Document(s) 9 of 19

¹International Water Management Institute (IWMI), Colombo, Sri Lanka
²Center for Irrigation and Water Supply Research, Vietnam Institute for Water Resources Research, Hanoi, Vietnam

Abstract

The use of urban wastewater in agriculture is a common practice for diverse reasons, not least of which are water scarcity, fertiliser value, and lack of an alternative source of water. It is necessary to have a clear understanding of wastewater’s importance and significance in terms of extent, agricultural production, and livelihood impacts before appropriate policies, strategies and guidelines for its use in an integrated water management framework are developed. The Vietnam nationwide assessment was the pioneer in a series of such assessments being undertaken by the International Water Management Institute (IWMI). Findings indicate that 75% of domestic wastewater in large cities and 45% in smaller cities are discharged into sewers. Wastewater is used for agriculture or aquaculture in 93% of the cities. On an average wastewater is used in at least 2% of the agricultural land around most cities, predominantly to grow rice. The nation-wide total of such irrigation is conservatively estimated at around 9,000 ha. Wastewater aquaculture is carried out in natural ponds which serve the dual purpose of inundation control and as collection sinks for city wastewater. Wastewater agriculture provides a primary or secondary source of income to 1% of the urban population. The corresponding figure for wastewater aquaculture is 0.1%. Factors that influence the use of wastewater in non water-short regions have emerged, showing a possible pattern of wastewater use under these conditions. A key result from this study is the need for a typology that effectively captures all these characteristics, as a prerequisite for a global assessment.

Introduction

The use of urban wastewater in agriculture is a common practice, not only in arid and seasonally arid zones but also in non water-short countries like Vietnam. The reasons for this are diverse and dependent on the situation and local context. For instance, in Pakistan, wastewater is used for its water value even in untreated form, and as a source of plant nutrients. In Ghana it is used because an alternative non-polluted source of water is not available. The added benefit of its fertiliser value is incidental. In Mexico, large areas of land are irrigated with partially treated and/or diluted wastewater.

The reasons for wastewater use, the diverse conditions under which it is used, and its impacts are still not clearly understood and require further research before amelioration techniques and technologies can be suggested.

In most developing countries wastewater is used untreated, partially treated or diluted, but policies governing its use are not adapted to the local contexts. A clear understanding of its importance and significance at a global level in terms of extent, agricultural production, and livelihood impacts would contribute to developing appropriate policy and legal frameworks for wastewater use within an integrated water resources management framework.

The Vietnam nationwide assessment is part of an initiative (part of the Comprehensive Assessment of Water Management in Agriculture) to assess the global extent of wastewater use. There are claims that worldwide more than 20 million ha are irrigated with urban wastewater but at present there is a gap in knowledge about global estimates, and the possible trade-offs between health and environmental impacts, and the livelihoods-related benefits for those using wastewater. A survey of literature on wastewater agriculture indicates that this was the first study of its kind ever attempted at a national level, necessitating the design of a research methodology suitable for this purpose. Documenting the situation in Vietnam provided insights on agricultural wastewater use practices where water scarcity is not always the major consideration. It also served to gain an understanding of the constraints and limitations of such an assessment, and the importance of developing a clear typology for future assessments.

Background

Vietnam is one of the developing countries where wastewater has been used for decades – even centuries – by poor farmers in urban and peri-urban areas for both agriculture and aquaculture. Located in the tropical monsoon belt of Southeast Asia, Vietnam has mean annual rainfall ranging from 1700 mm in the north to 2000 mm in the south with temperatures ranging from 13° to 35°C that are favourable for agricultural production, especially paddy rice cultivation. Its territory of 333,000 km², with a population of approximately 77.7 million people in 2000, is officially classified into eight geographical regions, namely: northeast (NE) and northwest (NW) mountainous regions, the Red River delta (RRD), north central coast (NCC), south central coast (SCC), central highland (CH), southeast (SE) and Mekong River delta (MRD).

