How Indoor Automatic Composting Systems Work

Indoor automatic composters let you turn your scraps into fertilizer inside your house.
Indoor automatic composters let you turn your scraps into fertilizer inside your house.
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If one man's trash is truly another man's treasure, then there are about 250 million tons of waste produced by Americans alone each year that are just waiting to be turned into riches [source: EPA: Waste]. It's not necessarily the cents and dollars type of wealth, but rather assets that can improve the environment.

As it stands, though, only a third of the waste produced annually in the United States is repurposed for such efforts, either through recycling -- which applies to paper, plastic, glass and metal-based products -- or composting, which reuses solid wastes such as kitchen scraps and yard clippings [source: EPA: Waste]. The process of composting is fueled by microorganisms present in soil that help break down organic materials within the waste, which is then converted into a fertilizer that can be used on lawns and gardens.

Traditionally, home composting systems have been outdoor ventures involving piles or heaps. Although this method offers more flexibility in terms of the amount of material that can be added at any given time, the process itself is one that requires constant maintenance, including keeping the pile moist and turning it regularly. However, indoor automatic home composting units have now been introduced to provide an easier way to get involved with the composting process and maintain it long-term.

In this article, we'll examine what makes an indoor automated composting system tick, from understanding the technology behind how they operate to getting a sense of what they actually look like and how much room they take up. Also, we'll look into how effectively these units perform the task at hand while sidestepping potential, unpleasant side effects, such as overpowering odors or costly upkeep. Finally, we'll review the bottom line: Do the requirements for maintaining such a system outweigh the potential benefits to the environment, or could the widespread use of these machines indeed make the world a better place?

Home Composting Basics

To understand how indoor automatic composting systems came to be, it's important to first get a sense of some outdoor home composting system basics. There are several large-scale approaches to outdoor composting, such as field, sheet and trench methods, but these are typically used in local communities or on a county or state level as an alternative to landfills.

When composting at home, you should begin by selecting a dry spot outdoors, ideally near a source of water. The size of the spot depends on how large of a pile you want to create or how big of a bin you want to use. Regardless, once the location is determined, the basic ingredients needed are the same:

  • Brown materials (such as broken branches and dry leaves) provide carbon
  • Green materials (such as vegetable and fruit scraps, grass, coffee grounds) provide nitrogen
  • Water helps the materials break down

[source: EPA: Compost]

One method is to mix the brown and green materials simultaneously while making sure to moisten anything that's dry, then covering it up with a tarp once complete. Another approach is to layer the ingredients starting with a 6-inch heap of the brown materials, followed by 3-inch layers of green then brown, and mix the pile around about once a week.

It can be anywhere from a month or to as long as a year or two before the compost is ready to be used. The time depends on a few factors, including:

  • Size of pile or bin at onset
  • How often new ingredients are added to the mix
  • Frequency of turns (usually done with a pitchfork or shovel), which helps the microorganisms break down the material

Once you have the basics of manual home composting down, it may be easy to understand why the automated method was created. Read on to find out what's involved in these systems.

Nuts and Bolts of Automatic Indoor Composters

Getting a traditional outdoor composting system to run efficiently at home can be a tricky process. You have to consider the initial construction of a compost, figure out how to keep the ingredients balanced, make sure piles are correctly cultivated and be aware of climate conditions, just to name a few. That's why automatic indoor composting systems were developed.

First things first: Let's take a look at the pieces involved a standard automatic indoor composting system and how they work together. Most automatic indoor composters are made up of the following key components:

  • Hopper -- the first "holding area" for added wastes before depositing materials into subsequent chambers below
  • Motorized mixing wand -- turns mixture continuously
  • Built-in heater -- keeps mixture at optimal temperatures, which helps accelerate the speed of the composting
  • Air pump -- draws in oxygen flow to "feed" microorganisms in soil
  • Carbon filter -- helps to absorb odors from waste
  • Cure tray -- collects fertilizer produced from composting process
  • Drip tray -- collects any excess liquid

To operate a unit, you should first deposit the wastes into the machine, which usually involves just lifting a hinged lid at the top. Depending on what type of unit you use, you also might need to add regular soil and sawdust pellets, along with a small amount of baking soda, which is often recommended to help balance acidity levels.

Wastes are then dropped into a preliminary internal chamber that takes care of heating, mixing, and aeration. The fertilizer that results is then deposited through a second chamber into a cure tray that can easily slide out. Most automated models also feature a control panel on the front that allows users to adjust the settings.

The cycle generally takes 10-14 days to complete. This is significantly faster than most outdoor home methods, which can take months or even years to complete. But the overall output from indoor systems is smaller than those outdoors (cure trays will hold up to about 5 pounds of waste before needing to be cleared).

