Listen to part of a lecture in an environmental engineering class.
Professor: At the end of yesterday's class, we were discussing landfills and the hundreds of millions of tons of everyday garbage which are deposited into them each year in the United States.
It's a growing problem!
Quite simply, we are running out of space to put our garbage.
And this is especially true for solid organic waste: food scraps from home or food processing plants, waste from farms, that sort of thing.
Did you know that two thirds of the waste sitting in our landfills is organic material?
We have government recycling programs for materials like plastics, glass and metal, yet widespread solutions for organic waste materials haven't really been addressed in the United States.
I think this is just asking for trouble in the future.
So today I want to talk about a technology that offers a potential solution to the problem—Anaerobic Phased Solids digestion, or APS digestion.
First of all, what does anaerobic mean? Anyone?
Student: Without oxygen?
Professor: Correct! APS digestion uses anaerobic bacteria, ones that thrive in the absence of oxygen, to consume, to break down organic material.
Student: Excuse me. Professor.
Um... those anaerobic bacteria you are talking about... well, aren't anaerobic bacteria also used in waste water treatment plants?
Professor: Yes. In fact they are.
Would you like to explain this to the class?
Student: Sure! So when waste water is treated, one of the byproducts is a thick liquid called sludge.
And aren't anaerobic bacteria used to break down the sludge?
Professor: That's right.
Anaerobic bacteria have been used in waste water treatment for decades.
Student: So how is this technology different?
Professor: Good question.
The anaerobic digestion systems used in waste water plants are designed to treat sludge, not solids.
Now, in the past, researchers have attempted to treat solid organic waste with that same equipment.
But there was always a problem.
In order to process the solid waste, the kind we find in landfills, you had to pretreat the solids to turn them into sludge.
First, by breaking the material apart mechanically into small particles and then adding a lot of water until you got a kind of thick, soupy mix that the equipment could handle.
But that extra step took time and required a lot of energy.
Student: That sounds like it would cost a lot.
Professor: That's right.
But APS digestion is designed specifically to handle solid waste.
So it is much more cost-effective.