Thursday, April 4, 2019

Biodigester at Fat Beet Farm

Fat Beet Farm


During the spring of 2019 I have been doing an internship at Fat Beet Farm in Tampa, Florida. The Curci family have envisioned a sustainable commercial operation that includes a farm, food commissary, two restaurants and an event venue. They have been working for four years on establishing the farm where they are currently growing hydroponic lettuce, micro-greens, and soil-based vegetables, including cabbage, cauliflower, green onions, and of course BEETS. New projects on the horizon include a worm farm as well as an innovative mushroom growing system inside a shipping container!
Jerry Comellas and I digging the future beet field
Fat Beet Micro-greens used at their partner restaurants Noble Crust
My internship has revolved around building and getting the Biodigester up and running. As I excitedly talk about my project, I'm often met with quizzical looks . . ."Uh, sorry, but what EXACTLY is a biodigester?" I even recently had a friend ask, "Can it eat people?" Well, the short answer is - yes, yes it can!

What is a Biodigester?

An anaerobic biogas digester turns food, animal and agricultural “waste” into energy! Microbes break down organic materials into methane (CH4), carbon dioxide (CO2) and digestate, which can be used as fertilizer. Anaerobic (without oxygen) digestion is a simple process that occurs naturally in lakes and bogs, and consists of the following four steps:



Anaerobic Digestion

1. Hydrolysis: Organic matter is broken down to molecules such as sugars, amino acids, and fatty acids, becoming available for the bacteria

2. Acidogenesis: Acidogenic bacteria convert these molecules into VFAs (volatile fatty acids) ammonia, hydrogen sulfide and carbon dioxide


3. Acetogenesis: Acetogenic bacteria continue breaking down matter to produce acetic acid, carbon dioxide and hydrogen


4. Methanogenesis: Methanogenic bacteria complete the break down process resulting in methane (biogas), carbon dioxide and water. 

In these four simple steps you can take any organic material including food waste like meat and dairy products, grease, moldy bread, rotten fruit and veggies, as well as any kitchen scraps. Additionally, you can use animal waste of any kind - horse, cow, pig, human, and even dog and cat! Also agricultural waste, such as grass clippings, dead flowers, husks and shells, and weeds can be added. In the end, any leftover indigestible material left in the digestate makes for excellent natural fertilizer. This process creates a close-looped cycle, turning "waste" into energy and fertilizer input. 


What we're doing at Fat Beet

At Fat Beet, there is an abundant amount of organic matter "waste," from the food processing facility for the Noble Crust restaurants and the agricultural processes. Although composting is currently an option, with future restaurant and agricultural expansion plans, there will be a surplus of organic waste. 

TH Culhane & Josie Curci
We have built a Puxin designed 10m3 biodigester, using Dr. TH Culhane's steel molds. Dr. Culhane has used these molds to build biodigesters around the world. He is my professor at USF's Patel College of Global Sustainability and founder of Solar C³ities, a non-profit international open-source platform for all things biodigester and biogas related.


 http://www.solarcities.eu/
http://en.puxintech.com/Home
  


After constructing the concrete shell, we installed a 6" pipe to input food waste, a 4" pipe for digestate output, and the Puxin dome lid, for the biogas release.  We made a steel stir pipe to prevent clogs. 


Typically, biodigesters operate by mesophilic digestion, with mesophiles being the primary microorganisms, at optimal temperatures of 30-38°C (86-100°F), with ambient temperatures between 20-45°C (68-113°F). Tampa’s average high temperatures surpass the minimum of this range, fluctuating from 21°C (70°F) in January to 32°C (90°F) in June, July and August. However, the average lows, dip below the optimal temperature of 20°C (68°F) from November through April, at 16°C (60°F), 12°C (54°F), 11°C (52°F), 12°C (54°F), 15°C (58°F), and 17°C (63°F), respectively. In order to keep the biodigester at a constant high enough temperature, an additional heat source is required. The Curcis and Dr. Culhane decided to install a solar powered hot water system of evacuated tube collectors and PEX coils positioned inside the biodigester.


500 ft. of PEX coils looped through cinder blocks, holding them in place and providing surface area for bacteria colonies. The coils connect to steel pipes we placed inside the concrete shell.

PCGS students came out to help install the 60 evacuated tube solar system


 Split solar water heater system

Bringing It All Together

After the solar water system was installed, we needed to connect everything. We used CPVC pipes to connect the steel pipes that the PEX coils are connected to inside the digester to the solar tubes. Through trial and error, we realized the CPVC wasn't strong enough to withstand the piping hot water coming out of the solar tubes, so we had to refit the system with copper. We completed our plumbing system, with several pressure relief valves to hopefully deter any future explosions. We wrapped all the plumbing with foam insulation to prevent heat loss throughout the system. 

Warped CPVC after system exploded from high temperatures


 
Jerry and I cutting copper pipes

I learned how to solder!

She's Alive!

After several weeks of inoculation and feeding the biodigester manure and food waste, she is now functioning. We have both biogas and digestate production. We have a temporary IBC tank system set up, capturing both byproducts. These will eventually be replaced with custom cone bottom tanks. The conical shaped tank will prevent a build up of sludge at the bottom of the slurry tank. 

Liquid digestate aka slurry


Temporary digestate and biogas IBC holding tanks


Future cone storage tank


Te Kā
 or Te Fiti?

Te Ka or Te Fiti

Anybody who knows me, knows I have a slight obsession with the greatest movie of all time, Moana. In the movie, the demigod Maui has stolen the heart of Te Fiti, i.e. Mother Nature, to give power to humanity. Moana's people are beginning to suffer with crop blight and dwindling fish populations. She embarks on a mission to return the heart to Te Fiti, overcoming many obstacles along the way. Her final battle is against Te Ka the volcanic fire-breathing demon. In the end, Moana realizes that Te Ka is Te Fiti who has been corrupted without her heart. Moana returns her heart, and Te Fiti reemerges as the green goddess, forgiving all and ending the blight.  

The story of Moana can be aligned to our current world. We have abused Mother Nature to such an extent that we are suffering many consequences. We have extracted fossil fuels in order to obtain power, despite the ill effects of doing so. Perhaps, if we are able to have a paradigm shift, and turn to renewable energy sources, such as biogas, we can undo or at least prevent further damage. Our biodigester is both Te Ka and Te Fiti. She is currently black and capable of breathing fire, like Te Ka (and her dragon counterparts). In the future, Josie Curci envisions growing vining plants on her as she creates life with her fertilizer output and provides biogas energy, as Te Fiti.  





5 comments:

  1. Beautiful narrative and metaphors!

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  2. Wonderful description of this project. Wondering how it's going two years later?

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