Modification Of Inorganic Flocculants Of Polymeric Ferric Sulfate And The Relevant Applications

With the development of industry, increasing emission of industrial sewage has caused serious impact on water resources in China. Serious water pollution not only leads to the depletion of water resources but also endangers the health of people, and even restricts coordinated development of China economy. How to reduce industrial pollution discharge and efficiently recycle water resources are the key to solve water scarcity. Flocculation method, being one of the most important operation units in wastewater treatment, has been regarded as an important safeguard to ease the water crisis. As such, it is highly desirable to develop efficient and low-cost flocculants for water treatment processes.The flocculants based on polymeric ferric sulfate (PFS) have the characteristics of high efficiency and low cost and have been used widely. In this dissertation, PO43-was introduced into PFS to affect the hydrolysis and polymerization of Fe3+species, which, in turn, are conducive to the formation of polynuclear complexes and network structures and, successively, enhance the performance of the resultant polymeric ferric phosphoric sulfate (PFPS) flocculants. Moreover, according to the fact that the flocculants based on chitosan (CTS), being a kind of natural organic polymer, have advantages of low dosage, fast flocculation speed, and easily biodegradable and environment-friendly properties, CTS-PFPS composite flocculants were designed and synthesized. Finally, the flocculation performance of the above two series of flocculants in treating actual wastewater was investigated. The main contents discussed were as follows:By adjusting molar ratio of phosphoric acid to sulfuric acid and using ferrous sulfate as initial material and sodium chlorate as oxidant, PO43-was introduced during the polymeric process of ferric sulfate, leading to PFPS. Combining single-factor with orthogonal experiments, the effects of various ratio of the raw materials, amount of oxidant, synthetic temperature on the flocculation performance of final products were studied. The obtained results showed that the reddish brown viscous liquid with basicity as high as14.3can be obtained when the synthesis process was conducted at80℃for2h with molar ratio of FeSO4·7H2O to H+, H2SO4to CH3COOH+H3PO4, CH3COOH to H3PO4, and FeSO4·7H2O to NaClO3being1:0.26,7:1,3:1, and1:0.15, respectively.The flocculants prepared under the above optimum conditions were used to pretreat landfill leachate. The influences of coagulation conditions, such as pH, dosage of flocculant, stirring speed, and stirring time, on the removal rate of chemical oxygen demand (COD) were investigated by using orthogonal design. The results showed that, by combining successive electro-catalysis oxidation process, the coagulation-electrocatalysis oxidation process can effectively remove suspended solids and lower COD, and the removal rates reach51.5%and69.1%, respectively. It should be noted that the coagulation-electrocatalysis oxidation process leads to complete removal of NH3-N, reaching the national standard for pollution discharge (GB16889-2008).Water-soluble CTS was prepared by means of oxidative degradation using perchloric acid as oxidant. The resultant water-soluble CTS was combined with PFPS. The effects of various ratio of raw materials, synthesis temperature, and synthesis time on flocculation performance of the composite flocculants were studied. The optimum synthesis conditions were obtained as follows:the volume ratio of CTS to PFPS is1:9, synthesis temperature is50℃and synthesis time is1.5h. The effects of stirring speed, stirring time, and settling time on flocculation performance of the composite flocculants was investigated in treating papermaking wastewater. It was found that the composite flocculants can destabilize and precipitate completely with stirring speed being550r/min, stirring time being5min, and settling time being1min. Furthermore, the composite CTS-PFPS flocculants showed superior flocculation performance than pristine PFPS flocculants for removal of COD in treating papermaking wastewater.