In spite of doi moi (renovation) reforms in 1986, the country is still rated one of the world’s poorest with a predominance of poverty in rural areas. Irrigation plays a significant role in agricultural production, which represents approximately 25% of the country’s gross national product. Despite the general abundance of freshwater resources, wastewater, both domestic and industrial, is used extensively in some areas, e.g. in the peri-urban areas of Hanoi particularly in the Thanh Tri, and Tu Liem districts, where it contributes significantly to food production and food security in the cities. About 80% of Hanoi’s vegetable demand is satisfied from wastewater agriculture (Tran Van Lai, 2000), and the system seems to be generally accepted by consumers.

Survey Design

Scope and sample selection

There are 57 provincial capitals in Vietnam distributed within eight geographical regions, and four cities directly under central government rule. In selecting a sample of cities/towns to be surveyed, the following were left out: those in the mountainous NW region (inaccessible), those that had no known wastewater irrigation (e.g. in predominantly forested provinces), and those in the delta floodplains (difficulty in designating specific wastewater irrigated areas). The sample of 30 cities finally selected represented different city classes that are designated in Vietnam according to population and available infrastructure facilities.

The sample cities covered seven of the eight geographical zones (NW excluded). In MRD only one city, Tanan (in Longan province), located southeast of Ho Chi Minh City, was included. The total population of the cities surveyed was 14.7 million amounting to approximately 19% of the total population of the country (Table 7.1).

Table 7.1. Provincial capital cities selected for Vietnam nationwide survey, roman numerals indicate city class.

Data Collection and Validation

Data on water supply, sanitation and sewerage infrastructure, wastewater generation (sources, management), wastewater agriculture and aquaculture (areas, production, characteristics), and general social, health, and crop impact were collected from secondary data sources and through a questionnaire survey accompanied by indepth interviews administered to officials of the Department of Land Administration, Statistics, Agriculture and Rural Development, Transportation and Public Works, Science, Technology and Environment, and the Irrigation and Drainage Management Company.

Working on the assumption that most wastewater use would be in urban and peri-urban areas of cities, simplified definitions for the following terms suited to the study were developed.

• Target study area – the metropolitan area of each city, including its urban centre and the suburban areas falling within the city boundaries.
• Urban wastewater – a combination of domestic effluent (both blackwater and greywater), industrial, commercial and institutional effluent including hospital waste, and other urban and storm runoff. Irrigation and drainage canals and other water bodies, which receive untreated wastewater and are highly polluted, may also be considered as wastewater.
• Wastewater irrigated area
  1. When water for irrigation was taken from a wastewater drainage canal the whole area irrigated with this water was included in the wastewater irrigated areas, e.g. Hanoi agricultural areas.
  2. When water was taken from an irrigation and drainage dual canal that was receiving wastewater, the area designated as wastewater-irrigated was limited to the area close to the receiving point where sensory negative impacts on users, e.g. bad smell, itching were known.
  3. When water was taken from an irrigation canal receiving city wastewater, the wastewater irrigated area was calculated as a fraction of the irrigated area within the city limits corresponding to the proportion of wastewater in the canal.
• Wastewater aquaculture – the use of natural stabilisation ponds and man-made ponds receiving wastewater to cultivate fish.

A pilot study was conducted in Hai Duong city, to test the questionnaire and its relevance, before launching the full-scale exercise. Maps were used when possible to localise areas, and field observations were made when time permitted. Written materials made available by local authorities were also used. Data validation for five selected cities was conducted either through a further visit or by telephone interviews with authorities. No major discrepancies were noted although it must be understood that some of the data were figures provided by the local authorities, with no independent confirmation. Due to lack of secondary data, e.g. domestic and industrial water demand, etc.

in many instances these had to be estimated by local officials. Data reliability turned out to be a major shortcoming that is likely to plague other attempts at national and global assessments despite clear definitions.

Results and Discussion

Classes of cities and population

The survey covered 50% of the largest cities in Vietnam. These cities account for 19% of the national population. The two largest cities, Hanoi and Ho Chi Minh City, accounted for 54% of the population covered.

Water supply and sanitation

Surface water provided the sole source of water supply in 12 cities (40% of all those surveyed). Groundwater alone was used in 5 cities (17%). In 13 cities (43%) both surface and groundwater were used. In some cities, although groundwater is the source, the wells are close to the river, e.g. the Red River in the case of Hanoi.

