Several solutions are available to redress the balance. On the demand side, it is possible to reduce waste by dealing with network leaks – in the order of 20% – , the in-adaptability of agriculture, and excessive consumption on the part of industrial and individual users. On the supply side, and in a context where fresh water is already in high demand, solutions can be found by reusing available but unclean water. Recycling is possible by desalinating sea water or reusing wastewater. These two technical solutions are not concurrent but complementary. Reuse is particularly promising because it is an easier and cheaper response to questions of decontamination and demand for irrigation water. With daily production of recycled water at 28million m3 in 2010 and estimated to rise to 79 million m3 in 2016 (almost 30 billion m3 per year), reutilization seems promising in principal and necessary in practice. An unavoidable market for public water hydrant attendants as long as they avoid the pitfalls…
Demographic growth worldwide and the increased toxicity in waste make opting for the recycling of wastewater a legitimate alternative or complement.
The number of inhabitants in zones where there is a shortage of water or severe water stress (less than 1000m3 of water available per inhabitant per year), is set to double between 2007 and 2025 (3.2 billion) according to the UNEP Sick Water Programme report. Countries under severe water stress are concentrated in South Asia, Africa and the Middle East. This growing pressure on the volumes of water available is made worse by deterioration in the quality of water available. In emerging countries in particular, moving to intensive agriculture, industrialisation and massive urbanisation only increases the toxicity of wastewater (according to the same report, 1.8 million children of under five die every year from water borne illnesses). Water resources are under heavy constraints which encourage local authorities and operators to search out alternative resources that meet environmental protection requirements as well as human demands. Blue wealth is also unequally shared. Africa and the Middle East represent 1.3 billion of the world’s 7 billion inhabitants but only have at their disposal 4500km3 of fresh water a year of a world total of 200.000, or 2% of fresh water supplies for 20% of humanity! The challenge is immense. The re-use of wastewater has therefore become a vital issue.
Reusing or recycling wastewater is done through two procedures. The first procedure is direct recycling which consists in using the water as soon as it has been purified. The prerequisite is that purification enables a sufficient quality of water to be produced so that it can be used immediately afterwards. The purified water is stored until it is used. The second procedure is indirect recycling where purified water is reinserted into the natural water cycle. What this means in practice is re-injecting the water either into a body of water in order to replenish low water levels (maintaining a minimum level in the body of water), or in humid zones or directly into the water table to be stored naturally or to combat soil salinisation.
As with every other recycled substance, recycling water meets the need to transform waste into a resource and is even more justified given the rarity of the resource. Recycling water also has an additional advantage in that it offers a way to improve health in a context of massive urbanisation and increase in the world’s population.
The advantages are multiple: increase available resources of purified water, limit the amount of polluted water that goes into the environment or the amount reused without actually checking its quality, and financing purification of waste water by identifying an outlet that justifies this purification. Having access to water resources is useful for municipalities interested in urban, peri-urban or rural development projects (watering recreational areas or agricultural lands) but its main interest is for agricultural exploitation.
Irrigation as a first outlet
Reutilisation projects mainly aim to fulfil irrigation needs be they for food produce or landscapes, given that these usages occupy the world’s fresh water needs. Targeting agricultural demand presents 4 advantages.
First of all, it replies to a huge demand for water. According to the World Bank, agriculture represents on average 70.2% of the planets consumption of fresh water, but the share is much larger in Sub-Saharan African countries (84.03%) or the Middle East and Northern Africa (85.5%).
By replying to agricultural demand, recycling wastewater is beneficial to a sector that has the largest potential and takes the pressure off conventional water resources. Conventional water resources (water tables, bodies of water…) can then be reserved for the production of purified drinking water and sanitary use, notably because consuming populations are more accepting of this type of usage.
The third advantage, limiting the need to resort by default to polluted water: the water cycle causes waste water that is not purified to be reused by default by actors present downstream, where there will be more or less dilution depending on the situation. Setting up a recycling programme is, at minimum, a way of improving the quality of wastewater which would have been reused untreated, with no sanitary control.
Finally, it is extremely simple to set up: agricultural irrigation also needs les purification than drinking water for domestic use and doesn’t generate a major psychological barrier.
Where direct benefits are concerned, recycling for agricultural and forestry use is the biggest user in terms of volume, with a variety of different methods where some perimeters are exclusively irrigated with waste water, and others are mixed or have a system for storage or transfer. Recycling for aquaculture is still in a somewhat embryonic state throughout the world but it is regularly used in Asia both as a treatment process and in the resulting fish production sector.
A simple procedure with many failures in terms of project implementation
Numerous projects have been launched and never reached the objectives fixed at the outset in terms of volume of water treated, water quality (sanitary risks, contamination) or access to the water (low adhesion by final users). It is difficult to make these projects durable or determine their economic viability. Over and above addressing a demand for water and giving a partial response to water stress, projects for recycling wastewater should be drawn up in a strict regulatory and economic framework. The involvement of the end user and the equal division of costs and benefits for each involved party are key factors to the sustainability of the system. The end user has to play a key role in the project. This can mean, for example, setting up a group of users where the end-user makes a contribution to the control mechanisms, to maintaining the infrastructure and ensuring that sanitary norms are respected or simply paying a license fee to have access to the purified water. To encourage local commitment, the project has to be integrated into a policy of integrated water resource management and provide answers to environmental concerns (preserving ecosystems etc.). Obviously, the project should also respect current sanitary norms and techniques. In the specific case of indirect recycling where water is reinserted into the water table, local authorities and the operator managing the project have to make sure all concerned parties have an understanding of the technique used and its effect on the environment. Wrongly perceiving this particular technique could lead to a project being rejected, as has been the case for fracking projects in France (with non comparable effects on the environment of course).
The project itself should be built around concrete and realistic objectives: decision makers and operators should have sufficient visibility on the availability of conventional resources, on the water requirements for each category of user and on the potential recycling of wastewater before laying out clear and precise objectives at the outlay.
Recycling wastewater is a process with a future and stands apart from pure water management in that an integrated approach to water from primary source to last usage has to be adopted so that the different intermediary usages can be clearly identified and then each step of the recycling process set up. The complex part is less in technical purification than in the ability of authorities and operators to work together towards a sustainable economic solution for everyone and that is sanitarily acceptable to users.