Discussion and Analysis

The vermicomposting project was divided into five parts and involved two years of observations. In Year 1, I established the optimum conditions for vermicomposting cat wastes with three basic experiments and hundreds of measurements. I found that the most important factors in creating a good environment for the worms were the level of moisture, the amount of aeration, and achieving the proper carbon-to-nitrogen ratio. The worms were able to adapt to slow changes in temperature and pH.

The worms, of course, asked, "What's for dinner?" Since Eisenia fetida manure worms will make use of almost any carbon and nitrogen source as food, the worms were not picky about cat waste. It is a common misconception that worms "eat" waste. The worms get their nutrition from the bacterial, fungal, and protozoal activity in the vermicomposting system. Since the worms have no teeth or digestive enzymes, the microorganisms "predigest" the worm's food and then become food themselves.

The end point of the composting was established when the E. coli colony count declined, indicating that the cats' fecal material had been decomposed. Comparison of colony counts was done by counting the number of E. coli colonies from an aliquot sample and then calculating the number of E. coli that would be represented in three ounces of cat waste (the ADP, or "average daily poop"). E. coli counts were taken on the vermicomposting bins on a weekly schedule.

(Coliform bacteria are a group of bacteria that are all of fecal origin and are normal in the intestinal tract but can also be pathological. Escherichia coli is the best-known coliform; Salmonella is probably the best-known coliform pathogen. I established that my cats did not have any pathogenic coliforms by having a diagnostic lab perform a culture on a composite stool sample.)

The E. coli colony count was reduced by 33%, 50%, and 88% by weeks 4, 5, and 7. I had read about municipal human-sewage systems in which 10,000 pounds of worms "ate" 10,000 pounds of sewage sludge in one week, and the coliform reduction was about 50%. The E. coli reduction of 88% in my system exceeded my expectations. It was also noted that the initially acidic system moderated to pH 6-7, and the nitrogen level was high at the end point.

Although worms adjust to changing temperatures, I maintained the system at 70° F, and the worms efficiently composted the feces in just two weeks. The optimum conditions achieved were when the weight of the worms equaled the weight of daily cat feces (ADP); the amount of carbon material present (shredded newspaper) was in a 2:1 ratio to the nitrogen material present (cat feces, or ADP); and daily feeding was performed. (It was awkward in class to continue to refer to cat feces, so I devised the acronym ADP to stand for "average daily poops." ADP doesn't provoke a gag response from the audience.)