Study On The Removal Of Pollutants From Municipal Reverse Osmosis Concentrate

With the increasing requirement of reclaimed water quality and the rapiddevelopment of membrane technology, reverse osmosis （RO） is widely applied in thefield of wastewater reclamation, resulting in the dramatic increase in the production ofRO concentrate （ROC）. ROC with high salinity, complex component and difficulty tobiodegrade, will severely contaminate the environment if not properly treated andresult in RO membrane fouling if further concentrated by RO process directly.Removal of hardness and the organic pollutants from the ROC of a reclaimed waterplant was researched in this paper.ROC contains a large amount of inorganic ions, among which calcium andmagnesium ions will form scale, and the high concentration of sulfate, nitrate andchloride will seriously damage the environment. Pellet softening method had a poorresult because ROC contained antiscalants. In the experiment, chemical precipitationmethod was employed to remove the hardness from the ROC and NaOH was chosen asthe softening agent, according to ROC characteristics. The result indicated that NaOHcould effectively remove the hardness, and it was beneficial to the hardness removalespecially with the help of CaCO₃powder. When the dosage of NaOH ranged from200to1200mg/L，the hardness and pH showed a linear decrease and a logarithmicgrowth, respectively.The organic matters in ROC mainly consisted of small molecules whosemolecular weight was less than1kDa, owing to the difficulty of degradation oforganic pollutants in the ROC and considering the strong oxidizing of hydroxyl radical（·OH）, Fenton reagent was used to oxidize ROC,·OH produced during the reactionprocess of Fenton method, a kind of advanced oxidation processes, can quickly andeffectively oxidize all kinds of refractory organic pollutants. Tests on the influencefactors of the Fenton reaction, including the reaction initial pH value, the molarconcentration ratio of H₂O₂and Fe²⁺, the dosage and dosing method of H₂O₂, etc.,were conducted to seek the optimum reaction condition for removing the organicmatter in the municipal ROC, which was as follows. The reaction system initial pHwas3.0, the molar concentration ratio of H₂O₂and Fe²⁺was1:3. The tests also revealed that when the H₂O₂dosage was330mg/L, the DOC removal rate was52.7%.One-time dosing and batch dosing of H₂O₂did not have significant influence. Whenthe dosage of H₂O₂was1000mg/L, the DOC removal rate could reach62%.