The challenges of wastewater irrigation in developing countries

The volume of wastewater generated by domestic, industrial and commercial sources has increased with population, urbanization, improved living conditions, and economic development. The productive use of wastewater has also increased, as millions of small-scale farmers in urban and peri-urban areas of developing countries depend on wastewater or wastewater polluted water sources to irrigate high-value edible crops for urban markets, often as they have no alternative sources of irrigation water. Undesirable constituents in wastewater can harm human health and the environment. Hence, wastewater irrigation is an issue of concern to public agencies responsible for maintaining public health and environmental quality. For diverse reasons, many developing countries are still unable to implement comprehensive wastewater treatment programs. Therefore in the near term, risk management and interim solutions are needed to prevent adverse impacts from wastewater irrigation. A combination of source control, and farm-level and post-harvest measures can be used to protect farm workers and consumers. The WHO guidelines revised in 2006 for wastewater use suggest measures beyond the traditional recommendations of producing only industrial or non-edible crops, as in many situations it is impossible to enforce a change in the current cash crop pattern, or provide alternative vegetable supply to urban markets.There are several opportunities for improving wastewater management via improved policies, institutional dialogues and financial mechanisms, which would reduce the risks in agriculture. Effluent standards combined with incentives or enforcement can motivate improvements in water management by household and industrial sectors discharging wastewater from point sources. Segregation of chemical pollutants from urban wastewater facilitates treatment and reduces risk. Strengthening institutional capacity and establishing links between water delivery and sanitation sectors through inter-institutional coordination leads to more efficient management of wastewater and risk reduction.     

The role and place of global surveys for assessing wastewater irrigation

This paper traces developments in understanding the practice of wastewater use, particularly of untreated wastewater, downstream of cities. The challenge for global assessments is discussed in the light of findings of a recent multi-country survey that attempted to understand the drivers and characteristics of wastewater irrigation in developing countries. The findings are used to show that applying a harmonized typology is a challenge that may not be necessary as measures of magnitude rather than exact data are often sufficient to bring issues to the policy agenda. Some key findings that characterize wastewater agriculture are presented, and the paper concludes that irrigation with untreated wastewater is a common reality of probably increasing concern, which requires not only conventional but also in particular alternative health risk reduction approaches.     

Urban growth, wastewater production and use in irrigated agriculture: a comparative study of Accra, Addis Ababa and Hyderabad

The relationships between urban development, water resources management and wastewater use for irrigation have been studied in the cities of Accra in Ghana, Addis Ababa in Ethiopia and Hyderabad in India. Large volumes of water are extracted from water sources often increasingly far away from the city, while investments in wastewater management are often lagging behind. The resulting environmental degradation within and downstream of cities has multiple consequences for public health, in particular through the use of untreated wastewater in irrigated agriculture. Despite significant efforts to increase wastewater treatment, options for safeguarding public health via conventional wastewater treatment alone remain limited to smaller inner-urban watersheds. The new WHO guidelines for wastewater irrigation recognize this situation and emphasize the potential of post- or non-treatment options. Controlling potential health risks will allow urban water managers in all three cities to build on the benefits from the already existing (but largely informal) wastewater reuse, those being the contribution to food security and reduction of fresh water demands.     

Irrigation management under water scarcity

The use of water for agricultural production in water scarcity regions requires innovative and sustainable research, and an appropriate transfer of technologies. This paper discusses some of these aspects, mainly relative to on-farm irrigation management including the use of treated wastewater and saline waters. First, the paper proposes some concepts relative to water scarcity, concerning aridity, drought, desertification and water shortage, as well as policies to cope with these water stressed regimes. Conceptual approaches on irrigation performances, water use and water savings are reviewed in a wide perspective. This is followed by a discussion of supply management to cope with water scarcity, giving particular attention to the use of wastewater and low-quality waters, including the respective impacts on health and the environment as water scarcity is requiring that waters of inferior quality be increasingly used for irrigation. The paper then focuses on demand management, starting with aspects relating to the improvement of irrigation methods and the respective performances, mainly the distribution uniformity (DU) as a fundamental tool to reduce the demand for water at the farm level, and to control the negative environmental impacts of over-irrigation, including salt stressed areas. Discussions are supported by recent research results. The suitability of irrigation methods for using treated wastewaters and saline waters is analysed. Supplemental irrigation (SI) and deficit irrigation strategies are also discussed, including limitations on the applicability of related practices. The paper also identifies the need to adopt emerging technologies for water management as well as to develop appropriate methodologies for the analysis of social, economic, and environmental benefits of improved irrigation management.     

