Community composting method-9: This cement tank system handles large quantities of food waste

August2015 958

The Saahas team led by Supervisor Narayana Swamy (left) turns tonnes of kitchen and dry waste into organic manure at BIEC, Tumkur Road. These high-capacity cement tanks make their job easy.

Turning quintals of food waste coming out of three huge exhibition halls and fallen dry leaves swept up from a humungous campus spread over 36 acres into organic manure is no silly task. Interestingly, all of it gets absorbed efficiently by a simple composting system designed and managed by Saahas Zero Waste Solutions at Bangalore International Exhibition Centre (BIEC), Tumkur Road.

The BIEC campus is dotted with three large exhibition halls covering a total area of 40,000 sqft and enjoys a decent green cover. The event schedule and turnout are anything but predictable. Although food waste can be as low as 5-15 kgs per day on non-event days, it can go up to 500-1,000 kgs on days when the place starts buzzing with activity. Since segregation at source is a far cry in such situations, Saahas’s four-member staff, led by supervisor Narayana Gowda, gets down to brass tacks and does its best to sort out truckloads of mixed waste to keep the rejects to the minimum.

Saahas, a brainchild of Wilma Rodrigues, entered the realm of e-waste management in 2001, much before half of the world started talking trash. Almost a decade later, it embraced the challenge and integrated all streams of waste into its work routine. Likewise, Saahas has many a feather in its cap. Recycling of 30 tonnes of tetrapacks per month into paper products, roofing sheets and chip boards is, I would say, the brightest among the latest of its ventures.

The infrastructure

It’s a large, well-aerated hall sitting on a crest and surrounded by gorgeous greenery. As I walked up the steps, I wondered when on earth did Bangaloreans evolve enough to give up such a beautiful spot for composting!

A board in green and white—“Proud to belong to a zero waste campus”—greeted me at the doorstep. The hall looks so clean and fresh that any hardcore cynic will think twice before rejecting composting as one of the dirtiest recycling options.

There are 10 compost cement tanks of 5 ft x 3 ft x 2.5 ft (L x W x H) dimensions which can take in 800-900 kgs of shredded food and garden waste. Two more tanks, almost double in length, are meant for storage. A chopper and a shredder work in pair to shred dry garden leaves and food waste, thereby reducing the volume significantly. Each tank has an outlet to release the leachate. All the 10 outlets are connected to a drain which takes the leachate out of the composting area and then gets connected to a series of water treatment channels and ends up finally in two tanks which supply water to the entire campus.

The process

The shredded food and garden waste is mixed with Bioculum, an inoculant that speeds up the composting process. The two types of waste get distributed equally and layered in all 10 tanks. The staff turns the piles once in 2-3 days to aerate it, thereby preventing anaerobic conditions which can cause bad odour. It takes around 30 days for the tanks to produce nice-smelling compost. The staff takes out the ready-to-use compost and stores it in the storage tanks.

Started five months ago, this venture has so far managed the waste sent from all the three halls and fallen dry leaves from the garden. Notwithstanding the huge quantity, this cement tank method seemed to be handling the challenges quite well. It’s simple, scalable and easily adaptable, especially by very large resident communities comprising units above 1000 and also offices fitted with canteens.


The hall is large, bright and well-aerated. Hygiene levels are high. Thanks to these qualities, the cement tank system looked pretty neat. Residential communities, if they want to adopt this method, should pay attention to the aeration aspects in particular.

Rodent & odour issues

Supervisor Narayana Swamy said they have not faced rodent problems so far. In fact, the tanks are left open without any mesh lid. Since the topmost layer of the substrate is layered with dry shredded leaves, it keeps fruit flies and other insects at bay. There was absolutely no odour.

Leachate loss

There isn’t much leachate going out, most probably because of the high quantities of dry leaves used.

The cost

Capital expenditure

(Since this composting is done at a commercial establishment, it is difficult to come up with a break-up for 100 homes.)

  • Food chopper: Rs. 2,50,000
  • Leaf shredder: Rs. 1,50,000
  • Tank construction cost, (approx): Rs 1000/sqft. Each tank is 24 sqft and there are 10 compost tanks and two compost storage tanks. Total cost (12*24)*1000= Rs. 2,88,000.