Most cities in Vietnam have some sewerage and wastewater drainage coverage. Sewerage systems are covered networks but the drains carrying city wastewater may be open. Data show that in larger cities about 75% of the domestic wastewater drains into municipal sewerage systems of some sort, and in the smaller cities this figure is 45%.

Discharge volume (million m³/d)

Fig. 7.1. Total wastewater discharge by region in Vietnam. (NE = northeast, RRD = Red River delta, NCC = north central coast, SCC = south central coast, CH = central highland, SE = southeast, MRD = Mekong River delta).

Industrial wastewater (%)

Fig. 7.2. Proportion (%) of industrial wastewater (including hospital wastewater) in total wastewater in various regions (see Fig. 7.1) of Vietnam.

Industrial wastewater is sometimes discharged into municipal collection systems when an alternative is not available. Industries close to rivers tend to discharge their wastewater directly into the rivers. There is no discernible pattern in the proportion of industrial wastewater to total wastewater that can be related either to the size of the city or the geographic region (Figs 7.1 and 7.2).

In total, out of 2.7 million m³/d of fresh water consumption in the 30 cities, 77% returns to nature as wastewater; domestic wastewater constitutes between 60–90% of this.

Pattern and extent of wastewater use

In 93% of the surveyed cities (28) wastewater is used for agriculture or aquaculture or both. More cities use wastewater for agriculture (80%) than for aquaculture (63%).

Agricultural land use

According to our definition of target study area, six of the 30 surveyed cities have urban and peri-urban agricultural land areas exceeding 10,000 ha. Three of the four city provinces (Hanoi, Ho Chi Minh, and Hai Phong) have the largest agricultural land areas constituting a high proportion (>45%) of the total land area in each city.

Wastewater agriculture

In the 30 cities surveyed, agricultural land accounts for 35% of the total land area. Wastewater irrigated areas vary from 0.5–5% (average 1.6%) with 70% of the cities falling within the range of 1–2% (Table 7.2).

On a regional basis, the highest proportion of wastewater-irrigated land is in NCC, possibly due to the water scarcity in that area. However, a similar pattern is not observed in SCC, which is also water-scarce but where most of the cities surveyed are coastal either without available agricultural land, or where most wastewater is discharged directly into the sea.

Cropping pattern related to wastewater use

Generally in Vietnam there are three cropping seasons; spring, summer and winter (Fig. 7.3). The predominant crop in both wastewater and non-wastewater areas is paddy rice, also called lowland rice. Rice is grown on 76% of the area in the spring and on 85% in the summer. Vegetables and upland crops (corn, maize, sweet potatoes, groundnut, soybean) are also grown. Wastewater is used markedly less in winter than in other seasons, because paddy rice that requires a lot of water, is not a winter crop.

Reasons for use of wastewater for agriculture

Unlike in many arid and semi-arid countries, where urban wastewater is sought after and used extensively, in Vietnam the underlying reason for its agricultural use is the unplanned discharge of wastewater into natural water courses, drainage canals or irrigation canals. However, intentional wastewater use occurs in some instances due to inadequacy of irrigation systems particularly at the tail end. Survey results show that approximately 60% of the cities use wastewater because of its unplanned management that results in discharge into natural watercourses or drainage canals. City officials who were interviewed recognise wastewater’s nutrient and water value, but less than 10% of the available wastewater is used. Farmers were not interviewed in this survey, but from the authors’ experience in other discussions, farmers value the wastewater particularly for aquaculture. Both officials and farmers are uneasy about using industrial wastewater. Wastewater is generally discharged directly to rivers from riverine cities, taking it away from the metropolitan area.

Cropping pattern (%) in wastewater irrigated lands

1. Spring
   
2. Summer
   
3. Winter
   

Fig. 7.3. Cropping patterns in wastewater-irrigated areas across regions (see Table 7.1) of Vietnam by season.

Table 7.2. Agricultural land and wastewater-irrigated agriculture by city class in Vietnam (surveyed cities).

^a Excludes Ninh Binh where most of the wastewater used is from a thermal power plant and is therefore not representative.

Nationwide Estimation of Wastewater Agriculture

An attempt was made to extrapolate the data from 30 cities to a national context using city class and regional averages. This approach has its limitations (as seen from Tables 7.3 and 7.4 below) given the wide variation in values within a class or a region.

