Novel Lignin-Modified Forward Osmosis Membranes: Waste Materials for Wastewater Treatment

Lignin, the second most plentiful biopolymer, is produced on a large scale as the waste of the pulp and paper industries. Conventionally, lignin is incinerated for energy generation, while less than 2% of the produced mass is converted to value-added products. Herein, we employed hydrophilic sulfonated kraft lignin (SKL) to modify the selective layer of thin-film composite (TFC) forward osmosis (FO) membranes. Different concentrations of SKL (1, 3, and 6 wt %) were dispersed in m-phenylenediamine solution prior to the polymerization reaction with trimesoyl chloride-heptane solution. The modified membrane with a maximum amount of SKL (M3) provided 33.5 LMH water flux, a twofold improvement compared to the pristine membrane, when tested in the FO configuration with 2 M NaCl and deionized water as draw and feed solutions, respectively. Moreover, M3 showed a significantly lower flux decline than the unmodified membrane in the fouling experiments against sodium alginate solution as a synthetic wastewater and boiler feed water as an industrial process-affected water of the oil sands industry. The water contact angle decreased from 88.7° for the pristine membrane to 70.6° for M3, indicating the enhanced wettability of the modified membranes by the incorporation of SKL particles. Our work presents a novel application for SKL to be used as a hydrophilic modifier in the synthesis of TFC polyamide membranes with enhanced permeation and antifouling performance.