Small Scale Anaerobic Digestion

Many people are interested in small scale anaerobic digestion. But, although in some developing nations there have been great advances in the numbers of home and community anaerobic digestion plants from single family sized, to community scale, the long-term results have been patchy.

Even in the successful campaign areas of the developing world, where uptake was initially high, there have been those that gave up using their digesters after only a year or two of use. So, continue to read this article while we take a good look at small scale digesters!

There is no doubt that many people have built and run small scale anaerobic digestion (biogas) plants very successfully. But, others just could not get on with them. It is not surprising that this has been the experience.

A whole host of factors are at play here, but the root of the matter is that running any size of AD plant requires a high degree of training and a real tenacity of will. When, as digesters will, the gas-yield tails off from time to time and the unpleasant task of draining a digester and starting off afresh becomes necessary, it can be hard to keep going.

If that happens, our suggestion is that you as around and find out what you did wrong with your digester. Then start again, and you will learn from experience.

It is, after all, a really wonderful thing to be making your own biogas! Never, forget that!

Small Scale Biogas Plants Can (and Shall) Be Designed Better for Easier Feeding and Greater Gas Yield

What the biogas industry needs is a biogas plant system which is much closer in its efficiency and robustness of operation to a cow, than any have been so far. Estimates of how many times more efficient a cow stomach is than a mechanical biogas plant range from 12 times to around 15 times. New biogas plant design are getting better all the time.

But, there is a long way to go, before we even get close to nature's efficiency…

Clearly, our AD technology needs to move on by huge strides in efficiency ease of use, and robustness against biochemical failure of biogas production. There is every chance it will, as scientists seek to much better understand, and control, the rate of biogas digestion. There are a huge number of research projects in progress right-now, looking at ways to do anaerobic digestion better.

Against this background we decided to cover as wide as possible a scope of small scale AD plant technologies, and sources of information about them as possible on this web page. Our listing for small scale AD systems, complete with attributions so that you can go and look them up, follow:

Small Scale Anaerobic Digestion on Farms/ for Agricultural Applications

Definition of Small Scale Anaerobic Digestion

For anyone arriving here is new to the subject, the following is a definition of the simple small scale digesters common in the developing nations, in the context of agricultural use:

A small-scale biogas reactor or anaerobic digester is an anaerobic treatment technology that produces:

(a) a digested slurry (digestate) that can be used as a fertilizer and

(b) biogas that can be used for energy. Biogas is a mix of methane, carbon dioxide and other trace gases which can be converted to heat, electricity or light.

Small-scale biogas reactors are typically designed to produce biogas at the household or community level in rural areas.

The airtight reactors are filled with animal manure from the farm. Kitchen and garden wastes can also be added and toilets can directly be linked to the reactor for co-treatment of excreta. via sswm.info

The following is a classic diagram showing a simple biogas plant of which probably hundreds of thousands have been made, and which can work well in hot climates, without heating:

Schematic of a biogas reactor. Source: TILLEY et al. (2014)

The following extarct supports the earlier statement we made about many of these plants being shut-down by their owners due to one reason or another:

1. SMALL-SCALE ANAEROBIC DIGESTION IN THE UNITED STATES: DESIGN OPTIONS AND FINANCIAL VIABILITY S. Lansing and K. Klavon Department of Environmental Science and Technology

This study demonstrates that anaerobic digesters can be cost effective for small scale systems, although their viability must be analyzed on an individual basis, as 63% of the systems analyzed were more expensive than the AgSTAR recommended capital cost of $1,500/cow.

However, with an increase in revenue, such as an increase in the price of electricity or the addition of tipping fees, a greater capital cost could be afforded by the farmer. The most cost effective method to create economically viable small-scale digesters is to lower the capital cost using cheaper materials.

With a 44% drop in capital costs, the UMD system without electricity generation would have been cost neutral.

While small-scale anaerobic digestion is economical in some cases, it is farm dependent and a majority of the systems analysis did not have a positive cash-flow. In this analysis, at least half of the existing digesters are now shutdown (4 out of 8), with three cases due to the dairy closing or management changes and not specifically related to a digester failure.

The longest running small-scale system has been operational for almost two decades, and there are four small-scale systems under construction, showing some success in the market.

Success appears to be dependent on the willingness of farmers to invest time and personal energy into the digester with economics being only one way to gauge the success of a project.

