legitimate from the Islamic religious viewpoint, and has therefore to be examined in each case from the aspects of health, cost, and public acceptance (Farooq and Ansari, 1983; Faruqui et al., 2001). Building community participation through water users groups (AICs) during the planning stages of projects can help build socio-cultural acceptance.

Economic

The current standards and restrictions on cropping patterns will need to be revisited. Current restrictions on the use of treated wastewater for higher-value crops discourage farmers from using this resource despite its highly subsidised price. This will necessitate a revision in the 1975 Water Code and the associated regulatory decrees. The Government is already thinking along these lines and will develop a revision of the Water Code that will result in a more practical pricing structure and a revision of the cropping restrictions based on the quality of treated wastewater. The Government’s emphasis on treated wastewater use in irrigation has not been based on a rigorous market assessment of real demand. Too often, the rates of return on wastewater treatment and reuse projects are artificially high because they assume a rate of use that is unrealistic. There is untapped demand for industrial and recreational use of treated wastewater. Implementation of a market-based strategy of treated wastewater use will necessitate greater coordination between the different stakeholders. The absence of a single coordinating agency will be a major hurdle.

Endnote: At the time of writing, the author was a Visiting Scientist at the South Asia Regional Office of the International Water Management Institute (IWMI) in Patancheru, India and Senior Economist in the Rural Development, Water and Environment Department, Middle East and North Africa Region of the World Bank.

References

Asano, T. and Mujeriego, R. (1992) Tunisia: Institutional Aspects of Wastewater Reuse. Mission Report prepared under UNDP/World Bank Water and Sanitation Program, Project RAB/88/009, January 1992, 33 pp.

Bahri, A. (2000) The Experience and Challenges of Reuse of Wastewater and Sludge in Tunisia. Paper prepared for Water Week, April 2000, Washington DC, 16 pp. (Unpublished, available from the author).

Farooq, S. and Ansari, Z. (1983) Wastewater reuse in Muslim countries: an Islamic perspective. Environmental Management 7(2), 119–123.

Faruqui, N., Biswas, A. and Bino, M. (eds.) (2001) Water Management in Islam. United Nations University Press, New York, 149 pp.

Government of Tunisia. (1987) Seventh Five-Year Plan, 1987–91, Ministry of Development and International Cooperation, Tunis, Tunisia.

Government of Tunisia. (1992) Eighth Five-Year Plan, 1992–96, Ministry of Development and International Cooperation, Tunis, Tunisia.

Government of Tunisia. (2002) Ninth Five-Year Plan, 2002–06, Ministry of Development and International Cooperation, Tunis, Tunisia.

Koundi, A.H. (2001) General survey of wastewater management in Tunisia. Presented at the Regional Workshop on Water Reuse in the Middle East and North Africa, 2–5 July 2001, Cairo, Egypt, Office National d’Assainissement (ONAS), Tunis. 6 pp. (unpublished).

Ministry of Agriculture. (1998) Développement de la stratégie pour promouvoir la réutilisation des eaux usées épurées dans le secteur agricole ou autres. Direction Générale de Ressources en Eau, Groupement Bechtel International/SCET-Tunisie, 138 pp.

UNDP (United Nations Development Programme)/FAO(Food and Agriculture Organization of the United Nations)/The World Bank/WHO (World Health Organization). (1992) Wastewater treatment and reuse in the Middle East and North Africa Region: unlocking the potential, July 1992, Project RAB/88/009, UNDP/FAO/World Bank/WHO, 171 pp.

World Bank. (1994) Republic of Tunisia: Water Sector Review. Report no. 4-TUN (September 1994). World Bank, Washington DC, 47 pp.

World Bank. (1997) Greater Tunis Sewerage and Reuse Project. Staff Appraisal Report, Private Sector Development, Finance and Infrastructure Operations Division, Maghreb and Iran Department, Middle East and North Africa Region, Report no.15432-TUN. World Bank, Washington DC, 145 pp.

World Development Report (2002) Building Institutions for Markets, New York, Published for The World Bank, Oxford University Press, Oxford, UK, 2002.

WHO (World Health Organization). (1989) Health guidelines for the use of wastewater in agriculture and aquaculture: Report of a WHO Scientific Group. WHO Technical Report Series 778. World Health Organization, Geneva, Switzerland, 74 pp.

Document(s) 17 of 19