This extrapolation to the national level gives the following figures for wastewater use in agriculture:

9,410 ha based on class averages,

5,957 ha based on regional averages

6,972 ha (i.e. 446,937 × 1.6% from Table 7.2) based on the overall average

A range of 6,000 to 9,500 ha is indicated as a national figure.

It must be noted that the magnitude of these figures largely depends on the initial definitions of target study area, wastewater, and wastewater-irrigated areas. This assumes that very little wastewater agriculture takes place outside of the city limits, but this is not so in Vietnam, where the pollution of irrigation canals extends the problems of wastewater irrigation beyond the city boundaries. Furthermore, the proportional method used to calculate the extent of land under wastewater irrigation in schemes served by canals receiving wastewater may have led to an underestimation of the real situation. This confirms the importance of proper definitions and the need for a standard typology if results from different countries are to be compared.

Table 7.3. Nationwide projection of wastewater-irrigated agriculture by city class.

Table 7.4. Nationwide projection of wastewater-irrigated agriculture by region in Vietnam.

Aquaculture Using Wastewater and the Role of Natural Stabilisation Ponds as Treatment Facilities

Of the 30 cities surveyed, 19 use wastewater for aquaculture. Natural stabilisation ponds, traditionally used for flood inundation control, that are prevalent across the country, are generally used for aquaculture but not exclusively using wastewater. Data were not comprehensive, but from available figures, the annual total fish production from wastewater in the cities surveyed is 6,359 t, of which more than half (3,380 t) comes from Hanoi, by far the largest fish producer using wastewater. Certain districts of Hanoi, e.g. Than Tri and Tu Liem depend almost entirely on wastewater for both agriculture and aquaculture. Five other cities annually produce around 100–200 t. Wastewater aquaculture appears to be more common in the larger cities, i.e. in eight out of the 10 class II cities. Tilapia and carp species predominate.

According to doctors interviewed, it seemed that little information was available in Vietnam about health risks associated with sewage-fed aquaculture (Dalsgaard, 1995).

Of the sample cities, 73% had stabilisation ponds, many of them over 10 ha in size. In many cities, due to the poor collection and disposal infrastructure for wastewater, these ponds serve the additional purpose of bio-treatment. However, the sizing of the ponds does not correspond to the degree of treatment required by the wastewater (Metcalf and Eddy, 1991). Estimates of retention times varied from 1–122 days.

Other than these stabilisation ponds other forms of urban wastewater treatment are virtually non-existent (Ha et al., 2001), but industrial wastewater in some instances undergoes some form of treatment before discharge. The applicability of natural pond systems as a low-cost method for the partial treatment of wastewater for agricultural use may prove useful in other countries, and should be further studied under Vietnamese conditions.

Livelihoods, Health and Environmental Aspects

An attempt was made through this nationwide survey to gather information on the number of households using wastewater as an income source. Data availability was sketchy at this level of assessment, and it was understood that more detailed studies on the livelihoods dimension of wastewater use were needed. In the context of this study livelihoods reflect the number of persons dependent or engaged in wastewater agriculture or aquaculture, using it either as a main or a secondary source of income.

Analysis of available information (Tables 7.5 and 7.6) showed 1% of the population depend on wastewater agriculture as a primary or secondary, but not necessarily sole, income source.

In the CH cities of Buon Ma Thuot and Plei Ku, a higher percentage (5%) of households use wastewater. This may be explained by the very small sizes of plots which allow for more households to cultivate vegetables.

Table 7.5. Livelihoods dependent on wastewater use by city class in Vietnam.

^a The population figure excludes cities where information on households was not available.

Table 7.6. Livelihoods dependent on wastewater use by region in Vietnam.

^a The population figure excludes cities where information on households was not available.

The proportion of the population engaged in wastewater aquaculture is only one tenth that of agriculture. In Hanoi however, with an annual fish production of 3,380 t, 0.3% of the population uses wastewater for aquaculture. Dalsgaard (1995) reports that farmers can make a net profit of around US$1,400 through wastewater aquaculture, and employees could earn around US$35/month.

Whilst the figures for both agriculture (1%) and aquaculture (0.1%) may be low in percentage terms, for Vietnam this is equivalent to nearly half a million people. The survey did not attempt to provide exact figures of incomes or the percentage of household income attributable to a wastewater source.

