Resumen de Nanofiltration and hybrid sorption: ultrafiltration processes for improving water quality
Reliable access to freshwater is one of the fundamental pillars for our society. Freshwater scarcity has become a major concern in many arid and sem i-arid countries worldwide to s uch an extent that water s upply for meeting current and future demands is one of our society challenges .The increasing of domestic and industrial discharges leads to increased salinity and the presence of new pollutants in freshwater sources . Consequently the development of efficient treatment processes is a major concern .
Different water treatment technologies including adsorption , coagulation, flotation, ozonation, IEX, and pressure-driven membrane processes such as microfiltration (MF), ultrafiltration (UF}, NF and RO have been thoroughly investigated for surface water and groundwater treatment. Nowadays, the availability to produce high quality drinking and industrial waters by removing target species is very important challenge.
NF is being promoted as a new technological solution to remove both major and minor organic and inorganic compounds from surface water . NF membranes have relatively large rejections of double-charged ions (up to 99%) and moderate rejections of single-charged ones in the range of20-70%. Solute transport through NF membranes is a complex process that depends on the micro hydrodynam ic and interfacial events occurring at the mem brane surtace and within the membrane structure . Membrane structure is still one of the main challenges to be solved as sorne authors consider it permanent in time (e.g. nanopores structure) while others consider only a free volume structure with no permanent structure (non-pores structure). The main purpose of such models is to incorporate as much physical realism of the membrane process as possible in order to better match measurable quantities to adjustable model parameters. As a direct consequence, developments in modelling have moved in parallel with improvements in the measurement techniques employed for the characterization of NF membrane·s and process streams, as only then a check of the appropriateness of model parameters will be possible.
NOM affects significantly many aspects of water treatment, including the performance of the unit processes, application of water treatment chemicals and biological stability of water. Enhanced and/or optim ized coagulation, as well as new process alternatives for the better removal of NOM by coagulation processes need to be investigated . Among them, the com bination or integration of IEX with coagulation or the integration of IEX with membrane filtration processes . MIEX resin has been used as pretreatment method prior to coagulation to enhance the efficiency ofcoagulation and reduce the coagulant dose (up to 60%), with reduced sludge formation and turbidity load. The MIEX process presents a very promising method to reduce DBP formation when used upstream of chlorination.
The fouling of mem branes and decline of flux are the major problems associated to' membrane techniques. Therefore a search for new solutions to overcome or at least minimize these drawbacks is needed. Among these approaches hybrid membrane processes are one potential solution. Often a combination of various water treatmenttechnologies is required to provide high level of water treatment and purification.
The main objective of this thesis is to study the possible integration of separation processes based on pressure-driven membrane technologies such as NF and hybrid technologies based on IEX resins and membrane UF to reduce salinity, hardness and inorganic pollutants (N03-, S042-) in surface and ground brackish waters and to reduce the presence of DBP precursors (DOM and Br-) in order to improve water quality and comply with increasingly demanding regulations.
