Enhanced Removal Of Organic Contaminants From Water By Manganese Dioxide Formed In Situ

Organic contamination of the drinking source water is a serious problem in water supply. The organics may form more toxic byproducts in the disinfection process with chlorine if they can not be removed in the process of coagulation. But the regular coagulants and coagulation process can not satisfy the new standard of drinking water for orgnanic micropollutants. New type of coagulant which has the advantage of high efficiency, convenience and no side effect should be developed.Manganese dioxide formed in situ was prepared by manganese sulfate and potassium permanganate online added under neutral pH condition. The mictopography of manganese dioxide formed in situ was characterized by AFM, FT-IR and BET. Results showed that the particles of manganese dioxide formed in situ are un-regularly spherical form and have small particle size less than 100nm. With the higher specific surface area, the particles of the manganese dioxide formed in situ will coagulate instantly as they are formed in aqueous solution.The pH of the aqueous solution affects the type of the reaction of manganese dioxide formed in situ with organics, as seen from the results of phenol reacting with manganese dioxide formed in situ. The adsorptive reaction was happened for manganese dioxide formed in situ with phenol under neutral pH condition, while the oxidation-reduction reaction was observed under strongly acidic condition and the phenol removal efficiency was very high. The oxidative products of phenol were p-benzoquinone and coupled phenol.Four kinds of organic compounds with different functional groups on aromatic, that are aniline, phenol, nitrobenzene and benzonic acid were chosen for adsorption experiments. In these four organics, the adsorption capacity increased in the order aniline>phenol>nitrobenzene>benzoic acid. According to the analysis on organics structure and the surface characteristics of manganese dioxide formed in situ, conclusion may be obtained that the surface area of oxide and electrostatic are important for adsorption and the hydrophobicity is the minor effect. The adsorption of organics by manganese dioxide formed in situ was more conform to the Langmuir adsorption mode.Manganese dioxide formed in situ was selected as coagulant and coagulant aid to investigate the organic removal in micro-polluted water and the technical parameters were fixed. Results showed that UV254 and TOC were removed as high as 40% and 20% respectively. Organics were mainly removed in the process of fast mixing. While UV254 and TOC can be improved more than 20% as the manganese dioxide formed in situ enhanced the coagulation of aluminum sulfate.Tannic acid was selected as a reproducible surrogate for NOM because it is present in natural waters and it resembles humic substances in some properties such as adsorption, color, and complex formation. Tannic acid also contains both saccharide and aromatic acid components that are significant in surface waters. The adsorption results showed that the removal efficiency for tannic acid adsorbed by manganese dioxide formed in situ is higher than benzoic acid. Calcium can accelerate tannic acid removed by manganese dioxide formed in situ. This means that the adsorption of organic acid by manganese dioxide formed in situ is correlated with the value of its molecule weight. The dose of KMnO4 is not the essential factor for tannic acid removal, while the adsorption of newly formed MnO2 is the most important factor for tannic acid removal.UV254 and TOC removal percentage were 40% and 20% respectively as 10mg·L-1 manganese dioxide formed in situ was added to treat micro-polluted Songhua River. But the residual turbidity and soluble manganese of disposed water are higher than the standard of drinking water. As manganese dioxide formed in situ was added with a dose of 1.37mg·L-1 to enhance the coagulation by aluminum sulfate (10mg·L-1), UV254 and TOC can be increased more than 20% and 10% respectively. The turbidity, soluble manganese and soluble aluminum of treated water were all satisfied the standard of drinking water. Results of coagulation on the water of Songhua River with standard materials showed that manganese dioxide can remove nitrobenzene, phenol and aniline in the Songhua River and the organic removal efficiency is more than 20%. Benzonic acid can not adsorb by manganese dioxide formed in situ no matter in distilled water or in Songhua River. Ca2+ existed in Songhua River has less effect on the adsorption of manganese dioxide formed in situ than in distlled water. Manganese dioxide formed in situ has higher TOC adsorption capacity for natural water than distilled water.