Author: Gina Talt

Welcome back! This week’s bioDIGESTer includes the summary of last week’s data,  a photo essay highlighting the compost off-loading process, and the biodigester’s interactive exhibit at the Frist GreenSpace.

Weekly Data: 10/22 – 10/26

Last week’s data were very similar to the week prior having loaded 3,703 lbs of food scraps and 1,100 lbs of wood shavings into the system.

	Food	Wood shavings (BA/CS)	% BA/CS	Compost Off-loaded
Week Totals (lbs.)	3,703	1,100	30%	3,000
CUMULATIVE (lbs)	14,278	4,109	29%	5,000

We also off-loaded a trailer bed’s worth of finished compost or around 3,000 lbs. This amount is roughly equal to the amount of food that we added in order to balance out the input-output  equation to prevent over-filling the system (Note: About 25%-30% of the mass of the cumulative feedstock is lost to water vapor which cancels out the addition of the wood shavings).

Herman Ishengoma ’22 assists with off-loading finished compost into the receiving receptacle. Visible is water evaporating from the finished compost as it transitions from a 100+ degrees F environment to ambient temperature on a chilly Fall morning.

 

Dr. Nick holds a small amount of our best batch of finished compost to date

 

 

 

 

 

 

 

After two off-loads, the trailer bed is full and is hooked up to a truck and taken by our Grounds crew.

A small amount of compost is salvaged for nutrient analysis testing using a UNIBEST resin capsule which will give us an initial read on the total plant-available nutrients in the compost. Stay tuned for results!

Biodigester at the Frist GreenSpace

The biodigester project is this semester’s featured exhibit  at the Office of Sustainability’s GreenSpace in Frist Campus Center. Stop by the interactive kiosk on the 100-level to learn more about the step-by-step operational process, the University’s  progress and approach toward recycling uneaten food on campus, and class projects and additional research opportunities available via the Campus as Lab program.

Welcome to the debut of the weekly bioDIGESTer! A new series consisting of weekly project updates and related news around food waste management. Check out what we were up to last week!

Operations

Over Monday, Wednesday and Friday, we loaded a cumulative 3,734 lbs. of food scraps into the system along with 1,100 lbs. of wood shavings which serve as a bulking agent/carbon source (Read a previous blog post to learn more about why we add wood shavings).

We are currently testing American Wood Fibers’ mini flake. These wood shavings account for ~30%  of the total weight of the food scraps feedstock in order to adequately account for the moisture level of our food waste stream.

As a result, the 1,500 lbs. of finished compost that we off-loaded was an ideal texture – not too dry and not too wet.

	Food Scraps	Wood shavings (BA/CS)	% BA/CS	Compost Off-loaded
Week Totals (lbs.)	3,734	1,100	29%	1,500

 

Finished compost after it was off-loaded from the system

 

Food waste in the news:

A diverse set of strategies will be needed if New Jersey plans to meet a state target of cutting food waste by 50% by the year 2030. The Princeton Biodigester project represents further investigation of the potential of on-site food waste re-purposing through in-vessel composting. Read more about the current legislative and technical landscapes around reducing food waste in New Jersey in this deep dive article from Waste Dive:

https://www.wastedive.com/news/new-jersey-food-waste-policy-landfills/539406/

 

 

 

 

 

After a busy summer preparing for the start-up, Princeton University’s biodigester is now operational! Many thanks to our campus partners and FOR Solutions for their on-going support and assistance.

Check out the video below from one of the first loadings and stay tuned for weekly updates as the project progresses!

 

 

In the last few weeks, we began a series of steps to prepare for our start date in June while also starting campus outreach efforts.  These included a system calibration test performed by FOR Solutions, two tours for the campus community, and the arrival of a  lift arm for loading buckets of the feedstock into the system’s hopper. See the photo essay below!

1. FOR Solutions performs a calibration test to insure the correct electrical set-up and proper rotation of the biodigester’s mechanical systems

2. Dr. Nick shares his journey into food scraps composting and why he founded FOR Solutions to our Earth Month tour group

3. The lift arm that we will operate in order to dump buckets of uneaten food and wood shavings into the loading hopper

See the below photo essay to see what we’ve been up to over the last month:

1 Arrival of a shed to store the wood shavings

2. Interior Lighting!

3.  Scale for weighing buckets of wood shavings and wasted food to insure accurate record-keeping. A big thanks to Eric Teitelbaum for assisting with set-up!

