| Aug 19, 2025 |
Self-driven hydrogel beads offer low-cost phosphorus recovery from wastewater
Researchers developed reusable self-driven hydrogel beads that enrich phosphorus and remove heavy metals from wastewater without external energy.
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(Nanowerk News) Phosphorus is an essential nutrient for life, yet only 16% of the phosphorus mined globally each year is absorbed in human food. The majority enters wastewater through agricultural runoff and animal waste, leading to resource waste and water eutrophication. Efficient recovery of phosphorus from wastewater has become a significant challenge in the environmental field.
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Currently, the recovery of phosphorus through the precipitation method using struvite (MgNH4PO4·6H2O) is widely studied. However, this technology faces two major bottlenecks: first, the phosphorus concentration in wastewater is generally low, requiring pre-treatment for enrichment; second, heavy metals in wastewater can co-precipitate with struvite, affecting the purity and agricultural value of the recovered product. Existing enrichment technologies often rely on membrane separation, which requires external energy, is costly, and struggles to simultaneously remove heavy metals, limiting practical applications.
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A research team led by Professor Xing Xie from the School of Civil and Environmental Engineering at Georgia Institute of Technology has published a study proposing a low-cost, energy-free solution—using negatively charged polyacrylate sodium (PSA) hydrogel beads as self-driven dehydrators to achieve simultaneous phosphorus enrichment and heavy metal removal.
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The article was published in Frontiers of Environmental Science & Engineering ("Self-driven phosphate enrichment by hydrogel beads for nutrient recovery").
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The chosen PSA hydrogel beads are a three-dimensional hydrophilic polymer network material that can absorb large amounts of water through swelling. The negatively charged nanoscale channels inside can selectively block phosphate ions through electrostatic repulsion.
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In experiments, the team systematically tested the performance of the hydrogel beads under varying phosphorus concentrations, pH levels, and ionic strengths. In a low-concentration phosphorus solution of 0.1 mmol/L, the hydrogel beads achieved a retention rate of 93.2%. Even when the phosphorus concentration increased to 10 mmol/L, the retention rate remained at 56.9%. Notably, when approximately 1% by weight of hydrogel beads was added to a 0.5 mmol/L phosphorus solution, phosphorus was concentrated by 3.6 times within just 3 hours, achieving a recovery rate of 70%.
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Importantly, these hydrogel beads have a "two birds with one stone" capability. Experiments showed that when both 0.5 mmol/L phosphorus and nickel ions were present in the solution, the hydrogel beads could concentrate phosphorus while 100% removing nickel ions, effectively preventing heavy metal contamination in the recovered product. Additionally, the hydrogel beads can be reused after drying, with no significant decline in swelling performance or phosphorus retention rate observed over four cycles, further reducing operational costs.
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This self-driven hydrogel technology requires no external energy and is easy to operate, providing a low-cost pre-treatment solution for phosphorus recovery from wastewater. If widely applied, it could enhance the efficiency and economic viability of the struvite precipitation method while ensuring the agricultural value of the recovered products by simultaneously removing heavy metals.
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The team emphasizes the need for further research on the effects of other pollutants in complex wastewater environments and optimization of swelling times and retention performance at high phosphorus concentrations. However, the current results already demonstrate the potential of this technology in promoting phosphorus resource recycling and advancing agricultural sustainability.
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