Recovery of phosphorus as soluble phosphates from aqueous solutions using chitosan hydrogel sorbents

Abstract

This manuscript presents new method of phosphorus recovery from aqueous solutions in a convenient form of readily-soluble phosphates using chitosan hydrogels. Non-modified chitosan hydrogel granules (CHs) and chitosan hydrogel granules crosslinked with epichlorohydrin (CHs-ECH) served as orthophosphate ion carriers. The developed method was based on cyclic sorption/desorption of orthophosphates, with desorption performed in each cycle to the same solution (the concentrate). The concentrations of orthophosphates obtained in the concentrates depended on, i.a., sorbent type, sorption pH, source solution concentration, and desorption pH. Phosphorus concentrations in the concentrates were even 30 times higher than these in the source solutions. The maximum concentrate concentrations reached 332.0 mg P-PO4/L for CHs and 971.6 mg P-PO4/L for CHs-ECH. The experimental series with CHs-ECH were characterized by higher concentrations of the obtained concentrate, however the concentrates were also more contaminated with Cl− and Na+ ions compared to series with CHs. The high content of chlorine and sodium ions in the concentrates was also favored by the low pH of sorption (pH < 4) and very high pH of desorption (pH > 12) in the cycles. After concentrate evaporation, phosphorus content in the sediment ranged from 17.81 to 19.83% for CHs and from 16.04 to 17.74% for CHs-ECH.

Desorption Strategies and Reusability of Biopolymeric Adsorbents and Semisynthetic Derivatives in Hydrogel and Hydrogel Composites Used in Adsorption Processes

“…In some specific cases, the contaminant might be recovered and reused for other industrial or agricultural applications. For example, Jóźwiak et al reported the recovery of P in a basic eluent (NaOH, pH 12–13), that was evaporated to obtain a sediment rich in water-soluble phosphate salts. This sediment has the potential to be used in agricultural industry .…”

“…For example, Jóźwiak et al reported the recovery of P in a basic eluent (NaOH, pH 12–13), that was evaporated to obtain a sediment rich in water-soluble phosphate salts. This sediment has the potential to be used in agricultural industry . However, not all contaminants can be easily recovered from the eluents, so other strategies are needed for better management and disposal.…”

“…This sediment has the potential to be used in agricultural industry. 136 However, not all contaminants can be easily recovered from the eluents, so other strategies are needed for better management and disposal.…”

Recovery of Phosphate(V) Ions from Water and Wastewater Using Chitosan-Based Sorbents Modified—A Literature Review

“…In another study [14], the efficiency of phosphate removal was compared using noncrosslinked chitosan hydrogel granules (CSHs) and those crosslinked with epichlorohydrin (CSHs-ECH). Two parameters turned out to be crucial for the efficiency of adsorption: the pH of the sorbate and the contact time of the sorbent with the sorbate.…”

Adsorption Characteristics for Cu(II) and Phosphate in Chitosan Beads under Single and Mixed Conditions

“…Meanwhile, at pH values below the pK a of chitosan, the NH 2 group is protonated into NH 3 + , which can remove anions such as phosphate [ 12 , 13 ] and arsenic [ 14 ] by forming electrostatic interactions. Moreover, phosphate (pK a1 = 2.1, pK a2 =7.2, and pK a3 = 12.3) existed as four different species (H 3 PO 4 , H 2 PO 4 − , HPO 4 2− , and PO 4 3− ) depending on the pH [ 15 ].…”