Enhanced phosphate removal by filler encapsulation and surface engineering using SA/PVA matrix: Fabrication optimization, adsorption behaviors and inner removal mechanism

Adsorption-based technology provides a feasible alternative for phosphorus control in waterbodies. Herein, Labiochar derived from toxic sludge was encapsulated into polymer matrix as functional filler, and then surface modification on formed hydrogel via in-situ polymerization of polydopamine (PDA) was realized to achieve enhanced phosphate removal from water. Effects of biochar content and PDA coating time on adsorption performance were investigated, and optimized composite beads could achieve experimental maximum capacity of similar to 13.74 mg P/g. Solution pH study implied favorable adsorption at pH 4-6, and coexisting anions noticeably facilitated phosphate capture owing to hydrogel swelling while reverse effect was observed for cation Ca2+. Kinetic study showed phosphate adsorption was chemisorption in nature, and overall adsorption process was mainly controlled by intraparticle diffusion stage. Adsorption isotherm using different samples suggested the transformation of sorption form from multilayer heterogeneous adsorption to monolayer homogeneous adsorption after PDA coating on hydrogel surface. Thereafter, the reusability of as-prepared hydrogel was investigated through cyclic adsorption-desorption experiments, and continuous treatment of phosphate-enriched water was conducted to evaluate its potential for practical application. This work could provide useful implication to the development of functional composite hydrogels for phosphate removal.