Please note: Depending on who you hire, the cost of constructing cement tanks can vary widely. In our community, a firm sent a Rs 1.5 lakh quote to build three simple cement tanks for vermi-composting. Eventually, we had it built for only Rs 35,000 with help from a local mason. Please read this post for more details.

Operational expenditure

According to Saahas, opex is Rs 2.4/kg. It is inclusive of field staff members, supervisory cost, protective gear and coordination costs.

If residential communities adopt this method, they will incur mainly labour cost and power expenses for shredding the waste. The inoculant Bioculum doesn’t cost much. In other words, the opex is very low.

This composting unit at BIEC is surrounded by beautiful greenery.

The composting unit at BIEC is surrounded by beautiful greenery.

Pros and cons

This method is space-intensive. It cannot be done in basements as it can cause odour problems due to lack of aeration. If you want to do it on the terrace, then you have to ensure a sturdy roof and proper water-proofing so that the leachate does not lead to leakages. Good plumbing work is a must.

Secondly, it is better to weigh all the pros and cons before saying ‘yes’ to this method. A negative aspect of constructing cement tanks is they are permanent structures and once built, there is no point of return. Some communities may not prefer permanent structures.

That said, to handle large quantities—anything beyond 250 kgs—this method works well as each tank can take in close to a tonne of shredded waste.

Contact details

Saahas, 433, 8th cross, Jayanagar 1st Block, Bangalore-560 011. Phone: 080-41689889. Email: Web:

19 thoughts on “Community composting method-9: This cement tank system handles large quantities of food waste

  1. Thank you Savita, for yet another great article. I am trying to make our community math {temple} events go zero-waste. They are held all over India mostly in open grounds with pendals. The volume of people is between 500-1500 each day. My query pertains to managing wet waste. How does one process such large amounts in temporary locations. Anaerobic composting by digging a pit is out of question as it has been ruled out by the management team. We can take them to nearby goshalas, but for a 7-8 day event, even the goshalas will be swamped with the volume. The next event is in Mumbai. Any tips for this query ? thank you in advance smita

    Liked by 1 person

    • Thanks for chiming in, Smita. Nice to know about your interest in zero-waste event managment. 🙂
      The best option is to look for any community composting unit closeby. But they are few and far between. Secondly, look for biogas installations. If these two options are not at your disposal, then composting so much of wet waste becomes difficult. Because composting doesn’t happen in short. With some very good accelerators, you can speed up the process to 15 days, max. It’s not like drywaste which can be sorted out and stored in bags either.
      BTW, how about looking for some piggeries? They will take in loads if segregated properly and shipped without delay.


      • We have been using cement tanks in all our large projects because of durability and concrete tanks also breathe without leaking out leachate. However, as Savita has pointed out, “fixed tank” is often an issue hence we are working with an FRP manufacturer for a mobile, lighter and relatively cheaper tank. The huge advantage is that the life time of these tanks will be very long, matching cement tanks. We have the sample piece ready, its being tested.

        Liked by 1 person

    • Wishful thinking… 😉 Growing veggies in place of ornamental plants is not THE thing to do. Isn’t it so fashionable to rattle off names like Balsam, Forest Fire, Pentas, Petunias… rather than tomatoes, brinjals and onions?

      Liked by 2 people

      • Going by the last pic above, seems it’s fait accompli as far as ornamental stuff is concerned.
        But somebody in BIEC ought to think of branching out into useful, income-generating plants or those than can be plucked for personal use by peeps in the area.

        Liked by 1 person

          • Dear Savita, I am so glad this topic is being discussed. Saahas in association with CHF is working on another small project where we are encouraging people to grow fruits and vegetables instead of ornamental plants in public places. We were able to convince few, Kumaran school has given us some space where we have planted an organic garden. We are also talking to Bangalore club and BIEC. Anyone interested please contact Mr. Srinivas 9449153143
            We would plant a 1000 sqft garden for free !!! Only condition is it should be in a public location even an apartment complex would do.

            Liked by 1 person

    • Dear Praveen, if you have aeration at the bottom, then there is no need for turning whatsoever. But if it’s a tank without a raised platform at the bottom, then you may have to turn once a week, max. Let the heat build up nicely and composting happen. Make sure there is no heavy moisture buildup at the bottom. If any, it should have an outlet. Dry leaves do not give out bad odor and are easy to handle. All the best.


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