A completely new approach to organic waste management

 

The first two decades of this century have seen a quiet revolution in organic waste management. Starting just after the turn of the century, anaerobic digesters have been springing up all over Europe and the United States. The assumptions of the last century that suggested such systems were not economically viable turned out to be completely wrong. From municipal waste management, to sewage treatment, dairy farms, pig farms, breweries, and any facility with an organic waste stream, anaerobic digesters have turned an ongoing cost into a revenue stream with a 100% ROI of between three to five years.

 

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How can Bootstrap Enterprises help you reduce manage your organic waste stream?

There are as many digester solutions as there are waste streams and operational circumstances. From 100 kilos per day to 100 tonnes per day, and even bigger, there is a digester design that can turn your waste stream into a revenue stream. While the process itself is fairly straightforward, the pros and cons of any given system in relation to the operational environment can get very complicated very quickly. 

Bootstrap Enterprises can help businesses such as farms, vineyards, orchards, and local councils find the appropriate digester solution to process organic waste and turn it into valuable products, energy and fertilizer, without the energy input, labour costs, and odour problems of legacy waste management systems.

 
 

The Process

Anaerobic digestion is one of the oldest biological processes on the planet. When organic materials are kept away from oxygen, anaerobic microbes kick into action, breaking down the complex material into a variety of much simpler byproducts, all of which have significant economic value

SOME MORE DETAILS

There are three interconnected groups of microbes involved in the anaerobic process. The first group feeds on proteins, lipids, and carbohydrates in a process called hydrolysis. The waste products of this process are simple sugars, amino acids, and fatty acids. The next class of bacteria is the acetogens and acidogens. These bacteria feed on the sugars, amino acids, and fatty acids and turn them into acetate, propionate, butyrate, and ethanol, along with a bit of carbon dioxide and hydrogen. The last class of microbes is the methanogens. These are the money makers that feed on the waste products produced by the other microbes and produce methane.

Frequently Asked Questions

 

1) How often would a typical family of four have to empty the digester, and how is this done?

There is an overflow pipe on the opposite side of the digester from the feed pipe. As the digester becomes full, the excess will naturally flow out the overflow pipe to be collected. As long as the maximum infill rate (100kgs/day for the digester in the above picture) is not exceeded, 99% of the material coming out will be fully digested.

2) Does it smell?

No, the digested material (effluent) has no real odour. 

3) Does it need secondary composting?

No, the liquid portion can be used directly. The remaining solids, in the form of sludge, can be used to cover soil directly, or it could be dried and composted further, depending on your needs.

4) Is it safe?

Yes, but there are caveats. If the material fed in to the digester is lawn waste, animal waste, and food waste, the effluent can be legally used on pretty much any crops you like. However, while overseas studies have demonstrated >99% pathogen removal, the system is not cleared as yet for use with human waste here in Tasmania. BE is looking into navigating that regulatory pathway ASAP. The hurdles to use are all regulations, rather than technical issues.

5) How much power can this produce?

Once it's full, the system pictured above should produce in the region of 8 to 15 cubic metres of biogas per day. This is good for about 15 to 22.5 kW/hr a day, if used to fuel a generator. High calorie food waste will produce more, animal waste will produce less. If the only revenue calculation you're running is electricity savings, then such a system would pay for itself in about 5 years. That's at domestic power prices. For a commercial power price the payoff would be faster.

6) What happens to the water?

Most of it is in the slurry, which can be put directly on gardens as is. A significant amount is pulled out of the gas stream as distilled water, which can be used however you like.

7) Can my grey water go into it as well?

It can, and the digester doesn't care. However, if you use shampoos and detergents with silicon in them, the gas produced will generate silicates (sand) in an engine, which will hasten wear and tear. 

8) What is the rough working lifespan of the system?

The plastic system pictured has a service life of 8 to 10 years. And I suspect most of that is down to eventual degradation of the plastic itself. The generator will need to be maintained, much like any other backyard generator. The same goes for the pump and the grinding unit. The catalyst material (iron oxide) in the desulfurizing unit can be refurbished simply with a few hours exposure to the air.

9) Regulatory Framework

Conversations with the local council indicated no issue with the digester itself on a property, but in dense housing, such as quarter acre sections, the noise of the generator would be a source of noise complaints. The EPA has no problem with them (and would probably like more of them around). All of the connections from the digester to the generator must be handled by a licensed gas fitter, and the electrical work from generator to certified inverter system must be handled by a licensed electrician, much like a PV installation.

10) What does it look like?

This is a photo of a digester unit that can take from 100 to 300 kilos of material per day, and produce from 8 to 15 cubic metres of gas per day, which equates to 16 to 22.5 kW/hrs of electricity per day. The variable numbers are due to the different amounts of gas generated from different substrates.

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If you have any further questions, please feel free to contact me.

 
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