Pitfalls of Previous Efforts
Until the 2017-18 school year, UCSD's Housing Dining Hospitality (HDH) used to send their pre-and post-consumer food waste to Miramar Greenery for composting. However, due to high levels of plastics contamination in post-consumer waste, Miramar Greenery was forced to stop accepting it, resulting in a large amount of perfectly compostable food to go to landfill.
Additionally, University Centers (UCEN) sends their food waste to Otay Landfill's composting centers. While this is a laudable effort, the emissions caused by transporting actual tons of food waste represents a significant downstream carbon cost and is therefore not the most sustainable option. Furthermore, only a handful of businesses in UCEN actually participate in this endeavor.
To remedy the lack of participation by businesses in UCEN collection, Roger's Urban Farmlab members concentrated on businesses that UCEN doesn't collect from. Our principle business include Jamba Juice, Lemongrass, Panda Express, Seed and Sprout, Subway, Tapioca Express, Y Mas, Zanzibar, in addition to the Art of Espresso (The Mandeville Coffee Cart). In Fall 2018, we added Perks Coffee Shop, Starbucks, and Sunshine Market, capturing preconsumer waste from 12 of 22 businesses operated by UCEN.
Every Monday, Wednesday and Friday, RUF collects 8-20 gallon buckets from each participating business or group. We try to avoid picking buckets up during peak lunch hour traffic and use only service alleyways to avoid spilling these wastes in public areas of price center. Furthermore, RUF has asked vendors to store these buckets in the back of their kitchens or in just outside in the service corridors so we don't interfere with their business.
UCEN has generously allowed us to borrow a pickup truck and furniture dollies to transport over 100 pounds of waste at a time from PC and SSC to RUF.
This quarter we are regularly picking up 2,000 pounds of food waste a week, up from just above 1,000 pounds at the start of this project, and above the 1,500 pounds during Summer Session.
After collection, we carefully weigh and chart the type of collected waste (vegetables, protein, etc.). At this point, a waste audit is performed to find materials suited for the Anaerobic Digester, which prefers softer foods like bread or vegetables.
Once the waste has been sorted, the non-digester waste is added to our two outer most compost piles. Waste is then covered with wood chip mulch (a combination of pine needles and wood chips from tree maintenance) produced by UCSD Facilities Management. We've noticed that adding mulch helps to reduce the often unpleasant-smelling odor associated with composting.
After the pile was first erected, it very slowly increased in temperature to around 120 F (48.9 C) after a few days. During this step, the pile produced a characteristic odor of volatile fatty acids (VFAs) which was likely caused by fermenting bacteria. Because of this we found it best to turn the pile after 1-2 days to minimize emissions of VFAs. At this stage, compost is moved from the outer two most bins into the two inner bins.
Following the first turn, the odor of VFAs disappeared and the temperature rose to above 140F (60C) in a couple of days. At these temperatures weed seeds and potential pathogens are killed. The compost is considered ready when the temperature no longer rises after turning, at which time it is moved into the central bin. This enables the most efficient production of compost, as once we've reached a few weeks old the usable organic matter left is only a fraction of what we started out with.
After all these steps have been completed, the compost is then added to the various planter bins, pots, and even RUF's orchard. This compost allows our garden to continually produce without having to worry about using potentially damaging artificial fertilizer. Additional benefits of the compost include its ability to trap water, minimizing loss to evaporation, and providing a safe habitat for beneficial insects.
We offer three sizes of buckets - 8, 12, and 20 pounds. Businesses can also elect to take multiple buckets depending on how much waste they produce.
We first weigh and chart our collected waste before adding it to our 5-bin system.
The above diagram depicts what Scientists believe happens inside a pile of compost.
New Composting Methods
In addition to traditional “hot composting”, RUF practices vermicomposting which uses red worms (Eisenia Foetida) to consume food waste. The end product is a rich, organic soil amendment called worm castings or vermicompost. They are easily reared all year round in dedicated worm bins.
RUF has begun rearing Black Soldier Fly larvae (BSFl). BSFl are vigorous consumers of any kind of organic matter and feed on anything from vegetable scraps to meats and feces. The grubs are housed in a special bin known by the brand name BioPod. The Biopod was placed in a small tent to keep adult flies in and therefore create a self-sustaining colony. These flies are then fed some food waste to help break down material that would otherwise take weeks or months in our traditional composting bins.
In addition to helping process high-protein food waste, BSFl can also be fed to our future livestock of chickens and tilapia, as they are rich in fat and protein. Thus, they are incredibly valuable in helping RUF reach our goals of local food sustainability.
Limitations and Improvements
After several months of running our composting system, we've realized a number of potential improvements and the limitations of our current design:
- The particular bin layout used makes it difficult to turn only a single pile
- Our compost can become highly anaerobic due to the number of coffee vendors we collect from. Coffee has an extremely large amount of nitrogen in it, resulting in a disproportionate number of nitrifying bacteria settling in our system.
As a result, we're experimenting with our partners, Oceanview Growing Grounds to develop aeration methods to allow colonies of other bacteria to flourish. Their success with the Food2Soil method of forced air injection has had promising results, and we hope to replicate this in RUF. This would enable us to expand to more coffee vendors on campus and preventing more valuable "waste" from going to landfill.