Effects of Compost Material on Various Degradable Lawn Bags

Joe Mautino

9th Grade

Central Catholic High School

Problem

• Plastic bags are used frequently and add to pollution problems

• Plastic bags are not thought to readily decompose

• Composting has been implied as an effective means of recycling organic materials

• Can composting degrade plastic bags as readily as paper?

Background (Composting)• Composting is the transformation of organic waste into

compost • Main components of composting

– Organic matter• Brown (leaves, twigs, manure) supply Carbon• Green (grass, fruit rinds) supply Nitrogen

– Bacteria• Mesophilic Bacteria Range (10 C° - 40 C° ) • Thermophilic Bacteria Range (40 C° - 65 C°) most desirable

– Oxygen• Oxygen is used up quickly by the microbes as they metabolize the

organic matter • Less oxygen, slower composting

– Moisture• Ideal range is 40% to 60% moisture• High moisture causes anaerobic conditions, low moisture inhibits

activity

Background (Plastic)

• Americans throw away approximately 100 billion polyethylene plastic bags a year

• Made from crude oil– Accounts for 4% of the worlds total oil usage

• The process of making plastic bags requires large amounts of electricity

• Does not readily decompose

Background (Paper)Paper production impacts the environment in many

ways• Collection of timber for production is long and

environmentally taxing• Water usage

– Thousands of gallons of clean H2O used to wash and bleach pulp

– Paper = 1 part pulp to 400 part H2O

Disposition of used paper• Landfills

– Takes many years to decompose

• Recycle– Requires extensive process to return to pulp

Background (BioPlastic)• New biodegradable & compostable

plastics derived from cornstarch, Mater-Bi– Made from starch, biodegradable polyester,

other natural plasticizers – Claim to biodegrade in 10-45 days– Biodegradable: degrade from composting into

carbon dioxide, water, and inorganic biomass

• Compostable: Meets ASTM -6400-99– Biodegradable– Disintegrate– Low eco-toxicity

Purpose

To determine the garbage bag that will decompose the most rapidly in a compost pile.

Hypothesis

In the test compost, Mater-Bi plastic bags will decompose more than polyethylene plastic bags. The paper bags will undergo the greatest degree of decomposition.

Null: No significant variation in decomposition rate will be composted between Mater-Bi, polyethylene plastic and paper.

Materials

• 10 Mater-Bi plastic 127 mm * 127 mm bag pieces

• 10 polyethylene plastic 127 mm * 127 mm bag pieces

• 10 paper 127 mm * 127 mm bag pieces

• Digital scale (.000) grams • 5 L of organic potting mix• 15 L of cut grass• 900 ml of cheese

• 500 ml of yogurt• 500 ml of cucumber • 700 ml of green pepper• 400 ml of broccoli • 1 22 L metal bucket• A small electric heater• 1 155 L insulated bucket• 1 measuring cup• Appropriate PPE

Procedure• Collected and used appropriate PPE• Cut 10 127 mm * 127 mm pieces of each bag

(Polyethylene plastic, Paper, and Mater-Bi plastic bags)

• Weighed each sample and recorded initial mass of each piece

• Created compost mixture with the organic materials (Approximately 20 L)

• Placed the compost into a 22L bucket.• Mixed all 30 samples (Plastic, paper, and Mater-

Bi plastic) into the compost mixture• Used a small heater under the bucket and set to

25°C

Procedure• Covered the small bucket with the 155L

insulated can to keep a constant temperature • Used a small shovel to mix compost weekly• After 4 weeks removed sample bags from the

compost• Cleaned bag samples by brushing all excess dirt

from bags• Let the samples dry overnight• Weighed final mass

Polyethylene Plastic Experiment Samples (Control)

Before After

Paper Experiment Samples

Before After

Mater-Bi Plastic Experiment Samples

Before After

Data

Average Polyethylene Plastic Bag

Average Paper

Bag

Average Mater-Bi

Plastic Bag  

Initial Weight (grams) 0.3884 1.3416 0.3746

Finial Weight (grams) 0.3827 0.1038 0.3579

Weight Loss (grams) 0.0057 1.2378 0.0167

Percentage of Weight Loss 1.47% 92.26% 4.46%

Anova Single Factor calculations for the

Average Weight Loss For the 3 Bag Types Anova: Single

Factor

SUMMARY

Groups Count Sum Average Variance

Mater-Bi Plastic 10 44.89 4.489 1.352121111

Polyethylene Plastic 10 16.33 1.633 0.278801111

Paper 10 924.61 92.461 157.6407656

ANOVA

Source of Variation SS df MS F P-value F crit

Between Groups 53323.18 2 26661.5918 502.1907951 4.39E-22 3.354131

Within Groups 1433.445 27 53.0905626

Total 54756.63 29        

Percentage Weight Loss for the Average of Each Sample Bag

92.26

4.461.47

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Polyethylene Plastic Bag

Paper Bag

Mater-Bi plastic Bag

Observations

• All elements in the compost biodegraded to rich black soil

• Mater-Bi plastic showed indications that decomposition had started

• The Polyethylene plastic did not show any signs of biodegradation

• Only little pieces of the paper bags were left

Future Improvements

• Fill actual bags with organic material

• Improve final cleaning to reduce residual compost on the samples

• Add additional composting bacteria to accelerate decomposition

Conclusion

• My alternate hypothesis was proven correct, that in the test compost, Mater-Bi plastic bags will decompose more than polyethylene plastic bags. The paper bags will undergo the greatest degree of decomposition.

• My null hypothesis was rejected, shown by the P value stated in the Anova calculations.