טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEven Ezra Itay
SubjectMembrane Filtration of Wastewater Following Chemical
Precipitation
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Michal Green
Professor Emeritus Carlos Dosoretz


Abstract

Due to the growing shortage in water supply wastewater reuse became increasingly one of the main sources of water. However, traditional treatment does not provide sufficient quality of effluent for unrestricted use. Membrane filtration is considered the most efficient way for achieving high quality effluent. The main difficultly in membrane filtration, especially in wastewater filtration, is the fouling of the membrane. Membrane filtration is usually done on secondary effluent, however biological treatment produce soluble microbial products (SMP) such as Polysaccharides which are suspected in increasing the fouling. This research suggests a different approach where instead of the biological treatment, the wastewater is treated by a Chemically Enhanced Primary Treatment (CEPT). Sequential Batch Reactor (SBR) and CEPT were compared as a pretreatment for membrane filtration. The membrane filtration included Ultrafiltration (UF) followed by Reverse Osmosis (RO). Despite of the higher quality of the biologically treated secondary effluent (14 ppm TOC and 8 ppm TSS in Comparison to 48 & 21 ppm), the flux decline in a UF membrane filtration (25kDa & 100kD) and permeate quality were similar for both CEPT and secondary effluents.  Particle size distribution showed that all particles over 100 microns were removed by the precipitation. Smaller particles tended to aggregate, so that the over all size of the smallest particles (colloids) in the CEPT effluent increased in a factor of 6 in comparison to wastewater. The smallest particles (colloids) are considered to be the main cause of irreversible fouling, hence the importance of increasing the colloids size. Gel filtration and FTIR results suggest that polysaccharides accumulated on the membrane. Comparison between RO membrane performances showed that the decline in the flux was much higher for the secondary effluent than that of the CEPT effluent (17% for CEPT and 46% for secondary effluent after 40 hr). Mass balance on the RO system showed 50 times higher  scaling of Ca, Mg & P on the membrane for secondary treated effluent as compared to  that of CEPT.

In summary, the research findings indicate that secondary effluent contains biological matter that accelerate flux decline. CEPT effluent, despite their lower quality, achieved similar membrane performance for U.F and higher membrane performance for R.O. Based on the above mentioned findings together with the well known CEPT advantages of low cost and simple operation, it can be concluded that CEPT presents a valid alternative for pretreatment of wastewater prior to membrane filtration.