The Study Of Wettability Of Filter Media And Influence On Oil-Removal Performance

Filtration process is a typical tertiary treatment method for oily wastewater, suitable for the lower oil concentration and oil particulates smaller than 10μm. The wettability of filter media probably has some significant influence on the oil removal efficiency, the surface physicochemical characteristic of filter media becoming universally concerned in research field at home and abroad in recent years. Therefore, to helps a lot in selecting and designing of more efficient filter media, the surface wettability of several commonly-used granular filter media with hard texture, i.e. nutshell, anthracite, manganese sand, ceramic granule, quartz sand and ceramic sand, were investigated in this thesis. At the same time, a laboratory simulated small scale deep bed filtration process was also constructed for anthracite, ceramic granule and quartz sand to get the relationship between wettability and oil removal efficiency.(1) Surface chemical composition of 6 filter media were characterized by X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infra-Red Spectroscopy (FTIR). Results show that nutshell surface is principally organic functional groups constituted of carbon and Oxygen elements, making it an apoler and lower energy chemical surface, anthracite also constituted of carbon and Oxygen elements, but has a little Silicon elements, is an apoler surface, manganese sand, ceramic granule, quartz sand and ceramic sand are mainly made up of Oxygen and Silicon, contain multivalent coordination compounds, which make them a polar surface.(2) The basic equation of dynamic pressure method for particles or powders wasdeduced asâ–³P² =(?). According to the basic theory of wettability and researchpurposes, a lipophilic hydrophilic ratio(LHR) concept was used to compare quantitatively thewettabilities of the 6 filter media. The calculation formula is: LHR = (?)Linear least-square fits for all wetting rates gave regression coefficients is more than 0.99, and the five times average LHR value of ceramic sand for hexamethylene and water are 2002.88±152.02 and 6932.78±550.46 respectively. It was confirmed by the great regression coefficients and reproducibility of wetting rates that the values have a good reliability and the technique is applicable.The calculated LHR values of nutshell, anthracite, manganese sand, ceramic granule, quartz sand and ceramic sand with a size range of 0.55-0.83mm were 66.87, 1.71, 1.24, 1.22, 1.16 and 0.80, which means nutshell is much more lipophilic while anthracite, manganese sand, ceramic granule and quartz sand is somehow more lipophilic than ceramic sand, which is hydrophilic. These results of LHR values are in accordance with the differences of filter's surface physicochemical properties. Namely, the surface is apolar and lower energy, it makes them wetting easily only to apolar oil, the surface is polar and higher energy, not only apolar oil, but also polar water are wettable favorably.(3) During a filtration period of filtration process running in a lab simulated small scale deep media bed, the oil removal efficiencies of anthracite, ceramic granule and were 86.9%, 71.6% and 69.3%, it shows that anthracite has the best oil removal efficiency, and ceramic granule is better than quartz sand. It can be confirmed from the filtration coefficient that the oil adhered on the ceramic granule surface is easier drop off than the others.Theoretically, there exists consistency from LHR and oil removal efficiencies, namely, the better the filter's lipophilicity is, the easier removal oil from wastewater, and vice versa. Similarly, the maximum volume-specific deposit were 678, 506 and 495g·m^-3, confirms that the maximum volume-specific depositσ_max in the filter layer are increscent gradually with the increasing ofthe LHR value.