The compostable material includes cooked and uncooked meat (ground beef, chicken), fish (shrimp, salmon), rice, noodles, tacos, vegetables, avocados, limes, lemons, and the like. In addition, all paper napkins, hand towels, paper plates, and other paper products generated in the restaurant. Cardboard, though compostable, is recycled. A rough estimate of the composted material is 20% fruit, 20 % vegetable, 20% paper material and the remaining 40% food waste. Because of the high nutrient value of the food waste, and the relatively low carbon ratio of the napkins, I have added sawdust and shredded leaves to try to achieve a better carbon nitrogen ratio for hot composting.
Two questions that I had for this site were: 1) how big of a system does the restaurant need, and 2) how fast can the freezer/composter get the compost to a curing point. The second question is hard to answer when using a “bild a pile as you go method” of composting as we are. Given that my patience level is slightly less than that of a gnat, I separated the compost into two groups at the end of week two.
Question 1, how big should the system be?
On November 5, 2012, we installed a medium size (15 cu. ft.) chest freezer/composter. A layer of course material (woody debris and ripped cardboard) filled the bottom 2 inches, then we layered in 2-3 weeks’ worth of collected compostable waste material (about 60kg). Over the next two weeks, restaurant staff added food waste daily and I layered the material with shredded leaves or wood shavings every second or third day for odour and fly control. I completely turned the compost about once every four days and measured the temperature of the compost whenever I was there. After the two-week period, the composter was about 70% full and we had two weeks of temperature records.
As shown in the chart at below, temperatures ranged from 80oF to 140oF (26 to 60 C) during the 14 day period. For a consecutive 10 day period, temperatures exceeded 104oF (40C) and on two of those days the temperature reached 40oF (60C), hot enough to kill some pathogens.
However, as the following picture shows, the “build a pile as you go” method does not produce compost within a 14 day period. Yes, some of the material has decomposed over the two week period, but other material has only just been added to the pile.
At the end of this two-week period, the freezer/composter was about 2/3 full. Given that the material shrinks during the composting process it is estimated that the 15 c.f. composter would be full within a 6-8 weeks. At this point, we removed about 90% of the material and began again to monitor how quickly the freezer/composter would fill up.
pile as you go