The straws in the dirt soaked with vinegar will decompose the fastest, because the vinegar will have the best reaction with the straw.

Acetic acid makes vinegar strongly acidic, with a typical pH of 2–3 (4).

 Lemons are acidic due to their high citric acid content, with lemon juice having a pH between 2 and 3. This makes it 10,000–100,000 times more acidic than water. The pH scale measures the acidity of substances, and lemon juice falls on the acidic side.

Acid is a chemical that gives off hydrogen ions and water. It forms salts by mixing with certain metals. It has a sour taste and can turn certain dyes red. Examples of acids are vinegar (acetic acid), lemon juice (citric acid) and detergents (sulphuric acid).

Some acids are safe to eat, but they will taste sour.  Other acids are harmful to humans and could even kill you.

More than 15 million metric tons of plastic enter the ocean each year. By 2025, experts predict that there will be one pound of plastic in the ocean for every three pounds of fish. Plastic straws are an unnecessary utensil for the vast majority of people and are usually thrown away after just one use.

Controlled variables (The thing that’s staying the same)

• The kind of straws
•  The kind of dirt
•  How deep the straws are buried

Dependent variable (being tested)

• Do different kitchen acids compost stuff faster

Independent variable( what’s being purposely changed) 

• The kind of acid

• Cut each straw to 4.5 inches long.
• Add half an inch of dirt to each container.
• In a measuring cup, add one cup of water and one tablespoon of sea salt.
• In another measuring cup add 1 cup of lemon juice.
• In a third measuring cup,use 1 cup of vinegar.
• Add 8 tablespoons of liquid  to the dirt, (or until dirt is completely covered).

• Bury the straws in dirt until covered.
• Straws were buried on December 10, 2024.
• Containers were placed on a heat mat.
• I refreshed the liquid on January 19, 2025.
• Straws were removed from the containers on Feb 2, 2025.
• Straws were buried in the dirt for a total of 54 days.

After 54 days I removed all the straws from each container and examined them. I needed to wear a mask and gloves because the containers all grew mold. 

Vinegar

The paper straw broke when I pulled it out of the dirt but it is mostly intact

The compostable straw shrunk in both length and width

The plastic straw looked the same as on day 1

Lemon Juice

There were a few small pieces of the paper straw left in the dirt

The compostable straw shrunk in both length and width

The plastic straw looked the same as on day 1

Sea Salt

There is no evidence of a paper straw anyqwhere in the container

The compostable straw shrunk in both length and width

The plastic straw looked the same as on day 1

In conclusion sea salt is the best acid for composting because of the high salt content, paper straws in the ocean hopefully dissapear and don't harm any animals. I wonder if compost facilities would consider adding salt water to their compost to help speed things up. 

This is important because we would just keep adding things that are compostable to our landfills which would hurt the environment. If we know that we can add different acids to compostable items to help break it down we can help the environment. 

There may have been too much moisture and the mold could have affected the amount of the straw that composted broke down

The amount of lemon juice because I did not have enough lemon juice the first time

I could have maybe weighed each straw before and after rather than looking at just length and width

https://actiumresources.com/

I want to thank my mom for helping me dig up everything and helping me with my typing. My dad because he works in the landfill and he is the one that told me they put water on their compost. Mrs Van den Eynden for helping me get everything in the platform and organizing the science fair.