Creating Sustainable Water Recycling in Growing Cities

Jim Crocker
20th February, 2024

Creating Sustainable Water Recycling in Growing Cities

Image Source: Natural Science News, 2024

Water is an essential resource, and with cities growing and climates changing, managing this precious commodity is becoming quite a challenge. Let's take Lima as an example. It's a bustling metropolis with a big water stress problem. Not only is the population growing, but the effects of climate change are making water scarcer, and to top it off, the current infrastructure for wastewater management is, let's say, rather long in the tooth. In plain English, Lima's system is centralized and a bit outdated, which makes it really tough to recycle water or extract other valuable resources from wastewater. Now, here’s where science kicks in, with a spark of environmental ingenuity. Researchers are always on the lookout for new and improved ways to handle challenges like Lima's water woes. They've been on a quest to find alternative wastewater treatment methods that could help reduce excess nutrients – which can be harmful – in water bodies (that's what we call eutrophication mitigation) and make wastewater clean enough to be potentially reused for drinking after further treatment (that's called indirect potable reuse, or IPR for short). They checked out a couple of different techniques for cleaning up the wastewater. To combat eutrophication, the team studied systems including MLE (modified Ludzack-Ettinger), Bardenpho (it's like MLE’s more complex cousin), Step-feed (feeding the wastewater in steps to bacteria that clean it up), and two types of Membrane Bioreactor (MBR) methods. For IPR, which is the next-level treatment to make the water extra safe, they examined combining secondary treatments with processes like ultrafiltration (UF), reverse osmosis (RO), and advanced oxidation processes (AOP). Imagine a system that could fit at a district level, like a network of mini treatment plants all working together. This idea is part of the bigger picture aimed at creating a circular economy, which is like a loop where resources are reused and nothing goes to waste. It’s a fantastic concept that not only helps the environment by recovering resources but also makes the city safer and more prepared for any disasters or future water scarceness. Now, how do you figure out which method is the best? This is where it gets really scientific. The researchers used Life Cycle Assessment to look at the environmental impact, Life Cycle Costing to consider the money side of things, and, because decision-making can be complex, they threw Multi-Criteria Decision Analysis into the mix. This last tool is super useful because it helps to combine both the number-crunching side and more qualitative aspects to look at the overall impact socially and how well the system might operate technically. When they crunched the numbers, aiming for the most eco-friendly and cost-effective methods, Bardenpho was the star for nipping eutrophication in the bud. And if the researchers cared more about how easy the system was to operate and the social benefits, then the High-Flux MBR (HF-MBR) took the gold. Now, the results are a bit like a diet label for wastewater treatment. For the Bardenpho and similar methods, carbon dioxide emissions were lowish, phosphorus (which causes eutrophication) was also kept on the low end, and the cost was relatively inexpensive. But when it came to IPR, the HF-MBR combined with RO and AOP was top-notch. Although the global warming potential – think of it as the carbon footprint – was higher, the process almost completely eliminated the eutrophication issue. However, the quality of the reclaimed water was so high that it justified the higher cost. This study, which was handled by the sharp minds at the Peruvian LCA & Industrial Ecology Network at Pontificia Universidad Católica del Perú, is really a guiding light, showing us how different treatment methods can achieve various outcomes, balancing environmental, financial, technical, and social priorities. It's interesting to see how scientists can develop multiple solutions to tackle the same problem, and each of these solutions has its own set of trade-offs. This research could potentially serve as a blueprint for other cities facing similar challenges, demonstrating that with the right technology and a comprehensive decision-making approach, water stress doesn't necessarily have to leave cities high and dry.



Main Study

1) A multi-criteria decision framework for circular wastewater systems in emerging megacities of the Global South.

Published 20th February, 2024

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