Now that you understand the basic parts involved in an automatic indoor composter, read on for some pros and cons to decide whether a system might be right for you.

Pros and Cons of Automatic Composters

Many automated indoor composters can accommodate up to 120 pounds (55 kilograms) of waste per month [source: Nature Mill]. However, along with the benefits of these units also come a few drawbacks. There are the usual maintenance issues, such as strong odors, additional energy usage and costs, and loud noises during operation. Plus, you need a compact way to house all the necessary parts, in addition to an accessible yet out-of-the-way place to store it.

Most automatic indoor composting systems are encased in some sort of stainless steel and aluminum combination, though many also feature plastic elements (often made from recycled materials). Newer models are quite sleek in their overall design, resembling a large, modern coffee pot, espresso machine, or slow cooker. Units tend to weigh between 10 to 20 pounds (4.5 to before composting. They generally take up about as much space as a kitchen garbage can (or about 20 inches in height and depth and 12 inches wide), though some models can actually be installed in cabinets, similar to trash compactors that slide in and out to blend in with your cabinetry.

Automated composters are primarily intended for indoor placement within a kitchen, laundry or utility room, or garage, but if you don't have room for one, many can actually be used outdoors if you choose. If you do plan on using one indoors, you might consider one that offers thermal insulation along with airtight sealing to prevent one of the main drawbacks: foul odors escaping into your home.

Wherever you use your composting system, combating and controlling the smell they produce can be tricky. If an overpowering odor is present, it's usually a sign that the system needs more turning and aeration. The automated system should maintain aeration on an ongoing basis, but you may need to check the unit to be sure it is working properly. You might also consider using carbon filters within indoor units to keep the smell in check.

Another potential drawback to consider is the noise the systems make during operation. Whirring and snapping sounds at the onset of the composting cycle are typical, along with humming from the air pumps. Most units produce minimal noise once materials have been heated and the actual process is underway. Before you buy one, you might want to read product reviews to see what other people have to say about the noise particular units make.

Lastly, as with any other home appliance you own, you also should be mindful of general upkeep and maintenance. Many machines start out with a minimum one to three year manufacturer's warranty, though there are options for extending or additional coverage. You'll also need to know how often to change the air filters and carbon filters, as well as when to empty and clean the system.

If you think an automatic composter might be something you'd like to add to your home, read on to find out what it could cost you.

Indoor Composting Costs

Is an automated indoor composting system worth the investment? To get started, a potential user can expect an initial investment of $300 to $400 for a base unit. This is slightly less than the cost of some other household appliances, such as a lower-end dishwasher, but it's still a bit steeper than what you'd spend on a blender or toaster oven.

In addition to the initial cost and setup, you also need to consider the energy costs. You can expect to add about 5 kwh (kilowatt hours) per month to your energy bill. Depending on your local rates, this should only set you back about 50 cents [source: Nature Mill].

It's also important to point out that there are indeed cheaper indoor alternatives. One involves anaerobic composting, which involves a fermentation process aided by the use of a wheat bran-based powder. These types of units are also about the size of a wastebasket and run around $60-$80. The trade off is you lose the automation process, and therefore the maintenance requirements and odor potential are much higher [source: Foley].

Another indoor method centers on vermicomposting, which uses worms to break down the materials -- and that revelation alone might be enough to ward a person off. If worms don't make you squeamish (and keep in mind, we're talking about hundreds to thousands of them in one unit), this system costs about half of what an automated unit might cost, but offers little to no odor protection. You also face the risk of worms escaping from the unit [source: Foley].

So, if you want to take a step into the composting world, can afford the initial costs, and are prepared to put up with a few of the drawbacks, then adding an automatic indoor unit to your household might be the way to go. With more easy-to-use models now on the market, along with the technological advances developed to help keep odors and noises to a minimum, these machines offer an efficient way to help protect and improve the environment.

Learn even more about composting at home and elsewhere by visiting the links on the next page.

Related HowStuffWorks Articles


  • Foley, Michele. "Indoor Composting Systems: Garbage In, Garden Out." CHOW. (12/14/2009.)
  • Free Patents Online. "Composting Systems and Methods." (12/14/2009.)
  • Nature Mill. "How It Works." (12/14/2009.)
  • Nature Mill. "XE Model Instruction Manual." (12/14/2009.)
  • Patent Storm. "US Patent 5187097 - Composting system and composting method." (12/14/2009.)
  • Spivey, Angela. "Talking Trash." NC State Magazine (Alumni Magazine). (12/14/2009.)
  • U.S. Environmental Protection Agency. "Create Your Own Compost Pile (12/14/2009.)
  • U.S. Environmental Protection Agency. "Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2008." (12/14/2009.)