Are Egg Shells Biodegradable?

Eggs are a staple of many people’s diets and their shells are often tossed in the trash without a second thought. But have you ever wondered what happens to eggshells once they are discarded? Are eggshells biodegradable or do they sit in landfills for years on end?

The answer might surprise you. While a mineral that is biodegradable in its pure form is present in eggshells, the answer to whether eggshells are biodegradable is not as straightforward. The chemical makeup of eggshells is complex and their biodegradability can be affected by a variety of factors such as the environment in which they are discarded and the presence of other substances. As we become more aware of our impact on the environment and the need to reduce waste it is important to understand the biodegradability of household items like eggshells. This is why we will explore the science behind eggshells and the factors that affect their decomposition.

Key Takeaways

  • Eggshells are primarily composed of calcium carbonate with small amounts of other minerals such as magnesium, phosphorus, and potassium.
  • Eggshells are biodegradable but their decomposition can be influenced by many factors, from environmental to man-made reasons.
  • Eggshells are not considered to be recyclable but they can be repurposed as a natural fertilizer, pest deterrent, or used in arts and crafts.

Chemical Composition of Egg Shells

Eggshells primarily consist of calcium carbonate which accounts for approximately 95% of the shell’s total weight. Other minerals present in eggshells are magnesium, phosphorus, and potassium. Calcium phosphate is also present in small amounts. The outermost layer of the eggshell contains pores or micropores that allow oxygen and carbon dioxide to pass through the shell.

The chemical composition of the eggshell also influences its color with brown eggs having a greater amount of pigments than white eggs. The thickness of the eggshell also varies based on factors such as hen breed and age. The mineral content of eggshells may vary depending on the soil in which the hens were raised.

Biodegradability of Egg Shells

Biodegradability of egg shells

Eggshells mainly consist of a mineral known as calcium carbonate which is biodegradable in its pure form. But the biodegradability of eggshells is not as simple as the biodegradability of pure calcium carbonate. This is because eggshells contain additional organic and inorganic compounds which can impact their decomposition.

Despite this complexity, eggshells are generally considered to be biodegradable. When eggshells are discarded in natural environments such as compost piles or soil they can break down over time through a process known as biodegradation. During biodegradation, microorganisms break down the organic and inorganic compounds in eggshells eventually reducing them to their basic components. These components can then be absorbed by plants and other organisms in the ecosystem, contributing to the nutrient cycle.

Factors Affecting the Biodegradability of Egg Shells

Several factors can affect the biodegradability of eggshells. Some of the prominent factors that can influence the degradation process are:

Factors affecting the biodegradability of egg shells

Environmental Conditions

The environmental conditions surrounding the eggshell will have a significant impact on its biodegradation rate. Temperature, moisture, pH, and oxygen levels are all factors that can influence the microbial activity surrounding the eggshell. For instance, the presence of moisture increases the likelihood of microbial activity which in turn facilitates eggshell decomposition.

Protective Coatings

Eggshells have a protective membrane on the surface that helps the eggshells to maintain their integrity. The presence of this coating makes it more difficult for microbes to colonize the eggshell and accelerate its decomposition. This means that eggshells with thick and durable membranes tend to decompose slower than those with thinner more delicate coatings.

Processing and Preparation

The processing and preparation of eggshells can affect their biodegradability. Eggshells that undergo high temperatures experience structural changes that alter their composition which can make them susceptible to decomposition. Processing eggshells through a heat treatment process can increase their biodegradability in some cases.

Presence of Contaminants

The presence of contaminants can also hinder the biodegradability of eggshells. Eggshells that are stored or disposed of in areas with high levels of toxins or pollutants can experience significantly slower rates of degradation. Contaminants tend to inhibit microbial activity and can damage the protective layers of the eggshell, making it prone to bacterial invasion.

Chemical additives

Chemical additives such as fertilizers, pesticides, or herbicides can stress microbes and affect their ability to break down eggshells. The use of chemicals on eggshells can also transfer harmful compounds to the environment impacting soil quality and detracting from the eggshell’s potential as a biodegradable material.

Time Taken for Egg Shells to Decompose

Time taken for egg shells to decompose

The time it takes for eggshells to decompose can vary depending on a number of factors including the conditions in which they are composted, the size of the eggshells, and the presence of other organic matter. In general, eggshells can take anywhere from 12 months to several years to completely decompose depending on environmental conditions. However, they will start to break down quickly and can provide valuable nutrients to the soil as they do so.

