With an IWA conference on water in industry coming up in September, Yongjun Zhang reviews some of the key points around industrial wastewater reuse.
The recycling of industrial wastewater is increasingly important to address water security, improve the environment, and capture resources that may otherwise be lost through discharges. Hence there is a move for more industrial sites to recycle and reuse water with this requiring appropriate treatment. The quantities and quality of water involved differ greatly depending on the industrial process concerned, along with the great variety of contaminants which require treatment. High-tech industries in particular may require ultrapure water, demanding more extensive and challenging processes.
Thirsty industries
When industrial sites are built in areas of high population density, in the vicinity of a mega city for example, regions can experience competing demands for water from industry, agriculture, and domestic use, placing pressure on resources and the environment.
Industrial processes require large quantities of water for cleaning, cooling, and emulsions, in addition to being used as a carrier fluid for processing systems.
The hidden water consumed by industrial processes can be surprising. The production of a single cotton T-shirt consumes 2500 litres of water (Singh et al., 2023); the production of a kilogramme of paper requires 10-100 litres of water (Esmaeeli et al., 2023); and a litre of beer uses 5-20 litres of water (Götz et al., 2014).
Furthermore, industrial wastewater contains various contaminants that are generated or leached from production lines, including additives, final products, solvents, salts, and more, which must be treated to meet discharge criteria.
Recalcitrant emerging contaminants
Industrial production relies on an array of chemicals, including per- and polyfluoroalkyl substances (PFAS), commonly known as ‘forever chemicals’. As a consequency of industrial processes and agricultural production, pharmaceuticals and endocrine-disrupting substances can also threaten the environment.
In addition, brine wastewater can be formed in industrial production lines and as a result of membrane processes such as reverse osmosis. In many cases, it can contain high levels of recalcitrant organics, which can negatively influence the performance of desalination processes, as well as the crystallisation and purity of recovered salts.
Certain industries can produce particularly high concentrations of contaminants in wastewater, with material synthesis, food processing, and dyes and paints sometimes producing wastewater with concentrations as high as in the tens of thousands of mg/l of chemical oxygen demand (COD), and thousands of mg/l of total nitrogen (TN) and salts.
Sustainability toolbox
To tackle competition over water resources and reduce discharges of industrial contaminants into the local environment, many countries and regions use a ‘toolbox’ of solutions to improve the sustainability of industrial water use, including tiered pricing, water auditing, and green labelling.
Many water treatment processes such as aeration, membrane separation, and evaporation are energy intensive. To reduce energy use, energy must be optimised at the level of the whole process. In addition, excessive heat and pressure in production lines can be integrated into water treatment processes. To achieve energy optimisation, synergies are required between R&D teams to improve the efficiency of water management processes and – more widely – collaboration between researchers, engineers, and institutions and enterprises is required.
Water reuse
Wastewater recycling is also an important tool for increasing water use efficiency and has proved to be viable in many applications across a broad range of industrial sectors, including those where water quality is important.
One example of successful reuse is in breweries, where it has been found that the volume of water required for producing one litre of beer can be reduced from 20 litres to two litres by integrating a water reuse process into the water system (Götz et al., 2014).
The benefits of water reuse include that less industrial effluent is discharged, more wastewater is recycled, and water security is improved, which is especially important in regions where water scarcity is a concern. We are even now seeing the construction of zero-liquid-discharge plants.
Membrane fouling and scaling
Membrane technology is key to many wastewater reuse processes. The high concentration and complexity of contaminants in industrial wastewater can easily cause membrane fouling and scaling, necessitating that sufficient pretreatment be deployed based on the nature of the wastewater to be treated.
Smart management
It is important to take into account the fact that industrial production often depends on market demand and supply chains. As a result, the composition and volume of wastewater can fluctuate dramatically, especially where several production lines are deployed. In addition, the water quality and quantity requirements of a process may also change frequently. To manage these fluctuations a smart management system is required to efficiently respond to production requirements across all treatment units in a system.
