Why building sewage treatment plants in cities on the Ganga is a challenge

Flood-prone low-lying locations add to the difficulty

By Shantanu Kumar Padhi, Rahul Mankotia
Published: Sunday 06 October 2019
Sewage pumping station near Numayadahi STP submerged in water.
Sewage pumping station near Numayadahi STP submerged in water. Sewage pumping station near Numayadahi STP submerged in water.

UP: Low-lying areas near Triveni Sangam flooded due to rise in Ganga, Yamuna River water level 

In Uttar Pradesh, Ganga Water Level Close To Danger Mark, Buildings Partially Submerged 

Bihar battles floods yet again, as rivers swell up due to heavy rain

Those are some of headlines which have become usual every monsoon. Recent history has taught us just how fast water can overflow river banks. Ever put a thought what happens to the water utilities during such adverse circumstances? 

It has become a major concern with the last floods – particularly flash floods. Drinking water and wastewater treatment plants are typically the most vulnerable to flooding. They should be top priority when major storms come knocking.

Flooding happens to be one of the most common hazards in the Ganga basin. The impact on a community is huge.

Waste water treatment plants (WWTP) usually floods from tropical storms, swollen rivers, dam failure, and more. Residents and businesses are affected. Loss of power, asset damage, and dangerous conditions for personnel have large impacts on wastewater and drinking water facilities. Excessive flooding affects treatment plants in many ways.

A wastewater treatment plant is most at risk of flooding when it is in a low-lying area near waterbodies for which it discharges its final effluent and enables gravity-fed collection systems. Pump stations, where head differential is insufficient for flow, is included in some systems and increases the likelihood of flooding. 

Although, sophisticated geographic information system mapping for site selection is prior done to identify the best possible site to construct the wastewater treatment plant but still more weightage is given to flood plain or low lying areas.

Technically, these areas are economical because it is easier to receive wastewater from city through gravity. Perhaps, in many cities, these low-lying areas are often free from any conflict or encroachment. Hence it is convenient for local bodies or ‘Jal Nigams’ to establish a plant in such areas. 

A wastewater treatment plant is a highly capital-intensive infrastructure. Although, measures and calculations are done to mitigate flooding in the WWTP, but still the plants remain shut down during monsoon.

The raw wastewater is discharged into river with a belief that Streeter-Phelps equation (a self-purification process of rivers) will save the plant during those days, hence, the raw sewage is indiscriminately discharged into ganga river. 

A team from New Delhi-based non-profit Centre for Science and Environment visited Prayagraj in August and September 2019 to study its sanitation scenario. Considering a sewage network has been laid on a mission mode in the city, the main focus was to study the peri-urban areas, which often lie outside the mandate of concerned authorities.

What was found

Except the 14 million litres per day (MLD) sewage treatment plant (STP) at Salori and the one at Naini, all STPs were shut down. There was no major rainfall in the preceding weeks there.

The shutdowns were attributed to a rise in Ganga’s water level that causes a backflow.

Clearly, locating an STP in low-lying areas close to the point of discharge has its advantages, but also downfalls.

Our team visiting Chunar to identify a site for an FSTP, we found that the proposed area was flood-prone.

Further complications: STPs in the Ganga Basin are not only designed to treat sewage transported through a sewerage network, but also to treat water from open nullahs, which contains faecal matter from non-sewered areas.

These projects require interception and diversion of existing nullahs to an STP. It would make sense for the STP to be located as close to the final disposal point. 

Many STPs connected to these interception and diversion projects run above the design capacity as open drains also contain storm water. The problem is exasperated during the periods of heavy rainfall when there is a spike in the water received by the STPs. Authorities normally bypass the excess water directly into the Ganga.   

Engineers working towards building STPs in the Ganga have toiled hard in finding solutions to this problem. An example is the 60 MLD STP at Rajapur, Allahabad, on the Ganga floodplains.

Nearly 10-metre-high embankments have been constructed around it to prevent flooding. It was also shut down in September due to flooding.

The situation of STPs in the Ganga Basin is a concern. Many function poorly. The National Mission for Clean Ganga has come up the ‘One City One Operator’ model – a single private sector agency tasked with to rehabilitating existing sewerage infrastructure and building a new one.

Adani Waters was roped in for Prayagraj and Va Tech Wabag for Agra and Ghaziabad. These projects have been tendered out under a hybrid annuity model wherein the private sector agency partly funds the project and recovers it over the contract duration.

These contracts potentially build incentives for designing and implementing efficient systems and streamlines the responsibility and monitoring of a complex sewerage system. How the engineers overcome flood-related challenges remains to be seen.

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