Research On Organic Fouling Of Reverse Osmosis Membrane

Reverse osmosis technology occupies unique advantages in water treatment field. However, membrane fouling is one of the most serious obstacle to restrict its widespread application. One of the critical issues is organic fouling, which not only reduces the permeate flux of a membrane and requires more frequent cleaning, but also shortens its life span.Fouling of RO membrane by the ubiquitous and recalcitrant dissolved organic matter (DOM), such as natural organic matter (humic acid), polysaccharides (alginate), proteins (bovine serum albumin), was systematically investigated. In addition, the significant effect was observed during combined fouling by both CaCO₃ and DOM. Finally, commercial antiscalant was adopted to alleviate the organic fouling of RO membrane, which is a new and effective method.Pilot study demonstrated that, humic acid, alginate and bovine serum albumin (BSA) could form compact gel layer on membrane surface,which lead to a severe flux decline. Especially,permeate flux decreased dramatically in the presence of calcium ions. This behavior can be attributed to calcium bridges between adjacent organic matter and the formation of organic macromolecule complexation. When langelier saturation index (LSI) was 1.1, organic fouling played a key role during the combined fouling of DOM and CaCO₃, which was the dominant factor of reducing permeate flux. Specifically, we investigated the effects of chemical (solution pH, ionic strength, and foulant concentration) and physical (initial flux, solution temperature ,concentration flux and spacer) factors on the membrane fouling mechanisms.The introduction of antiscalant to feed water was found very effective for lessening organic-fouled RO membrane in the presence of calcium ions. Antiscalant lessens organic fouling by the following three ways. Firstly, it is proposed that antiscalant lessens organic fouling significantly by removing free and organic-complexed calcium ions, which could decrease the quantity of macromolecule complexation. Secondly, antiscalant, organic foulant and calcium ions could form a kind of hydrophilic compound, which adsorption onto the membrane surrface could make membrane more hydrophilic and significantly lower fouling. Thirdly, the introduction of antiscalant could enhance electrostatic repulsion and antiscalant is also a kind of very excellent disperser to organic matters.