ABOUT TRASH TROLLS

 

The Problem

Climate change is one of the world’s most pressing issues. It is the result of increasing concentrations of greenhouse gasses in the atmosphere trapping heat from the sun, which leads to a net rise in global temperatures as well as numerous secondary effects, such as desertification, species loss, habitat loss, and ocean acidification. Methane represents 10% of yearly greenhouse gas emission according to the EPA. Methane has a global warming potential of 25, meaning that one unit of methane causes a warming equivalent to 25 units of carbon dioxide over a 100-year period (Overview of Greenhouse Gases, 2019). Humans are a major contributor to global methane emissions. We are trying to create a product that will reduce these emissions. Particularly, we are interested in landfill emissions, which represent 24% of all anthropogenic methane emissions in the US. Many landfills do not yet have the infrastructure in place to recover methane for energy and even with gas recovery systems,10% to 65% of all methane emissions throughout the landfill’s lifetime go uncaptured (Huber-Humer, Gerbert, & Hilbertm, 2008). Thus, there is plenty of opportunity to improve efficiency of methane emission capture from landfills.

 

Our Product

Our product consists of pea sized spheres that are meant to be scooped into a trash bag before it is taken to the dump. These spheres are made up of a biodegradable plastic and three species of naturally occurring microbes. These microbes, known as methanotrophs because of their use of methane as a carbon source, are put into a state of dormancy before being packaged into a biodegradable plastic. As these spheres decompose in a landfill, the methanotrophs get wet, which brings the methanotrophs out of dormancy. These microbes convert methane into carbon dioxide as part of their normal metabolism and so reduce the total amount of warming caused by landfills.

 

This is a short presentation about our product one of us did for a 5th grade class after being contacted by a teacher from Fortuna Middle School.

 

These model landfills compare methane capture rates before and after the addition of our product. The green beads represent trash bags and the orange beads represent our product. "Before" rates are based on traditional landfill gas capture system efficiencies during the four phases of a landfill's life cycle. "After" rates combine traditional capture system efficiencies with estimated methane capture efficiencies for our product. (A) Operation Phase. (B) Landfill Closure Phase. (C) Active Aftercare Phase. (D) Passive Aftercare Phase.

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Design Process

Project initiation: As part of a brainstorming session for the Biodesign challenge River came up with the idea that he initially called the “methanobrick”. He was inspired by an article he had read about Henk Jonkers’ “self-healing” concrete, which contained dormant bacteria that would be woken up by water when cracks formed. He was interested if a similar idea could be applied to methanotrophs. The idea was to create some form of material that would encapsulate them and over time that would degrade allowing them to grow. He decided to focus on methane because of its high warming potential and prevalence as a greenhouse gas. The idea was pitched to the entire UC Davis Biodesign class and we three gravitated toward it as a fascinating opportunity. While Ale and Devyn had proposed their own ideas, they realized that this idea was one of the only one proposed to the class that would have an immediate impact on climate change.

Orientation/research: We all have backgrounds in science and know that climate change is one of the biggest problems our generation faces. We knew that methane as a greenhouse gas is under-represented when discussing how to combat climate change when compared to carbon dioxide, so we knew that River was on to something. We performed extensive reviews on current information about methanotrophs to help us better understand their metabolism and effect on local ecosystems. Particularly, we focused on determining the unique capabilities of the species we decided to focus on and how they are suited for the landfill environment.

Strategy: We began by making sure that our product was a necessary addition to the product market by researching similar products (which there weren’t any of) and other ways of reducing methane emissions.

This is the result of one of many brainstorming activities where we discuss the important issue we might face when making our product.

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​​​Exploration: We looked at other sources of methane and found that agriculture was another major methane-producer. We thought about directing our efforts towards this sector but realized that landfills are responsible for a large portion of methane emissions and are more easily treatable than cows.


Development: After learning that landfills are composed of both aerobic and anaerobic areas, we decided to use both aerobic and anaerobic methanotrophs in our product. We originally planned to make our methanotroph-based product into a brick or pod that was about the size of a golf ball but then realized that it might be better to make a lot of smaller units for better dispersal. 


Refinement: After research, we narrowed our materials down to PVA  (for inner and outer membranes), aerobic methanotrophic bacteria, and a complex of anaerobic methanotrophic archaea and anaerobic bacteria. Originally, we had considered other membrane materials, but PVA worked best due to its solubility in water and stronger tensile strength when compared to other biodegradable materials. The organisms we chose are culturable and ideal for our product because combined they reduce methane in both aerobic and anaerobic environments. Also, the aerobes can be induced into dormancy and come out of dormancy when exposed to water, hence the need for a water-soluble membrane. 


Production: Due to the COVID-19 outbreak and shelter-in-place orders, we are still in the prototyping phase for our product.

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Our Video