History of Aerobic and Anaerobic Digestion

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Aerobic and anaerobic digestion systems have been in use for several hundred years. The earliest regular use of aerobic treatment was in activated sewage treatment. This uses, low temperature bacteria, aeration and oxygen to motivate the bacteria to break down the sewage sludge. The waste is then filtered.

An anaerobic system or anaerobic fermentation action linked with water spraying, is the normal way a Sewage Treatment Works breaks down human waste.

typical sewage treatment plant

The History of aerobic digestion, was In most cases sewage systems, have moved ahead slowly with small changes and advancements 0ver the years . If it is not broken why try to fix it.

Bacteria has temperature ranges they are happy to grow and multiply within. Hence, with less than ideal weather, which are too cold or hot, they can stop working. A result in using activated sewage systems being installed into environments that are too hot to process and having the bacteria die off. With the inevitable smell and with waste that is not processed. The history of aerobic digestion though is on going and constantly changing.

A consideration of the weather, its impact that we are experiencing in many countries. This over the next couple of years, could also affect the UK particularly parts of Wales and the south of the England. As the average temperature starts to increase aerobic capacity in a sewage plant decreases. It would make established activated sewage treatment plants need higher temperature bacteria to work.

,Moving forward it was realised that using aerobic principles was a realistic way of processing other biological materials as well.

Early developments to today

1 tonne a week digester - some still in use.
Early Mk 1 digestor which would process 1 tonne of waste a week,

Early aerobic system digesters

The earlier aerobic digesters were sold to schools and hotels for converting food waste to a biomass energy fuel to go into a biomass boiler.

The aerobic capacity of a one tonne machine would process a tonne of food waste per week. With the advent of the ‘Renewable Heat Incentive’ scheme it meant that the food waste digestate burnt too hot and exceeded the RHI regulations.

To meet the RHI scheme and get money back from the UK Government, it meant that the waste biomass energy material needed to be mixed with wood pellets. This meant the digestate accounting for around 30% of a mix, with wood pellet accounting for the rest.

The extra digestate mix pushed the average temperature output from a biomass boiler up to 80 deg C compared with just burning wood. Most systems were add-ons to existing heat systems to produce a pre heat system. The customer saved money in the amount of gas or oil used in their traditional boiler They also were getting a monthly payment from the Government. A big advantage to a hotel was they did not have to pay to get rid of their food waste. A win win cenario ,

Anaerobic systems, using anaerobic digestion, in contrast, for organic waste, are normally large plants. Each are used to extract marsh gas which is blended with other gases before being used into the towns mains.

Typically anaerobic digestion plant are expensive to build, are large in size and need to have a feed stock of wheat and barley. Normally anaerobic only convert around 50-60% of the waste to gas. The whole process normally takes a month or more to work. There are advantages – but not something you could install currently into a local hotel, although, some farms have raised money to install an anaerobic system on site to take in waste locally and through the use of biogas drive electric turbines.

Aerobic System

The advantages of an aerobic system allows a processing system which is efficient and small in size which utilises all of the waste.

Video showing early digester

As RHI has diminished in pay out, the machines need to be more efficient. Aerobic system Food waste was introduced either through a small shredder or directly into the main chamber. The waste would come out through a side auger or down a high level slide into a biomass boiler. The only output from the machine was carbon dioxide that came through a fan to extract it. The above pictures shows an old 1 tonne machine. The cost of the machines, made it hard to sell to a client to justify the expenditure, without using the RHI. fuel tariff

What does the future hold?

So what does the future hold. We still manufacture at present the Version 2b machine. By this time we have ironed out a lot of the issues with earlier versions. As a food waste digester, however, the physical design of the Mk 1 & 2 was not ideal. It had a lot of waste of space. We are now manufacturing a MkIII.

The use of aerobic digestion can be utilised within hospitals through to the degrading of prescription drugs and amphetamines as well as heroin and cannabis. All organic waste can be processed to either degrade or change the use to a fuel or compost.

The aerobic digestion in comparison to anaerobic digestion as a process by product is water, CO2 and heat. This is due to the reaction of the bacteria digesting the waste. It does not produce gas. Biomass Energy is produced from the waste.

Unlike Anaerobic It does not have large amounts of waste that ends up in land fill. Aerobic glycolysis is quick, efficient and effective.

We are now manufacturing machines which are effective, efficient and range from an under the bench kitchen version through to 30 tonnes processing a day.

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