The right to water is a theme that (Re)sources has carried and defended since 2005, as a founding right of human development.
Taking all treatment technologies together, it takes an average of 102 kWh to supply an inhabitant with drinking water and to collect and purify wastewater for one year. Approximately 40% of this energy is consumed for drinking water supply and 60% for wastewater treatment.
Energy consumption is very sensitive to the choice of infrastructure, resources and treatment processes, so taking energy into account from the outset of a project is essential in order to aim for optimum energy efficiency.
Sanitation costs twice as much as drinking water, but overall, water and sanitation services are not very energy intensive. The energy consumed for these two services represents a very small share of the energy consumed by households: 1.2% of the electricity consumed by an OECD inhabitant and 2.9% of that consumed by an inhabitant in the Middle East. Supplying an inhabitant with water and sanitation for one year represents 0.7% (35 kg CO2eq) of the total CO2 emissions of an inhabitant of the earth. Even if this represents only a very small part of the emissions, levers for reduction must be found because the objective of the "factor 4" is to reach 2 teqCO2 emitted per inhabitant per year in 2050.
A first step is to optimize the pumping efficiency. Improving the aeration of the basins is a second way: reducing aeration by setting up control instructions and more efficient equipment can lead to a saving of 20% to 25% in the energy consumption of a wastewater treatment plant.
The aim is to develop wastewater recycling techniques; to build treatment plants that are as self-sufficient as possible; to develop new desalination technologies that are less energy consuming and that use cogeneration. All of this, today, is the subject of very important research and development activities, both in the public sphere and in private companies.
On the network side, reducing drinking water losses also contributes to improving the energy performance of infrastructures because it means having less water to draw from the resource, to treat and to pump.
Diverse and innovative recycling and reuse solutions are being developed, such as recycling of production and injection water, treatment and reuse of wastewater. The development of closed-circuit cooling thermoelectric power plants, for example, makes it possible to use up to 25 times less water.
The stakes are above all local. Both in terms of production and distribution. This requires a clear deepening of the interactions between water and energy through local actors, whether they are industrialists, operators, local authorities or financiers.
Local actors have a duty to integrate and inform civil society and populations on the challenges of resource preservation, but also on the real costs of services.
For example, in some countries electricity pays for water. Electricity tariffs in a single contract pay for water, which is subject to a social tariff that is much lower than its production cost.
Similarly, it seems essential to integrate water and energy into multisectoral planning and land-use policies.
The challenges of energy management in water and sanitation services are based on different levers of action:
The rationalization of the existing
Reducing line losses on the water network not only helps to supply more people with the same water production at the plant, but also to improve the energy performance of the infrastructure.
For desalination, when the choice is made for thermal processes, desalination plants are installed alongside existing electrical installations, allowing the reuse of residual energy (steam generated by electricity production units). Membrane technology of the reverse osmosis type, which is more recent, has seen its energy needs halved thanks to the optimizations carried out over the past 20 years.
The use of renewable energies
Today, more and more drinking water plants and sewage treatment plants are examples of energy efficiency. In Sydney, Australia, a wind farm has been installed on the desalination plant, making it possible to fully offset or even exceed the plant's electricity needs.
Recovery of non-recovered energy
Sewage treatment plants have a high potential for energy production: recovering the heat contained in wastewater is a first option. Energy from sludge digestion is another, more widely used option: it enables the production of biogas that can be recovered directly in a boiler or burned in a cogeneration engine to produce electricity. The electricity thus produced can satisfy part of the energy needs of a wastewater treatment plant.
- Sanitation has a high energy potential thanks to the recovery of organic matter in biogas.
- At the international level, there is a need to support more binding legislation on discharge standards for polluted water and on the recycling of industrial water.
- Priority should be given to the financing of combined water and electricity infrastructure projects, with a focus on energy efficiency.