Home Composter in Bangalore for Houses, Flats & Gated Communities

Observing the waste generation pattern across several apartments in Bangalore, the most common number we see is an average of 0.8 kg per home per day. This is an average figure in an apartment complex, some homes will have very little, some much more, and some flats may be vacant.

A cycle time of 12 days has been observed for any month of the year and over a four-year period in Bangalore. In warmer months, we have observed a cycle time of less than 12 days; however, for capacity calculations, we use 12 days. This period is also called the "in-vessel" time, where the material needs to be mixed daily and most of the composting action takes place.

We observe a sharp rise in core temperature to more than 50°C and often crossing 65°C. This phase (thermophilic phase) lasts a few days and then temperature gradually drops to a few degrees above the ambient temperature. Most of the composting would be done, and the rest can happen in the curing bag/container over a further period of 20 days. This (curing) is a passive phase and no stirring or mixing is needed.

If the composters are getting filled in less than 12 days, then additional capacity is needed.

As an example, if you have 4 composters, each of 180 litres, then the daily fill rate should be less than 60 litres/day (un-shredded volume equivalent of 40 kg/day).

It is difficult to generalise and be accurate since the type of waste varies a lot. However, if we take a non-homogenous quantity (which is typical when considering waste from several homes), we have observed that wet waste has a density of about 0.6 kg/litre.

For monthly estimates, we recommend purchasing 15% by weight. So, if an apartment generates an average of 50 kg/day, the cocopeat requirement will be 7.5 kg/day or 225 kg/month.

When purchasing cocopeat, you will notice that the cost of the cocopeat is much lower than the cost to transport it to your premises. Hence it is good to purchase as much as can be carried in one trip of the van, provided storage space is not a problem.

In the above example, 225 kg would be 9 bags. If we purchase 1,000 kg (a typical full load for a small van), then we would need to buy 40 bags or about 4 months supply.

Both leaf powder and cocopeat serve the purpose of supplying carbon to the microbes in the composting process. In addition, both help to absorb extra moisture and any odour also. In either case, it is important to ensure that cocopeat / leaf powder is dry.

Sawdust is obtained from the processing of wood which has been treated with chemicals like formaldehyde known to kill bacteria and micro-organisms which are essential to composting. The presence of such chemicals will prevent composting action and give rise to a very strong stench which cannot be controlled.

The differences arise from a few practical issues, summarised below:

While the “in-vessel” time for compost is 12 days, the curing period is about 20 days. If we let the compost rest in a curing container for two cycles, it would be 24 days and is more convenient to estimate the time. Taking into account the shrinkage of compost during the cycle, we recommend having curing containers which are about 1.5 x the volume of a composter. If you have 360 Lit composters, it is convenient to have a curing box with a volume of more than 540 Lit along with each composter.

The reduction in weight of wet waste (after mixing with cocopeat and composting) would be approximately 60% to 70%. If we begin with 100kg of wet waste we would end up with 30kg to 40kg of compost.

Here below is a tabulation for an apartment with 150 homes., showing the full sizing and operating-cost estimate.

These numbers are estimates and can be manually rounded when preparing a quotation. For a tabulation specific to your community size, please get in touch.

Shredding is a must. For small amounts of waste, hand shredding using garden shears is possible, else powered shredder must be used. Just like animals bite and cut food before swallowing, shredding helps in faster composting by exposing larger surface area to microbial action.

A lot of energy is consumed in the processing of food right till it is served on the table. Purchase (by car/delivery van), Cold storage (till use), cooking, mixing/grinding, heating etc. It is only after all this that we discuss the disposal (or composting) of food in the form of waste. Taking a holistic view, one cannot stop using power to treat waste but surely one must minimise it and use it only where really needed. This is applicable to shredding as well.

Assuming a 200 home apartment generates about 160kg of waste per day, a 1.5HP shredder would consume about 1.1 units per day or just 33 units per month. For 200 homes, this power consumption is negligible.

Aerobic composting, as the name suggests, is a process where we allow air to circulate within the pile of waste. To enable this, we must maintain the following 4 steps:

• CHOP the raw waste into smaller pieces
• COAT the raw waste with cocopeat (which provides carbon and also absorbs excess moisture)
• MIX waste once daily (to expose it to air)
• MAINTAIN MOISTURE: not too wet not too dry

1. Foremost benefit for residential areas is that no odourous gases are generated. Be sure - If there is odour, then the process has not been followed correctly.

