Study On Treatment Of Oily Wastewater And Filter Surface Modification

The wettability of filter media has some significant influence on the filtration treatmentefficiency of oily wastewater which are，commonly used quartz sand filter with smallspecific surface area, weak polarity. Due to its hydrophobicity，the effect on oil wastewatertreatment is poor. In order to improve the affinity of quartz sand and treatment effect of oilwastewater, we put forward the concept of surface modification which is becominguniversally concerned in research field at home and abroad in recent years. Surfacemodification refers to changing the chemical structure of raw material particles to becomelipophilicity and hydrophobicity by the physical and chemical reactions，thus to improving thetreatment effect. The paper selectes silane coupling agent KH-550, titanate coupling agentDN-101and aluminate coupling agent DL-411as surface modification agent to modify thequartz sand filter, study the wettability before and after quartz sand modification. With staticsimulation experiment of oily wastewater, unmodified and modified quartz sand filtration oilremoving performance are investigated.The relationship between the wettability and oilremoving effect are revealed to provide a theoretical basis for the production of new modifiedfilter.（1）In order to evaluate and compare the wettability of unmodified and modified quartzsand filter conveniently, according to the Laplace and Young equation, the relation equationbetween wetting weight and contact angle is derived for the first time. the basic equation is：cosθ=r_eff/2γ_LG gw/επR²For the quartz sand filter with particle diameter of0.45⁰.9mm, research on thewetting process of unmodified and modified quartz sand with dynamic weight method.Results show that the deionized water and cyclohexane lead to the fastest wetting rate in20sand then slowly level off for unmodified and modified quartz sand filter. Around180s, thewetting process achieves a balance, wetting weight almost ceases to increase, indicating thatthe dynamic weight method is feasible to study the wettability of unmodified and modifiedquartz sand filter. The results are accurate and reliable.（2）The optimum modification conditions for titanate coupling agent were: the couplingagent concentration was15%，reaction temperature was90℃and stirring time was15min.The optimum conditions for silane coupling agent and aluminate coupling agent were:coupling agent concentration was15%，reaction temperature was110℃and stirring time was15min．The water wettability of quartz sand could be reduced from1.5589g to0.0282g by titanate coupling agent modification，the water wettability of quartz sand could be reduced to0.607g by silane coupling agent modification，and the water wettability of quartz sand couldbe reduced to0.2664g by aluminum coupling agent modification．The lipophilicity andhydrophobicity has been greatly improved. In summary, DN-101modified quartz sand hadthe best effect, KH-550modified filter took second place, DL-411modification had the worsteffect.（3）Surface physical morphologies and chemical compositions of unmodified andmodified quartz sand filter were characterized by Scanning Electron Microscopy, X-rayPhotoelectron Spectroscopy （XPS） and Fourier Transform Infra-Red Spectroscopy （FTIR）.Results show that unmodified quartz sand surface was coarse with many grooves and pits,showing the crystal structure and anisotropic characteristics. Modified quartz sand surface arecovered with coupling agent showing lighter color and sharp edges cut andfine particles are greatly reduced. XPS and FTIR analysis results show thatthe unmodified quartz sand is mainly composed of O， Si, the multi-valence inorganiccompound formed easily, and strong polarity. After being modified by coupling agent,the filter surface was covered with a layer of non-organic molecular compounds, whichenhanced the non-polar of filter surface. KH-550modified quartz sand consists of O, Si, andC which comes from silane coupling agent KH-550. DN-101modified quartz sand consists ofO, Si, C and Ti which comes from titanate coupling agent DN-101. DL-411modified quartzsand consists of O, Si, C and Al which comes from aluminate coupling agent DL-411.（4） Oil removing experiments show that DN-101modified quartz sand has the best oilremoval effect, the oil removal rate is increased from33.55%to58.74%compared to KH-550modified filter with oil removing rate of50.59%; and that of DL-411of43.18%. Comparedwith the unmodified quartz sand filter, the oil adsorption capacity of quartz sand which aremodified by KH-550，DN-101and DL-411increased by33.67%、42.87%、22.30%,respectively.（5）Oil adsorption isotherm of modified filter studies shows that the Langmuir adsorptionisotherm is more suitable to describe the adsorption process of unmodified and modifiedquartz sand, then quartz sand adsorption of oil is mainly manifested in the monolayerchemical adsorption. Kinetic Studies of the modified filter media for oil shows thatcorrelation of pseudo-second kinetic model（R²â‰¥0.977）is higher than the pseudo-first-orderreaction kinetics model（R²â‰¤0.965）,then the unmodified and modified quartz sand adsorptionof oil is more in line with the pseudo-second kinetic model.