Here’s what’s wrong with “crush-and-flush” approach to waste

Bengaluru has set out on a journey of managing its waste sustainably. Going for pulverisers that further increase the load on sewage treatment of the city may not be a solution for this city.

The Mayor of Bruhat Bengaluru Mahanagara Palike recently announced a scheme to crush the waste and flush it to sewage drains. Activists and solid waste management enthusiasts are opposing it and petitions are floating around. Why? Not without solid reason. Here is a list of all that is wrong with ‘crush-and-flush’ approach.

1. It will waste a lot of fresh water for flushing.

Each kitchen will need between 10-20 litres of extra fresh water every day to flush down the pulverized food. This is like having four extra full flushes in your toilet, on daily basis!

Already Bengaluru has acute shortage of water, which is projected to reach 50% in next five years.
We simply don’t have additional fresh water for flushing the crushed food down the drain.

2. Increased BOD will kill STPs

The food will kill Sewage Treatment Plants, thanks to 3.5 times more Biological Oxygen Demand (BOD) of the sewage. That means our STPs have to be 3.5 times larger overnight.

A typical kitchen generates 1.4 kg of wet waste per day (about 0.7 kg COD or 0.4 kg BOD).
At present, each household produces 600 lpd of sewage with 250 mg/l BOD (which means 0.15
kg/day BOD).
Thus, if a kitchen pulverizer is made mandatory, it will add 2.5 times BOD to the sewage!
You will need a much larger STP to digest this “fortified” sewage!
• 3.5 times larger aeration tank
• 3.5 times larger air blower (much higher electricity bill!)
• Larger filter to deal with higher sludge
• Larger dewatering plant

Our STPs are not designed for this load. They will simply fail, and we will have to discharge partially treated sewage to the drains and lakes. If you continue to operate the same STP, you will have to release 70% untreated sewage to the lakes.

3. The oil and fat content will cause foaming in STPs, and kill the bacteria

In the new system, people will pour their used oil and fat in the kitchen sink. This will straight away reach the STPs (either belonging to the apartment, or BWSSB). The fat content will cause a blanket of thick, brown foam on the STP tanks, which lowers the efficiency of the bacteria, and also reduces aeration. This is another reason why the STP will be killed.

4. The food sludge will settle in sewerage pipes, and block them

Our drainage system is mainly gravity-fed, not pumped. In this type of pipelines, when the sewage flow slows down, it leaves sediments behind. Thus the sediment builds up gradually, and reduces the flow even further. Ultimately it blocks the pipe completely.

5. The flooding of city will get aggravated.

In many parts of the city, the same drains carry rainwater and raw/treated sewage. When these common drains will get blocked with food sediment, it will affect the carrying capacity of the drains. Already Bangalore sees regular flooding of some areas. This flooding will increase multifold.

6. The row sewage will emerge out of manholes and flow on roads

When the pipes are blocked, the raw sewage will burst out of the manholes and flow freely across the roads.

7. The raw sewage will reach drains and lakes

When STPs belonging to apartments and BWSSB are killed, the raw sewage will reach the drains and lakes. This will kill even those lakes that are rejuvenated recently.

8. The lakes will have a far higher foaming

When the oil and fat reaches the lakes, there will far higher foaming under windy/rainy conditions.
In addition, the smell problem will worsen due to partially treated sewage.

9. Cost of handling the wet-waste will be atrocious

Bengaluru spends Rs 62/kl to get water from far off places. This precious water would be wasted to just push the food waste in a pipe. The total cost of handling wet waste, which is pegged at approximately Rs 7/kg, will simply go up by at least 5 times.

10. The abundance of food will cause explosion of cockroach population in sewers

If the sewer system has a lot of crushed food, it will result in explosive growth of population of cockroaches. They cause a lot of diseases, including dysentery, cholera, leprosy, allergy, asthma, etc. In other words, we can expect epidemics of these diseases in the city.

11. The SWM system is already capable of handling the wet waste!

Bangalore city generates 4600 to 6000 tonnes of waste by various estimates, out of which 60-75% is wet waste. So even a most conservative estimate will still leave 1300 tonnes of the wet waste to be handled through other means. As a city, we have already built capacity to handle 3500 tonnes of wet waste daily!

The government has no way to control this situation!

You might think that even if such an ill-advised scheme is proposed, the government will have enough checks and balances to stop this.

But as the following sections show, the government cannot offer such protection, and only citizen vigilance can prevent any damage to the environment!

1. There are no government checks and balances (read “law and order”)!

You might think that even if such an ill-advised scheme is proposed, the government will have enough checks and balances to stop this.

But as the following sections show, the government cannot offer such protection, and only citizen
vigilance can prevent any damage to the environment!

