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2. Why foaming happens?

Due to presence of SURFACTANT in water, from:  

  1. Industrial effluent
  2. Household laundry detergent and cleaning
  3. Dead and decaying plants

 

Bellandur lake had 15-20 ppm of anionic surfactant. Most of it was from untreated Household sewage (40% of 530MLD inflow).

Hypothesis:

It is possible that surfactants get accumulated in the lake sediment in significant proportions. This when churned by heavy runoff, has a very great potential to form large quantities of foam. 

Fig 3: Hypothesis : surfactant desorption from sediment due to rainfall

 

OPEN

3. Sediment Characterization

Aim: 

  1. To  charecterize Bellandur sediment
  2. Sorption kinetics of anionic surfactant(SDBS) on sediment.

 

Fig 4: Sampling locations of sediment around Bellandur Lake

Aim 1: Sediment Characterization

Table 1: Sediment charecteristics

 

Inference 1: 
  1. The Bellandur sediment was predominently sandy.
  2. Sample B2 and B4 had highest organic carbon content , comparable to STP sludge
  3. Bellandur sediment had adsorbed anionic surfactant at ranges 2.9-4.9 g/kg (dry wt) 

 

Aim 2​: Sorption Kinetics 

Sediments 0.3 g (d.w.) were shaken with 50 ml of 10 ppm SDBS soln for various periods of time. After centrifuging at 10,000 rpm for 10 min, SDBS in the supernatant  was determined. 

 

Fig 5: Absorption kinetics of surfactant on sediment with respect to time

Inference 2:
  1. Carbon content in sediment was proportional to amount of anionic surfactant adsorbed    [Sludge>B2>B4>B5>B3>B1]
  2. Absorption time (6 hours) << HRT of Bellandur lake (10 days ).This ensures no washout of surfactant from lake.

 

OPEN

1. Foaming Lake or Snowy Swiss locale??

Fig 1: Foaming Urban Indian Lake- Bellandur Lake. Foam reaches 6-7 feet height, disrupts traffic and emits smell.

 

When foaming happens?

Fig 2: News clippings showing foaming occurs only after rain

 

OPEN

4. Role of sediment in foaming

Aim : To analyse foam stability due to sediment

Different conc. of sediments were foamed with SDBS soln. (10 ppm).  Time needed for the foam to subside was indicative of foam stability

 

Fig 6: Foam persistence time with varying sediment concentration

 

Inference:

1. Increasing sediment concentration added to foam persistence time. Increased surfactant concentraion noted in supernatant

This proves that surfactant gets desorbed from the sediment.

2. beyond 20 g/l total solid conc. the foam persitence dropped.This is due to viscous drag provided by sediment particles.

 

 

 

 

OPEN

5. What did we find?

  1. Household laundry detergent  gets absorbed onto the Bellandur sediment.
  2. Absorption of surfactant is proportional to the carbon content in the sediment
  3. Rain desorps the surfactant and adds to the foaming intensity

 

Is there any novelty?

Absolutely!  This is the first study on sediment of foaming waterbody. We also address the reason behind seasonality of such foaming events.

OPEN

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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.

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.

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