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第一段
1 .Listen to part of a lecture in an Environmental Engineering class.
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第二段
1 .At the end of yesterday's class, we were discussing landfills and hundreds of millions of tons of everyday garbage which are deposited into them each year in the United States.
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2 .It's a growing problem.
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3 .Quite simply we're running out of space to put our garbage.
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4 .And this is especially true for solid organic waste: food scraps from home or food processing plants, waste from farms that sort of thing.
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5 .Did you know that two-thirds of the waste sitting in our landfills is organic material?
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6 .We have government recycling programs for materials like plastic, glass and metal.
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7 .Yet wide spread solutions for organic waste materials haven't really been addressed in the United States.
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8 .I think this is just asking for trouble in the future.
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9 .So, today I want to talk about a technology that offers a potential solution to the problem: anaerobic phased solids digestion or APS digestion.
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10 .First of all, what does anaerobic mean? Anyone?
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第三段
1 .Without oxygen?
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第四段
1 .Correct. APS digestion uses anaerobic bacteria, ones that thrive in the absence of oxygen, to consume, to break down organic material.
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第五段
1 .Excuse me, Professor, um, those anaerobic bacteria you're talking about, well, aren't anaerobic bacteria also used in wastewater treatment plants?
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第六段
1 .Yes, in fact, they are.
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2 .Would you like to explain this to the class?
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第七段
1 .Sure, so, when wastewater is treated, one of the by-products is a thick liquid called sludge.
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2 .And aren't anaerobic bacteria used to break down the sludge?
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第八段
1 .That's right. Anaerobic bacteria have been used in wastewater treatment for decades.
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第九段
1 .So how was this technology different?
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第十段
1 .Good question.
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2 .Uh, the anaerobic digestion systems used in wastewater plants are designed to treat sludge not solids.
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3 .Now, in the past, researchers have attempted to treat solid organic waste with that same equipment but there was always problem.
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4 .In order to process solid waste, the kind we find in landfills, you had to pre-treat the solids to turn them into sludge:
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5 .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.
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6 .But that extra step took time and required a lot of energy.
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第十一段
1 .That sounds like it would cost a lot.
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第十二段
1 .That's right. But APS digestion is designed specifically to handle solid waste so it's much more cost-effective.
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2 .The new technology processes organic waste in two phases.
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3 .Remember, APS stands for anaerobic phased solid digestion.
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第十三段
1 .First, the waste material is loaded into a large closed container along with different types of anaerobic bacteria.
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2 .The bacteria break the solids down into acids and hydrogen gas.
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3 .The hydrogen is extracted and the remaining acids are transferred into a different container for the second phase of the process.
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4 .There another type of bacteria converts the acids into methane gas.
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第十四段
1 .Aren't hydrogen and methane gas bad for the environment though?
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第十五段
1 .The answer in this case is no because they don't escape into the atmosphere.
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2 .The gases are captured and can be burned to produce electricity which saves a lot of money and ultimately decrease our need for fuels like petroleum and coal which are not only expensive but are also polluting.
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第十六段
1 .So organic waste from landfills could be processed this way?
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第十七段
1 .It's certainly one possibility.
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2 .And APS digestion systems are very versatile.
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3 .They can be installed just about anywhere.
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4 .See, anaerobic digestion systems used in wastewater treatment plants are huge tanks that hold thousands of gallons of wastewater.
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5 .But the APS container is small enough to be set up on site where the waste is generated, like, uh, food processing plants or on farms.
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6 .So garbage doesn't have to be transported long distances.
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7 .As a matter of fact, a couple of universities successfully set up demonstration projects.
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第十八段
1 .They collected food scraps from dining halls and local restaurants and processed them in APS facilities.
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2 .Not only did the universities save money, we're also learning even more about the APS process.
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3 .What's the next step forward?
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4 .Well, APS digestion uses several different types of anaerobic bacteria, right?
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5 .So what are the most efficient bacteria in the process?
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6 .If researchers can figure that out, the highest performing bacteria mix for a system could be determined.
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7 .Ultimately, the goal would be to grow enough of these particular bacteria to support large-scale commercial APS systems.
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