Development of a novel laboratory technique for characterizing scaling threshold limits in high recovery RO systems. Its main practical use would be in providing a hitherto lacking reliable test method for selection of the most cost-effective anti-scalant. Preliminary tests carried out successfully in three feed water systems: feed prone to silica scaling, feed prone to CaSO4 scaling and feed prone to CaCO3 scaling. Recently a new project started, related to prevention of calcium phosphate salts.
Scale prevention along concentrate discharge pipe
Ellimination of concentrate from inland brackish water desalination is a serious issue. In some cases it is possible to transfer the concentrate to the sea via a long pipe. A research is being conducted in order to find condidtios to prevent salts precipitation and pipe clogging.
Removal of supersaturation from Brackish Water Concentrates
Removal of supersaturation by salt precipitation in a crystallizer, overcoming the action of the anti-scalants allows to circulate the concentrate back to feed point. This will increase recovery from a certain water source, reduce significantly the purge stream which will run saturated, without the ability of salt precipitaion along discharge pipe.
Membrane based pretreatment methods widen possibilities for use of poor quality waters as RO feed water. Work undertaken includes integration of dynamic membranes in pretreatment schemes.
Residense time distribution
A technique involved with injection of salt tracer followed by conductivity detection at concentrate and permeate streams was used. The technique allows to investigate the residence time distribution and hence the nature of the axial velocity distribution within the membrane module. Dead volumes may be detected, axial dispersion of the flow may be estimated and the influence on mass transfer and flow related problems may be understood. The work may lead for better modules design.
Flow visualization close to membrane wall
Investigation of the flow within the turbulence promotor unit cell, using Particle Image Velocimetry technique is in high gear. The technique allows measurement of the velocity field at different distances from the wall. Turbulence intensities can be calculated and possible increase without influence on the pressure drop along the membrane. This, in turn may improve mass transfer through the membrane, and decrease concentration polarization effects.
Utilization of
membranes in wastewater reclamation
Microfiltration and ultrafiltration membranes may be used to remove suspended matter from wastewater. This can be used with and without prior biological treatment for removal of organic matter, nitrates, amonia, etc. The dissolved organic matter in treated water may be removed by adsorption using active carbon or other adsorbents. This may be followed by the use of nanofiltration or reverse osmosis membranes to remove dissolved salts. Many parameters are involved in the process that will allow recovery of fresh water for unlimited use.
Wide reuse of treated municipal wastewater for agricultural purposes is restricted by the high salinity of such waters. The risk is that these waters would act to increase the salinity of acquifer reservoirs. Possibility of reduction of surface waters salinity by membranes has been studied.
The hardness of the water supplied in many locations in Israel is undesirable both in home usage and in industrial water usage. Several technologies are available for reducing water hardness: different membrane processes and different chemical softening processes. Data are being collected for making techno-economic comparisons among the various alternatives. Some of the techniques will allow removal of heavy metals and / or some organic contaminants.
Well waters in some locations are contaminated with relatively high concentration of nitrates. Again, several technologies are available for nitrate removal: ED, RO, LPRO, NF and IX. Data are being collected for making techno-economic comparisons among the various alternatives.
Non-Condensable gases in vapor stream reduce heat transfer coefficients due to partial pressure reduction, diffusion resistance and passage blockage mechanisms. Simulation studies are being carried out for studying non-condensable effects in some specific MED designs.
Various aspects of scale formation and prevention in thermal and membrane units are being investigated.
Development of flat foils falling film evaporator enabling concentration of heavily scaling solutions close to the point of zero discharge. Scale accumulation is controlled by periodic flexing of the foils. Studies characterizing heat transfer have been carried out with two feeds: brackish water precipitating CaCO3 and CaSO4 and concentrated DSW brine solutions precipitating NaCl.
Development of compact bundles incorporating better heat-transfer load per unit evaporator volume, based on flat heat transfer elements and/or corrugated surfaces. Aim is to apply robotics construction of low cost-high efficiency heat exchanger.