With the appearance of multiple private companies attempting to fill the niche of small-scale anaerobic digestion with modular and proprietary designs, this technology could see much greater implementation in the coming years. via  ANAEROBIC DIGESTION IN THE US …

However, the real breakthrough of the universal implementation of small-scale anaerobic digestion will not occur until much better AD process designs are achieved, hopefully through the research efforts underway.

Nevertheless, there are more benefits from small scale anaerobic digestion than cited for any other related energy technology, these being:

1. Reduction of Indoor Air Pollution
2. Energy Production and an Alternative Cooking Fuel: Methane
3. Addresses Unsustainable Deforestation Caused by Wood Fuel Use
4. The Empowerment of Women
5. Treatment of Animal and Human Waste
6. Anaerobic Digestion Generates Less Biosolids for Disposal
7. Nutrient-Rich Effluent as a Fertilizer
8. Mitigation of Methane and Carbon Black Released into the Atmosphere.

Take a look at our video below which is based upon the above list!

Next, is a look at:

Small Scale Anaerobic Digesters for Urban Use and in the Developed Nations

Small Scale Food Waste to Biogas AD Systems Ready to Deploy in UK

Update July 2020: Item on Burdens Environmental removed. The company is no longer trading. 

MUCKBUSTER ®

Designed to deal with slurry, sludge and a wide variety of similar waste streams, the Muckbuster is a fully-functional, automated anaerobic digester. It turns problematic farm waste or sewage into useful energy and offers a financially viable solution with short pay back periods.

FLEXIBUSTER^™

Designed to capture the energy locked up in a wide range of organic waste streams, Flexibuster is an ideal solution for any business producing 500kg to 3000kg of organic waste on a daily basis. Delivered to site ready to plug-and-play, the Flexibuster containerised anaerobic digester includes a pasteurisation process and safely turns all types of food waste into useful and valuable energy. … via SEAB Energy

Small Scale Anaerobic Digestion, on farm Slurry only Biogas Plants | Renewable Heat & Electricity from slurry biolectric biogas plant.

24/7 Heat and Electricity generation from Slurry

The small scale anaerobic digestion plant from OMNI Heat & Power produces biogas from slurry alone, this biogas is stored and used as fuel in a combined heat and power engine (CHP).

This combined heat and power engine (CHP) drives a generator which produces electricity which can be used on the farm, stored in batteries on the farm or exported to the grid.

Water used to cool the combined heat and power engine (CHP) can then be used on a district heating system to provide heating and hot water across different buildings on the farm, including the milking parlour, farm house, holiday lets and offices etc. via OMNI Heat & Power

The Future of Anaerobic Digesters: Increasing Efficiency and Cooperative Efforts

Adding food waste to raw manure increases the biogas production of an anaerobic digester, as does adding plant matter. You get 8 times more biogas from a system digesting silage than manure because manure has been stripped of some of its organic matter energy potential by the cow that produced it. Baking wastes, waste grease, food waste, and brewer’s grain silage are among the substances whose processing yields some of the highest potential biogas yields. While on-farm co-digestion of manure and food waste together is currently allowed with the proper permits in New York State, human waste processing is not.

Since anaerobic digesters work best on a large scale, one creative solution to this challenge for small farms is an integrated, cooperative model in which one or a few anaerobic digesters could be utilized by a group of small farmers, thus allowing the farmers to pool their capital resources to build a large enough digester that engine generator efficiency would not be an issue. The community energy model has been successfully implemented in parts of Europe, reducing the amount of time it takes to fill the digester and eliminating the need for a small, custom-made electrical generator. via Cornell.edu

Allen Farms Small- Scale Digester

Small scale, distributed anaerobic digestion plants could offer an environmentally and economically stable solution for locally produced biogas.

In Germany government incentives have led to the development of over 6000 anaerobic digestion (AD) facilities, generating twice as much power as all of the country's waste to energy facilities combined. [But, that led to problems relating to their large size, and government subsidies have been reduced. The result has been that fewer are now being built, which leaves an opportunity for small biogas plants to be profitable, by serving the digester owner's farm only.]

A new system from Austrian firm, Bio4gas could offer the ideal solution. Available in two sizes – 20/25 kW and 50 kW – the system enables farmers to use animal slurry from their own farm to generate heat, power and digestate.

