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Tuesday, 19 June 2012






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Kitchen waste converted to energy in form of bio-gas

Kitchen waste with its high water content is an ideal carrier of disease and odour, but, Bio Fuels Lanka, solves these problems by converting food waste to energy in the form of biogas. The BFL CSTR AD biogas plant or the Continuous–Flow Stirring Tank Reactor is a unit which operates at maximum efficiency, reducing waste volumes to energy, thereby curtailing labour and energy costs. It also reduces costs associated with waste transportation, disposal and pest control and the time and efforts needed for trash removal. The BFL CSTR AD bio-gas plant which is easy to operate is clean and almost maintenance free.

The CSTR AD bio-gas plant (CSTR) is a vertical, cylindrical digester, the first ever CSTR bio-gas plant in Sri Lanka. Mixing of its contents is by a centered vertical low-speed agitator, characterized by a high circulation rate where the digester content is perfectly mixed, while the low rotation speed guarantees gentle treatment of the anaerobic micro-organisms. Due to the continuous mixing, it provides an optimal substrate transport for the bacteriological degradation of the organic substances into biogas. The CSTR digester is suitable for the treatment of high solid materials such as bio waste and sludge as well as for scum developing material. Sediments can be easily removed during operation. It is specially suited as a large scale bio-gas plant.

This prototype digester is applicable for the treatment of all kinds of degradable organic material such as waste water or sludge, manure, renewable primary products, municipal bio waste, restaurant and market waste, food industry waste, slaughterhouse waste, sewage sludge etc. It’s a new configuration of digesters for improving biogas production that has been investigated. Results showed tht the serial CSTR could obtain an 11 percent higher biogas yield compared to the single tank reactor. The increased biogas yield in the serial CSTR is mainly from the second reactor, which accounts for 12% to 16% of total bio-gas yields in the 80/20 configuration respectively.

VFA, or the volatile fatty acid concentration in the serial CSTR is high in the first reactor, but very low in the second reactor. Results from an organic pulse load test showed that the second reactor in the serial CSTR helped utilizing VFA produced from overloading in the first reactor which improved the effluent quality and conversion efficiency of the serial CSTR.

Presently BFL converts food waste into bio-gas while using it only as a form of heat for cooking purposes, replacing LPG. BFL has successfully used biogas for lighting purposes as well, by using bio-gas lamp.

On a small scale, we also generate power, using biogas generators. However, BFL is now looking at using biogas to fuel gas operated commercial laundry machines, boilers and larger generators.

BFL is in the process of developing a low cost, portable design domestic plant to replace LPG cylinders in homes and restaurants. BFL is exploring the possibility of designing and constructing a 12 megawatt Independent Power Plant (IPP), to supply electricity to the national grid, using food waste and market waste in partnership with a foreign collaborator. In order to adapt to the changing energy landscape together with the challenging requirements of continually increasing capacity, the proposed reduction of GHG emissions and dependence on imported fossil fuels, an innovative and renewable generating concepts will be required.

Other renewable sources such as solar, wind, energy, etc, will undoubtedly play a key role in building this capacity, but mainly rely on a grid that should be flexible enough to accommodate and react to their generating profiles.

Waste to energy projects can allow us to close the loop on energy production and consumption cycles and can make our contributions be more resilient with a distributed generation approach.

Presently we have five plants to cater to 10 kg inputs up to 300 kg inputs per day, the price ranging from Rupees eighty-eight thousand (88,000) for domestic plants to Rupees four million, three hundred and eighty eight thousand, nine hundred (4,388,900) only for larger requirements. The above quotes are exclusive of taxes.

How can you explain or justify the payback period?

In a biogas plant such as the BFL CSTR AD 20 model, when you have an input of 100 kg of food waste the biogas yield will be approximately 45 M3 per day. Going back to the question, it is our responsibility to achieve the maximum methane percentage and we have a proven ability to obtain 75% of methane per M3 of bio-gas.

Now do a simple calculation, 45 metre cubes of biogas with 75% methane is equal to 33.75 M3s of methane, which when multiplied by 37 mega joules is = 1248.75 mega joules. How many kgs of LPG will this replace? = 1,248.75 / 50 = 24.975 kg of LPG.

How can you assure that the plant will continue to produce bio-gas and what are the maintenance factors?

There are 8 microbial community observation points in the BFL CSTR model. We have an agitator fan installed in our CSTR plants to do the stirring. The fan will revolve at 7 rpm to optimize the process.

Are there similar plants in existence and what are the BFL CSTR AD bio-gas plant plus points and importantly what is the lifespan of your plant?

The capacity and capability of the plant have been discussed and you yourself will in the future, bear witness to the BFL CSTR AD bio-gas plant’s output. The lifespan of the BFL CSTR AD bio-gas plant can easily be stated to be over 25 years.


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