No substantive evaluation of environmental and health impacts was carried out at this stage, but the perceptions of authorities were recorded. Of those interviewed, more than half of the local authorities dealing with wastewater in the surveyed cities were aware of the negative impacts of wastewater use on human health and crops. Local officials based on observation and discussion with farmers, gave importance to such visible medical symptoms as skin irritations, and listed poor crop quality and yields as negative impacts. They stated that they would prefer an alternative water source, but in the meantime, wastewater use did not seem to be actively discouraged, and they did not have plans for developing alternative sources.

Institutions for Wastewater Management

Although a series of legislation and decrees emphasising the State’s commitment and outlining the responsibilities for water resources protection and management exists, there is no single fully constituted entity responsible for wastewater management per se in Vietnam.

Prevention and mitigation of negative impacts on the environment are regulated by environmental legislation under the Ministry of Science, Technology and Environment (MOSTE). At the provincial and city level, the Department of Science, Technology and Environment (DOSTE), which reports to the Provincial People’s Committee (PPC), is responsible for environmental protection and management [extracted from the ‘Law on Environmental Protection’ (Vietnamese National Assembly, 1994)].

Operation and management of city sewerage systems is under the authority of the Urban Management and Planning Company (UMPC) by decree. The UMPC is supervised by the Department of Transportation and Public Works, or Department of Construction, but reports to the PPC or to the City People’s Committee (CPC). In principle wastewater pipes cannot be connected to the city sewerage systems without the approval of these organisations, and this is subject to toxic substances in wastewater being treated to required standards provided in the legislation [extracted from ‘Responsibilities of Ministry of Agriculture and Rural Development (MARD)’ (Government of Vietnam, 1999)]. However, these are not always enforced.

The Irrigation and Drainage Management Company (IDMC) manages the ponds and irrigation and drainage canals into which the urban sewerage systems are usually discharged. In cities close to rivers, wastewater is pumped directly into the rivers where possible.

Conclusions and Lessons Learned

Pioneer national assessment

The Vietnam national assessment was conducted to acquire an overview of the importance and significance of wastewater agriculture in terms of extent, agricultural production, and livelihood impacts. Such an overview could contribute to developing appropriate policy and legal frameworks for wastewater use within an integrated water resources management framework for Vietnam. It is the first time that such an assessment to acquire a national perspective has been attempted in any part of the world.

• The assessment showed that 93% of the cities sampled use wastewater for agriculture or aquaculture or both. In larger cities in spite, or because of urbanisation, urban and peri-urban agriculture appears to play a significant role in providing food to urban populations
• Wastewater irrigated areas vary from about 0.5%–5% (average 1.6%) of the total agricultural land in the cities; with 70% of the cities in the range of 1–2%.
• The predominant wastewater crop in Vietnam is paddy rice, grown on 76% of the area in the spring and 85% in the summer seasons
• Extrapolation of these findings to national level gives a range of 6,000–9,500ha as a national figure for wastewater-irrigated agriculture
• 1% of the urban population derives incomes from wastewater agriculture and 0.1% from wastewater aquaculture. Whilst these figures may be very low in terms of percentage, for Vietnam this represents close to half a million people
• Stabilisation ponds serve the dual purpose of inundation control and de facto bio-treatment. The latter is not very effective as the ponds were not primarily designed for this purpose. These ponds are also extensively used for aquaculture especially in the larger cities.

It must be noted that the magnitude of these figures largely depends on the initial definitions applied to target study area, wastewater, and wastewater-irrigated area. It assumes that very little wastewater agriculture takes place outside of city limits, which is not necessarily the case in all situations in Vietnam, where the pollution of irrigation canals extends the problems of wastewater irrigation beyond city boundaries. Furthermore, the proportional method used to calculate the extent of land under wastewater irrigation in schemes served by canals receiving wastewater, may have been an underestimation of the real situation.

For all these reasons the importance of developing a typology before proceeding to a global assessment clearly emerges.

