Climate change mitigation and energy efficiency: challenges in the wastewater sector

Abstract: The wastewater sector provides water sanitation to populations in order to preserve humanhealth and the natural environment. In developed countries, due among others to increasingpressures coming from climate change and population growth, the wastewater treatment isaffected and needs to adapt to such changes. As a result, effluent requirements arebecoming more stringent, nutrients and organic removal capacity increases. But also newuncertainties surround this sector. For example, how population habits will change in thefuture in terms of water use, quantitatively and qualitatively? A transition towards more asustainable society is slowly taking place, and within the wastewater sector the transitiontowards new innovative systems is happening, as illustrated by the case studies performedin Sweden, France and Australia.More often than not, these considerations and the pressing necessity of preserving thenatural environment lead to an increase of the amount of energy required for processing thesewage. In addition, increasing energy prices, the reduction of availability of fossil-fuelbasedenergies, and GHG emissions targets impact more and more the way the water andwastewater sector operate. Energy and climate policies as well as legislation also affectwastewater treatment plants. Despite the fact that the wastewater sector is not energyintensive, no sector in today’s society can be exempted from acting on its impact on theenvironment and from reducing its use of fossil-fuel-based energy. Large organizations arestarting to develop strategies to reduce their GHG emissions and develop more efficientenergy systems.Besides operating processes more efficiently in terms of energy and GHG emissionsreleases, a way forward is to look at the content of wastewater which is rich in resources: water, nutrients and energy. These resources can be valorised as by-products. In the past, ithas been common practice in many developed countries to convert the sludge originatedfrom the wastewater treatment into fertiliser for the agriculture purposes. More recently,biogas has started to be produced through sludge digestion, thereby creating synergiesbetween the wastewater sector with other sectors such as transportation, an intensiveenergy sector. In fact, wastewater treatment can be one of the rare renewable energysources available in the urban environment. Innovation and technology support thesedevelopments, but policies and legislation also need to be adapted to valorise the potentialsand opportunities throughout the transition towards a more sustainable urban watermanagement.