Here’s a solution that suits both small apartments and bulk generators like large-sized apartments, restaurants, schools, institutes, hospitals, school and corporate canteens. If you want a combined package of ease of use, aesthetics, zero operational costs and capital payback in a few years, go for EcoDigester.

This waste-to-energy technology designed and developed by Eco Positive Solutions (India) Pvt. Ltd., a FutureIP Group Company, converts food and other organic waste into fuel (methane-rich biogas) which can be used for cooking, heating and to generate electricity.

For my case study, I picked out Ace Designers Limited located in Peenya Industrial Estate. The solution has been working here efficiently and the biogas produced is being used in the canteen. Installed just five months ago, the plant has already produced 2,47,866 litres of biogas.

A shredder is necessary

As written in a previous post, a shredder is a must to speed up the process. However, Ace Designers wasn’t shredding the waste as most of it is already in a condition to be used directly.

The process: As simple as it gets

This waste is mixed with water at 1:1 ratio and the feedstock is fed through an inlet. In this case, feeding nearly 20-25 kgs of waste takes just ½ an hour per day. One worker is enough to handle up to 100 kgs of waste. “For feeding larger quantities, we suggest using a pump,” says Gururaj Kanade, CEO, Eco Positive Solutions.

Once the feeding is done, you can immediately get back to your routine. A carefully prepared multiculture microbial solution built into the biodigester works its magic on the foodwaste and methane-rich biogas begins to collect in the balloon. This balloon can be placed on the terrace or a spot close to the canteen. This is then connected to a gas burner to fuel cooking activities. Similarly, biogas can be used to generate electricity as well. Eco Positive is currently developing suitable options.

A wind turbine keeps on stirring the organic matter inside the bioreactor. The higher the wind, the better. But the spot selected at Ace was close to the canteen and wasn’t getting high winds. The stirrer rotating even at a snail’s pace was enough to keep the microbial activity ticking inside. The resultant slurry gets recycled back through the feed preparation, if required.

The rest comes out as murky but viscous slurry though an outlet which can be directed to a tank supplying water for gardening. The slurry carries with it huge amounts of nitrogen, soluble phosphorus and other essential nutrients.

Please note: The input decides the output. You cannot expect a perfect output packed with all micro- and macro-nutrients regardless of what goes in. By the way, if there is a lot of cooked waste, oil, non-vegetarian leftovers, the microbes will simply love it. The quantity of biogas also goes up depending on the amount of fat content the waste carries. Conversely, it comes down if you put higher quantities of vegetable or green waste.

Aethestics

Quite pleasing. Since all the waste is fed through one funnel, the rest of the plant remains untouched by foodwaste or leachate. Once it goes in, not a scrap of kitchen waste is in sight. Wiping the dust off the biodigester and the stirrer panels will be good enough. In short, low maintenance.

The microbes & the magic

Promoting monoculture works against the basic principles deployed by nature to maintain that seamless and delicate balance in the soil. Hence, a carefully curated multiculture microbial solution is a must. Gururaj spoke at length on the research that went into studying the fermentation methods practised vastly in India for toddy preparation. The team used all the positive features of this traditional method and tweaked it a bit to come up with a highly effective microbial culture.

“We have done changes to the traditional culture development process and adopted it to enhance seed culture quality. The initial culture preparation for the seed microbial population is given doses of natural nutrients rather than dosing synthetically-enriched additives to enhance and strengthen the microbial growth. This produces the appropriate microbial strains of robust nature…” says Gururaj.

According to him, to develop a robust culture of microbes, a proper supply of the required nutrients, early development strengthening inputs, exposure to the changes in the operational environment and maintaining biodiversity is important.

“In this context, we have to view a bioreactor/biodigester as a colony of a variety of micro-organisms working in the given space in a harmonious manner rather than a physical device like an electromechanical machine targeted to produce a given output. The organisms broadly categorised as hydrolytic, acidogens, acetogens and methanogens work in a syntropic manner to break down the organic input to produce biogas and slurry.”

EcoDigester can survive without food for more than one month. This is important because things can get dicey if a plant calls for every day feeding as canteens may remain shut for days on end.

The digestate or slurry

When diluted slurry is supplied to the garden on a daily basis, microbial activity in the soil increases, thereby enriching it. In fact, soil enrichment is everything. It boosts the immunity of the plants and reduces pest attacks.

“The slurry is a good source of NPK, plant macro-nutrients. More importantly, part of the phosphorus is in soluble form which helps the integration process with the soil. However, the amount of soluble phosphorous and other nutrients available is a function of the input composition and its characteristics.”

