Concrete solutions do exist to decrease energy consumption in favour of water production.
Consuming less energy for water production and vice versa
An average 102 kWh is needed to bring drinking water, collect and treat wastewater of one citizen over a year, all treatment technologies combined. About 40% of this energy is used for the water provision and 60% for sanitation.
Energy consumption levels are highly sensitive to the technical choices of infrastructure, resources and treatment method, therefore taking energy into account from a project’s inception stage is crucial to reach maximal energy efficiency.
Sanitation costs twice as much as potable water yet globally, water and sanitation services are not highly energy intensive. Energy consumed for these two services represents a modest share of the energy consumed by households: 1.2% of electricity consumed by an OECD country citizen and 2.9% of a Middle-East one. Providing water and sanitation to one average person on the planet for one year represents 0.7% (35kg CO2e) of total CO2 emissions of that person. Although it only represents a tiny share of emissions, reduction leverages must be found as the “factor 4” goal is to reach 2 tCO2 emitted by inhabitant per year in 2050.
The optimization of pumping efficiency is a first option for optimizing energy. Improving aeration of basins is another: reducing aeration by installing more performant commands and devices notices can lead to a 20-25% saving on a wastewater treatment station total energy bill.
Solutions exist: developing wastewater recycling techniques, building as autonomous treatment station as possible, developing new desalination technologies that are less energy intensive and use cogeneration. All of these technical options are being studied and receive large research and development budget both from public agencies and private companies.
As for networks, reducing leakage of potable water contributes to improving the energy efficiency of infrastructure as reducing such losses also means reducing the volumes of water to draw from the resource, treat and pump.
Diverse, innovating solutions for recycling and reuse are being developed such as injection water and produced water, treatment, and reuse of industrial wastewater. The development of closed-loop cooling systems for thermoelectric plants allows using 25 times less water.
Promoting local synergies to improve access to energy
Challenges are first and foremost local, be it in terms of production or distribution. This requires gathering a deeper understanding of interactions between water and energy through local actors, from industries and operators to local authorities and financing bodies.
Local actors also have the duty to provide civil society and local populations information about resource conservation challenges on the one hand, and about the actual cost of services on the other hand.
As an example, in some countries electricity finances water. Electricity tariffs are combined in a single contract and pay the water bill, which is subject to a social tariff scheme, and is priced below its production cost.
Likewise, water and energy must be integrated into multi-sectoral land use planning policies.
A toolset of technical solutions to improve energy efficiency
Energy efficiency challenges in water and sanitation services fall within a set of levers:
Streamlining existing infrastructure:
Reducing losses on the water network contributes not only to provide more people with the same volumes of water produced in the plant but also to improve the energy efficiency of the infrastructure.
As for desalination, when it comes to thermal processes desalination units are built in the proximity of existing electricity facilities, allowing reuse of residual energy (steam generated by electricity production units). Reverse osmosis membrane technology, the most recent one, divided its energy needs by two over 20 years of optimization.
An increasing number of drinking water plants showcase exemplary energy efficiency standards. In Sidney, Australia, a wind farm was built on top of a desalination plant and allows to fully compensate and even surpass the plant’s electricity needs.
Valuing underutilized energy
Wastewater treatment plants’ potential for energy production is very high: using heat from wastewater is a first option. Energy produced by sludge digestion is another, more widely used: it allows to produce biogas that can be directly used in a stove or burnt in a cogeneration engine to produce electricity. The electricity produced can then partly cover the energy needs of a wastewater treatment station.
- Sanitation offers a high energy potential through the valorization of organic matter into biogas
- It is essential to support binding legislation at the international level on wastewater discharge norms and industrial wastewater recycling.
- Priority must be granted to the funding of multi-sectoral water and electricity infrastructure projects, that promote energy efficiency.