再生水灌溉水质安全性分析与评价研究

对北京市主要污水处理厂出水的再生水常规(农田灌溉水质标准涉及的)水质指标、持久性有毒有机污染物进行了监测,结合国外再生水灌溉作物类型、发达国家的水质标准进行分析,得出北京市再生水的水质指标符合相关标准,持久性有毒有机污染物的毒性较小,风险极低。应制定与完善适合我国国情的再生水灌溉水质标准、再生水灌溉技术规范、再生水农业利用区划导则、再生水灌区环境影响评价规程、再生水灌区工程管理规范等标准规范,实现再生水安全利用。     

Faecal contamination and hygiene aspect associated with the use of treated wastewater and canal water for irrigation of potatoes (Solanum tuberosum)

Clean water has become one of the main limiting factors in agricultural food production in Europe, especially for countries around the Mediterranean, who now face more severe and frequent seasonal water shortages. In order to overcome water shortages the European Water Framework Directive encourages and promotes the use of treated urban wastewater in agriculture. However, the use of poor quality water in agriculture poses potential health risks. The application of wastewater through subsurface drip irrigation lines could possibly overcome public health concerns by minimizing contact with wastewater by farmers, farm workers but it is uncertain if the risk for consumers of wastewater irrigated produces would be acceptable. The objective of the current study was therefore to assess whether subsurface irrigation of potatoes with low quality water was associated with higher food safety and reduced human health risks as compared with surface irrigation. The microbial quality of soil and potatoes irrigated by sprinkler, furrow and subsurface drip irrigation, using treated urban wastewater, canal water and tap water were compared at experimental sites near Belgrade, Serbia and in Bologna, Italy. Water, soil and potato samples were collected from March 2007 to September 2008 and their faecal contamination estimated by enumeration of the faecal indicator Escherichia coli. In addition, water and potatoes in Italy were analysed for the presence of helminth eggs, another important indicator of faecal pollution. A quantitative microbial risk assessment (QMRA) model combined with Monte Carlo simulations was used to assess whether the different irrigation practices and associated health risks complied with guidelines set by the World Health Organization (WHO). The study found low levels of E. coli in irrigation water (Italy mean value: 1.7 colony forming units (cfu)/ml and Serbia 11 cfu/ml), as well as in soil (Italy mean: 1.0 cfu/g and Serbia 1.1 cfu/g). Similar low concentrations of E. coli were found on potatoes (Italy mean: 1.0 cfu/g and Serbia 0.0 cfu/g). The vast majority (442/516) of the collected different samples were free of E. coli. No helminth eggs were found in any types of irrigation water or on the surface of potatoes. The risk assessment models found the use of treated wastewater to exceed the levels of risks for gastro-intestinal disease (1.0 × 10⁻³ disease risk) as recommended by the World Health Organization (WHO) for the accidental ingestion of soil by farmers (Serbia: 0.22 and Italy: 5.7 × 10⁻²). However, samples that exceeded disease risks set by the WHO were collected before initiation of wastewater irrigation and were limited to a few numbers of samples, which would indicate environmental contamination not linked to irrigation practice. Disease risk from consumption of potatoes in Italy and in Serbia was found to be within acceptable levels. No relationship was found between E. coli concentrations in irrigation water, soil and produce. Similar lack of association was found for E. coli findings in sprinkler, furrow or subsurface drip irrigated soils and produce. This indicates that subsurface drip irrigation can be practiced while ensuring food safety and protecting the health of consumers and farmers.     

Quantifying the effect of Managed Aquifer Recharge on the microbiological human health risks of irrigating crops with recycled water

Managed Aquifer Recharge (MAR) is increasingly being used for water recycling via aquifers and recovery for irrigation. Quantitative Microbial Risk Assessment (QMRA) was used to assess the human health risks from irrigation using reclaimed water and to evaluate the reduction in risk where MAR is used for irrigation management. Four MAR sites (Shafdan, Israel; Nardò, Italy; Bolivar, Australia; and Sabadell, Spain) that use reclaimed water for crop and/or park irrigation were evaluated, and the risk to human health was quantified in terms of DALYs (Disability Adjusted Life Years). The results indicated that median risks for all scenarios and pathogens evaluated were acceptable (<10⁻⁶ DALYs) with the exception of risks from accidental aerosol ingestion and bacterial pathogens at the Nardò site. MAR was found to be one of the most important treatment barriers in terms of log₁₀ inactivation credits and hence a useful tool for recycled water irrigation management. The Shafdan site relied almost completely on the MAR treatment to reduce the human health risks from irrigation to acceptable levels. For the Nardò site MAR was also an important barrier, where if MAR had not been used as part of the irrigation system the risk would be unacceptable for protozoa and viruses. The Bolivar and Sabadell sites had much larger and more technologically complex recycled water treatment systems and as such MAR was not a critical barrier in managing human health risks.     

