While you sat comfortably (or not – depending on what you ate the previous night) in your cosy bathroom, waiting for your anal sphincter muscles to work its magic and push out the smelly undigested contents from your body, have you ever wondered what happens to your poop after it goes down your commode?
Bet you didn’t! So here is what happens to your poop in Bengaluru.
Where the trail begins
After the whirling water sucks out all the solid content in the toilet bowl (there is much more than poop that people flush down the toilet), the mixture passes through the drain pipes or the “lateral system”, into the “sub-mains” that are laid just beneath the roads.
A group of sub-mains from different areas collectively empty their contents into the “outfall-sewers”. These outfall sewers are connected to Sewage Treatment Plants (STP) that operate in various parts of the city.
Bengaluru’s poop trail has two branches:
The core city area which comprises of the old Bengaluru that was under the ambit of the Bangalore Mahanagara Palike (BMP) until 2006-07. Let’s call this ‘Old Bengaluru’.
The seven City Municipal Councils (CMC), one Town Municipal Council (TMC), and 110 villages located on the periphery of the BMP that were merged into a larger municipal body, the Bruhat Bengaluru Mahanagara Palike in 2006-07. This comprises areas like Bommanahalli, Kengeri, Mahadevapura, Byatrayanapura, K R Puram, K R Pura, Yelhanka, etc. We will call this ‘New Bengaluru’.
Where does the poop of old Bengaluru go?
For everyone living in the Indiranagar, Ulsoor, Rajajinagar, Malleshwaram, and Nagarbavi areas – there is reason for relief. The sewage lines in these areas – the Under Ground Drainage – were laid some decades ago.
All your poop traverses several kilometres in the city and finally ends up in the STP. Sewage Treatment Plants, in case you forgot.
What happens inside an STP?
Once the sewage gets to a treatment plant, first plastics and other solid materials (razor blades, condoms, empty files of tablets, food packets etc) are separated from the rest of the ‘raw’ sewage (comprising toilet and kitchen sink / basin contents).The rest of the ‘raw’ sewage is sent for removal of sand and other particles.
After de-nitrification, faecal matter is broken down. This semi-solid mixture, called sludge, eventually dries up and is then sold as manure to farmers. The water, which emerges crystal clear, fit for any non-drinking purpose, is let out into the city’s valleys – such as the Vrishabhavati valley near Kengeri, Koramangala and Challaghatta valleys (popularly referred to as K&C Valley), and ultimately joins the river.
For instance, the Mylasandra STP releases water into the Vrishabhavati river which flows into Tamil Nadu. Other rivers flow into the Cauvery.
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The process in a sewage treatment plant
Don’t be too happy though. The process described above is when the system functions the way it is supposed to.
Broken sewage pipelines are common sight in the city. In such cases, the sewage does not go to the STP; instead it overflows into Storm Water Drains (SWD) that eventually flows untreated, into a valley, lake or stream. And that’s one reason why lakes are getting killed. Also the STPs in Bengaluru don’t work to full capacity, so the sewage that can't be treated, is let into water bodies untreated.
What happens to poop from ‘New Bengaluru’ and the 110 villages?
Some real bad shit happens here. Underground drains in this area are still UNDER CONSTRUCTION.
BWSSB Executive Engineer VC Kumar says, “We have laid 2,300 km long network covering 93 per cent (of the CMC area), but it is not connected to STPs yet as there are lacunae in some portions and in termination points. Therefore in some places it is flowing into the storm water drain,” he says.
Basically what he means is that the UGD is there in most places, but not connected to STPs. (Termination points refer to the ends of major pipelines, and also to the last point where the seweage is supposed to reach – the STP) So the poop and rest of sewage is released into water bodies. Untreated.
The 110 villages on the other hand, have no UGD lines at all. A proposal to bring these villages within the UGD system awaits the assent of the central government, Kumar says. That means any proper disposal method is a far away dream.
What exactly happens to untreated sewage from these areas?
The untreated sewage water enters the SWD. Gravity and Bengaluru’s geography, mean that the water and sewage from SWDs flows into lakes and valleys and finally makes it way to the rivers – which your drinking water supply is sourced from.
Here are two examples where this happens:
Example 1: Mahadevapura and Bommanahalli areas were formerly under CMC. The UGD system construction is still underway. So the poop generated from the plush IT companies and apartment complexes gets discharged into SWDs and eventually flows into Bellandur lake. The poop-water mixes with fresh water in the lake and then flows down-stream into Varthur lake. (Varthur and Bellandur lakes are connected.) Varthur empties its fecal matter containing water into South Pennar River which, behold, enters Tamil Nadu. Varthur and Bellandur lakes were in news recently for water foaming on to the roads.
Example 2: Kengeri too was part of the CMC bordering Bengaluru until 2007. No UGD yet. Sewage including faecal matter from this area is discharged into Vrishabhavati valley, that enters the Byramangala lake, which flows into Arkavathi River and which in turn, flows into Cauvery River. All of this, the Cauvery river carries into Tamil Nadu.
Now you understand why the Tamil Nadu government recently approached the Supreme Court urging it to direct the Karnataka government to stop discharging untreated sewage and industrial effluents into Cauvery River and its tributaries. Tamil Nadu does have tertiary treatment plants to treat the water and make it potable, but, it says that the untreated sewage and sludge is killing the Cauvery.
Tests in February 2014 showed that faecal E.coli bacteria and other substances in the Cauvery water were much higher than permissible standards.
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Where does Bengaluru’s drinking water come from?
Once known for its 1,000 lakes (once upon a time), the Garden City of Bengaluru also derives its potable water from Cauvery. The Cauvery River originates at Talacauvery in Bhagamandala in Kodagu district. The river charts its course through the towns of Kodagu, Kushalnagar, Mysore before the water is pumped to Bengaluru by BWSSB from a pump house in Thorekadanahalli (TK Halli), located about 100 km from the city. All these towns discharge their sewage water into Cauvery.
Therefore, we too get the same water that Tamil Nadu would get from us. An STP in TK Halli conducts tertiary treatment of water. Tertiary treatment is the first step to making water potable after it undergoes secondary treatment.
The real issue
A large amount of Bengaluru’s poop is let into water bodies, untreated. Ultimately, our drinking water is mostly safe authorities claim, but do give a thought to the water bodies that are getting killed in the process. And to stop their slow death, it is important that the city and its growing population get proper underground drainage.