Wasted Energy?

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by Casey Furlong

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According to an EPA report (1), approximately 20% of all trash is managed using Waste to Energy (WtE). Most of us know this as incineration. The same report describes a considerable amount of that garbage consists of paper, plastic, metal and food scraps. Incinerating trash at a WtE plant as a method of municipal solid waste (MSW) management misses the opportunity to optimize resource recovery. It converts almost everything to heat and ash. Food consists mostly of water, so does it make sense to burn it?

WtE

Government officials in charge of improving recycling rates have a difficult task, especially in areas that have WtE plants, which require a constant supply of trash. However, officials may be surprised that a facility’s generating capacity won’t be significantly diminished if some or all of the food scraps are eliminated from the trash.

Moisture in food inversely correlates to heating value of MSW

A paper titled “The Effect of Food Waste Diversion on Waste Heating Value and WtE Capacity(2)” evaluated how heating potential of garbage changed as increments of food waste were removed prior to being disposed of in an incinerator. The authors found by removing just one quarter of the food scraps (7.3% of the total trash), the heating value per ton of incoming trash reduced by 3.4%. The affect is nearly linear with 50%, 75% and even the unlikely 100% diversion of food scraps from the landfill.

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If a community was to redirect all of their food scraps to anaerobic digestion and composting, there would be almost 30% less trash being burned at the WtE facility, but only a 14% reduction in heating value. So, the overall amount of energy generated is less, because less garbage is incinerated. However, the amount of energy per ton of garbage is actually higher without food waste. The moisture content contributed by food inversely correlates to the heating value of general MSW.

Starving a landfill after starving an incinerator

In order to avoid an expensive service shut-down and power supply interruption before the incoming trash runs out, the authors suggest officials redirect certain waste streams from landfills to make up tonnage shortfalls. Starving a landfill after starving an incinerator — now that’s a conclusion I agree with.

(1)United States Environmental Protection Agency. 2015. Advancing Sustainable Materials Management: Facts and Figures 2013. http://www.epa.gov/waste/nonhaz/municipal/pubs/2013_advncng_smm_rpt.pdf

(2)LoRe, Anthony M. and Harder, Susana Harder. 2012. “The Effect of Food Waste Diversion on Waste Heating Value and WtE Capacity.” 20th Annual North American Waste-to-Energy Conference 2012. http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1716375

Casey Furlong is an Environmental Specialist for InSinkErator. With an extensive background in landfill engineering, Casey has designed, permitted, constructed and operated municipal solid waste landfills and large-scale food and landscape waste compost facilities. He is a certified landfill manager in Wisconsin and registered professional engineer in the states of WI, IL and IN.

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Elemental Composition of Biosolids vs. Soil

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Center for Urban Horticulture, University of Washington. 2002. “Using biosolids for reclamation and remediation of disturbed soils.” Plant Conservation Alliance, Bureau of Land Management, US Department of Interior, U.S. Environmental Protection Agency. Special thanks to Ned Beecher and Chuck Henry

 

Better than dirt

As I mentioned in my post last month, biosolids are the byproduct of wastewater treatment and are processed to reduce pathogens, which results in a material that’s much different than human waste. Biosolids are comprised of the remaining cell walls of microorganisms left over from the treatment process, as well as the organic biomass remaining after digestion. On an elemental level, the composition is somewhat similar to soil. Except it’s better.

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The main difference between biosolids and soil is that biosolids have more Carbon and less Silicon. It also has more Nitrogen and Phosphorus. So not only are biosolids good fertilizer, the organic content of biosolids actually helps to replenish soils by adding more carbon.

Biosolids also help soil retain more water. Replacing carbon and improving the moisture holding-capacity of soils reduces the negative impacts of erosion, a challenge for all farmers.

Contrary to what people think, biosolids are a lot more (and less) than a bag of waste.

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The Boundaries of Biosolids

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Have you ever considered doing something completely out of bounds? How about eating a strange animal while visiting another country? What is taboo in the U.S. may be perfectly acceptable in another country, and vice versa. Personal boundaries not only vary from person to person, they are often different in other parts of the world.

Last month I took part in the Wetskills student competition at the Milwaukee Water Summit co-sponsored by UW Whitewater and the Kingdom of the Netherlands. The event encouraged students to develop innovative solutions for water challenges posed by case sponsors. It featured a number of Dutch students and wastewater professionals and provided a great opportunity to connect people of different backgrounds. Today people are more connected than ever via the Internet and social media, so knowledge sharing between peoples of different cultures transcends geopolitical boundaries. Today I’d like to discuss a boundary in the environmental realm most rarely consider.

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Wetskills Water Challenge – Alisa Doornhof, Michael Keleman, Nould Kuilder, Paul Proios

Many people are unaware of what happens to our waste after we flush, and take it for granted that it will disappear and never return. But the remaining byproduct of wastewater treatment – biosolids – must be managed. In the U.S. over half of all biosolids generated by water resource recovery facilities are beneficially reused, such as being used for land application as fertilizer. Most end up on corn and soy bean fields. In the Netherlands, however, land application of biosolids is not practiced and is considered unacceptable, largely because of the fear of pathogens (disease-causing organisms). In the United States, to meet Class A pathogen reduction requirements, biosolids must contain less than 1000 fecal coliforms/gram of solids. Class B requirements are much higher – 2,000,000 fecal coliforms/gram of solids.

Biosolids are the byproduct of the wastewater treatment plant but are explicitly processed to reduce pathogens so that they are much different than “humanure.” Biosolids are basically comprised of the remaining cell walls of microorganisms left over from the treatment process as well as whatever organic biomass remains after digestion. Much of the organic material has been degraded, in many cases by as much as 40-50% (measured as volatile solids destruction). For comparison, biosolids are very similar to soil on an elemental level. The main difference is that biosolids have more Carbon and less Silicon, as well as more Nitrogen and Phosphorus. The next post will show this in graphical form.

Pathogens have been significantly reduced in the treatment process; much more than manure from hogs, poultry and cattle in the agricultural sector, which has been used for centuries around the globe. Yet there is so much fuss across boundaries regarding the beneficial reuse of biosolids. Isn’t it just a superior fertilizer?

 

 

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