CC BY
15
Fontana K.A.1, Fontana C.2 ©
1Senior scientist, PhD, Central Economics and Mathematics Institute RAS, Moscow;
President of European Irrigation Association, Brussels
WASTEWATER USE: A NEW OPPORTUNITY FOR THE GREEN ECONOMY.
GENERAL OVERVIEW
Summary
In the present article the use of recycled water is analyzed for use in irrigation to match increased pressure on natural water resources for agricultural production and city beautification. Scarcity of water is becoming a relevant issue in many areas of the world and need to be faced with new technologies and practices.
Keywords: reclaimed water, water reuse, water scarcity, water treatment, recycled water, irrigation, wastewater, climate change, urban economy, water economy.
Actually, a number of rising issues strains global water resources. In the last century, the consumption rise at twice the speed of the world's population growth while word's population is expected to rise by over 30% by 2050.
Furthermore, an unseen change in the structure of food consumption is adding further pressure on the world water resources and according to available data, freshwater withdrawals are projected to expand by 55% by the middle of the century, further increasing food scarcity concerns.
As food production is actually using about 70% of all freshwater consumption, is mandatory to explore new ways to increase the water supply available for irrigation.
Considering the above, the use of treated wastewater for crop cultivation is a key to increase food security; at the same time, wastewater supplies the irrigated plant with many of the nutrients it requires, as well as other micronutrients and organic matter.
Actually available technologies allow already today to recycle water to the necessary level at a relatively low cost. In addition, modern irrigation technologies allow for a dramatic decrease of the quantity of water needed per yield. These agronomic and environmental benefits make effluent water usage in irrigation a highly attractive solution.
The implications of wastewater usage in irrigation are even more significant given the recent UN General Assembly's adoption of the "17 UN Global Goals for Sustainable Development". Led by a call to end global poverty and hunger, the Sustainable Development Goals also include achieving food security, promoting sustainable agriculture, and ensuring sustainable management of water for all.
According to "The 2030 Water Resources Group", an influential group formed by leading companies as The Barilla Group, The Coca-Cola Company, The International Finance Corporation, McKinsey & Company, Nestlé S.A., New Holland Agriculture, SABMiller plc, Standard Chartered Bank and Syngenta AG, domestic, industrial and agricultural wastewater can be turned into resources.
In one of its reports, it claims that: "Wastewater reuse is an important lever to tackle water scarcity, mitigate climatic change but can be also considered as a way to recover value from wastewater (water, energy, nutrients, etc.) and secure agricultural and human activities (industries, tourism) at the national or local level. Matching unconventional water resources (domestic wastewater) and uses (agriculture, landscaping, golf courses, etc.) requires setting up a water reuse chain, i.e. a combination of technologies (wastewater treatment, distribution, storage, and irrigation equipment), re-use practices (water management, crop and irrigation practices) and social, economic and institutional arrangements to manage those. Across the globe, policy makers, civil
© Fontana K.A., Fontana C., 2016 r.
society and the business sector are increasingly becoming aware of the challenge facing global water resources, and the need to carefully manage these resources".
Agricultural productivity is a fundamental part of the solution. In all of the case studies, agricultural water productivity measures contribute towards closing the water gap, increasing "crop per drop" through a mix of improved efficiency of water application and the net water gains through crop yield enhancement. These include the familiar technologies of improved water application, such as increased drip and sprinkler irrigation. The full suite of crop productivity measures includes, among others, no-till farming and improved drainage, utilization of the best available germplasm or other seed development, optimizing fertilizer use, and application of crop stress management, including both improved practices (such as integrated pest management) and innovative crop protection technologies.
Different water for different purposes
In discussing wastewater reuse, one need to keep in mind that not all water is the same. Water can be of different quality, spanning a continuous spectrum that goes from ultra-pure water, to potable water, to "gray water", to water that can only be used in agriculture, to water of impaired quality that is not fit for any use. Different types of water along the quality dimension are not necessarily fungible: water that is perfectly fit for agriculture may not be adequate for industrial use or human consumption and would require treatment in order to be used.
Similarly, reliability defines different types of water. Water that is available all the time is different from water that users can rely on only 90 percent of the time. Water that is available year-round is different from water that users can rely on only in a single season.
Both quality and reliability differentiate water, as they distinguish between the activities that can be supported, and therefore the value that water can have. Low-quality, low-reliability water cannot be used for human consumption in a city, for example, although it may be used as supplemental irrigation in lower-value crops. High-quality, high-reliability water, on the other hand, is very valuable.