2. It generates internal heat which helps faster composting.

3. The cycle time is much faster. (About 30 days, of which only the first 10 to 15 days will need the waste to be inside the composter, followed by about 20 days of curing / maturation.

It is to be mixed in the ratio of 1:3 by volume: 1 measure of cocopeat for 3 measures of wet waste. We had provided a 10 Lit measuring can which has a mark at the 3.3 Lit level to make this easy. This measurement is to be done with the un-shredded waste. After shredding there will be some reduction in volume. Note that this is only the initial (first-day) addition. More cocopeat or more water may need to be added on the remaining 11 days of the 12 day cycle.

In one sentence: not too wet (soggy), not too dry. Just damp! On the practical side here are some thumb rules which make it easy to follow

• There should be no dripping of leachate from the pile. If there is dripping, then it is too wet and air cannot circulate. This would lead to anaerobic conditions and odour
• To reduce moisture add a little cocopeat (or leaf dust) at a time and mix till the mass is easy to toss and tightly packed.
• If the pile is too dry, then the waste just gets de-hydrated and the colours of the waste do not change to brown and then black.
• If moisture (and cocopeat) is right, the core temperature would rise to 50°C and higher after the first couple of days. This make take longer if the amount of waste is too little in a large composter.
• If we insert a fork, the waste should be easy to toss around – indicating that there is no compaction due to excess moisture.
• Within a few days the colour of the waste should turn a dark brown and towards the end of the 12-day cycle should become black.

As explained above, the aerobic composting process would generate internal heat. In summer, the pile can quickly lose moisture due to internal and external heat. Hence water has to be sprinkled to prevent drying up of the waste. In the monsoons, since the air is humid, the waste will not lose (or lose less) moisture. In addition, there could be some ingress of moisture too due to rain water seeping through any cracks that have developed. This is the season in which we are most likely to see odour issues. Hence the moisture has to be reduced by adding cocopeat (or leaf powder) bit by bit.

Mixing not only keeps all the waste composting at (almost) the same rate but also makes sure there are no lumps, all portions exposed to air for at least a few minutes a day. The bacterial growth will be about the same in all portions. In short , the entire pile would soon become homogenous.

Divide the container into quarters (as viewed from above) and turn over each quarter completely. Go right down to the base of the composter and scrape it clean. Then carve out a cylindrical cavity in the centre and bring turn the waste up and down. This is only to ensure that when drawing out the quarters, no portion in the centre was left un-done.

A perfectly aerobic process will generate no odour, as the resultant gas is CO₂ which is odourless. To keep the composting process free of odour – the aim should be to encourage all conditions which help aerobic composting which are

• Moisture: Excessive moisture tends to bind the waste into lumps which do not allow air to pass through. Keep the pile just slightly damp. This is a common reason during the rains when operators leave the composters exposed to rain and the whole pile becomes soaked with water. Very soon there will be foul smell. The remedy is to add enough of dry cocopeat or leaf powder (or just allow the pile to dry up sufficiently if there is sunshine)
• Lumps: Avoid lumps (small balls) in the pile by shredding and breaking them up. Inside the lump there can be anaerobic conditions – which means waste will be slow to decay and can give off odours. Periodic and proper mixing should break up any visible lumps.
• Aeration: In a pile, aeration is possible due to natural convection if the composting vessel is designed to self-aerate like in Marigold. Here the self-heating creates currents of warm air above and a suction of fresh air from below. However, the centre of the pile will always have more efficient heat retention (characterised by high temperatures) as compared to the boundaries or periphery of the composting vessel. The only way to homogenise the pile is by proper mixing from the centre outward from the periphery to the centre, from top to bottom etc. Hence a motorised agitator or mixer can ensure much better efficiency (shorter cycle times)
• Carbon: When there is deficiency of carbon the bacteria produce Ammonia which has a sharp pungent smell. Hence there should be adequate carbon in the form of cocopeat or dry-leaf powder. Sometimes the composting conditions can promote very rapid consumption of carbon. This is characterised by sharp and high temperatures. So if the foul smell is accompanied by high temperatures (beyond 650C) then the remedy is to add more cocopeat so that the temperature drops and the smell abates.
• Spacing of composters: The physical spacing of composters can be increased to the extent that the site permits. This has a simple effect of diluting any foul-smelling gases in the event of malfunction or operator errors. The gases are not aggregated and easier to manage when composters are spaced apart. Placing composters on the terrace (as done in some apartments) also enables the light gases to escape upwards in the event of a malfunction.
• Preservatives in wood: Saw dust is often derived from wood which has been treated with strong chemicals which inhibit microbial action. There is then a stench of rotting which cannot be remedied. The entire pile has to be discarded. Hence it is most important to completely avoid saw dust unless one creates this from virgin natural wood chips / garden waste without any chemicals.

