Some thoughts about the Management of Organic Waste – Liquid and Solid.
This document was last modified on: November 18, 2016
Did you know that mankind is generating more than 3.5 billion tons of organic waste per year, from home as well as our other activities?
Why we should be thinking of ways to better manage our organic waste, is due to the fact that anthropogenic (manmade) emissions of methane, comes from the way we are managing this waste, liquid as well as solid. These emissions surpassed that of natural sources and are rising at an alarming rate in the last 150 to 200 years.
It is for sake of completeness that I need to mention that a substantial amount of atmospheric methane is destructed (sinks), due to stratospheric free radicals like OH–, which are reducing methane to CH3 and water vapor.
Let’s assume that we cannot realistically manage natural emissions from wetlands, forests and others, but there is enough reason to tackle those emissions due to the way we do our daily business.
Areas of these emissions are mainly:
- Maintenance of Industrial Installations, to stop or reduce leaks.
- Agricultural Practices and Animal Husbandry in general.
- Handling of Waste in cities and other communities.
As in Agriculture, rice paddies are a major source of Methane emission if the water in these paddies is not regularly refreshed. Circulating water by irrigating of the paddies, introducing more oxygen, is essential. New Zealand with a considerable agricultural/animal husbandry industry, which is for 50% responsible is contemplating destocking of cattle. This fits into the philosophy to eat less meat .
In general we should adapt a paradigm shift in the way we manage Our Waste and Organic Waste in particular, NOT AS JUST WASTE, BUT AS A RESOURCE. This means we have to Reuse, Reduce and Recycle all waste to infinity. That is the only way to sustainably keep our planet free of waste and hence control pollution in a general sense.
Importance of Managing Organic Waste
It is of the ultimate importance to improve the management of Organic Waste Liquid as well as Solid, as unmanaged storage of this material contaminates soils, waters and air. Think of all the bad odors in rivers and in certain neighbourhoods. In rural areas near live stock farms.
In the first place all residues from residencial, comercial and industrial areas should be separated in three different categories: Organics, Anorganics and Sanitary. In the Waste Management Companies further separation will take place. The Organic part should then be decomposed, either by aerobic or anaerobic systems.
The organic material needs to be shredded to particles smaller than one cm. This proces takes place at open air and needs to be mixed with soil and fertilizers, especially carbon and nitrogen, to obtain a useful mix as organic fertilizer.
Many micro and macro organisms are instrumental in the decomposing process. Further de material need to be aerated and watered frequently to avoid overheathing This proces takes place in Psychrophilic (12-22°) and Mesophilic (25-40°) temperature ranges, with specific bacteria.
But during the process certain Greenhouse Gases are escaping into the atmosphere, such as CO2, CO, N2O, H2S and some minors
The organic material needs to be shredded or ground to particles smaller than one cm. This process takes place in Biodigesters with methanogens under conditions without air. These are closed systems and have the advantage that the Greenhouse Gases captured, s.a. CH4, CO2, N2O, H2S etc., are not escaping in the atmosphere, making it the decomposing system of choice.
Short History of Biodigesters
There is evidence, that gas produced in biodigesters was used for heating purposes in Middle Eastern countries in the 10th -16th Century and in the 17th Century European investigators confirmed that there was a flammable gas in decaying organic material. And in the next century it was confirmed that a correlation exist between the amount of organic waste and the amount of gas produced.
In the 19th Century it one investigator confirmed that methane was the main gas produced during anaerobic digestion of animal manure. A few decades later the first anaerobic digestion plant was built in Bombay (now Mombay) in India, while at the end of the 19th Century, in England gas was captured from a sewer facility to use in street lighting. Further microbiological studies identified anaerobic bacterias were instumental in producing methane gas and what were the conditions for this production.
Many low technology digesters were built in China and India to treat waste in rural areas, while in Europe studies were followed up to buid more sophisticated anaerobic digesters. Sweden, Germany and Austria were taking the lead. Many types of material from other industrial waste were treated or pretreated in biodigester to lower cost and capture gases.
