Water scarcity is a pressing global issue, with 38% of Europe's population affected in 2019 alone. But what if we could transform industrial wastewater into a valuable resource? Enter water-smart industrial symbioses (WSISs): In this approach, the industry and the water sector cooperate for their mutual advantage to recover and reuse water, materials, and energy, reducing reliance on scarce freshwater resources.
Our recent study, “Innovative pre-treatments for reverse osmosis to reclaim water from biotech and municipal wastewater for the industrial symbiosis in Kalundborg” (Denmark), explored the potential of WSISs by testing advanced methods to treat municipal wastewater for industrial reuse. We set up a pilot plant to evaluate various membrane filtration techniques, aiming to produce high-quality water for industrial cooling systems.
The Challenge of Complex Wastewater
What sets our research apart is the challenging mix of wastewater being treated. The wastewater treatment plant in Kalundborg processed standard municipal wastewater and pre-treated industrial and power plant wastewater. This created a highly complex effluent with elevated concentrations of certain substances, testing the limits of current and new water reclamation technologies.
To tackle this, the study focused on three types of membranes used as pre-treatment steps for reverse osmosis to mitigate fouling processes: ultrafiltration (UF), a novel ultra-tight UF, and nanofiltration (NF).
Key Findings: Efficiency vs. Complexity
Despite having larger pores, the conventional UF membrane outperformed the denser options, achieving the highest water recovery rate of 87% while using the least energy. While ultra-tight UF and NF membranes were more effective at removing specific contaminants, they couldn't match the overall efficiency of the UF membrane.
However, membrane performance wasn't the only factor influencing success. Our study highlights a persistent challenge: biofouling, the buildup of microorganisms on the membranes. Even the densest membranes couldn't prevent biofouling on their own. A practical solution was biocide dosing, while UV treatment was shown to be an environmentally friendly alternative.
The Environmental Trade-offs
The study doesn't stop at technical performance—it also examines the environmental impacts through a life cycle assessment. We compared the water reclamation process to two alternatives: sourcing fresh water from a nearby lake and desalinating seawater.
Here's what we found:
Using lake water had the lowest carbon footprint but impacted water availability.
Desalination had the highest carbon footprint but didn't directly affect local water resources.
Water reclamation, balancing energy use, carbon emissions, and water availability impacts offered a middle ground.
One critical aspect was the treatment of brine—the concentrated waste stream generated by reverse osmosis. Treating brine significantly increased the energy consumption and carbon footprint of the water reclamation process. This underscores the importance of considering the entire water treatment cycle when evaluating sustainability.
A Path Forward for Sustainable Water Management
Our research demonstrates that even complex municipal wastewater, mixed with industrial effluents, can be treated to produce high-quality water for industrial reuse. By embracing these methods, industries in water-stressed regions could significantly reduce their reliance on freshwater resources.
However, the study also highlights the complexity of finding the most sustainable solution. The best approach depends on local conditions, available water sources, and the region's energy mix. In some cases, water reclamation may be the optimal choice. In others, desalination or careful management of local freshwater resources might be more sustainable.
The Bigger Picture: Circular Water Systems
The key takeaway from our research is clear: we have the technology to create circular water systems where wastewater becomes a resource instead of a waste product. As climate change, population growth, and industrial activity intensify water scarcity, these water-smart industrial symbioses could ensure sustainable water management for industries and communities.
Our study advances our understanding of water reclamation and emphasizes the importance of innovative, site-specific solutions. By turning wastewater into a resource, we can move closer to a future where water is managed sustainably despite growing global challenges.
KWB authors
