How AC FOX Works

An ethanol plant
An ethanol plant
Image courtesy U.S. Department of Energy

Imagine for a moment that you own a factory that makes ethanol fuel from corn. You are a large, industrial manufacturer of corn-based ethanol, and you can make 25 million gallons of ethanol a year.

Because gas prices are so high right now, and because the President and Congress have put a lot of emphasis on ethanol, and because GM is running their huge Go Yellow ethanol ad campaign, you should be sitting pretty. Unfortunately, you have a small problem.


The problem is the river of wastewater that corn ethanol creates. To understand this waste stream, think about the manufacturing process:

  • You take corn
  • You crush the corn
  • You mix the corn with water
  • You add enzymes (to turn the corn into simple sugars)
  • You add yeast
  • You let the yeast ferment the sugars to create alcohol.

So far so good. Now you distill the alcohol out of the water and create a gallon of ethanol that you can sell. That's great too.

The problem is that for every gallon of ethanol you sell, you also create 10 gallons of polluted water. The water that is left over after distillation is full of proteins, sugars, enzymes, bits of dead yeast cells and a little remaining alcohol. What do you do with this polluted water? And keep in mind that there are 10 gallons of polluted water for every gallon of alcohol that you create. So if you are making 25 million gallons of ethanol each year, you have to deal with 250 million gallons of polluted water. Since industrial ethanol plants typically range in size between 25 million and 100 million gallons of ethanol a year, and there are a number of these plants in the United States, you can see that ethanol wastewater becomes a big problem.

But the corn ethanol production process isn't the only manufacturing process that results in wastes and by-products. If you make biodiesel fuel, you get a by-product called crude glycerol that you have to deal with. If you have a food factory you may have a similar problem. Say you make pancake syrup or frozen pizzas, and you use water to clean parts of the assembly line. This water is now polluted, and the local sewage treatment plant may not want it. What are you going to do with it?

Now there's a completely new process available to handle water that is polluted with organic material like proteins, sugars, glycerol or even pizza debris. That process is called Activated Carbon Facilitated Oxidation, or AC FOX. AC FOX has huge advantages over the traditional ways of dealing with "organically contaminated waste streams."

In this article, you will learn all about AC FOX and how it can help manufacturers of a wide variety of products save money, help the environment and speed up their production lines. Let's take a look.


The Advantages of AC FOX

The Activated Carbon Facilitated Oxidation reactor, or AC FOX, is a way to use waste for energy. Learn what processes could benefit from it.
The Activated Carbon Facilitated Oxidation reactor, or AC FOX, is a way to use waste for energy. Learn what processes could benefit from it.

So let's go back to our ethanol factory. The factory creates 10 gallons of wastewater for every gallon of ethanol that it produces. The wastewater contains proteins, sugars, enzymes, DNA fragments and a little left-over alcohol.

How do you get rid of this wastewater? Ethanol plants today usually handle it by evaporating the water and making animal feed from the solids that are left behind. The sale of the animal feed does not cover the cost of evaporating the water, but it does solve the wastewater problem.


Another way to handle the wastewater is to treat it like sewage. Let's look at the sewage approach, since that can be applied to all waste streams that we are talking about. With sewage, you let the water stand in large tanks or holding ponds and you let bacteria eat all the organic material in the water. That works, but there are three problems:

  1. The process often takes a lot of space
  2. The bacteria are slow
  3. The process completely ignores the fuel value of the wastewater

The third problem is key. Any stream of wastewater contaminated with lots of organic material like sugars and proteins can be thought of as a waste fuel. If you could somehow burn this fuel, you could use the resulting heat to do all sorts of things. You might use the heat in part of your manufacturing process, or use it to generate steam and make electricity. One great thing about this heat is that it would be free. Currently you are letting the bacteria eat that fuel, and it is all going to waste.

It turns out that, up until this point, burning wastewater has been impossible. Imagine trying to burn pancake syrup. Pancake syrup contains a huge amount of energy because of all of the sugar, but up until now there has been no way to "burn" it because the water in the syrup makes burning impossible. Even if you dehydrate the syrup and try to burn the dry sugar, it doesn't burn very well.

