Approximately 3.5 billion people will be living in water-scarce areas by 2025, while water demand is expected to soar by 30% by 2050. The current situation calls for thought to be given to efficient alternatives that reduce the water footprint and optimize resource management.
Consumers are also beginning to insist that companies should adopt environmental sustainability policies and actions. In fact, the “Leading the way to a global circular economy: state of play and outlook” study conducted by the European Commission highlights the need to focus on a circular, more sustainable economy, given the expected increase in the world’s population, the emergence of a new middle class in emerging countries and rapid urbanization.
In line with this social imperative, the UN Sustainable Development Goals, in goal number 6 – Clean Water and Sanitation – have already included water as an asset to be protected in the 2030 Agenda.
For all these reasons, water reuse is a growing trend that supports the circular economy, reducing the water footprint and contributing to reaching the SDGs.
Reuse: on trend in 2023
Along these lines, wastewater treatment for reuse plays a central role as “part of the solution to water scarcity and pollution problems,” according to Jennifer Sara, Global Director, World Bank Water Global Practice. In turn, Diego Juan Rodríguez, co-author of the report “Wastewater: From Waste to Resource”, and a Senior Water Resources Management Specialist at the same organization, focuses on water reuse as a trend, as this could reduce sanitation service costs, making them sustainable and adding value to the economy, as a way to help countries.
Thus, WWTPs are beginning to introduce technological improvements to help reduce water pollution centering on eliminating discharges and minimizing the emission of chemicals and hazardous materials. According to the United Nations University and the University of Utrecht, in an article published in the Earth System Science Data journal, wastewater treatment has increased by 50% worldwide, thanks in part to continuous improvement in technologies. However, the authors of the study point out that in developing countries, infrastructures and technologies still require upgrades and the issue of the lack of qualified staff needs to be solved.
In Europe, on May 25, 2020, the European Parliament and the Council approved Regulation (EU) 2020/741 on minimum requirements for water reuse. One of the main objectives of this regulation is to increase sixfold the volume of treated water currently reused by 2025.
The requirements of this new regulation set limits that divide treated water into four quality categories which establish which uses water can be put to. Classification is based on compliance with restrictions based on:
- Physical parameters: total suspended solids (TSS), nephelometric turbidity unit (NTU)
- Chemical parameters: biochemical oxygen demand (BOD5).
- Microbiological parameters: E. coli, Legionella spp., intestinal nematodes, coliphages and clostridium spores.
Therefore, water reuse is a growing trend for social, environmental, economic and political reasons, and technology plays a key role in this process.
Technologies for reuse
In this sense, guaranteeing public and environmental health and complying with the physical, chemical and biological parameter requirements set by the pertinent authorities requires a series of technologies that will be increasingly implemented by water utilities in 2023 and the following years:
- Physical-chemical treatments. Mainly coagulation-flocculation.
- Adsorption. A tertiary process based on the adsorption of soluble components on the surface of a solid material (adsorbent).
- Ion exchange. Anionic and cationic resins with different types of radicals used to retain one or more types of ions found in the water to be treated.
- Advanced filtration processes. Microfiltration, ultrafiltration, nanofiltration and reverse osmosis, ranked from largest to smallest pore size, are applied to remove compounds that exceed the pore size of the material used. Reverse osmosis achieves the highest purity water, eliminating monovalent salts, vitamins and sugars.
- Electrodialysis reversal (EDR). Electrochemical ion separation is achieved by applying a direct current field. This is mainly used for desalination processes.
- Disinfection processes. The aim is to eliminate pathogenic microorganisms from wastewater. For this purpose, strong oxidants such as free chlorine, chlorine dioxide, sodium hypochlorite, chloramines, ozone, potassium permanganate and silver salts are used. The water can also be irradiated with UV.
- Advanced oxidation. These processes generate hydroxyl radicals (OH-) with a higher oxidation power than the previous disinfection processes. These treatments are used when the aim is to decompose contaminants, such as pesticides and pharmaceuticals.
Disinfection processes and advanced oxidation are the most effective technologies on the above list. Disinfection processes must be more reliable and efficient to comply with the more stringent quality standards imposed by the new European regulations on pathogen concentrations. In the longer term, advanced oxidation processes will gain ground in urban wastewater treatment plants, as more and more evidence emerges about the harmful effects of emerging pollutants (medicines, drugs, perfluorinated compounds, agrochemicals, etc.) on public health and the environment.
The choice of the most appropriate technology is one of the most sensitive issues facing water treatment plants seeking or forced to reuse their water. The purification performance of each of these technologies must be taken into account, but special attention must also be paid to the following:
- Operating costs: energy and reagent consumption
- Waste generation: related to brines and chemical sludge, as well as the environmental impact generated by these residues and the technical and economic feasibility of managing them properly.
- Technical capabilities: the number of staff needed to operate the selected technology and the level of training required.
- The potential for automating and monitoring the process.
The role of digital transformation in water reuse
Digital transformation plays a key role in expanding and improving WWTP infrastructures that seek to reuse the water they treat.
The digital transformation of these processes starts with monitoring the main variables that regulate them. These are usually found in multiple sources, such as LIMS, SCADA and CMMS. This causes difficulties when processing information and creating indicators that combine data from different sources, hindering decision-making and causing processes to operate below peak efficiency levels.
Based on this knowledge, the screens where the process KPIs will be displayed are calculated and designed, with all the variables sharing a common platform. The next step is to create predictive models that anticipate decision-making and detect process deviations by comparing the value obtained with the estimated value.
Finally, machine-learning algorithms can be trained to analyze all input variables to optimize the amount of energy and reagents used in the process, guaranteeing target quality standards at all times. The output of these algorithms can be sent directly to the plant’s SCADA to update the operating setpoints. Alternatively, the operator can be notified so that they can decide whether to carry out the recommended actions. The latter is known as Decision Support System (DSS) and is increasingly gaining traction in the industry.