Assessing environmental impacts of reclaimed wastewater irrigation in paddy fields using bioindicator

Irrigation water quality influences many aspects of agroecosystems, but less is known about how complex microbial and biological communities respond to changing water quality due to causes such as reuse irrigation. The objectives of this study are to monitor and assess the environmental impacts of reclaimed wastewater irrigation on water quality and soil that might cause potential health hazards and to assess its agro-environmental effects. Two sites, which are irrigated by filtered wastewater after UV (Ultraviolet) treatment and from an agricultural reservoir that satisfied the agricultural water quality standards of Korea, were selected as treatment and control, respectively. The environmental impacts of irrigation water quality on paddy soil, microorganisms, and arthropods were investigated. Monitoring results for water, soil, health risks, and eco-environments of the reclaimed wastewater irrigation site demonstrated no adverse effects in the paddy field. This research showed that reclaimed wastewater irrigation did not present significant environmental risks for the rice paddy agroecosystem, although long-term monitoring is needed to fully characterize its effects.     

不同处理等级污水中氮素对农田土壤环境的影响

通过土柱模型试验,模拟研究了两种处理等级污水中氮素对农田土壤环境的影响。试验结果表明,采用1级处理污水中铵氮基本不会在土壤各层累积和淋溶,而硝氮和总氮则随着灌水次数的增加,向更深层土壤运移、累积和淋溶。对于2级处理污水,由于其各态氮素浓度均比较低,土壤各层浓度也相对较低,土壤中各态氮素浓度为土壤中原有氮素和污水氮素共同作用的结果;随着灌溉次数增加,硝氮和总氮也有向下淋溶的趋势。试验结果还表明,相对于2级处理污水,长时间采用1级处理污水灌溉,将对土壤环境和地下水环境带来高的污染风险。      

Olive tree response to irrigation with wastewater from the table olive industry

A field experiment was conducted to examine the effect of drip irrigation using wastewater from a table olive industry on physiological, nutritional and yield parameters of olive trees (Olea europaea L.). Very limited information, if any, exists, on the potential of recycling this kind of wastewater in agriculture. Two types of wastewater were used in the experiment, the first with SAR and EC values of 12–56 and 3.5–4.2 dS m⁻¹, respectively, and the second 73–90 and 4.3–6.0 dS m⁻¹. In general, this kind of wastewater has a highly variable composition and SAR values that are too high for agricultural purposes. Olive trees rapidly responded to wastewater application. Compared to the control (fresh water), the more saline wastewater caused important decreases in leaf water potential, stomatal conductance to H₂O and the photosynthesis rate after only 15 days of irrigation, the reduction being more pronounced after 2 months of irrigation. This treatment also caused a rapid, significant reduction in leaf N concentration, as compared with the N level in the trees before irrigation. Both types of wastewater significantly reduced olive yield, compared to that obtained in the control. These results indicate that this kind of wastewater is unsuitable for application to olive orchards under irrigation. Received: 16 August 1999     

Reuse of tertiary municipal wastewater effluent for irrigation of Cucumis melo L.

The reuse of tertiary wastewater for crop irrigation presents itself as an alternative to the scarcity of quality water suffered by many countries in the Mediterranean region. Furthermore, this resource can provide an important saving of fertilizers as well as benefits to the environment, as it avoids the discharge of contaminated water into public waterways. This study focuses on the effect of irrigation with ozonized wastewater on the melon crop. In this study, melon crops were irrigated with either ozonized wastewater or ground water commonly used in the agricultural area (control treatment). Fertigation, by means of drip irrigation, was delivered according to the crop’s needs, evaluating the fertilizers contributed by each of the waters and that added in mineral form. Throughout the crop’s development, the characteristics of the water, soil and plant (leaf and fruit) were studied from a chemical, physicochemical and microbiological perspective. The results obtained show that irrigation with ozonized wastewater, in these conditions of crop growth, produces similar effects as ground water on the soil properties, on the concentration of macroelements in the leaf and fruit and on the yield of melon fruit. Furthermore, the reuse of this effluent leads to a greater saving in nitrogenous and potassium fertilizers compared to fertigation of the crop with ground water.     

