Get Rid of Those Leftovers: How Much Organic Waste Can Composting Worms Eat? *

Abstract

Figure 1. This photo shows examples of organic waste. (City of Davis, California; 2010.)

Although organic waste is biodegradable, it is a big problem for the environment. In landfills, it decomposes anaerobically to produce a gas called biogas, which is mostly methane, a significant greenhouse gas. It also breaks down from a solid state into a liquid leachate, which can contaminate ground water and release heavy metals, such as mercury from old batteries, into the ground water. In sewage systems, some organic wastes can also contain heavy metals or nutrient pollutants, and uncontrolled disposal can lead to water pollution. Despite the difficulties in its disposal, organic waste is a highly valuable resource. It is energy-rich and full of nutrients. When processed properly, it can greatly enrich soils or run biogas generators to produce electricity.

In this environmental science project, you will explore how composting worms, called red wigglers or Eisenia fetida, can be used to break down organic waste, like food leftovers.

Figure 2. This photo shows a red wiggler, a special type of worm used in composting. (Wikipedia Commons, 2006.)

Click here to watch this DragonflyTV episode as Kevin uses food leftovers to build a worm farm. This video was produced by DragonflyTV and is presented by pbskidsgo.org.

Using the DragonflyTV video on the right as a guide, you will build a worm farm, and then test how much organic waste your worms can process, and how fast they can do it. You will need to collect data for several weeks. You will measure out and record a sample of organic waste, add it to the worm farm, and then record how many days it takes for the sample to disappear. You can then create a bar chart, graphing the weight of each sample on the x-axis, and the number of days it took for each sample to decompose on the y-axis.

As variations, you could consider keeping the weight and type of organic waste samples a constant, but then collecting temperature or pH data to see if that has any impact on the rate at which the worms decompose organic waste. You can also collect and measure "worm urine" from the bottom of your worm farm and see how it impacts the growth of identical plants. Use plain tap water as a source of water for some plants, and worm urine as a source of water and fertilizer for the others.

Credits

Kristin Strong, Science Buddies

This science project was inspired by the following DragonflyTV Episode:

• Twin Cities Public Television, Inc. (2006). Worm Farm by Kevin. Retrieved May 25, 2010, from http://pbskids.org/dragonflytv/show/wormfarm.html

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Bibliography

In this video, you can learn how to build and test a worm farm:

• Twin Cities Public Television, Inc. (2006). Worm Farm by Kevin. Retrieved May 25, 2010, from http://pbskids.org/dragonflytv/show/wormfarm.html

This source describes ways in which different countries handle organic waste:

• Practical Action. (n.d.). Recycling Organic Waste. Retrieved May 27, 2010, from http://practicalaction.org/docs/technical_information_service/recycling_organic_waste.pdf

This source provides information about making your own worm farm:

• Louisiana Department of Environmental Quality. (2008). Making a Worm Farm. Retrieved May 27, 2010, from http://www.deq.state.la.us/portal/default.aspx?tabid=2101

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