1. There are no government checks and balances (read “law and order”)!

According to the Water Act 1974, any source of pollution to the water bodies must be approved by
KSPCB (State Pollution Control Board), This used to be done in a two-stage approval process:

1. CFE (Consent for Establishment): Approval to launch the project, after checking the data
submitted for the proposed project– The quality and quantity of sewage that will be
generated, and the proposed treatment.

2. CFO (Consent for Operation): Approval to operate the STP; if it meets all norms.
The STPs are designed for a domestic sewage with 250 mg/l BOD and for 700 kld per household.
The currently existing STPs are given CFE and CFO for this processing capacity only.

But if the “crush-and-flush” scheme is implemented, the same STPs will have to treat sewage
with 3.5 times the sanctioned BOD limits.

Earlier, there was a check-and-balance: If the quality of sewage changes, the CFE-CFO become automatically invalid. Then the proponent of STP must seek fresh CFE-CFO for the new type of

In other words, KSPCB was supposed to re-evaluate all the private and public STPs afresh, and
certify whether they can digest the “fortified” sewage. In fact, KSPCB was supposed to disallow
an STP from functioning if it cannot handle the incoming sewage.

But this check-and-balance does not exist any more!

In fact, KSPCB has given up the job of inspecting and issuing CFE-CFO for new STPs. It also stopped periodic inspection of the existing STPs. So now this area has become completely lawless.

Result? All STPs can fail without active intervention from KSPCB.

But this check-and-balance does not exist any more.

In fact, KSPCB has given up the job of inspecting and issuing CFE-CFO for new STPs (forget periodic inspection of the existing ones). So now this area has become completely lawless.

Result? All STPs will fail without fuss.

2. There is no legal way to upgrade the existing STPs!

Even if KSPCB or BBMP finds that most of the STPs need a huge upgrade in capacity, how will
they enforce this? Already they have failed to force old apartments to retrofit STPs. This new adventure will add all the existing STPs to the “problematic STPs” list. There is no way out. Therefore the only prudent option is not to make kitchen pulverizer mandatory.

3. KSPCB’s failure to fulfill its duties aggravates the situation

Under Water Act, 1974, KSPCB is tasked with the following duties. Here is a partial list of its duties (from Section 17)

(a) to plan a comprehensive programme for the prevention, control or abatement of pollution of streams and wells in the State and to secure the execution thereof;
(b) to advise the State Government on any matter concerning the prevention, control or abatement of water pollution;
(e) to collaborate with the Central Board in organising the training of persons engaged or to be engaged in programmes relating to prevention, control or abatement of water pollution and to organise mass education programmes relating thereto;
(f) to inspect sewage or trade effluents, works and plants for the treatment or sewage and trade effluents and to review plans, specifications or other data relating to plants set up for the treatment of water, works for the purification thereof and the system for the disposal of sewage or trade effluents or in connection with the grant of any consent as required by this Act;
(h) to evolve economical and reliable methods of treatment of sewage and trade effluents, having regard to the peculiar conditions of soils, climate and water resources of different regions and more specially the prevailing flow characteristics of water in streams and wells which render it impossible to attain even the minimum degree of dilution;

However, instead of fulfilling these duties, KSPCB has gone and devolved its power to inspect and approve new STPs to BBMP (violation of part (f) above).

But BBMP does not have the trained manpower for the inspection and approval of new STPs.

So it was incumbent on KSPCB to plan a systematic handing over as required by parts a and b above. But KSPCB has failed to plan this transition (violation of parts a and b).

Further, KSPCB has failed to “secure the execution of the plan” as stated in part a.

What’s the solution?

Separate solid waste from sewage at source

The solution is to separate solid waste from sewage and compost it directly, which is far simpler and much more economical.

All restaurants must use a simple chamber called “oil-and-grit separator”. This chamber is fitted under the sink, and separates oil and food from the sewage.

In fact, BBMP in consultation with KSPCB must set up a citywide logistics to collect used oil from all restaurants and dispose it off. This will ensure that oil and fat does not reach the drains and lakes.

Encourage people to compost locally (or locality/ward level)

Already 1+ Lakh homes create compost through the Swachagraha campaign.

BBMP has done great work by conducting composting Santhe to showcase various ways to compost at home and community level.

Are there other examples?

Well, Mumbai, Chennai, Noida and many other cities have already made it mandatory.

Alappuzah made it mandatory in 2012. now it is counted in top 5 cities for waste management in the world by UN. (Also counted in Top 5 cleanest cities in India, as judged by CSE.)


  1. Dr (mrs)Kamlesh Ojha says:

    Segregation at source &composting should mandatory

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