EFFECT OF DISSOLVED SALTS
ON THE FILTRATION OF
COLIFORM BACTERIA
IN SAND DUNES
J. GOLDSHMID*, D. ZOHAR, Y. ARGAMAN and Y. KOTT
♦Ambient Purification Technology, Inc., Riverside, California 92502, USA
The plans for the Dan Sewage Reclamation Plant call for infiltration through sand
dunes followed by a 400-800 day lag period, as the final treatment step, before pumping
the reclaimed sewage from the aquifer into the drinking water supply. The extent of
treatment required prior to ground infiltration thus depends, among other things, upon
the efficiency of bacteria removal in the last two stages. The data available in the
literature regarding bacteria removal through ground infiltration usually give the distance
from the recharge area to the place where no coliform bacteria are found. However,
because of the large quantities, high infiltration rates and long duration planned for the
Dan Sewage Project, the question arose as to how far the available data could be
extrapolated.
After analysing data available in the literature it was felt that better understanding of
the forces and mechanism responsible for bacteria removal in sand dunes was required if a
reliable estimate of the sand dunes capacity for bacteria removal over the plant life was to
be made. The work described here, elucidates the effect of concentration and
composition of dissolved salts in the treated effluent, on the filtration efficiency of
coliform bacteria in sand dunes.
Lamanna et al (8) classify bacterial suspensions in water as hydrophilic biocolloids.
They carry a negative zeta potential at pH 7 and are extensively solvated. Brinton (3) in
reviewing the literature regarding electrophoretic mobility of biocolloids states that the
surface properties of a population of the same kind is amazingly uniform. This charge
comes from the dissociation of various ionogenic groups like carboxylic and amino groups
located on the bacterial surface; thus charge density and consequently zeta potential
depend upon the ionic strength and the pH of the solution. It follows that the stability of
bacterial suspensions in water depends largely upon the ionic strength and pH of the
suspension medium. At low ionic strengths, the importance of pH in determining the
surface electrical characteristics of the bacteria increases. Bacterial colloids react to the
addition of electrolytes like other hydrophobic colloids (10). At the pH of interest
bacteria are negatively charged, thus bivalent cations are more effective than univalent
cations in reducing the zeta potential and decreasing hydration, and trivalent cations
more effective than bivalent. James (6) showed that the action of electrolytes is
reversible. When a bacterial suspension, to which an electrolyte has been added, is
washed, it regains its colloidal properties.
Chemical analysis of sand from the designated area of the Dan Region infiltration
ponds showed the following composition (4): Si0 2 — 92.35%, CaO — 2.5%, Carbonates —
2.4% as CaC0 3 , Fe 2 0 3 +Al 2 03 - 0.77%, Organic Matter - less than 0.1%. The sand is
basically quartz with some calcium carbonate. Pure quartz sand when wetted carries a
negative electric charge and has a zeta potential of 50 mV (12). Ives and Gregory (5)
found the zeta potential of sand to depend on the pH and the concentration and
composition of the electrolytes present.
Van der Vloed (12) found that negatively charged organic substances become attracted
147
ON THE FILTRATION OF
COLIFORM BACTERIA
IN SAND DUNES
J. GOLDSHMID*, D. ZOHAR, Y. ARGAMAN and Y. KOTT
♦Ambient Purification Technology, Inc., Riverside, California 92502, USA
The plans for the Dan Sewage Reclamation Plant call for infiltration through sand
dunes followed by a 400-800 day lag period, as the final treatment step, before pumping
the reclaimed sewage from the aquifer into the drinking water supply. The extent of
treatment required prior to ground infiltration thus depends, among other things, upon
the efficiency of bacteria removal in the last two stages. The data available in the
literature regarding bacteria removal through ground infiltration usually give the distance
from the recharge area to the place where no coliform bacteria are found. However,
because of the large quantities, high infiltration rates and long duration planned for the
Dan Sewage Project, the question arose as to how far the available data could be
extrapolated.
After analysing data available in the literature it was felt that better understanding of
the forces and mechanism responsible for bacteria removal in sand dunes was required if a
reliable estimate of the sand dunes capacity for bacteria removal over the plant life was to
be made. The work described here, elucidates the effect of concentration and
composition of dissolved salts in the treated effluent, on the filtration efficiency of
coliform bacteria in sand dunes.
Lamanna et al (8) classify bacterial suspensions in water as hydrophilic biocolloids.
They carry a negative zeta potential at pH 7 and are extensively solvated. Brinton (3) in
reviewing the literature regarding electrophoretic mobility of biocolloids states that the
surface properties of a population of the same kind is amazingly uniform. This charge
comes from the dissociation of various ionogenic groups like carboxylic and amino groups
located on the bacterial surface; thus charge density and consequently zeta potential
depend upon the ionic strength and the pH of the solution. It follows that the stability of
bacterial suspensions in water depends largely upon the ionic strength and pH of the
suspension medium. At low ionic strengths, the importance of pH in determining the
surface electrical characteristics of the bacteria increases. Bacterial colloids react to the
addition of electrolytes like other hydrophobic colloids (10). At the pH of interest
bacteria are negatively charged, thus bivalent cations are more effective than univalent
cations in reducing the zeta potential and decreasing hydration, and trivalent cations
more effective than bivalent. James (6) showed that the action of electrolytes is
reversible. When a bacterial suspension, to which an electrolyte has been added, is
washed, it regains its colloidal properties.
Chemical analysis of sand from the designated area of the Dan Region infiltration
ponds showed the following composition (4): Si0 2 — 92.35%, CaO — 2.5%, Carbonates —
2.4% as CaC0 3 , Fe 2 0 3 +Al 2 03 - 0.77%, Organic Matter - less than 0.1%. The sand is
basically quartz with some calcium carbonate. Pure quartz sand when wetted carries a
negative electric charge and has a zeta potential of 50 mV (12). Ives and Gregory (5)
found the zeta potential of sand to depend on the pH and the concentration and
composition of the electrolytes present.
Van der Vloed (12) found that negatively charged organic substances become attracted
147