Field comparison and crop production modeling of sweet corn and silage maize (Zea mays L.) with treated urban wastewater and freshwater

In Australia, interest in wastewater reuse has grown. While wastewater can potentially offer a nutrient advantage over conventional irrigation, crop yield increases may be offset by effects of high salinity. Effects of wastewater irrigation on crop production and soil health were investigated in two ways: a field experiment addressing short-term effects and modeling longer-term impacts. The field experiment was established at the Shepparton Wastewater Treatment Plant in Shepparton, Victoria, to compare effects of wastewater irrigation to conventional irrigation. Silage maize and sweet corn (Zea mays L.) were grown over the summer of 2012–2013 under the following flood irrigation treatments: wastewater and freshwater with and without fertilizer. Both harvests produced yields and qualities comparable to commercial farm standards, and no significant differences were found between water types. Maize production with long-term wastewater irrigation at various salinities was modeled, and no significant yield losses were observed after 50 years of simulated irrigation. Topsoil electroconductivity doubled after the field trial and simulation results predicted significant soil salt accumulation by factor of 2. Mean wastewater sodium absorption ratio of 4.52 and electroconductivity of 1.52 dS/m indicate potential for sodicity-related soil problems for long-term irrigation. Management of soil health may be necessary.     

Wastewater production, treatment, and irrigation in Middle East and North Africa

The Middle East and North Africa (MENA) region is the driest region of the world with only 1% of the world’s freshwater resources. The increasing competition for good-quality water has cut into agriculture’s water share but since the use of freshwater for domestic, industrial and municipal activities generates wastewater, the volume of wastewater used in agriculture has increased. About 43% of wastewater generated in the MENA region is treated; a relatively high percentage compared to other developing-country dominated regions. This is because of the perceived importance of wastewater as a water resource and several oil-rich countries with the resources to treat wastewater. The MENA region has an opportunity for beneficial reuse of wastewater but few countries in the region have been able to implement substantial wastewater treatment and reuse programs. The major constraints leading to seemingly slow and uneven reuse of wastewater are: inadequate information on the status of reuse or disposal of wastewater and associated environmental and health impacts; incomplete economic analysis of the wastewater treatment and reuse options, usually restricted to financial feasibility analysis; high costs and low returns of developing wastewater collection networks and wastewater treatment plants; lack of wastewater treatment and reuse cost-recovery mechanisms and lack of commitment to support comprehensive wastewater treatment programs; mismatch between water pricing and regional water scarcity; preference for freshwater over wastewater; and inefficient irrigation and water management schemes undermining the potential of wastewater reuse. However, some countries such as Tunisia, Jordan, and Israel have policies in place that address wastewater treatment through a range of instruments. Policymakers in these countries consider use of treated wastewater to be an essential aspect of strategic water and wastewater planning and management. With flexible policy frameworks addressing rapid demographic changes and increasing water scarcity in the MENA region, water reuse has great potential if integrated with resource planning, environmental management and financing arrangements.     

Affluent effluent: growing vegetables with wastewater in Melbourne, Australia—a wealthy but bone-dry city

Water scarcity in Australia has become a significant challenge for all water users and water reuse is now a critical component of Melbourne’s response to this water crisis, particularly for food production. While most vegetable production occurs in a large-scale commercial environment, there is a significant proportion produced in backyards. With the introduction of severe water restrictions, commercial vegetable production now relies heavily on high quality Class A reclaimed water, while households have turned to the use of greywater. While there are many benefits of wastewater reuse, there are also many potential risks to plant, environmental and human health. A quantitative microbial risk assessment of the two systems was conducted to evaluate the human health risks associated with both large-scale and backyard reuse of water for vegetable irrigation. This preliminary model suggests that for irrigation with typical greywater, the annual infection probability for enteric viruses is >10^?4, even after a two week period of no irrigation with greywater. The human annual enteric virus risk from Class A reclaimed water was much lower.     

再生水灌溉下重金属在植物-土壤-地下水系统迁移的研究进展

再生水灌溉作为解决水资源紧缺的重要途径之一日益受到人们的重视。然而其水源中含有的重金属可能会对生态环境造成影响。回顾了国内外再生水灌溉下重金属在植物-土壤-地下水系统中的运移、分布、积累规律的研究现状与问题,在归纳分析的基础上提出了今后的研究方向。短期再生水灌溉一般不会增加植物体内重金属含量,再生水灌溉显著增加植物生物量对重金属所形成的"稀释效应"可能是其原因之一;不同的植物品种对不同重金属在植物、土壤中运移、分布和积累的影响有很大的差异;再生水短期灌溉往往不会降低土壤的环境质量,但长期灌溉再生水有可能会使土壤质量恶化,造成地下水重金属污染。     

