The removal of inorganic phosphate from water using carboxymethyl cellulose‐iron hydrogel beads

Abstract BACKGROUND Inorganic phosphate (Pi) is key to improved crop yields; however, agricultural drainage leads to the accumulation of this nutrient in aquatic ecosystems and promotes the formation of harmful algal blooms. The aim of this study was to produce a hydrogel with high binding capacity and affinity towards Pi produced from carboxymethyl cellulose (CMC) and iron (III) chloride (FeCl3). RESULTS CMC was converted to CMC‐Fe composites by incubation with FeCl3. The half‐lives (t1/2) of CMC functionalization with 25 mmol L−1 FeCl3 were 11.56 min (1.5% CMC) and 13.91 min (3.0% CMC). The apparent dissociation constants (KD App) of CMC‐Fe were estimated to be 33.99 μmol L−1 (1.5% CMCFe) and 24.81 μmol L−1 (3.0% CMC‐Fe). The phosphate binding capacity (PBC) of the hydrated hydrogels were 74.0 ± 3.06 mg g−1 (1.5% CMCFe) and 91.4 ± 4.51 mg g−1 (3.0% CMC‐Fe). Laboratory‐scale continuous flow filtration studies showed an average removal of 91.3% (mixed filter) and 52.5% (unmixed filter). Batch type treatment of agricultural drainage showed a reduction in Pi content from 0.40 to 0.11 mg L−1 (1.5% CMC‐Fe) and 0.17 mg L−1 (3.0% CMC‐Fe). The amount of bound‐Pi was 26.7 ± 0.63 μg g−1 (1.5% CMC‐Fe) and 32.8 ± 1.31 μg g−1 (3.0% CMC‐Fe). The iron leached from 1.5% and 3.0% CMC‐Fe beads was 11.98 ± 1.80 and 3.57 ± 1.63 mg g−1, respectively. CONCLUSION The CMC‐Fe hydrogel shows great promise as a Pi‐adsorbing material with applications in the treatment of agricultural drainage. © 2020 Society of Chemical Industry (SCI)