The need for biodigestion
We should drastically increase the use of these anaerobic biodigesters because of, at least, the following benefits:
- Capturing and utilizing a potent greenhouse gas.
- Reducing harmful organic waste.
- Reducing odor.
- Destruction of pathogens from the waste.
- Reduce contamination of soils and water bodies through leaching.
- Carbon neutral technology.
- Producing an organic fertilizer without harmful effects.
- Avoiding leakage of toxins and pathogens from animal products .
- Avoid tree felling for charcoal production.
- Clean fuel for generating electrical energy with at least 50% less CO2 emission.
A biodigester is constructed of metal and concrete or durable and flexible plastics en is meant to contain slurry of water and shredded, mostly herbaceous organic matter, but also material from slaughter houses, droppings from mainly cattle and other ruminants. Material from slaughter houses may increase the production of CH4, significantly, although has many challenges. There are processes to cope with these challenges.
Under anaerobic (without air) condition, various species of bacteria, prevailing under this condition decompose the organic material. During this process gases are formed, cq. released, and captured in a dome like upper structure. The decomposed material or digestate sinks to the bottom and can be reclaimed from time to time, with special slurry pumps.
There are a multitude of different models of biodigesters and in sizes from small for uses in one family homes to medium or small businesses to large and larger used in businesses of substantial size. You also may find lagoon type digesters, which are frequently used in larger farms and animal husbandry enterprises. These lagoons are covered with durable flexible polypropylene plastics, which are fairly easy repaired, if punctured.
In the state of Jalisco, Mexico, I visited some porciculture farms, annex animal food processors. They use lagoon type biodigesters fed with excrements of the pigs and covered with tough polypropylene. You can walk on top of it although a bit wobbly. From the gas produced, a generator is run, which provides electricity to the food plant.
Although some biodigesters are meant to be used for one badge at a time, the majority are designed for continuous operations. At one end, the shredded material is fed though an intake, constructed in such a way, that the material enters in the slurry in the container, avoiding the gas to escape. At the other end, a tube enters up to the bottom of the container, to make reclaiming of the decomposed digest possible.
The EPA in the USA estimates a potential for biodigesters in rural areas of 8000. (this will be verified, as it seems very few in my opinion)
In Europe, Germany has almost 7000 anaerobic digesters installed. Austria more than 500, while the rest of Europe accounts on the average just over 100. In developing countries, small-scale anaerobic digesters are used to meet the heating and cooking needs of individual rural communities. China has an estimated 8 million anaerobic digesters while Nepal has 50,000.While in the rest of Asia and Africa over the 500,000 are installed.
In Latin America and the Caribbean a Network for Bio Digester Technology (REDBIOLAC) was set up, coordinating the construction of biodigesters in the region. Already some eleven countries are participating in this NETWORK.
In various countries septic tanks are used, to process the sanitary waste of family homes and businesses. The process is similar as that of biodigesters but the gases are released freely into the air via a standpipe. This should be a good opportunity to convert them to biodigesters with all the advantages of these systems.
Sweden has done extensive studies with biodigestion and in the 18 years experience, filed patents for the various sub-processes. The have demonstration plant in Linköping, Sweden and one in the State of Michigan, USA. They also provide the technologies to overcome many of the challenges.
The Processes of Biodigestion are:
The organic matter complex, carbon hydrates, fats and proteins are broken down into glucose molecules, fatty acids and amino acids.
Bacteria decompose glucose molecules, fatty acids and aminoacids into volatile fatty acids and alcohols.
The volatile fatty acids and alcohols are converted into hydrogen, carbon dioxide (CO2) and ammonia (NH3).
Bacteria also called Methanogens are converting the hydrogen and resulting acetic acid into methane (CH4) and carbon dioxide (CO2).
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