Soapnut detergents cannot fully eliminate pollution in lakes – here’s why


A file pic of a frothing Bellandur lake. Pic: Sanchayan Nath

Promoting the use of soap nuts to control chemical detergent pollution in lakes is an admirable green initiative. But it is wrong to project that it would totally eliminate the foam at Bellandur lake.

This not only is false, but it also deflects the focus away from the real issues plaguing Bellandur lake. The Government of Karnataka has allocated 50 crores to the tasks outlined in the National Green Tribunal’s Expert Committee Report. The work on those fronts needs to start soon.

The foam issue is very minor compared to heavy metals in the water, which poison both water and food, and cause large-scale kidney failures, cancer and other health issues. In comparison, foam causes inconvenience only for half a kilometer stretch of the channel. But Government of Karnataka has done nothing to address the issue of heavy metals. Industrial areas like Peenya, Kalasipalya, Anepalya and Adugodi continue to produce heavy metals, and there is not a single Effluent Treatment Plant (ETP) that is needed to treat these pollutants. Such untreated sewage also directly comes to Bellandur lake.

Can soap nut offer a medium-term solution to the foam? The devil lies in details. Here are some details to test this claim:

1. No study to estimate the amount and effect of phosphorus on foam

The foam will subside only if the concentration of phosphorus falls below a certain threshold. But there is no study to find what concentration of phosphorus causes the foaming.

Phosphorus (P) comes from not only detergents but also from human excreta. Treating the incoming sewage in STPs has no effect, because the conventional STPs cannot treat phosphorus. Just the human excreta produced in Bellandur catchment overloads the Bellandur lake by a factor of 240! Is that much amount not sufficient to produce foam? There is no study on this.

Secondly, there is no study to find out how much of phosphorus comes from detergents. Then how can we say that the foam is caused by the phosphorus coming from the detergents only, and not human excreta?

Moreover, even if we manage to eliminate the detergents totally, the human excreta factor still remains. Then how can we say that if soap nuts replace the detergents, the foam problem will vanish?

2. Wrong assumption that soap nut can replace detergents in short term

It is assumed that the soap nut would replace the detergents completely. This assumption is not realistic, because of the following factors:

At present, the soap nut extract is not in a position to give a fight to detergents, because,

(a) It is not offered in equally attractive form or packaging as the detergents.
(b) The shelf life of the extract is very low. Extending it is a big challenge.
(c) People would not be easily convinced that soap nut can remove all stains as easily.
(d) Demand for soap nuts is going to be huge, with not enough supply. It takes 10 years for the soap nut tree to produce the berries, hence it’s going to be a huge challenge.


In summary, a soap nut-based solution is not likely to make a big disruptive impact on lake water quality or the detergent market in near future. Saving lakes needs a different more scientific robust strategy.

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About Nagesh Aras 24 Articles
Nagesh Aras is a resident of Bengaluru. He works on urban governance issues like mobility, lake and water management, and STPs.


  1. The most cost effective removal of both nitrates and phosphates in water is by plants. Not only is it fast but efficient. Growing plants and trees is the only solution. Creating swamps with standing trees will be the best, because the carbon and nutrients would be trapped in wood and not returned to the water rapidly as in decomposing parenchymatous tissue.

    • Actually removal of NP by plants is not all that efficient: A wetland can remove P at the rate of 1 g/sqm/year. On the other hand, an average human contributes P at the rate of 180 g/year.

      The normal STPs cannot treat NP, so our NP remains unaffected even if we have STP.

      That means we need 180 sqm of wetland per person to absorb the P fully.

      But Bangalore has no wetlands (either constructed or natural). So the lakes infested with macrophytes serve as wetlands.

      Even if the entire Bellandur lake is fully covered with macrophytes, it can neutralize human excreta from 4000 homes (=20,000 people). In this, we are not even talking about the P contained in the detergents!

      Thus absorption of NP remains an unresolved problem.

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