Compost Bioreactor: Design and Build

Materials:

Recycled Plastic Bottle. 20oz or experiment.
Breathable/Porous material for cap.
Air chamber material may include recycled plastic, pebbles... be creative.

Equipment:heavy-duty scissors, utility knife, drill

Skills

Measurement, layout and material fabrication.

A bioreactor is a biosphere designed to accelerate the decomposition of matter. A healthy environment that supports microorganisms' growth will significantly reduce the time to make dirt from scraps. A plastic bottle of varied sizes will work, 16oz, 20oz, 1 liter...

Some design variables to consider:

Airflow (aeration) – Airflow is created with holes in the bottom, through the air chamber, and out a porous cap. The air chamber panel should be stiff and have holes for airflow. Its purpose is to contain the compost mixture while allowing air to flow through the mixture. A breathable cap made from a porous material (i.e., cheesecloth) is used to release air and prevent insect contamination.

Temperature – Use a stem thermometer to monitor temperature during the decomposition process. Access needs to be provided for the temperature probe. A hole in the cap or top to accommodate the probe diameter will work.

Since increased temperature promotes decomposition, insulating the bottle may aid the process.

Insect and odor control – Your bioreactor should not attract fruit flies. The proper balance of aeration, compost mix and moisture content throughout the process should be part of the plan. Collect data at scheduled intervals.

Data Collection and System Monitoring

The health of a composting bioreactor is a measure of temperature and moisture content. Monitor the temperature at planned intervals (i.e., every day). Insert a probe thermometer to read the temperature at the sample's core.

Record your data and graph the results. Does the graph approximate the three composting phases?

Optimize your Design

There are may variable that can be considered to optimize this design . With the goal of reducing the time to make better dirt, some research questions to consider may include:

Insulation -- Will insulating the bottle increase heat gain?
Compost mixture – What is the maximum size of pieces in the compost mix?
Moisture content – What is the best moisture content range to maximize temperature increase?
Aeration – What is the best air hole size?
Compost Volume – Is a 16oz bottle better than a 1 Liter bottle for reducing decomposition time?

Conduct experiments to determine the best design practices. Download an 'Experiment Log'HERE.