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Biogas Generation

Biogas is produced through anaerobic digestion. Organic matter is broken down by microbiological activity in the absence of oxygen. It occurs naturally at the bottom of ponds and marshes resulting in marsh gas or methane, which is a combustible gas.

 

There are two common man made technologies for purposely generating biogas for use as a combustable fuel: 

 

The more commonly employed method is the fermentation of organic waste in a digester, which simulates the naturally-occurring methane production.

 

The second is a more recently-developed technology for capturing methane from municipal landfill sites.

 

The scale of simple biogas plants can vary from small household systems to large commercial plants of several hundred-thousand cubic foot capacities.

The digestion of fecal matter and other organic waste yields several benefits:

• the production of methane - fuel 

• the volume of waste is reduced to a nutrient-rich slurry - fertilizer

• pathogens are eradicated  - environmental safety

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Biogas has a variety of applications. The following lists typical (residential) applications for one cubic meter (35.3 cu ft) of biogas:

• Lighting - 60 -100 watt bulb for 6 hours

• Cooking - cook 3 meals for a family of 5+

• Fuel replacement  -  0.7 kg of biofuel 

• Shaft power - runs a one horse power motor for 2 hrs.

• Electricity generation - 1.25 kilowatt hours of electricity

 Source: adapted from Kristoferson, 1991.

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Liquid biofuels

 

Liquid biofuels are derived from biomass and processed to produce a combustible liquid fuel.

 

There are two main categories:

alcohol fuels - these include ethanol and methanol

vegetable oils - derived from plant seeds, such as sunflower, sesame, linseed and oilseed rape.

 

I. Alcohol Fuels

   

  1) ​Methanol

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Methanol is produced by a process of chemical conversion. It can be produced from any biomass with a moisture content of less than 60%; potential feedstocks include forest and agricultural residues, wood and various energy crops.

 

 

  2) Ethanol

 

Ethanol is the most widely used liquid biofuel. As with methanol it can either be blended with gasoline to improve the octane rating of the fuel or used in its neat form. Both ethanol and methanol are often preferred fuels for racing cars.

 

Ethanol is an alcohol fermented from sugars, starches or from cellulosic biomass. Most commercial production of ethanol is from sugar cane or sugar beet, because starches and cellulosic biomass usually require additional expensive pretreatment.

 

It is used as a renewable energy fuel source as well as being used for manufacture of cosmetics, pharmaceuticals and also for the production of alcoholic beverages.

 

Many engines that run strictly on gasoline have been replaced by neat ethanol engines and by gasohol engines that burn a mixture of 78% gasoline and 22% ethanol by volume.

 

Technological advances, including more efficient production and processing of sugarcane, are responsible for the availability and low price of ethanol. The transition to ethanol fuel has reduced dependence on foreign oil (thus lowering import/export ratios), which has created significant employment opportunities and greatly enhanced urban air quality. In addition, because sugarcane-derived ethanol is a renewable resource (the cane is replanted at the same rate it is harvested), the combustion of ethanol adds virtually no net carbon dioxide to the atmosphere.

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II. Vegetable oils

 

A further method of extracting energy from biomass is the production of vegetable oils as a fuel known as biodiesel. The process of oil extraction is carried out the same way as for extraction of edible oil from plants. There are many crops grown in rural areas of the developing world which are suitable for oil production – sunflower, coconut, cotton seed, palm, rapeseed, soy bean, peanut, hemp and more. Sunflower oil, for example, has an energy content about 85% that of diesel fuel.

 

There are two well-established technologies for oil extraction:

1. The simple screw press, which is a device for physically extracting the oil from the plant - this technology is well suited to small-scale production of oil as fuel or as foodstuff in rural areas. The press can be motorized or hand-operated.

2. Solvent extraction is a chemical process which requires large, sophisticated equipment. This method is more efficient - that is, it extracts a greater percentage of the oil from the plant - but is less suited to rural applications.

 

 

Biogas & liquid fuels

 

Oils, as well as being used for lighting and heating, can be used as fuel in internal combustion engines. Biodiesel production is not complex and can be done on a small scale.

 

Vegetable oil is converted to a useable fuel by adding ethanol or methanol alcohol along with a catalyst to improve the reaction. Small amounts of potassium hydroxide or sodium hydroxide (commonly called lye or caustic soda used in soapmaking) are used as the catalyst material. Glycerin separates out as the reaction takes place and sinks to the bottom of the container. This process removes the component that gums up the engine so that a standard diesel engine can be used. The glycerin can be used as a degreasing soap or refined to make other products. 

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The utilization of glycerin as a byproduct of biodiesel refinement in a residential or very small industrial endeavor, is integral to the cyclical, resilient and sustainable nature of the entire shelter system.

Source: Goldemberg et al, Renewable Energy, Sources for Fuels and Electricity, 1993

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Optimization of Resources

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To augment the volume of lipid-producing biodiesel feedstock, a small or large vegetable-oil producing operation, residential to large-scale industrial, can utilize this favored algal photobioreactor, with the sensible utilization of polyethylene membranes. This closed system for maximizing the production of algae, for a variety of purposes is relatively inexpensive to acquire, is a superior use of materials compared to other PBRs, and is perfectly scalable to any size required.

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The following is a comparative list of oil yields:

 

Yields ( Gallons of oil per acre per year )

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• Corn                18

• Soybeans        48

• Safflower         83

• Sunflower      102

• Rapeseed       127

• Oil Palm         635

• Micro Algae  5000-15000

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Additionally, non biofuel applications dependent upon the cultivation of different algal species are available to entrepreneurs. An algal photobioreactor is perfectly suited to algal production for the production of the following industrial needs:

• nutrition

• animal/fish feed

• medicine and pharma

• specialty chemicals - 

  • agrochemicals

  • lubricants

• plastics

• environmental remediation

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The rapid and sustainable regeneration of products and sensible use of byproducts is a critical element of current and future residential, commercial and industrial developments. Applicatory to poverty alleviation, new urban plans and housing developments ideally include these opportunities for residents' entry to the global economy.