Effects on the purification of tannic acid and natural dissolved organic matter by forward osmosis membrane

Abstract

The purification performance of tannic acid and dissolved organic matter (DOM) contained real surface water by forward osmosis (FO) was investigated systematically. Since representing the main characteristics of natural DOM fractions, tannic acid was first used as a surrogate for natural DOM analysis. The FO could reject tannic acid effectively with removal efficiencies of approximately 99.0%, as well as for natural DOM removal. The more severe fouling flux decline accompanied with lower tannic acid retention was found at greater draw solution concentrations and in the active-layer-facing-the-draw-solution (AL-facing-DS) orientation, which was ascribed mainly to the more severe fouling resulting from greater tannic acid adsorption in the porous support layer of the FO membrane under these conditions. In the AL-facing-DS mode, it was revealed that the higher the concentrations of initial substances (i.e., tannic acid and calcium ion) in the feed water, the more notable fouling flux decline and tannic acid retention occurred. In natural DOM purification experiments, the main factors investigated had the similar influences on FO performance as those mentioned above. Further, the membrane orientation has a minor impact on the natural DOM removal by FO membrane. The permeation drag influenced by the water flux probably played a critical role in the retention of tannic acid and natural DOM contained surface water by the FO membrane in AL-facing-DS mode.