中水微灌系统生物堵塞特性探讨

使用中水微灌作为缓解农业水资源危机的一种灌溉方式，可以将污水灌溉对环境和农作物造成的污染减轻到最小，但中水微灌溉将会加大灌溉系统堵塞的可能性。通过对造成中水微灌系统生物堵塞的水质、堵塞原因及堵塞的严重程度的分析认为，中水中的有机污染物和微生物会造成微灌系统的堵塞，但中水中的无机颗粒是造成灌水器堵塞的首要原因。微灌系统的堵塞取决于污水的处理工艺及中水水质标准，其中主要与灌溉水的pH值，TSS和BOD5等参数有关，这3个水质参数可以用来对微灌系统的堵塞的危险性进行评估。对于微灌系统堵塞问题，可以通过改善水质，合理配置过滤设备及使用大流量灌水器和具有自冲洗功能的灌水器等方法来解决。     

Sewage disposal in the Musi-River, India: water quality remediation through irrigation infrastructure

The disposal of untreated urban sewage in to open water bodies is common in most developing countries. This poses potential negative consequences to public health and agricultural sustainability. Hyderabad, one of India’s largest cities, disposes large amounts of its wastewater untreated into the Musi River, from where it is used, with the aid of irrigation weirs, for agricultural production. This paper presents a 14 month (December 2003 – January 2005) water quality survey which aimed to quantify spatial and temporal changes in key water quality parameters along a 40 km stretch of the Musi River. The survey found that river water quality improved dramatically with distance from the city; from untreated sewage in the city to irrigation water safe for use in agriculture 40 km downstream of the city. This improvement was contributed to by different treatment processes caused or aided by the irrigation weirs placed on the river.     

Emitter and filter tests for wastewater reuse by drip irrigation

Agriculture is the main user of water in Italy, as in most regions of the world. Particularly in Mediterranean regions, where it is more difficult to meet the agricultural water demand with conventional resources, wastewater reuse represents a viable option. Drip irrigation is particularly suitable for wastewater reuse because it minimises the health risks to farmers and product consumers due to contact with the wastewater. The performance of drip irrigation systems using wastewater is mainly limited by emitter clogging, and this discourages farmers from introducing it. The paper gives the results of experimental trials on the behaviour of six kinds of filters (gravel media, disk and screen) and four types of drip emitters (vortex and labyrinth) using five kinds of municipal wastewater that have not undergone previous advanced treatment. The performance of the emitters and filters tested depends on the quality of the wastewater: total suspended solids and organic matter content influence the percentage of totally clogged emitters, the mean discharge emitted, the emission uniformity coefficient, and the operating time of the filter between cleaning operations. Vortex emitters were more sensitive to clogging than labyrinth emitters. The gravel media filter guaranteed the best performance, but the disk filter, which is cheaper and simpler to manage, assured performance similar to that of the gavel media filter. The test showed the importance of the technology used in manufacturing disk filters. Screen filters were shown to be unsuitable for use with wastewater, with the exception of diluted and settled wastewater. The theoretical discharge of filters, suggested by the manufacturers for clean water, is not adequate for wastewater of the kind used in the trials (suspended solids greater than 78 mg/l and BOD₅ more than 25 mg/l of O₂). The operating times of the filters between cleaning operations, less than 1 h in most trials, suggest the use of automatic cleaning systems. The existing clogging risk classifications proposed for clean water can only be considered reliable for wastewater when labyrinth emitters and gravel or good quality disk filters (such as Arkal) are used; they are not adequate for vortex emitters or screen filters.     

Non-conventional water resources and opportunities for water augmentation to achieve food security in water scarce countries

Given current demographic trends and future growth projections, as much as 60% of the global population may suffer water scarcity by the year 2025. The water-use efficiency techniques used with conventional resources have been improved. However, water-scarce countries will have to rely more on the use of non-conventional water resources to partly alleviate water scarcity. Non-conventional water resources are either generated as a product of specialized processes such as desalination or need suitable pre-use treatment and/or appropriate soil–water–crop management strategies when used for irrigation. In water-scarce environments, such water resources are accessed through the desalination of seawater and highly brackish groundwater, the harvesting of rainwater, and the use of marginal-quality water resources for irrigation. The marginal-quality waters used for irrigation consist of wastewater, agricultural drainage water, and groundwater containing different types of salts. In many developing countries, a major part of the wastewater generated by domestic, commercial, and industrial sectors is used for crop production in an untreated or partly treated form. The protection of public health and the environment are the main concerns associated with uncontrolled wastewater irrigation. The use of saline and/or sodic drainage water and groundwater for agriculture is expected to increase. This warrants modifications in the existing soil, irrigation, and crop management practices used, in order to cope with the increases in salinity and sodicity that will occur.