Abstract
With population surge, industrialization and urbanization; use of
surfactants has increased manifold. After their use in households and
industries, surfactants either end up in sewerage systems or are
directly discharged into surface waters. They can hence be found
dispersed in water phase or adsorbed onto aquatic sediments and sewage
sludge. Due to limited metabolic pathways, most of the common
surfactants are not degradable in anaerobic conditions that generally
prevail in sewage ingressed water bodies so sludge accumulated in these
water bodies after the anaerobic digestion process is rich in
surfactants (Ying, 2006, Environ. Int.). Sediment is a complex mixture
of organic (bacteria, proteins, humic and fulvic acids, humin, etc.) and
inorganic (silica, minerals, metal oxides and hydroxides,
aluminosilicates) components. Absorptivity of surfactant depends on the
sorbent composition and type of surfactant (Ishiguro & Koopal, 2016,
Adv. Colloid Interface Sci.). A crucial question related to surfactant
absorption is its reversibility- as to whether the surfactant can
desorb. The knowledge of this can be beneficial in understanding the
environmental fate of surfactants. The presence of surfactants in water
bodies can form foams. Generally, foaming in surface water is a result
of a mixture of surfactants from various sources (Schilling & Zessner,
2011, Water Res.). However, contribution of sediment as a source of
surfactant in a foaming water body has not been studied adequately.
Also, existence of surfactants in water, beyond certain concentrations
not only induces unpleasant taste and odor, but also causes undesirable
changes in the ecosystem. Thus, it becomes imperative to study the ratio
of the surfactant associated with water, to the extent of surfactant
associated the sorbent such as sediment/sludge to understand the
environmental risk associated with surfactant. This study aims to
understand a foaming urban lake which foams only after heavy rainfalls.
This study tests the hypothesis that surfactants accumulate in the lake
sediment in significant proportions and desorbs upon dilution occurring
due to addition of rainwater into the lake. This when churned by heavy
runoff causes large quantities of stable foam. This study aims at
analyzing the role of lake sediment in foaming of a lake.