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