Factors that can impact the time it takes for eggshells to decompose include the temperature and moisture levels in the compost pile as well as the presence of other organic matter such as food scraps or yard waste. Eggshells that are crushed or ground up will decompose more quickly than those that are left whole as they have a larger surface area for microorganisms to work on. It is worth noting that while eggshells do eventually decompose they can take longer than other organic materials like vegetable scraps or leaves so it is important to be patient and wait until they have fully broken down before using the compost in your garden. Overall with the right conditions, eggshells can be a valuable addition to a compost pile and a great way to reduce waste.

How to Dispose of Eggshells?

How to dispose of eggshells

It is important to dispose of eggshells properly to minimize their impact on the environment. The first step in disposing of eggshells is to clean them thoroughly. Rinse and remove any remaining contents and allow them to dry properly. This will help to prevent odors and keep bacteria at bay. Once they are cleaned and dry there are several ways to dispose of them.

An eco-friendly option is to add them to your backyard compost pile. Eggshells contain calcium which is a nutrient that is beneficial to plants. The shells will decompose quickly and eventually add to the nutrient level of your compost.

Recycling Egg Shells

Recycling egg shells

Eggshells are not generally considered recyclable as they fall under the category of organic waste. Still, they can be repurposed in a number of ways. One of the most common ways to reuse eggshells is to add them to compost or use them as a natural fertilizer in the garden. Eggshells are rich in calcium which is essential for the growth and health of many plants. Ground-up eggshells can be mixed with soil to help improve the soil’s nutrient content and texture.

Another popular use for eggshells is as a pest deterrent as they can help to repel slugs, snails, and other pests from plants. Eggshells can be utilized for a variety of other purposes such as crafting or making homemade beauty products. Eggshells can be dried and ground up into a fine powder to be used as an abrasive in cleaning products or as an exfoliant in facial scrubs. They can also be used to add a decorative touch to crafts like mosaic art as the colors and patterns of the shells can be quite striking. While eggshells may not be able to be recycled in the traditional sense their natural properties and versatility make them a valuable resource that can be used in several ways.

3 Great Ways to Use Egg Shells For Sustainable Use

Eggshells are a common kitchen waste item that many people compost or discard. However, they have a number of useful applications and can be repurposed in a variety of ways such as:

Natural Fertilizer

One of the most common uses for eggshells is as a natural fertilizer for plants. Eggshells are a good source of calcium which is an important nutrient for many plants. To use eggshells as fertilizer simply crush them into small pieces and sprinkle them in your garden or around your plants. The eggshells will gradually break down and release calcium into the soil helping to promote healthy growth and prevent blossom-end rot in tomatoes and other plants.

Natural fertilizer

DIY Calcium Supplements

Eggshells can also be used to make DIY calcium supplements. Simply clean and sterilize the eggshells by boiling them for a few minutes then crush them into a fine powder. You can add this powder to smoothies, juices, or other recipes to increase your calcium intake. Eggshell powder is a great source of calcium and is also rich in other minerals like magnesium and potassium.

Diy calcium supplements

Art and Crafts

Eggshells can be used in a variety of art and craft projects. For example, you can paint or dye eggshells and use them as decorative accents or jewelry. You can also use eggshells to create mosaics or other intricate designs. Eggshells can be a fun and eco-friendly material to work with and can add a unique touch to your creative projects.

Art and crafts


1. Are eggshells biodegradable in compost?

Yes, eggshells are biodegradable in compost. They will break down over time and provide valuable nutrients to the soil. 

2. How long does it take for eggshells to biodegrade?

Eggshells can take anywhere from several months to a year to fully biodegrade depending on the conditions. But they will start to break down quickly in a compost pile.

3. Can eggshells be used as a natural fertilizer for plants?

Eggshells can be used as a natural fertilizer for plants. They are a good source of calcium which can help promote healthy growth and prevent blossom-end rot in tomatoes and other plants.

Final Thoughts

Eggshells demonstrate a high biodegradability potential towards the environment. The natural decomposition of eggshells relies on a variety of factors including environmental conditions, processing methods, and the presence of contaminants or additives. Despite their protective coating, microbial activity in favorable environments can break down eggshells over time. With proper management and control of these factors, eggshells can be utilized as a sustainable and eco-friendly material in the agriculture, construction, and packaging industries. Increasing awareness about sustainable practices and the application of eggshells will ultimately support a more comprehensive waste management plan to lessen environmental impact.


Todd Smith is a trained ecologist with five years of experience in environmental conservation and sustainability. He has a deep passion for promoting sustainable practices and has developed a thorough understanding of the natural world and its complex interconnections.

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