October 20, 2009 | General

Focusing On Waste As Resources

BioCycle October 2009, Vol. 50, No. 10, p. 43
Climate Change Connections
Sally Brown

I AM at a biosolids conference in Texas listening to the miracles of ATAD, advanced thermophilic aerobic digestion for wastewater. You pump so much air in that the wastewater gets really hot and all of the organics turn right into CO2 and disappear. What could be better? Also with this process a lot of the nitrogen turns right into ammonia and volatilizes too. No problems with excess nutrients. What could be better?
I was at another meeting recently, a tour of one of the King County, Washington wastewater treatment plants with people from the Gates Foundation. Talk turned to the new plant under construction. It is being built using a membrane bioreactor, a very innovative technology that makes very clean, very low nutrient water. It is also a high energy system. The Gates people are very confused. They are trying to develop treatment systems that conserve nutrients and use as little water and power as possible. Nutrients are a resource for them; the fixed carbon also is a resource. These are not things you throw away. These are things you try to conserve.
All together, from these two recent meetings and at many others, I’ve come to realize a basic truth of greenhouse gas (GHG) accounting. On a fundamental level, GHG accounting goes way beyond figuring out how much gas you emit. It even gets past calculating nitrous oxide emissions from combustion. I am not saying these aren’t important to consider. What I am saying is that to truly get at the heart of what we need to do to reduce carbon emissions, we need to revisit and alter some of our basic assumptions.
All of the waste management industry (the name of the industry says it all) is based on making things disappear. The basic deal with solid waste is that we want someone to come pick it up and not put it down. For wastewater we want to take all the stuff that has gotten into the water and make it leave. But if we want to really reduce our GHG emissions and live sustainably, we need to recognize that we have to replace waste disposal industries with resource conservation industries. We also need to stop generating so much stuff in the first place.


The atmosphere is full of nitrogen gas – 77 percent or so in fact. Plants can’t use nitrogen gas to grow. It has to be transformed into fixed or mineral nitrogen in order for plants to use it. Nitrogen is fixed by soil organisms or can be manmade using the Haber Bosch process. Many wastes have high nitrogen content. And the nitrogen is in a fixed form that plants can use. Fixed nitrogen is not a waste product.
Manmade nitrogen, on the other hand, costs 4 units of CO2 for each unit of nitrogen fixed. The heart of the green revolution that has prevented large-scale starvation in the 20th century was synthetic fertilizers. Today, fertilizer N is in short supply. Instead of treatment processes to turn it back into gas, we need to focus on conserving and using this resource.
The point is especially clear with phosphorus. Each unit of synthetic P requires about 1.75 units of CO2 to produce. More importantly, we are looking at running out of our reserves of P in about 30 to 50 years. Try and grow a plant without phosphorus, try to operate your body without phosphorus and you will see that this is a resource to be conserved.

Then you can start considering the fixed carbon – the organic component of solid waste. The only way we know to fix carbon is through photosynthesis. We don’t actually know how to do this. We only know that plants do this. All of the fixed carbon that we have is from atmospheric CO2 that plants have turned into solid form. (That is not completely correct, as inorganic carbon and the carbonate cycle also account for a significant fraction of fixed carbon but for the purposes of this column I am going to ignore that). The fossil fuel reserves come from plant biomass. Your plastic bags and cardboard containers came from plant biomass.
Each year plants fix a certain amount of carbon from the atmosphere and turn it into solid form. Each year a certain portion of that fixed carbon decays and turns back into CO2. We have accelerated that release and decay by burning fossil fuels. We are also accelerating that release and decay by not taking advantage of the fixed carbon that we have that is currently called waste. Appropriate use of residuals, as an energy source, as a source of carbon for soils, as a substitute for fossil fuel based organic products, offers the potential to substantially reduce our carbon footprint. Recognition of this resource is not going to occur until we stop viewing this stuff as waste and having a range of industries based on making it go away. Those need to be replaced by a range of industries that optimize the value of this resource.
Our waste disposal industries have prospered from our luxury of excess. We love to get lots of stuff (a technical term for both the excess in your garage and the precursor to waste). The stuff comes from all over the place and it comes to us wrapped in more stuff. When we get tired of the old stuff or just want some new stuff, the old stuff and the packaging from the new stuff gets tossed. Thinking of where it goes and the implications of all that stuff have not entered into our collective conscious. With the stuff that we toss, we have been able to afford to yield to the yuck factor instead of the potential resource factor because of our ability to always get more. Greenhouse gas considerations as well as considerations of resource limitations suggest that the days of this type of mindset are limited.
EPA has recently realized this. As of January 18, 2009, the Office of Solid Waste changed its name to the Office of Resource Conservation and Recovery. EPA has also realized this by coming up with a new way to categorize our GHG emissions ( In its report, “Opportunities to Reduce Greenhouse Gas Emissions through Materials and Land Management Practices,” EPA presents a more comprehensible way to understand why the per capita GHG emissions in the U.S. are so high. Instead of the normal categories – fuel use, electricity use, landfill emissions, etc. – the report divides things into categories based on materials and land management practices. Viewed this way, management of stuff accounts for 42 percent of the GHG emissions in this country. Management includes the whole life cycle of stuff, from manufacture, getting it from the store to your closet, and then eventually getting it to the landfill.
By understanding the full implications of stuff, we have the potential to significantly reduce our carbon emissions. This requires a two-part change in mindset. The first involves recalibrating our understanding of what we actually need, and what the true costs of things are, aka get less stuff. Lifecycle analysis can be used to achieve that understanding. The second part, and what this column focuses on, is an understanding of how to maximize the recognition of the value of the remnants of stuff, heretofore called waste. From now on, refer to it as a resource.

Sally Brown – Research Associate Professor at the University of Washington in Seattle – is a member of BioCycle’s Editorial Board, and authors this regular column on the connections of composting, organics recycling and renewable energy to climate change. Email Dr. Brown at

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