טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentGur-Reznik Shirra
Subjectthe impact of Activated Carbon on the
Removal of Dissolved Organic Material (DOM) as a
Pretreatment to Desalination of
Secondary Effluents
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Emeritus Carlos Dosoretz


Abstract

A major impediment for implementation of membrane technologies for wastewater treatment in general, and in desalination particularly, is the accumulation of organic material at the membrane surface, which subsequently causes its contamination.  The overall objective of this research was to characterize the efficiency of granular activated carbon (GAC) as a pre-treatment to reverse osmosis (RO) membranes, used for the removal of dissolved organic matter (DOM).  Although activated carbon adsorption is a well-known process for removal of hydrophobic, dissolved, organic contaminants, its application in combination with membrane separation devices for wastewater purification requires further understanding. 

Adsorption isotherms were characterized on the basis of dissolved organic carbon (DOC).  Continuous experiments conducted in laboratory GAC columns, at varying speeds (1-12 m/h) showed that at complete breakthrough eluting concentration was 60-80% of the feed concentration, probably due to biodegradation of DOC.  Moreover, the breakthrough curves do not start from zero indicating the presence of a non-absorbable-hydrophilic fraction in the feed (20-30%).  It was also found that approx. 80% of DOC present in MBR effluents is adsorbed whereas approx. 60% of the DOC is of hydrophobic nature.

Comparative desalination tests of secondary effluents without and with GAC adsorption pretreatment were conducted in pilot plant columns.  After pretreatment with GAC the quality of the permeate increases (DOC concentration slightly over 1 ppm) in comparison with the permeate without pretreatment (DOC close to 2 ppm).

Beyond the differences in the DOC level in the permeate, the findings show a formation of scale on the membrane surface, probably phosphate and carbonate based scale, a fact that mask the influence of DOM on RO membranes. In most industrial processes, where scaling is prevented, the impact of DOM on membrane performance will be especially significant.