Factors for rationalising wastewater use

Another reason for carrying out a national survey was to gain a clearer understanding of the reasons behind the use of wastewater in a national context in order to identify key factors that influence such use. Such information is not only useful for national policy, but also provides more generic information for application at a global level. The survey elicited the following:

• In Vietnam the underlying reason for its agricultural use is the unplanned discharge of wastewater into natural watercourses, drainage canals, or irrigation canals. This is unlike the situation in many arid and semi-arid countries, where urban wastewater is sought after and used extensively for its water and nutrient value. In some water-scarce areas of Vietnam, or under poorly maintained or managed irrigation systems, intentional wastewater use is noted
• 77% of the city’s freshwater supply returns as wastewater, of which the domestic content varies between 60 and 90%. These figures provide first estimates of possible wastewater return flows in Vietnam and similar countries in the region
• Data show that in larger cities about 75% of the domestic wastewater drains into municipal sewerage systems of some sort and for the smaller cities this figure is 45%. These figures are indicative of the situation in many similar less-developed countries and could be used as the starting point for global estimates of available ‘channelled’ wastewater that can be put to other uses
• In riverine and coastal cities, both industrial and domestic wastewater is discharged directly to the rivers or to the sea and is not usually used by farmers
• Rice and vegetable cultivation are the highest consumers of wastewater. Both may have substantial impact on human health particularly the possible presence of heavy metals in wastewater-irrigated rice systems.

Emergence of a typology and its requirements

A key lesson from this survey is the realisation that a more descriptive typology (or a classification of the most common forms of wastewater use in irrigation) is a prerequisite to the global assessment of wastewater agriculture, providing a framework to describe different practices and defining what is included in the assessment. A typology that can effectively capture these characteristics will ensure that those involved in this field are aware of the important differences that exist, and are able to identify where a given research finding, policy instrument or technical intervention will or will not find relevant application (Cornish and Kielen, Chapter 6, this volume; van der Hoek, Chapter 2, this volume).

Acknowledgements

The work outlined here has been carried out with Danish International Development Agency (DANIDA) funding, which is gratefully acknowledged. The authors would also like to acknowledge the contribution of their partners, the Royal Veterinary and Agricultural University, Denmark (KVL), Danish Hydraulic Institute (DHI), University of Copenhagen and the National Institute of Hygiene and Epidemiology, Vietnam (NIHE) who helped in the questionnaire design and review of the document. Special thanks are extended to the coordination provided by the Center for Irrigation and Water Supply Research (CIWSR) of the Vietnam Institute for Water Resources Research (VIWRR) and its survey team who collected the field data.

References

Dalsgaard, A. (1995) Public health aspects of re-use of wastewater in aquaculture in Vietnam. Department of Veterinary Microbiology of the Royal Veterinary and Agricultural University, Copenhagen, Denmark. (Draft report)

Government of Vietnam. (1999) Extract on the responsibilities of the Ministry of Agriculture and Rural Development (MARD) in relation to the protection of water resources as cited in the Vietnamese Government decree No: 179/1999/N§-CP for the implementation of the Law on Water Resources dated December 30th 1999, National Political Publishing House and Science and Technics Publishing House, Hanoi, Vietnam.

Ha, Tran Duc, Toan, Nguyen Duc, and Thao, Li Hien. (2001) Current status of pollution and management of urban drainage, lakes and canals. In: Proceedings of the International Seminar on Urban Sewerage in Vietnam, Water Supply and Sewerage Association (VWSA), Vietnam, pp. 343–349.

Metcalf and Eddy Inc. (1991) Wastewater Engineering: Treatment, Disposal and Reuse, 3^rd edn. revised by Tchbaroglous, G. and Burton, F.L. McGraw-Hill Inc. International, New Delhi, India.

Tran Van Lai. (2000) Perspectives of peri-urban agriculture in Hanoi. In: Proceedings of an Action Plan Development Workshop, organised by the CGIAR Strategic Initiative for Urban and Peri-Urban Agriculture (SIUPA), Hanoi, 6–9 June 2000, prepared by the Centro Internacional de la Papa (CIP) Lima, Peru.

Vietnam National Assembly. (1994) Extract from the Law on Environmental Protection passed on December 27th, 1993 by the Vietnamese National Assembly, 9th Legislature, at its 4th Session and effective January 10th, 1994, National Political Publishing House and Science and Technics Publishing House, Hanoi, Vietnam.

Document(s) 9 of 19