Effect of Biological Slime on the
Retention of Alkyl Benzene
Sulfonate on Granular Media
B. B. EWING, Professor of Sanitary Engineering
S. K. BANERJI, Research Assistant
Department of Civil Engineering
University of Illinois
Urbana, Illinois
The use of synthetic detergents has greatly increased since their advent
about 15 years ago. These detergents have, of necessity, been discarded
with waste waters to the environment. Because the surface active agents in
the packaged product, unlike soaps, are not readily degraded by bacteria in
soil, streams, and sewage treatment plants, the pollution of the aqueous environment has been recognized as a serious problem almost since the first
inception of their use. The complaints have included frothing in waste treatment plants and streams as well as taste and odor problems and foaming of
drinking water taken from grossly polluted streams.
Not until 1958 were there instances of contamination of ground water
reported (1). Since this time there have been numerous reports (2, 3,4,5, 6,
7, 8) of ground water contamination by surface active agents originating from
detergents. Most of the cases have been in suburban areas where each lot has
a shallow well for a water source and a septic tank or cesspool for waste disposal. There have been several cases involving more widespread pollution
of ground water from municipal or industrial waste ponds or recharge pits
(6.9).
All these reports indicate that the surface active agent (surfactant) travels
through the soil at a much slower rate than the water carrier and the area affected by large sources of contamination, such as oxidation ponds and seepage pits from commercial laundries, is more extensive than in the case of
small sources, such as household septic tanks and cesspools. It appears,
therefore, that the movement of the surface active agent is retarded by adsorption on the soil and on bacterial slime associated with the soil. The purpose of the research reported here is to evaluate the role of the slime in adsorbing the surfactant.
Once waste water has percolated through a few ft of soil or sand, the
organic subtrate contained in the waste will have been essentially removed
and there will be insufficient nutrient to support the growth of a biological
slime. Since there will be no slime growth beyond the first few ft, the principal mechanisms of retarding movement of surfactants in the zone of saturated flow below the ground water table must be adsorption on the minerals
composing the aquifer. Withi" the first few ft of soil from the face of the
seepage pit or cesspool or in a percolation field from a septic tank installation, however, there may be a considerable amount of the surfactant adsorbed
on biological slime which coats the soil grains.
- 351 -