At the heart of the product is the patented ‘Thermal Gas Lift' – a passive mixing system that Benton said offers reduced energy consumption through the use of gas pressure to force the slurry mixture through holes in the bottom.

The smaller of the two systems features a 220 cubic metre tank that is dug into the ground and holds 180 cubic metres of material. In addition a double chamber digester produces more biogas than a single tank.

The advantages offered by a more distributed approach to biogas are significant, with potential returns on investment ranging between 12.5% and 16.4% based on conservative figures.

Small scale biogas production could free the operator from the “whims of the market”, insulating them from rising biocrop prices and the prospect of falling gate (tipping) fees when feedsocks arrives at the biogas plant.

Additionally, as all of the feedstock is sourced from the host farm itself, the digestate can be used to fertilise the farmer's own land with no solid waste permit or license is required.  via Allen Farms – BIOFerm™ Energy Systems

Other Small Scale Biogas Systems Offered

Whatcom County Small-Scale Biogas … Advanced small-scale anaerobic digester design tailored … a bench scale study of a high solids anaerobic digestion … via Small-Center for Sustaining …

Promoting Small Scale Anaerobic digestion systems Santino Di Berardino, LNEG, Alexis Chatzimpiros and Olga Bourka, EPTA 1. INTRODUCTION Current management Organic … via Promoting SS AD systems

AD Plant installed on industrial sites can generate energy for you. We can show you examples of food and beverage industry sites creating renewable energy via Ad Plant – On Site Anaerobic Digestion Solutions

IEE/13/477/SI2.675801 Handbook: small scale AD BCMs 3 / 29 1. Introduction Anaerobic Digestion (AD) for biogas production is a proven technology that is well known in the via Handbook: Small Scale (AD) Business …

1 Increasing Deployment of Small-Scale, On-farm Anaerobic Digestion Plants Introduction* The UK Government is committed to seeing a substantial increase in the use of via Increasing Deployment of Small-Scale, On-farm Anaerobic …

Kent farmers, Clive and Richard Apps are experiencing the benefits of a new revenue stream and source of sustainable energy through small-scale anaerobic digestion … via SSAD plant benefits Kent …

Farm Gas Power specialise in the design, … Specialists in the design, planning, construction and project management of small scale anaerobic digestion plants. via Farm Gas Power

The On-Farm Anaerobic Digestion Fund has been developed to help farmers in England get financial support to build small-scale AD plants on their farms. via On-Farm Anaerobic Digestion Fund – WRAP UK

Anaerobic digestion has been cited by the UK Government as a way of reducing carbon emissions, providing energy security and generating green jobs. A new … via Speeding up small SS Digestion – Renewable …

Small-scale tubular anaerobic digesters are an attractive technology for treatment of livestock waste in the developing world. These systems produce biogas (a m via Review of small-scale tubular anaerobic digesters treating …

Small-scale anaerobic digestion (AD) plants can help livestock units become more efficient and self-sufficient. The technology can provide a safe route for via SSAD has a place on UK farms – Farmers Weekly

Design of a Household Human Waste Bioreactor … as feedstock in a small-scale bioreactor to produce … materials to the bioreactor to enable anaerobic digestion. via Design of a Household Human Waste Bioreactor

Biogas and How to Make a DIY Anaerobic Digester … But it seems pretty clear that small-scale urban farm biogas digestion has great potential for gleaning … via How to Make a DIY Anaerobic Digester.

Small-Scale Digestion in Maryland; Low-cost Anaerobic Digesters for Dairy Manure Treatment and Renewable Energy Production The … via Dairy Manure Treatment …

Economic analysis of small-scale agricultural … Anaerobic digestion Small-scale Manure … Economic analysis of small-scale agricultural digesters in the … via Economic analysis of SSAD …

Top 5 Highest Trending Small Anaerobic Digestion Site Articles List for 2017

1. Small-Scale Anaerobic Digestion to Optimize Agricultural Waste Management • BiogasWorld via SSAD to Optimize Agricultural Waste Management • BiogasWorld
2. What is the Future of Small-Scale Anaerobic Digestion? • BiogasWorld via What is the Future of SS AD? • BiogasWorld
3. Speeding up small scale anaerobic digestion via Speeding up SSDigestion
4. Anaerobic Digestion (Small-scale) via Anaerobic Digestion (Small-scale)
5. On-Farm Small-Scale Anaerobic Digestion seminar a success via Seminar a success