High tech industries
Different water quality criteria are defined for different industrial water uses. Some applications do not require water of a very high quality – irrigation and floor cleaning, for example. However, some sectors – high tech sectors in particular – may require extremely high-quality ultrapure water.
“Countries and regions use a ‘toolbox’ of solutions to improve the sustainability of industrial water use”
The European Pharmacopoeia categorises water quality for pharmaceutical production into two grades with differing Total Organic Carbon (TOC) concentrations: purified water (TOC <500 μg/l, conductivity ≤4.3 μS cm–1), and water for injection (TOC <500 μg/l, conductivity ≤1.1 μS cm–1) (Rögener., 2024).
The production of semiconductors requires ultrapure water (TOC <3 μg/l, conductivity 0.055 μS cm–1), necessitating critical steps including wafer rinsing, the preparation of chemical solutions, and photolithography immersion, with an average water consumption of approximately 8.22 l/cm2 (Wang et al., 2023).
Computer services
Data storage centres consume a lot of water, directly for cooling and indirectly through electricity consumption. It is projected that per capita water use for data handling will be 1100 litres in Europe in 2030, 3.8 times higher than the value in 2020 (Farfan et al., 2023), emphasising how important water security is for the technology systems that the world now relies on.
Given the importance of industrial wastewater reuse and the strong demand for innovative solutions, IWA will be holding a ‘Water in Industry’ conference
in Nanjing, China, on 23-27 September to provide a communication platform for both researchers and practitioners. This is planned to develop into a series
of events to encourage synergies to be established, collaboration kindled and innovative solutions to be incubated. •
References
- B.J. Singh, A. Chakraborty, R. Sehgal, ‘A systematic review of industrial wastewater management: Evaluating challenges and enablers’, J. Envrion. Manage., 348 (2023) 119230. https://doi.org/10.1016/j.jenvman.2023.119230
- A. Esmaeeli, M.-H. Sarrafzadeh, S. Zeighami, M. Kalantar, S.G. Bariki, A. Fallahi, H. Asgharnejad, S.-B. Ghaffari, ‘A Comprehensive Review on Pulp and Paper Industries Wastewater Treatment Advances’, Ind. Eng. Chem. Res., 62 (2023) 8119-8145. https://doi.org/10.1021/acs.iecr.2c04393
- G. Götz, S.U. Geissen, A. Ahrens, S. Reimann, ‘Adjustment of the wastewater matrix for optimization of membrane systems applied for water reuse in breweries’, J. Membr. Sci., 465 (2014) 68-77. https://doi.org/10.1016/j.memsci.2014.04.014
- F. Rögener, ‘Increasing the Sustainability of Pharmaceutical Grade Water Production,’ Chem. Ing. Tech., 96 (2024) 522-527. https://doi.org/10.1002/cite.202300152
- Q. Wang, N. Huang, Z. Chen, X. Chen, H. Cai, Y. Wu, ‘Environmental data and facts in the semiconductor manufacturing industry: An unexpected high water and energy consumption situation’, Water Cycle, 4 (2023) 47-54. https://doi.org/10.1016/j.watcyc.2023.01.004
- J. Farfan, A. Lohrmann, ‘Gone with the clouds: Estimating the electricity and water footprint of digital data services in Europe’, Energy Conversion and Management, 290 (2023) 117225. https://doi.org/10.1016/j.enconman.2023.117225
The author: Yongjun Zhang is a professor at the School of Environmental Science and Engineering, Nanjing Tech University, China, and executive conference chair of ‘Water in Industry’ 2024
Water in Industry 2024
The Water in Industry Conference 2024 will be held at the Yangzi River International Conference Center, Nanjing on 23-27 September.
Topics will include: zero liquid discharge; resource recovery; removal of recalcitrants and metals; pre-membrane treatment; cooling water; water energy nexus; and best practice examples.
More information
To find out more about ‘Water in Industry’ 2024 and register to attend,
visit https://www.iwa-win.org/
