Considering Pelletizing of Bio-Waste as a Source of Food & Energy


As we consider what an compact Arcology themed Ecovillage might look like as the first step towards larger more ambitious EcoCity Development, we need to look at where the energy is going to come from. Its seems to be understood that such a model of development should be self-reliant in the production of energy if possible. The type of energy mix would depend on the location and assets of the property where the project was located.

While Arcosanti itself may not seem like the ideal location for a biofuel facility given that is located in a arid/semi-arid region of the world, the fact that much of the property of the project is part of riparian zone does permit some consideration of woody biomass potential. Indeed several of the buildings at Arcosanti are heated by fireplace and despite this it seems to only have scratched the surface of the total woody biomass capacity of the site, as evidenced by the many fallen branches and trees seen on a hike of the riparian areas.

Regardless I wanted to talk a bit about the promise that pelletizing might have in relation to converting waste biomass into fuel and feed in a ecovillage with many characteristics similar to Arcosanti.

Eric Fedus and I have been discussing ways to pelletize organic waste/bio waste streams. I actually came across this idea when I took a workshop in Berkeley CA on Bio-Gasification around July 2011 that centered on their main product the GEK Gasifier (Gasifier Experimenters Kit) by All Power Labs.

While I felt they had a really great core technology with their GEK system, I found it odd that they had not figured out how to power their facility with their GEKs at the time. It was probably a question I should have asked but did not at the time. Possibly their inability to convert their manufacturing facility to run on wood gas had to do with my observation that there were issues revolving around how to prepare the wood chips for usage in the gasifier in an efficient way. Issues at the time revolved around developing some kind of way of processing the wood chips in an assembly line to remove moisture and also to ensure the required consistent size and shape.

I had considered that it might be simpler to just develop a simple manufacturing process to dry, grind up and then pelletize the wood and/or woody biomass.

With the case of Eric’s work and areas of interest, its a bit different. His goal is to convert food production byproducts into fish food for aquaponics systems taking advantage of new regulations in the state of MA that now are phasing in some of the strongest landfill regulations in the nation pertaining to biowaste. One of the challenges is to convert rotting food waste into a stable sanitary feed medium for fish that can be fed as needed in aquaponics systems. A readily available supply of locally produced economical feed is one concern for aquaponics growers. There are several major issues that aquaponics growers face before the sector really becomes a viable agribusiness

  • Cost of energy to keep the fish and greenhouse warm
  • Cost of feed for the fish
  • Cost of labor to process the food produced in the greenhouse part of the system

Passive Solar Greenhouse designs provide a way to address the cost and in colder climates a back-up system using either biogas, woog gas/bio-gasification or solar hot water from a nearby array can eliminate fossil fuel costs from the equation.

In relation to the food side of aquaponics, I have been studying the Growing Power Website recently. They make an important point about how the nutrients that fish produce can only enable the production of certain foods such as basil and tomatoes. Their solution is to develop a hybrid system that includes adding compost blocks made of worm castings. I found this to be a novel way to introduce additional nutrients to the aquaponics system. It seems to be from reading the page, to be an open loop system with the nutrients in the plant compost blocks being released and distributed through the system.

What I have been exploring in my research is that we look into a way to directly convert food or other organic waste streams into both fuel and food for a food production that focuses on producing high value produce and fertilizer. The fuel would be produced through an anaerobic digester that converts a portion of the waste biomass into biogas that can be used to power the site. While the exact ratios vary based on the type of waste, typically the anaerobic processes convert the waste into three fractions – effluent, biogas and sludge – each with about 35% of the original volume.

Eric read a book pellets called The Pellet handbook (its 500 plus pages mainly about pellets produced for energy and not for food) and noted noted the following:

  • Pellets for energy are relatively new to the market. They’re established in countries like Germany and Austria but new to countries like Canada and the UK. There is a developing international export market for pellets and the US & Canada are likely to become larger exporters because we have much more biomass capacity than in Europe, but that raises a lot of questions in terms of the energy to ship and produce these renewable energy products.
  • Pelletsare produced for many, many reasons, including:
    • Energy
    • Beer production (pelletized hops)
    • Insulation (waste paper, old bank notes)
    • Anaerobic digestion (apparently to add anaerobic bacteria)
    • Pelletization is sometimes used in developing pharmaceutical products
    • Animal bedding (made from hay, sawdust, etc.)
  • It seems under their cost analysis, while not surprising, large and medium sized plants are the most economical. That said, they did say depending on the context small scale operations can be economical. The key seems to be inexpensive raw material access and it seems to be that costs and availability vary dramatically throughout the year

He concludes that:

“there are probably many unseen and untested opportunities out there in a variety of pellet markets. The fact that they sometimes refer to things that have been tested in the lab but not in the marketplace further backs that idea.”

Whether it would make sense to pelletize food wastes for energy burning has to do with a variety of factors including the moisture, cellulosic and CO2 content of the waste. With higher nitrogen lower cellulosic content and high moisture the potential advantages of pelletization go down as the costs to prepare the material go up. Most like food wastes that have liquid content and low CO2 levels do have “higher value use.” This is particularly the case in countries that have access to significant woody biomass wastes Potential hurdles for Pelletizing food for energy, feed, or other uses would have to tackle some hurdles:

  1. Pelletization requires a certain low moisture range. Not too low though or it won’t even work.
  2. Requires fats and starches in the raw materials. Food wastes, depending on their source, might even be good for that.
  3. Residential/institution food wastes might vary too much to make a consistent product. One of the things that the book emphasizes is that the market took off due to standardization of pellet sizes and consistency of product.

Pelletization does offer various benefits in terms of creating a different storage form for an organic waste. For the end-user, in the case of feed, for instance, it means being able to have the feed available year round without necessarily having the source product available year round. With regards to Pelletization the size of the material may be a limiting factor. Eric says that from his research he concludes that wood chips are not great for making energy pellets because they’re large. He adds “that larger plants with the right equipment can do it economically, but no one can really take logs as an input source an economically reduce them to size for pelleting.” However there are industrial technologies available to convert sizable wood chunks into sawdust that include the use of heavy duty grinders and hammer mills. This includes the possibility of using a devise playfully called the Muffin Monster. While originally designed for sewage pump and piping systems to ensure no obstacles would enter the pump housing and ruin the pump, it has become a machine commonly used in the scrap and recycling industry due to its ability to grind almost anything into shreds. When I was doing my research I found this page that lists other uses of sawdust besides a potential fuelstock. So again whether to determine that a material has a higher value use relates to the quality of the sawdust and the ability to easily convert it to that use rather than simply burning it for energy. He suggests that Mycelia pellets and Leaf pellets are two possibilities. I think leaf pellets could be a solution but the fluffiness of leaves may be an issue. Most likely would want equipment that could compact it to high enough density on the collection route to address the logistical costs of collection. I think that with Mycelia pellets you have to consider that the mycilia most like would have a higher value use than as a biofuel for gasification.

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