Turning waste into compost the modern way

  • Lifestyle
  • Tuesday, 03 May 2011

When properly handled, waste from gardens, kitchens and farms can give us compost and biogas.

EVERY day, some staffers of the Malaysian Nuclear Agency in Bangi, Selangor, can be seen lugging three-litre thermal food containers – the type commonly used by nasi lemak sellers to keep rice warm – to work. No, it is not their packed lunch inside but something entirely different: leftover food from home.

Research officer Shyful Azizi Abd Rahman had requested that his 50 colleagues in the agrotechnology and bioscience division bring him the food scraps instead of junking them. He even provides them with the containers to make it convenient and, of course, less messy.

All the waste goes into a 60kg composting machine which Shyful is testing out. The Cowtech Composting & Biogas Production Machine breaks down organic waste with the help of bacteria to yield nutrient-rich compost and biogas, an energy source. For the past six months, Shyful has been feeding the machine all kinds of organic discards in order to assess its efficiency, biogas production and the quality of the compost.

“We first tried agricultural waste but the methane is low. We switched to food waste, and the biogas production is very high, about five to six litres a day,” he says.

Organic waste, such as those from farms and kitchens, forms some three-quarters of our waste stream and has always been troublesome. Wet and smelly, it also emits methane when degrading in airtight landfills. Composting is one way to treat organic waste but when done traditionally, will take months. Now, new technologies are being introduced to speed up the process and Cowtech is one of them.

Developed in Thailand over 10 years ago, the technology was introduced here last year by CH Green. Company chief executive officer Ang Lee Kaw says unlike other composting machine which yields only compost, the Cowtech system allows the tapping of biogas generated from waste decomposition as well.

The technology has found favour among several local companies which have had to grapple with disposal of organic waste from landscaping work, food production, staff canteens and agriculture.

Smaller carbon footprint

In the Cowtech system, waste is composted anaerobically (without oxygen) inside the composting machine. Methanogenic bacteria (inoculated into the machine during manufacture) break down the waste into compost, while releasing biogas which is typically made up of methane (50% to 70%), carbon dioxide (24% to 50%), hydrogen sulphide (3% or so) and small amounts of nitrogen, hydrogen and oxygen.

The biogas is piped through a scrubber containing iron wool to filter out most of the carbon dioxide and hydrogen sulphide (which is corrosive), leaving behind a 60% content of methane. This is good enough for direct heating (in stoves and lamps) and in a gen-set to generate electricity. (To use biogas in vehicles, the methane content must reach 80%).

After a retention time of some 15 days, you can harvest the resulting compost, a sludgy slurry (because of high moisture content in food waste,) rich in nutrients welcomed by plants and soil.

More importantly, the system prevents emission of methane from organic waste dumped in landfills. “We keep the methane and use it, such as for cooking,” says Ang. “Flaring (burning) methane is better than releasing it into the air as it has 21 times more global warming potential than carbon dioxide.”

The beauty of the Cowtech system, according to Ang and Shyful, is that it uses little energy. When waste is fed into the machine, the motor needs to run for only about 20 minutes for the mixing. After that, the bacteria get down to work. The machine is turned on only at the next feeding. If there is no electricity, there is a crank to manually churn the waste. Ang calculates the electricity consumption of a 100kg a day machine to be a mere RM1.40.

“You don’t want a system that needs electricity,” he says. “Long hours of heating defeat the purpose of reducing greenhouse gases.”

The system is self-sustaining, he adds, as the digesting bacteria requires no top-up because of the continuous operation. He says in some composting machines, you have to constantly replenish the micro-organisms and maintain a high temperature by heating.

Ang says the Cowtech machine works best at temperatures of around 30°C; so the machine should preferably be placed in or near open shade. The digestion process slows down during wet days and at lower temperatures. He assures us of the safety of the system. “Biogas is light, so it quickly disperses if leaked. The pressure of the tank is under 2psi, so it will not explode. It is not like LPG (liquid petroleum gas, the normal household cooking gas) which is kept at high pressure and compressed.”

Another safety feature is the water jacket (a layer of water that surrounds the fermentation chamber); any leaked gas will just bubble through the water. An alarm will trigger in the event of a gas leak.


Shyful sees promise in the technology as it not only prevents methane discharges but reduces waste at source.

“It works well in our warm climate and should be encouraged here. We will try to promote it in critical areas of waste management such as markets and hawker centres, so that waste is managed properly in these places.”

He says the Science, Technology And Innovation Ministry intends to place the machine at some 30 sites, such as in flats, residential areas, food courts and markets, and the community will be trained to run the machine. The first site will be at a market in Tangkak, Johor. The 150kg or so discarded daily will be composted and the gas piped to several hawker stalls.

“The traders now pay daily for waste collection ... this will reduce their waste management costs,” says Shyful.

From his trial runs on the machine, he has figured out areas requiring attention: a better filter, design improvements and better gas storage tank. The tank is important – it acts as a buffer as gas production fluctuates during decomposition.

As for which composting method is preferable, aerobic (degradation with oxygen) or anaerobic (degradation without oxygen), Shyful says it all depends on the purpose. “If you want to produce only compost, then use an aerobic digester as composting is quicker. To produce biogas, you need an anaerobic digester.”

The Cowtech system costs from RM39,000 for a 10kg unit to RM235,000 for a 500kg one. Many find this daunting but Ang says one could exploit the Government’s incentive for green technology.

“Under the Accelerated Capital Allowance for Environmental Management, companies using environmental protection equipment are eligible for an initial allowance of 40% and an annual allowance of 20% on the qualifying capital expenditure. The full amount can be written off within three years.”

Ang is hopeful that such fiscal support will encourage more Malaysian companies to compost their waste instead of dumping it. He says in Thailand, the technology has enabled hotels, hospitals, canteens, food outlets, hypermarkets, municipal markets, farms and factories to be responsible for their own waste.

The Baan Nam Kiang Din restaurant in Bangkok, for instance, has a 800kg compost machine to handle its food waste. A Tesco hypermarket in Bangkok also has one, and it sells the biogas to operators in the food court.

In a bid to better inform the public of this waste-reduction technology and for R&D purposes, Ang provides small-capacity compost machines to schools and universities.

Eager to share this knowhow, he says: “Possible wealth can be generated from various kinds of organic, yard and garden wastes, with appropriate and innovative technology, while practising sustainable environmental initiatives.”

For more information, go to chgreenz.com.

Related Story: Companies get into composting act

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