Brilliant Biodegrading
Sophie Liu, Angela Wilks
Burnaby South Secondary
Floor Location : J 170 V

Many people have become discouraged when compost biodegrades much slower than expected. We were interested in whether or not the types of food put in the compost had an impact on how quickly the compost decomposed. We then came up with the question “Which organic material biodegrades/composts the fastest?”

In our preliminary research we found that there are two types of compost--aerobic and anaerobic. Aerobic involves exposure to air and anaerobic does not. We decided to study
aerobic.

In a healthy compost there are the browns and the greens. Browns being carbon rich materials, and greens being nitrogen rich. The recommended ratio of carbon to nitrogen in a healthy compost is 30:1. We decided that we would use food scraps that one might find in an average backyard compost (lettuce, spinach, peas, apple peel, and banana peel) as our greens and newspaper as our browns. This does not, however, mean that our ratio of newspaper to food scraps was 30:1. Since vegetables contain carbon as well, the appropriate ratio of greens to browns is 2:1. We measured the ratio by weight, not volume, because some vegetables are denser than others. Our control was all newspaper.

Our hypothesis is: We predict that the compost will biodegrade fastest if spinach is added.

We placed our samples of two parts food substance (by weight) to one part newspaper into ziplock bags with straws, to allow for airflow. Qualitative observations were made every five days. After a time period of 26 experiment days, we found that out of the three nitrogen rich food scraps (spinach, lettuce, and peas) lettuce biodegraded best, closely followed by spinach while the peas got moldy. The banana peels stiffened, darkened, and grew slightly moldy, and the apple peels dried up and grew some mold as well.

In conclusion, our experiment confirmed our research--that when adding the nitrogen rich vegetables, we met the recommended ratio of carbon to nitrogen and the biodegradation process was much faster than the food scraps with less nitrogen.