Study On The Treatment Of Textile Reverse Osmosis Concentrate Based On Forward Osmosis Technology

The discharge amount of textile wastewater is huge.Reverse osmosis?RO?technology has been widely used in the advanced treatment of textile wastewater due to its advantages of good treatment effect,strong adaptability and convenient operation.However,the reverse osmosis concentrate?ROC?produced in the process of reverse osmosis usually has a high concentration of salts and organic matters,and is hard to be degraded.The purpose of this work is to further treat and reuse the ROC of textile wastewater,the quality of textile ROC was characterized to explore the characteristics of the textile ROC quality.Then the forward osmosis treatment of ROC was investigated for the water recovery and the change of ROC quality during operation.The treatment of textile ROC The mechanisms of the forward osmosis membrane fouling was finally explored propel the application of forward osmosis in ROC treatment.The main research contents and conclusions are listed as follows:?1?The analysis of physical and chemical properties of reverse osmosis concentrate.The results showed that the water quality of ROC fluctuated greatly and the concentration of TDS ranged between 5500 and 7400 mg/L.The highest concentration of three ions were SO₄^2-,Na⁺and Cl^-.Besides,the ROC had a certain hardness and scaling trend.The ROC was found mainly contained soluble microbial products and a small amount of humic acid.The amount of hydrophobic acid substance and hydrophilic substance were 51%and 33%respectively,and the content of weak hydrophobic substance was lowest which was 3%.The molecular weight of ROC was3 to 10k Da,accounting for 72.4%,followed by 15.6%of ROC with molecular weight less than 1k Da,and the content of ROC with molecular weight greater than 30k Da was the lowest.Combined with FTIR and GC-MS analysis,it can be concluded that the functional groups of organic compounds in ROC were mainly C=C stretching vibration and C-H bending vibration,and there were chlorobenzene,phthalic acid,long-chain alkane,cyclosiloxane and other complex components in ROC which were mostly the intermediate products of industrial substances such as dyes and surfactants.?2?The treatment of textile ROC by forward osmosis process.When the CTA membrane was used as the forward osmosis membrane,the real textile wastewater was used as FS,the recovery reached more than 90%when 2 mol/L Na Cl was used as DS,while the recovery was 71%when 2 mol/L NH₄HCO₃ was used as DS.The reverse solute flux of NH₄HCO₃ was much higher than that of Na Cl,and the rejection rate of divalent inorganic ions in ROC both reached more than 99.4%.According to the SEM-EDS and XRD,the main pollutants on the surface of membrane was Ca CO₃.The particle size of Ca CO₃ was larger and more regular when the DS was NH₄HCO₃.Due to the reverse salts of HCO₃^-in NH₄HCO₃,the formation time of Ca CO₃ precipitations was earlier than that of Na Cl,and the concentration of Ca²⁺in the concentrated ROC was about 1 mg/L,which was far lower than that of Na Cl.Nevertheless,the Ca CO₃pollutions had little effect on water flux which was mainly attributed to the fact that the FS was concentrated and the DS was diluted.The four circles performances indicated that the forward osmosis membrane was strong calcium-resistant.?3?The study on the calcium carbonate scaling mechanism in forward osmosis.For CTA membrane,the increase of calcium concentration in the feed solution didn't significantly affect the water flux,but for TFC membrane,the water flux decreased with the increase of calcium concentration.No matter for CTA membrane or TFC membrane,the antiscalants had no significant effect on the water flux within a certain concentration range.But if the concentration of antiscalants continued to rise,the calcium carbonate particles on the membrane surface would agglomerate which aggravated the membrane fouling,and the water flux would decrease.Since the presence of sulfate would change the morphology of calcium carbonate particles on the membrane surface and when the draw solution was NH₄HCO₃,the water flux of both CTA membrane and TFC membrane decreased.When the draw solution was Na Cl,the repeatability of the forward osmosis membrane was higher than that of NH₄HCO₃,and the anti-calcium scaling performance of CTA membrane was better than that of TFC membrane.In this paper,the reverse osmosis concentrate was systematically measured and analyzed,the treatment potential of forward osmosis technology in textile ROC was explored,and the fouling membrane in the treatment process was characterized and its mechanism was studied,which provided a possible direction for the near-zero discharge of textile wastewater.