A typical graph of daily temperature log would look something like below. The dotted area shows the intense (thermophilic) composting activity

The shaded green band marks the thermophilic zone (≥50°C), where pathogens and weed seeds are destroyed. Peak temperature observed: 73°C on Day 6.

We differentiate our system from others in the following ways

• The composter (or bioreactor) is designed to optimise aerobic composting with a high temperature thermophilic phase giving temperatures even beyond 700C. This gives a shorter cycle time in-vessel and dark black compost.
• The thermophilic phase ensures that plant pathogens and weed seeds are destroyed. Hence compost will not sprout weeds or other un-wanted plants (whose remains/seeds were present in the waste) but support the growth of new plants sown in it.
• The additives used are commonly available agriculture waste like cocopeat (made from coconut husk) or leaf powder (shredded dry brown leaves) or any other carbon rich material devoid of any chemicals.
• Our composters are built from stainless steel and can be kept in the open without the need for special shelters. [From the year 2021, even the frame, lid and drain tray which were previously mild steel have been built from stainless steel to give years of maintenance-free life on the field]
• The amount of plastic used is almost nil: just the acrylic transparent lid. Everything else is stainless steel. This ensures that even at the end of life, there is almost nil plastic that goes out as waste.

In the Marigold System – there are two stages: one which is the high temperature stage where the material is left for temperature to rise beyond 50 deg C (sometime even up to 70 0 C) and then fall again to a little over ambient. At this stage the material is moved to the curing box which is the 2nd stage of composting – with no mixing. It is left here for 24 days.

This is done so that the composter (made from stainless steel) can make way for fresh waste. If we were to keep the waste beyond the high temperature period, the investment needed by the customer would increase. Hence after the high temperature stage, it is moved to a low-cost wooden container.

So even in our system, the cycle time (of composting + curing) would be about 36 days. 12 days in the steel composter, 24 days in wooden box.

We have not seen other systems (in the segment where we operate) where high temperature (thermophilic) composting is demonstrated. Those with short cycle times (even 24hrs) use heating. The features in our system which enable this natural rapid rise in temperature

• Double walled composting vessel for heat retention
• Sufficient perforations at base and at top for natural convection
• Operator checks to see that there is no liquid dripping. The moisture is reduced / maintained so that natural convection of air can take place through the pile. Daily monitoring of temperature by our staff shows that the process is taking place correctly. An excessively wet pile will not allow natural convection and hence temperature rise will be sluggish. Not to mention chance of foul odour due to anaerobic action.
• The curing box has no features for heat retention and has only perforations on the side.

We have observed that due to the fine particle size of cocopeat (or leaf powder – which is even finer) the volumes are not additive. Adding 3 Lit of cocopeat to 10 Lit of wet waste will not increase the volume beyond 10 Lit (maybe very slightly) when it is mixed well. The fine powder gets into the gaps between pieces of shredded waste. In terms of weight, yes of course they will add. But not in terms of volume. [In the earlier years, we used brown leaves and at that time the volume would be additive. Moving to leaf powder or cocopeat not only has the advantage of volume not being additive but the leaf powder coats all portions of the wet waste and almost eliminates the chance of odour.]

Over a complete 12-day cycle, we notice that (just before removing the material for curing) the volume will reduce by about 25% to 30%. So a 360 Lit mass would become around 250 Lit when moved to the curing box. Hence a single curing box of 640 lit is more than sufficient to take 2 cycles of waste from a single composter of 360 Lit.

As mentioned in Q1, there are 2 stages – the active high temperature stage and the passive (curing stage). In our system, as waste (mixed with appropriate amounts of cocopeat) is added to a composter, it is blended with the material from the previous day(s). Hence the waste from day #2 benefits from the microbes and heat generated by day#1. Likewise, if the same composter is fed waste on Day#3, then this waste benefits from the waste of Day#1, Day#2 as well. [So this process is non-linear] Yes, there will be waste (of the last batch) which would not get the full benefit of the double-walled steel vessel and will be transferred to the curing box allowing the balance composting to happen in the curing box where it will be embedded in waste which has seen a full cycle.

We remove the waste when the temperature has risen (above 50 deg C) and fallen (below 40 deg C).