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

BACKGROUND Inorganic phosphate (P i ) 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 P i produced from carboxymethyl cellulose (CMC) and iron (III) chloride (FeCl 3 ). RESULTS CMC was converted to CMC‐Fe composites by incubation with FeCl 3 . The half‐lives ( t 1/2 ) of CMC functionalization with 25 mmol L −1 FeCl 3 were 11.56 min (1.5% CMC) and 13.91 min (3.0% CMC). The apparent dissociation constants ( K D App ) of CMC‐Fe were estimated to be 33.99 μmol L −1 (1.5% CMCFe) 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% CMCFe) 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 P i 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‐P i 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 P i ‐adsorbing material with applications in the treatment of agricultural drainage. © 2020 Society of Chemical Industry (SCI)