The reuse of water is just one source of water that has potential for use in an agricultural setting. Reused water does, however, have a major advantage in that it is usually a constant and reliable supply, particularly with sources such as treated sewage effluent or industrial discharges. As well as being a constant source of water, many waters suitable for reuse are produced in large volumes, which if not used would be merely discharged into the environment. It is well known that discharge of effluents, treated or non-treated, into the environment, particularly natural water bodies such as lakes, rivers and the coastal marine environments can cause severe degradation of these water ways. The degradation is often related to the presence of organic and inorganic nutrients, which can cause problems such as eutrophication and algal blooms. Reusing these discharged effluents can have a significant impact on reducing or completely removing the impact of these effluents from receiving environments. In addition, the reuse of wastewaters for purposes such as agricultural irrigation reduces the amount of water that needs to be extracted from environmental water sources.
Wastewaters can often contain significant concentrations of organic and inorganic nutrients for example nitrogen and phosphate. There is potential for these nutrients present in recycled water to be used as a fertilizer source when the water is recycled as an irrigation source for agriculture. Soil microorganisms have been observed to have increased metabolic activity when sewage effluent is used for irrigation.
The use of recycled water for the irrigation of crops has benefits in using a resource that would otherwise be discarded and wasted. Using recycled water also reduces the pressures on the environment by reducing the use of environmental waters. There are factors that need to be considered, including the presence of pathogens and chemical contaminants as well as salinity and impacts on soil structure. These can all be controlled through treatment and effective farm management practices. Ongoing research and development will also improve and increase the use of recycled water for irrigation purposes as well as increasing public confidence.
Wastewater and grey water reuse is emerging as an integral part of water demand management, promoting the preservation of high quality fresh water and reducing both environmental pollution and overall supply costs. Recent developments in technology and changes in attitudes towards wastewater reuse suggest that there is a potential for grey water reuse in the developing world. Grey water is defined as wastewater generated from domestic activities such as dish washing, laundry and bathing, whereas black water consists of toilet water. Gray water represents the largest potential source of water savings in domestic residences, accounting for as much as 50-80% of the total water use. The most common application for gray water reuse in urban areas is toilet flushing which can reduce water demand within dwellings by up to 30%. However, other applications such as irrigation of green areas in parks, school yards, cemeteries, golf areas, car wash, and fire protection are practiced. The use of gray water for irrigation is one of the methods which is currently widely used. This is particularly important in arid zones, where water is scarce and reuse of gray water for irrigation could reduce potable water use by up to 50%. In some arid and semi-arid areas municipal water consumption typically increases by 40-60% in summer months due to landscape irrigation.
Benefits and disadvantages of Agricultural Reuse
Summarizing the benefit of water reuse in agriculture we underline the following: this kind of water has a high concentration of nutrients, thus reducing or even eliminating the need for fertilizer, it brings to long-term soil enrichment, decreases demand on potable water supply, provide for additional treatment in soil, gray water not discharged to receiving waters.
As main disadvantages need to be noticed a potential health risk from associated pathogens, health risk from other contaminants (e.g. metals, chemicals, and pharmaceuticals), risk of decrease in soil quality from accumulation of metals and acidification if not appropriately managed, infiltration of groundwater.
Urban Wastewater Reuse
Firstly, let's agree on the definition of what is recycled urban wastewater or reclaimed water: urban wastewater that has undergone additional treatment following secondary treatment in order to be reused rather than discharged into the environment.
The use of such water can substantially reduce strain on potable water supply.
The biggest constraint in the use of recycled urban water is the need to build a is a dual distribution system, with a network of pipes to deliver reclaimed water to the public, that run separate but parallel to potable water pipelines, with the potential problem of cross connection and consequent contamination of potable water.
Urban reclaimed water can be used mainly for such purposes as irrigation of public parks, schools, road medians, any landscaped areas, golf courses, commercial purposes as vehicle washing facilities, laundry facilities, window washing, mixing pesticides and herbicides, construction - dust control, concrete production, toilet and urinal flushing, fire protection.
Anyhow, to implement the use of urban reclaimed water, considerations of public health and reliability of the system need to be taken into consideration, also to overcome concerns from the public, which are often a major constraint in the implementation of any recycled water system. For this, need to be evaluated the following: water must be of acceptable quality for intended uses, system must be maintained and operated properly, reclaimed water pipes must be clearly marked.
Retrofitting reclaimed water system in existing cities can be expensive but can be cost-effective especially if water supply is of poor quality and/or water supply does not meet demand and an advanced wastewater treatment is already required.
Conclusions
As of today, more and more, effluent water is becoming a resource. Its use is one of the most viable ways to save natural water resources and to match demand and supply in a sustainable way, both economically and ecologically.
Primarily in the agricultural sector there is already today a large know how in the use of irrigation systems with effluent water and modern irrigation technologies. This experience needs anyhow to be extended wherever possible.
A key to achieve relevant results is needed, first of all, to bring the concept to the attention of politicians; in particular those directly involved in water resources management, as well as open a discussion with the large publics about the advantages and risk of water reuse.
Further scientific investigations, advanced technological solutions, statistic data and corresponding mathematical methods need to be the base for an adequate state policy on the matter, aimed to achieve viable and economically feasible solutions to the use of reclaimed water.
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