Membrane and Desalination Technologies - TCE Moodle Website

652 P. Kajitvichyanukul et al.
Feed
UF pump
UF module RO module
RO pump
remove nearly all the oil and some COD. An example of Flow schematic of a unit combination
of UF/RO processes is shown in Fig. 15.4.
Lin and Lan (65) investigated the treatment of waste drawing oil which is a high-strength
waste oil–water emulsion commonly used in the cable and wire industries. Semi-batch
ultrafiltration and reverse osmosis processes along with prefiltration by a microfilter were
employed to treat the waste oil–water emulsion. Drawing oil or cutting machine oil is a
typical oil–water emulsion which is commonly used in the precision machining and cable and
wire industries. The oil–water emulsion serves the purposes of lubrication, cooling, surface
cleaning, and corrosion prevention in the manufacturing process. Depending on specific
applications, the oil emulsion can consist of up to 97% water, the rest being a complex
aqueous mixture which comprises different kinds of oils – mineral, animal, vegetable and
synthetic, alcohols, sequestrants, and surfactants. The test results show that the ultrafiltration
treatment is very effective in reducing the COD and copper concentrations and in improving
the turbidity, but it is relatively ineffective in reducing the conductivity of the ultrafiltration
permeate. In conjunction with the reverse osmosis treatment, the final permeate quality is
found to be excellent with over 99% improvements in the COD, copper, conductivity, and
turbidity (65).
3.5.2. Combination of Ultrafiltration/Nanofiltration Processes
Permeate
Concentrate
Fig. 15.4. Flow schematic of a unit combination of UF/RO processes (64).
Combination of nanofiltration with other types of membrane is also used in treating
industrial effluent. Generally, the nanofiltration process is carried out under lower operating
pressures than reverse osmosis and with lower molecular weight cut-offs (MWCO) than
ultrafiltration. Thus the combination of nanofiltration with either reverse osmosis or ultrafiltration
membrane is possible with the use of nanofiltration as either a primary or secondary
treatment. The application of the ultrafiltration process as a pretreatment step for industrial
effluents replaces the conventional methods of pretreatment for nanofiltration, resulting in
longer membrane life, and the ability to operate the nanofiltration system at higher flux rates.
Karakulski and Morawski (66) investigated the integrated membrane system based on
ultrafiltration and nanofiltration in purification of effluents from a cable factory. The application
of ultrafiltration membranes with MWCO of 100 kDa results in the complete rejection of
suspended solids and the retention of oil and lubricants at a level of 99%. The resulting
ultrafiltration permeate was further purified by nanofiltration to achieve the retention of
remaining pollutants (oil and lubricants) and to reduce the content of copper ions. As a result
of the nanofiltration process, the content of organic compounds in the permeate determined
as total organic carbon was below 1 mg/dm 3 , and the rejection of copper ions obtained.