Some thoughts about the Management of Organic Waste – Liquid and Solid (3).
Bio gas is the product of anaerobic (in absence of air), digestion of organic material at various temperature ranges, depending on the outside temperatures, de type of material and the methanogens, which are decomposing this material. There are numerous methanogens for different materials, temperatures, acidities etc. It at times will be necessary to start a culture if optimal results need to be obtained. This is especially the case in complex processes like slaughterhouse residues.
Biogas consists of an average of 55 – 65% Methane (CH4) and 30 – 40% Carbon Dioxide (CO2). Further may contain Nitrous Dioxide (NO2), Hydrogen Sulfide (H2S), Sulfur Dioxide (SO2), and traces of others. Safety Note: H2S should be dealt with, as it is aside from highly toxic also very flammable and corrosive. It may damage biodigesters and cause leaks, with dangerous results.
The compound of the captured gas depends a lot on the input material. If more woody material is used, obviously this will raise the CO2 content, while high protein material, influences H2S formation and so more. There are cures for many of these challenges.
It serves to determine the chemical composite of this input material. Not only to predict the composition of the output but also to avoid feeding high levels of toxins as this might kill the “workers”, the bacteria or methanogens. This will immediately affect the gas production.
The gas can normally be used for generating electricity, heating and cooking, with the use of equipment with special nozzles. It is used for this reason in rural areas and thereby replaces wood and charcoal equipment, which is an enormous gain in eliminating emission of smoke, CO2 and other contaminants, affecting the health of individuals.
Although in many cases the output gas can be used as is, it may be necessary to upgrade the gas if used in engines. It is essential to remove most of the CO2 gas and also get rid of any Sulphur oxide and remnants of H2S, as this affects moving parts and oxidation/erosion of most metals.
It forms with the catalyst, nitrous oxide, the acid H2SO4. Sulfur Dioxide is also a minor Greenhouse Gas. It is recognized by the strong pungent, choking odor. Already in the biodigester process a chemical compound, Ferro Chloride (FeCl3), can be used to precipitate the Sulphur or Sulfide into elemental, insoluble sulfur, avoiding most of it to enter in the output gas. The rest will be removed in the following step. So there are ways of getting rid of solids and other unwanted gases too.
There are various technologies in use, to upgrade biogas to renewable natural gas, with methane contents of 90 to even 98%. The most common are:
- Water scrubbing, most used practice
- Chemical scrubbing, using amine solutions
- Pressure Swing Adsorption (PSA)
- Temperature Swing Adsorption (TSA)
- Membrane technology, There are two membrane separation techniques: high-pressure gas separation and gas-liquid adsorption
- Finally, a better alternative is to use biological purification, less cost of investment and operation.
With overwhelming evidence that the globe is heating up and all negative effects of that, it should be a must for everyone to participate in those measurements to mitigate the emissions of the gases causing this effect. With the right mindset, the task can be done. The longer we wait for action the greater this task will be.
Let us see to it that organic matter in our community is properly handled. There is now sufficient information available to do just that. Removing the gases in this material, should reduce the concentration in the atmosphere and as an important side result, provide a cleaner energy source.
Ordinary organic matter can be fed to the proper biodigester to produce methane gas and a cleaner organic fertilizer for traditional purposes. This material may consist of herbaceous plant material and animal waste at a 15 to 1 ratio.
The residues of slaughterhouses will have to be handled through biodigesters to avoid affecting public health in the most extended way possible. Sweden has some 18 year experience in this matter and applied for many patents. There are lots of challenges, but there are also solutions.
The Biogas produced, normally consists of an average of 60% Methane gas, 30 Carbon Dioxide and some other trace gases. Although this biogas can be used for heating and electrical energy generation, it is advantageous also to remove these trace gases from the biodigestion stage into the upgrading stage, to end up with renewable natural gas, with a methane content up to 98% and a much improved caloric value. As a fuel, this causes 50% less CO2 emission compared to fossil fuels and can be used in moving and stationary industrial energy applications, as is, or compressed in cylinders.
Imagine a rural world, where people can just flip a valve and start preparing their meals instead of having to start a polluting wood or charcoal fire. Imagine a city or other community where the garbage is no garbage, but properly separated and the organic matter used to produce renewable natural gas, offsetting much of the cost of waste management. Eliminating landfills with garbage comes brightly in the picture.
I stay open for whatever discussion about this matter. Use the contact form for questions and for comments you will find a form to ventilate your opinion, at the bottom of the article.