Gururaj advises that if you cannot utilise the slurry for gardening, you can simply let it flow into the STP tank or a drain. This is a stabilised slurry, not a harmful pollutant. The microbes present in it thrive in anaerobic conditions. If they pass through a clogged drain with all kinds of waste, they may actually act on it and unclog it to an extent. Please note: No study has been conducted on this aspect thus far. The slurry is viscous enough to keep flowing and hence, have no worries about it clogging the outlet pipe.

Biogas production

The plant at Ace has been producing nearly 2-3 kgs of methane-rich biogas per day. This technology has also been adopted at the Institute of Ayurveda and Integrative Medicine, Yelahanka. The institute is saving nearly Rs 5,000 per month through LPG and has been using the slurry to fertilise its garden. If you factor in the amount saved in transporting the wet waste through a contractor, you can add Rs 3,000 or more to the savings. Thus, more than Rs 8,000 worth of savings per month for generating just 35kgs of food waste. We are not even adding the cost of the fertilisers.

“For optimal biogas production, C:N ratio is considered as one of the important parametres. But with EcoDigester, we have seen optimal gas production even with low C:N ratio of the input feedstock. Hence, we don’t recommend treating the input waste with specific additives or waste material to balance the ratio.”

Not water-intensive or space-consuming

As the process permits reuse of effluent slurry, the amount of water used is significantly low. The plant is designed in such a way that the bioreactor fits even in cramped corners. It does not call for skilled labour, complex methodology or monitoring.

Safety concerns

Unlike in the floating drum model, methane does not escape into the atmosphere as the bioreactor is shut tight and a valve is used to let out the methane into the balloon. The biogas balloon can be placed in a safe spot away from any fire hazard. It is made of high-quality rubberised material tough enough to withstand heat. However, a roof over it will increase the safety net. To make it rodent-proof, you can get a mesh enclosure done. “The possibility of blast is almost nil as the methane is stored at near atmospheric pressure levels. On the contrary, LPG cylinders contain pressurised gas. In the worst-case scenario, even if a tear happens or rodents bite into the balloon, the methane escapes into the atmosphere as it is lighter than air,” says Gururaj.

Zero operational costs

One of the best features of this product is how it exploits natural elements. You do not need power to stir the slurry in the digester nor to heat the same. The wind powers the stirrer. The body of the biodigester is made of high-quality FRP which utilises the sunlight quite efficiently to create conducive atmosphere inside. That means zero operational cost. However, if you want the plant installed in your basement, then you will need machines to power the stirrer and to produce heat.

Fitting EcoDigester into a residential community

Not that easy, I agree; but not impossible either. If the residents’ association gets consent from the community to supply methane to a few nearby flats or villas, the problem is solved forever. Progressive architects can design upcoming properties in such a way that this bio-methanation plant comes as a built-in feature. For existing communities, the positive features of this product far outweigh the initial struggles of fitting the plant into their living space. But easy maintenance, zero operational costs and well-designed aesthetics will leave your efforts worthwhile in no time.

Capital investment

Approximate cost:

1. 15 kgs – Rs. 1,75,000.
2. 30 kgs – Rs. 2,50,000.
3. 50 kgs – Rs 3,50,000.
4. 100 kgs – Rs 6,00,000 to Rs 6,50,000.
5. 250 kgs – Rs 10,00,000 to Rs 12,50,000.

Please note: The cost includes all these items: A shredder, plumbing work and a simple canopy for the biogas balloon. However,  a site-specific enclosure for the balloon is out of scope. Also, any site-related specific requirements such as civil work, fabrication to create space is not baked into the cost.

Capital payback calculation model

Model: EcoDigester^TM – 5K (30kgs of wet/cooked food waste per day)

1. Assuming Biogas output of 4-5 cubic meters per day.
2. In terms of calorific heat energy capacity, it’s approximately equivalent to 1.75 kg to 2 kgs of LPG per day.
3. Currently, commercial LPG costs Rs 90-100 per kg.
4. The cost of 2 kgs of LPG is approximately Rs 180. Approximately, Rs 5,400-6,000/month.
5. Liquid fertilizer, 30-40 liters per day. If sold at Rs 3/litre, it will fetch Rs 2,700-3,500/month.
6. Assumed average monthly recovery = Rs 8,000.

A simple estimated capital payback will be approximately 3.5 years.

For more details, contact Mr Gururaj Kanade, 080 -25633803 / 9845452542; email: gururaj@futureip.com, ecodigester@ecopositive.co.in