Micro sewage treatment plants, dept-wise measures proposed to check froth in river

Following a recommendation from the Delhi government, The Energy and Resources Institute (TERI) has developed a comprehensive strategy to tackle frothing in the Yamuna, which has been a visible sign of the river’s poor water quality for many years.

The study, which is funded by the Delhi government and commissioned to “study of frothing in Yamuna in Delhi”, is to be released in two weeks. It identifies major pollution sources and reasons of frothing, assesses their impact and proposes department-specific recommendations for various departments of the Government of NCT of Delhi.

According to Dr Nupur Bahadur, Director of TERI’s NMCG Centre of Excellence on Water Use, which is established by the Union Ministry of Jal Shakti, the primary contributors to frothing are “untreated sewage from unauthorised colonies and informal settlements, mixed industrial effluents. Besides, open dhobi ghats contribute significantly”.

“Water hyacinth, which releases biosurfactants like saponins, further intensifies froth formation, especially during rainfall, when turbulence mixes these pollutants,” she added.

However, the phenomenon is not unique to Delhi.

Dr Bahadur explained that globally, rivers such as the Rhine in Europe, Lake Erie in the United States and the Tiete river in Brazil have experienced similar frothing episodes in the past due to untreated sewage and industrial discharges.

Within India, froth has been recorded in the past at Marina Beach in Chennai, Bellandur Lake in Bengaluru and the Sabarmati river in Gujarat. The TERI report emphasises that addressing point-source pollution, such as directly tackling untreated sewage and industrial effluents at point source, is key to preventing froth.

For areas where space is limited, such as dhobi ghats or densely populated informal settlements, TERI proposes micro sewage treatment plants (micro-STPs) using advanced oxidation processes (AOPs).

“These systems treat mixed sewage and industrial wastewater without requiring extensive space or conventional biological treatment, which can fail during high rainfall or other disruptions,” Dr Bahadur explains.

The report also recommends upgrading the existing infrastructure with technologies like Biological Nutrient Removal (BNR) to treat ammonia and phosphate, which conventional treatment plants often miss.

“These interventions, combined with regular removal of water hyacinth, control of water turbulence and improved monitoring, are expected to significantly reduce froth,” Dr Bahadur said.

She estimated that visible improvements could be seen within a year, with a largely clean river achievable within three years, provided consistent, coordinated efforts across departments.

Chemical defoaming agents, such as silicone-based or polyoxypropylene compounds, have been used in the past to manage froth. However, Dr Bahadur stressed that these are temporary measures effective only for small froth patches. “When pollution will reduce upstream there will be no froth downstream and such agents will not be required,” she said.

She added that defoaming agents have minimal impact on the river ecosystem, given the river’s robust self-cleansing capacity. The report also recommends greener alternatives to conventional detergents. Phosphate- and sulphate-free, zeolite- or enzyme-based detergents can reduce the surfactant load in rivers.

Dr Bahadur pointed to international examples to highlight potential solutions. “In the Rhine, 20-30 years ago, frothing caused by untreated effluents was successfully mitigated through systematic pollution control measures. Similar approaches, adapted to Delhi’s context, can help restore the Yamuna,” she said.