AC FOX completely changes the equation. The goal of AC FOX is to quickly and efficiently "burn" all of the fuel in any stream of organic wastewater. With AC FOX you can, in fact, "burn" pancake syrup and capture all the heat. You can also "burn" the effluent from your ethanol factory, or glycerol, or water with lots of pizza crumbs dissolved in it. Any organic wastewater stream turns from "sewage" (which is a problem) into "fuel" (which is cool) if you have an AC FOX reactor in your factory.

By "burning" your wastewater, you now have an asset instead of a liability. You can use the free heat created by the AC FOX reactor anywhere in your factory. You can also immediately reuse the water, because it is clean. And you also speed up the whole process. Instead of letting the wastewater stand for days in a settling pond or bacterial digestion tank, you can "burn" the wastewater quickly, as soon as you create it.

Now you can understand why manufacturers are starting to get so excited about AC FOX. Next, we'll see exactly how it works.


How It Works

The core idea behind AC FOX is both ingenious and remarkably simple. You start with a big, rotating tube. The size of the tube depends on the size of the waste stream you have. If the waste stream is small, the tube might be the size of an office desk. If your waste stream is huge, the tube could be as big as a tractor trailer.

You then fill the tube with activated carbon. Activated carbon is nothing but charcoal that has been "activated" to give it more surface area. It's the black granules that you find in aquariums and gas masks, and it's a completely safe, organic product.


The tube is motorized so that it rotates and stirs the carbon granules. This rotating tube full of activated carbon is the AC FOX reactor.

Now you take your wastewater stream and inject it and a source of oxygen (typically air) into the reactor. What happens next is the key to AC FOX. Here are the steps:

  • The activated carbon has a huge surface area (5 million square feet per pound), and that surface area grabs hold of all of the organic molecules in the wastewater that you injected.
  • Because the reactor is hot, the oxygen that you injected wants to react with something.
  • All those organic molecules trapped on the surface of the carbon granules are an easy target for the oxygen atoms inside the reactor.
  • The oxygen reacts with the organic molecules.

The reaction is very fast, and it produces three things:

  1. Carbon dioxide and water vapor from the reaction of oxygen with the organics
  2. Lots of heat, which boils off the water in the wastewater and keeps things hot
  3. A little ash containing mostly nitrogen and other inorganics in the waste

The ash is a great fertilizer, and the excess heat can be used anywhere that you need it in your factory. Or, you could use the heat to generate steam and drive an electric generator.

With an AC Fox reactor, we have taken what used to be sewage and we have turned it into fuel.

The AC FOX reactor can do even more. It turns out that there are lots of places in factories that use activated carbon for filtering. Refineries, for example, use lots of activated carbon in their filters. The carbon granules do their filtering by adsorbing and holding onto molecules (see How Gas Masks Work for details). Once the carbon granules in a filter get "full," you have to either throw them away or "reactivate" them.

With AC FOX, you have a reactor that is perfectly suited to reactivating carbon. You load the reactor up with spent activated carbon, let the AC FOX reactor do its normal thing, and then take the carbon back out a day later. The newly reactivated carbon is ready to go back into the filter. This ability to reactivate carbon can also save factories a huge amount of money.

If you have a factory or process that currently produces a stream of organic wastewater, you are probably dealing with the wastewater as "sewage". If you use an AC FOX reactor instead, the wastewater turns into "fuel":

  • You "burn" all the organics in the wastewater in a bed of activated carbon and capture the heat from the reaction.
  • The heat comes out in the form of steam, which you can use anywhere in your factory.
  • After using the heat, you can condense the steam and reuse the water in your manurfacturing process.
  • In addition, you can use your AC FOX reactor to reactivate carbon for filtration.

AC FOX is a great way to turn lemons into lemonade.

AC FOX has an estimated payback period of less than two years. If you can use the AC FOX reactor to reactivate carbon as well, the payback period is even shorter.

AC FOX is the invention of Hugh McLaughlin, Ph.D. The AC FOX reactor is currently being used several factory environments and licensing rights are available. You can learn more by visiting

For additional information on AC FOX and related topics, please see the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links

  • AC Fox
  • The History Channel's Modern Marvels Invent Now Challenge
  • Hot Idea -- the Boston Globe, May 6, 2006