CNG from Sugar Waste

The reliance of Asian economies on agricultural production is well documented, and it’s perfectly justified for those involved in these industries to focus on optimising their end product. However it is becoming increasingly important for financial survival to look at related profit opportunities, and one of these may be a possible better use of the waste from processes we use to refine the agricultural product for consumption. Agricultural waste in any form is a problem, and whilst in recent year’s great strides have been made to recycle waste into usable materials and soil enriching products, in the SE Asian region scant attention has been given to the potential for methane production from the waste generated from sugar, oil palm & tapioca processing.

Biodigester side

The concept of bio-digestion of agricultural waste in Europe has been developing for decades and in some areas bio-methane from agricultural sites is being fed back into the municipal gas distribution system augmenting profit from agriculture and obviating the need for disposal of waste by other methods. It may not be clear to the reader at this point as to the uses the gas may be put, but methane is a naturally occurring gas. It’s the gas that bubbles from swamp, the gas that provides the stench of effluent and is the principle component of the gas we know in Thailand as CNG. In future it may well be the gas that provides us with that elusive “renewable” energy source that we will need to power our vehicles and off highway equipment.

So how do we go about producing methane? The basic science is that the methane is produced when certain acids are consumed and digested by any methanogenic organism, the most common culprit being methanogenic Archaea, a single cell organism that looks like a microscopic shrimp and flourishes in anaerobic environments. All air breathing organisms (yes humans too) have these organisms in their digestive systems and secrete methane as a product of digestion. This accounts for our need to occasionally pass wind and for those embarrassing moments in meetings when we do. For industrial purposes though, systems need to be fairly efficient.

Archdaea the organism responsible for methane production

The modern anaerobic bio digesters involve large chambers into which are installed heaters agitators and stirrers to accelerate the process. This synthesises conditions that the Archaea love and gives them the optimum environment in which to work ensuring optimum efficiency. The good news is that as far as organic agricultural waste is concerned there is virtually nothing that these animals will not digest. With correct husbandry bio digesters can handle literally tonnes of waste (even sugar waste effluent) into a pure methane rich gas which can be used for a number of industrial applications or refined and compressed for vehicle applications. One of the biggest manufacturers of bio-digester plant in Europe is Schmack Biogas Srl. in Bolzano Italy where Dr Mauro Nicoletti oversees the design production and installation of biogas production plants throughout Europe.

Dr Nicoletti explains “The biogas generated from our bio-digester units is usually around 60% methane with around 40% CO2. Bio-gas can be refined further with an “upgrading” process which separates the CO2 and by this time the gas is around 95-97% methane and therefore sufficiently pure to be pumped into the gas grid in most countries or used directly in a natural gas engine”.

The digester plants create an anaerobic environment in which is introduced organic waste. This means virtually any type of organic waste, including vegetable and food waste, animal dung, grain based waste and human excrement. Within these digesters the waste is encouraged by bacterial degradation to break down into hydrogen, carbon dioxide and acetic acid. The Achaea then consume the acids converting all of the waste to carbon dioxide and methane. The bio-methane gas can be used, bottled, or stored, and the bi products of the process are a pure organic liquid fertilizer and of course the CO2 liberated by refining the gas. Both have a commercial as well as environmental value. This process happens naturally requiring nothing more than the right conditions”.

Obviously there are variables, in particular feed balance (excessive high protein can cause over acidification) and both mechanical agitation and finite temperature control help promote the effectiveness of the process. This sounds complicated and on a small scale the monitoring and feeding process can be quite challenging. Dr Nicolletti explains further “Usually after a year in operation our customers feel that the process is user friendly and operation of the plant and maintenance is not a complication”. However on a serious production scale these plants can be almost fully automated and experts agree that although the design of such plants are well developed there is still much scope for process improvement and the potential from economy of scale which would be bought by more widespread adoption of the gas as a fuel.

Biogas could become a truly renewable source and one that makes increasing long term sense. A study by Schmack srl. which looked at the SE Asian markets identified that the potential to recover energy from sugar waste (filter cake and waste water) would generate around 700 million cubic meters of methane annually, and that from palm oil waste (POME & EFB) 4 billion cubic meters could be expected. There would also be tremendous potential for other crop wastes such as tapioca. Bio-digestion coupled with methane capture using these processes would minimise overall emissions of methane which is one of the most damaging “greenhouse” gasses, and provide a commercial use for much of our agricultural and food processing wastes rather than having constantly to find disposal for this growing problem.

Although modern installations are demonstrably effective and prove financially viable in Europe the markets in SE Asia have not embraced this technology so far, and it may be that they never will. Many Asian concerns have been too parochial to recognise that such an investment is good for business and that a more holistic approach to processes can pay dividends. Also modern bio-digestion plants are not cheap and although small installations can be successful the plants that could handle the serious amounts of waste produced in SE Asia would have to be integrated at the design and construction stages of mills and crushing plants.

This will not happen overnight but driven mostly by the demand for natural gas for the automotive and commercial vehicle sector bio-methane could replace CNG imports and provide a so far untapped profit source for agricultural product processers. However, to become really effective this will need widespread government support and a paradigm shift in the business model operated by many of the players. I fear that despite the potential profit and environmental advantages of bio-methane the necessary support may be a while coming.