Oily wastewater treatment by coupling membrane filtration and ozonation | |
| Author | Suthi Panpanit |
| Call Number | AIT Diss. no.EV-01-2 |
| Subject(s) | Sewage--Purification--Oil removal Sewage--Purification--Ozonization |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | The present research was undertaken to investigate the potential of Ultrafiltration (UF), Nanofiltration (NF) and UF membrane coupled with ozone for treating oil/water emulsion from car wash wastewater. UF Experiments were conducted to identify and describe the membrane fouling phenomena due to oil adsorption on membrane surface. The effect of operating parameters such as membrane material, operating pressure, chemical-cleaning, membrane morphology and the effectiveness of bentonite addition to control membrane fouling and flux behavior were examined. For NF experiments, the study emphasized the evaluation of operating parameters affecting NF performance for producing high quality water in the car wash rinsing process. Batch filtration in cross-flow mode was conducted for both UF and NF experiments, while an ozone column reactor was used to investigate the role of ozone in treating oil/water emulsion. The results revealed that the ultrafiltration of oil/water emulsion with high operating pressure promotes a compact oil adsorption layer on membrane surface, which is considered major irreversible membrane fouling. Membrane fouling for cellulose acetate membrane was less than that for polysulfone membrane. The addition of bentonite clay reduced the adsorption layer on cellulose acetate UF membrane, resulting in a reduction of total membrane resistance (Rt). The results revealed that for cellulose acetate membrane, a 40% flux augmentation was obtained with the increase of bentonite concentration to 300 mg/L. The major possible mechanisms of the role ofbentonite in oil/water emulsion on UF flux augmentation are: (i) bulk oil/water emulsion concentration reduction (ii) particle aggregation and (iii) detachment of the adsorbed gel layer by shear force. Adsorption of oil emulsion by bentonite can lead to the significant reduction of bulk oil emulsion concentration, one of the major causes of flux enhancement. Results show that contact of oil emulsion with bentonite forms larger particles resulting in flux increment. An optimum particle size of 37 µm corresponds to the bentonite concentration of 300 mg/L, providing the highest flux. Beyond this limiting concentration, flux improvement started to decline gradually due to packed cake particle formation on the membrane surface. The presence of bentonite in the oil emulsion promotes high shear stress, which acts against the gel layer. This high shear stress is caused by bentonite particles and cross flow velocity, reversing the oil adsorption layer from membrane surface to the bulk of the liquid phase. However, the polysulfone membrane did not show the significant flux enhancement with an addition of bentonite in oil/water emulsion. This was a result of its strong hydrophobicity. The effect of oil/water emulsion adsorption with bentonite was also a major cause for an increase of oil removal efficiency in terms ofTOC. Chemical cleaning experiments after ultrafiltration of mixed bentonite with oil/water emulsion showed that the presence of bentonite inducing the transformation of irreversible fouling which was caused by oil emulsion to reversible fouling, and could be periodically cleaned chemically. For the cellulose acetate membrane with lower molecular weight cutoff (MWCO), higher flux and better permeate quality were obtained more than the membrane with higher MWCO. The reason was the difference in membrane structure morphology. The membrane with lower MWCO but having high porosity and small pore size was less susceptible to fouling and pore plugging by oil/water emulsion molecules. ll1 In nanofiltration of oil/water emulsion, the effect of applied pressure, emulsifier type and hardness concentration was investigated in order to examine the NF potential for producing high quality water in car wash rinsing process. The NF experimental results showed that the oil removal efficiency in terms of TOC is approximately 99%. The NF flux increased linearly with pressure. By filtering anionic emulsion, the reduction of NF flux was less than nonionic emulsion. That was caused by the negative charge repulsion between anionic emulsion and NF membrane charge resulting in protecting the oil emulsion adsorbed directly onto the membrane surface. With an increase of hardness concentration in nonionic oil/water emulsion, the results showed positive response to NF flux and TOC removal efficiency. However, the presence of hardness in anionic oil/water emulsion reduced the NF flux considerably due to organic sulfate salt formation on NF membrane surface. This salt formation occurred due to chemical interaction between the anionic emulsion and divalent metallic cations of Ca2+ and Mg2+. In the coupling of UF membrane and ozone experiments, the influence of feed emulsion concentration, ratio of H202 and 03 concentration, contact time and pre-treatment with membrane were examined. The experimental results revealed that ozone and peroxone (mixture of ozone and hydrogen peroxide) alone were not effective for oil/water emulsion removal. The maximum oil/water emulsion removal in terms of TOC was about 30%. In addition, the pre-treatment with ultrafiltration prior to ozonation did not show significant improvement in TOC removal. Because an oil/water emulsion molecular structures were like alkane hydrocarbons such as paraffin. They are poorly reactive under the direct attack by ozone and hydroxyl radical. |
| Year | 2001 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Visvanathan, C.; |
| Examination Committee(s) | Muttamara, Samorn ;Fukushi, Kensuke;Rakshit, Sudip K.; |
| Scholarship Donor(s) | Petroleum Authority of Thailand; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2001 |