After 101 years, the Seine, the river breathing life into the people of Paris had welcomed swimmers once again in the 2024 Paris Olympics. Back in 1923, the quality of the water was so unhealthy and adulterated that the government at that time outright banned anyone from ever using the Seine for any purpose, let alone for a swim. 

So, what steps did Paris undertake to not only clean up the once murky bacterial filth but also filter the water to such an extent that it could host the Olympic Triathlon? And can similar steps be taken for Dhaka’s Buriganga? 

The task at hand 

Just like the Buriganga and most other major bodies of water hosting a large city, the river Seine was fuming with human excrement, as the entire sewer system of Paris was directly connected to its riverbanks, often causing the river to become visibly murky and brown whenever the heavy rain flooded the sewer system. 

Despite such an intricate supply chain of human feces plaguing the river for over a century, French President Emanuel Macron famously proclaimed that he would take a bath in the Seine ahead of its debut in the 2024 Paris Olympics. 

The city of France took on a mammoth task, committing €1.4 billion to clean up the river. The first challenge appeared in its outdated sewer systems. Many cities built in the 1800s such as New York, London, and Paris, were all designed to dump their wastewater directly into their corresponding rivers. 

New York did it for the Hudson, London for the River Thames, and the Seine was the victim of the wastewater management policies of 19th-century French engineers. This management system of the 1800s is known as the combined sewer system, where stormwater management meets the wastewater management system as they both take the same path towards their final destination, the Seine. 

As a result, the question for 21st-century engineers was simple. How do we redirect the sewage water and clean it up before it reaches the river outflow ducts? The answer was a 13.2 million-liter capacity underground tank with connecting tunnels throughout the city.

Known as the Austerlitz Basin, it aims to capture the mixed storm and sewage water before it reaches the Seine. Holding it up to its capacity for further treatment, as well as decreasing the overflow of the sewage in times of heavy rain. 

However, it does not hold any filtration or cleaning system within it; it is built for the purpose of containing the sudden increase of outflow. The wastewater will be rereleased into processing centers; from there it can be safely discharged into the river. 

The results

Even just 2 months before the Olympics held in July 2024, Paris was struggling to properly achieve the required threshold for E. coli contamination. The basin had been operational for only a month, but results did follow suit, just at a slower pace. 

In April, the Seine failed its required E. coli limits, exceeding 20,000 E. coli per 100 millilitres of samples. Although there was much controversy and doubt as to whether the French would be able to pull it off in the last minute, the Seine had reached well below its desired level of E. coli 2 days before the triathlon, and so, after more than a century, it welcomed back happy swimmers not only for pleasure but also aiming to win a gold for their respective nation. 

Comparing with Buriganga 

Seine, in its size and girth, is far larger than Buriganga, which at first might make the average person think that implementing the same measure would be easier. However, reality is not so straightforward. 

In the 1960s and 70s, the Seine was declared biologically dead just as the Buriganga. The Buriganga, when last estimated, carries a BOD of 13–23 mg/L which is a result of virtually no treatment. 

This high level of BOD indicated the nature of the Buriganga, which is as dead as it can be. Along with high BOD levels, the particulate and heavy metal ratios within the water are extremely high. The Seine contains virtually no heavy metals as it is processed, yet the Buriganga, with its welcoming industrial waste and lack of regulations, contains Fe ~31 mg/L; Mn ~1.56 mg/L which can significantly harm any human being who is unlucky enough to drink a sip of it. 

The first challenge in building such an engineering infrastructure is for the infrastructure to even exist. Unlike any other city, Dhaka was never made in accordance with a centralised plan. Therefore, very little of its wastewater or sewage water outside of the riverbanked areas of Buriganga ever make it to Buriganga. Therefore, in many areas such as Dokkhinkhal, Mirpur, Demra, and even Dhanmondi, the lack of sewage infrastructure clogs up the road with the slightest amount of rain. 

Whatever waste management that even reaches Buriganga, goes in it directly with ducts directly feeding it to the riverbanks. Paris already had a system of wastewater refineries with a multitude of filtration systems and tunnels scattered around its city’s sewage plants. The one refinery Dhaka has, named Pagla Sewage Treatment Plant, aptly lives up to its given name. The plant processes only about 40 MLD, i.e., ≈ 33 % of its intended capacity. Moreover, just 20% of Dhaka’s population is connected to the Pagla sewer network . 

There is also the issue of septic tanks used by Dhaka’s ever ignorant landlords. These tanks are not connected to the Pagla Treatment system and most of the time are illegally constructed. The lack of oversight and the lapsed laws around construction make it so that any new development can simply connect its sewage to the existing pipeline without any regard for whether it is connected to the Pagla STP or not, resulting in clogging up sewage every few years.  

The solution 

The World Bank has already agreed to invest in upgrading Pagla STP and increasing its capacity from 40 MLD to 200 MLD. In July 2023, the foundation was laid for a new 200 MLD, energy-neutral Pagla STP, backed by the World Bank, AIIB, and to be built by VA TECH WABAG. 

This does not address the big picture. The disconnected nature of Dhaka’s sewage system means that it is inevitable for Dhaka’s streets to get clogged up again and again whenever there is heavy rainfall. 

There should be a central redistribution plan enacted at first to redirect all of Dhaka’s sewage to a select few locations, it can be all towards the river Buriganga, or it can be to the opposite side in the north, Turag. A city of this dense population also can not function with just one sewage plant. The aptly named Pagla sewage treatment plant can not possibly handle all of Dhaka’s waste alone even if it operates in full capacity. And finally, an actual burst of conscious effort needs to be manifested by the political leaders and the citizens. 

Millions suffer from diseases and deadly bacterial infections stemming from adulterated water and lack of hygienic treatment systems, and no city deserves to call itself the capital of a country whilst forcing its citizens to live in inhuman conditions. That is why, when the Mayor of Paris first declared that France had taken the step to clean up the Seine, it was not met with jubilation; the decision was rightly met with anger and frustration from the public, as they wondered why, after a century, their leaders had finally decided to clean up the mess so vividly present in front of their eyes for the past 100 years.