The world faces an unprecedented combination of water security and resilience challenges, including population growth, increasing urbanisation, a decline in traditional sources of water, and water scarcity driven by climate change.
The water sector needs to adopt new technologies and ways of working, many of which may be seen as disruptive when compared to traditional methods of water supply and wastewater treatment. However, if such technologies are to be truly effective, they must enshrine energy and resource efficiency.
The monitoring and optimisation of wastewater treatment and sewer and sewage monitoring have both been identified as opportunities where water and sludge treatment technologies can be updated and improved. By 2025, about 80% of utilities in large cities of advanced countries and half of the utilities in large cities of developing countries are expected to have water supply systems that incorporate digital water features like advanced metering. Satellite data can also be used to monitor catchments and water distribution systems.
To truly deliver savings in water use and energy, water companies must completely digitise their supply chains and wastewater infrastructure, deploying sensors in the field and using electronic flow meters in the system, including at a customer level. One of the key potential benefits of increased digitisation in the water sector, as well as reduced water use and improved demand balancing, is reduced energy use through improved efficiency.
We have already seen increased use of rain capture and brown water reuse for cleaning and toilet flushing in many buildings, but there is increasing interest in treating wastewater streams to make them potable and immediately returning them to the water supply system (direct reuse). In order to become widely adopted, society needs to accept that suitably treated wastewater is a desirable source of usable potable water.
To truly deliver savings in water use and energy, water companies must completely digitise their supply chains and wastewater infrastructure
Resource recovery is another key aspect of a true circular economy. Every cubic metre of recycled or reused water results in a corresponding reduction in mains water demand and wastewater discharge. There are also benefits in terms of the energy and carbon footprints associated with material recovery when compared with primary extraction and processing, together with further environmental benefits from reduced waste disposal impacts.
As far as the wastewater industry is concerned, nutrients such as phosphorus are one of the prime contenders for nutrient recovery, although as the sector moves forward a wider range of chemicals, such as ammonia nitrogen and sodium-based products, can be recovered. Fouling is a real concern during many material recovery processes, but specially designed scraped-surface heat exchangers will maintain thermal efficiency and remove fouling as it occurs.
Another form of resource recovery is the recovery of energy from wastewater streams. While anaerobic digestion is recognised as a water treatment technology around the world, its capacity for energy generation (either through the use of combined heat and power production or to produce sustainable biomethane gas) is less well developed. Ambitious goals for sustainable development will mean that wastewater treatment plants (WWTPs) will need to achieve net zero carbon balances by 2030. Achieving this will require recovery of the energy contained in the incoming wastewater streams and using it to provide the heat and power necessary for wastewater treatment and solids handling. It has been estimated that at present, most WWTPs are capable of producing 20 to 25% of their own energy requirements in this way.
Therefore, increasing energy production at WWTPs will be critical to making the sector self-sufficient in terms of energy. But on its own, it is unlikely to be sufficient to meet the net-zero goals. Reduced energy consumption through the use of new and more efficient processes will also be required. Sludge processing and energy efficiency are intrinsically linked.