image: Fig. 1. Waste derived hydrogel beads for phosphate capture. Graphical abstract showing bead preparation, phosphate adsorption, regeneration, molecular analyses and preparation-stage environmental assessment.
Credit: Chong Liu, Wei Yu and Brent Young.
Waste seaweed and low-grade magnesite mining residue can be turned into reusable beads that capture phosphate from water, researchers at the University of Auckland report in Green Chemical Engineering. Their study combines nutrient capture with easier collection of the adsorbent and examines the environmental impact of making it. The work provides a laboratory proof of concept for recovering phosphate with waste-derived beads.
“Phosphorus is essential for agriculture, but excess phosphate in water can fuel algal growth and damage aquatic ecosystems,” explains first author Chong Liu. “Recovering it could help address water pollution while conserving a valuable resource. One practical challenge is collecting fine adsorbent powders after treatment.”
The team converted waste seaweed into hydrochar, a carbon-rich material produced by heating biomass in water. They added magnesium obtained from magnesite mining residue, then enclosed the material in a chitosan hydrogel to form millimetre-sized beads that can be separated from water.
“Capturing phosphate is only part of the challenge. We also need materials that can be collected from water and used again,” says Liu. “By incorporating this material into beads, we aimed to bring these needs together while making use of waste resources.”
The beads captured phosphate under near-neutral laboratory conditions and retained 87.03% of their initial adsorption capacity after five adsorption and desorption cycles. At 45 °C, the Sips adsorption model estimated a maximum capacity of 85.35 milligrams of phosphorus per gram of adsorbent. Spectroscopic measurements and molecular calculations indicated that magnesium-containing sites, together with carboxyl and amino groups, help bind phosphate. Meanwhile, analysis of binding-site energies showed that the strongest sites were occupied first, offering clues for improving future materials.
The team also assessed environmental impacts from raw-material supply through bead production. “Chitosan and preparation of the magnesium-modified hydrochar accounted for the main burdens,” shares Liu. “Identifying where changes to materials and processing could make the preparation route greener.”
The authors noted that longer-term tests in real wastewater and further process development are needed before scale-up. “Using phosphate-loaded beads as a slow-release fertilizer remains a possibility for future evaluation,” adds Liu.
Contact the author: Chong Liu, Department of Chemical & Materials Engineering, University of Auckland, Auckland, 1010, New Zealand. Email: 17609858895@163.com
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Journal
Green Chemical Engineering
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Marine waste-derived hydrochar beads for circular phosphate recovery: site energy distribution, molecular interactions and life cycle assessment
COI Statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.