4. Utility sink for hand-washing

5. Dr. Nick visits and speaks to students in ENE 202: Designing Sustainable Systems. Two teams of students will design and build systems for the biodigester for their semester projects.

• Patrick Brucki ’21, Tom Johnson ’19 and Max McPherson ’19 will be “Hacking” the scale to be able to collect, store, and organize the weight data on an in-house server for easy access.
• While Lena Dubitsky ’18, Oliver Hsu ’19 and Izzy Mangan ’19 will be building a smart solar air heating system.

 

 

Now that the biodigester has been installed, we are actively working on pulling together the final operational pieces to get the system up and running. The first item to arrive: wood shavings! 

[Food waste is not the only item being recycled by the campus biodigester, but wood shavings as well! We will be using the wood shavings in these bags which were byproducts of a NJ-based woodworking company]

Why are wood shavings needed?

For efficient aerobic decomposition to occur, organic matter should contain both nitrogen (i.e. food scraps) and carbon. Recommended carbon sources for composting traditionally include dead leaves/vegetation, paper, shredded cardboard, hay/straw, and woody materials.

Adding these “browns” to nitrogen-rich food scraps, or “greens”, creates the perfect environment for composting by providing all three inputs to support key microbial activity: nutrients, water,  and oxygen:

Organic matter + H₂O + O₂ -> COMPOST + byproducts (CO_2, H₂O, Heat)

The carbon and nitrogen in the organic matter provide energy and protein building capacity, respectively, to support the presence of microbes that transform the uneaten food and wood shavings into compost. Water embedded in the food waste provides moisture necessary for microbial growth. However too much moisture can restrict airflow, depriving the microbes of oxygen. When mixed with the food waste, the carbon source facilitates aeration by absorbing excess moisture and creating spaces for airflow.

At the start of the composting process, the ideal carbon to nitrogen (C:N) ratio is cited to be around 30:1. Although a useful goal to achieve, this ratio may differ depending on the bioavailability of the materials used, or the composition of the feedstock. For example, relatively more carbon-rich material needs to be added to the feedstock if a) the material has a low carbon content, b) the carbon is stored in compounds highly resistant to decomposition or c) in cases of high-moisture food scraps (think soupy v.s. starchy mixtures).

For the biodigester, acceptable materials include shredded cardboard, straw or hay, wood chips, and wood pellets; however, the founder of FOR Solutions has found that kiln-dried wood shavings (such as those pictured below) are the best option for the following reasons:

1. They are dry enough to absorb the excess moisture in the recovered food to achieve the desired moisture content of the feedstock
2. They have a high enough carbon content to provide for the optimal C:N ratio in the feedstock, which is 15-30:1, and
3. They maintain their unconsolidated consistency even when wet, so they contribute to the porosity of the feedstock inside of the digestion vessel, allowing for air exchange.

Research by the founder of FOR Solutions has confirmed that a 4:1 ratio by weight of recovered food to wood shavings is optimal. However, we may need to alter that ratio as necessary depending on the make-up of our food scraps.

Aeration of the digestion vessel is achieved by a regenerative blower that provides a complete exchange of all air inside of the digestion vessel every 15 minutes.  The digestion vessel rotates once every hour.  This contributes to the decomposition of the recovered food and forces the feedstock to migrate from the input end to the discharge end of the digestion vessel, ready to be recovered and put to good use!

Stay tuned for more project updates!

Sources and to learn more general information about the composting process:

• “Compost Questions” by Willi Evans Galloway of Rodale’s Organic Life
• Cornell University’s “Science of Composting”

 

Come hear the latest on the biodigester and learn more about local and global efforts around food waste reduction at Princeton Studies Food’s conference, RIPE FOR THE PICKING: Repurposing wasted resources in our food system

Event is free and open to the public, but registration is needed to receive lunch.

Learn more about FOR Solution’s innovative composting technology from founder, Dr. Nick Smith-Sebasto.

Great article by Victor Hua ’21 highlighting the biodigester and how it contributes to the University’s sustainability goals:

http://www.dailyprincetonian.com/article/2018/01/new-biodigester-improve-ecosystem