circular economy

By Sally Brown, University of Washington

Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.

  1. Environmental Engineering fo the 21st Century: Addressing Grand Challenges

  2. Transition towards circular economy in the food system

  3. Recirculation of human-derived nutrients from cities to agriculture across six continents

  4. Phosphate and potassium recovery from source separated urine through struvite precipitation

  5. Feeding the Corn Belt: Opportunities for phosphorus recycling in U.S. agriculture

Billy Preston likely wasn’t thinking about the circular economy back in 1972 when he sang ‘Will it go round in circles’ but that is the song that came to mind as I assembled the articles for this library. Too often with this library I have to focus on the you need a microscope to be able to see it level.  Here I am talking about the part per trillion contaminants that people worry about.  This month we go up several thousand feet to provide some perspective on the broader implications of what you all do and provide.  The term circular economy refers to understanding the value in wastes.  Instead of our traditional acquire use and dispose, a circular approach replaces dispose with repurpose reuse and recycle. Understanding and explicitly designing the value of the ‘waste’ material into the cycle of things is the key to the term circular economy.  Some of you may already have an inkling of how this applies to biosolids and composts. 

The first paper in the library is a new report from the National Academy of Sciences on challenges for environmental engineers.  While circular economy is not in the title of this report it is all over the challenges that the report focuses on:

1: Sustainably supply food, water, and energy
2: Curb climate change and adapt to its impacts 
3: Design a future without pollution and waste 
4: Create efficient, healthy, resilient cities
5: Foster informed decisions and actions 

vertical agricultureThe report is an interesting easy read and many of the points made tie into residuals and wastewater.  For example, reading about vertical agriculture made me immediately think about setting up these farms next to treatment plants for use of effluent. 



There is a discussion of water use by continent.  Also on sources of water including grey water and reclaimed water.  Big section on food waste.  Green infrastructure brought to mind uses for composts.  The discussion is not fully US centric and so it is also interesting to consider these issues in a global context.  There is also the section on adapting to climate change with associated changes in sea levels and frequency of flooding.  This is something all plant managers have to deal with. Ecosystem resilience is another section - we know that biosolids and compost are part of a solution here.  The chapter entitled ‘Design a Future Without Pollution or Waste’ is also pertinent and ties directly into the concept of a circular economy.  Much of this is stuff that we do and think about on a daily basis but it is very nice to have a glossy publication from NAS that recognizes it.

The next article continues on in a similar vein with a focus on the circular economy in terms of our food system.  Here it is in a nutshell:


A critical portion of a circular food system is appropriate management of waste materials.  Here is a sentence from the paper: The potential solutions identified in this paper related to nutrient cycling include recovering nutrients from manure, recovering and reusing nutrients in sewage sludge, cascading use of materials, as well as supporting local farms and de-specialized agricultural holds (Table 1).  Granted, they say ‘sewage sludge’ and not biosolids.  Table 1 focuses on P recovery from wastewater.  However, it is still nice to see biosolids as part of a solution in a broad issue paper on food systems.

The meat of the library starts with article #3 - thanks to Bill Toffey for this one.  This article takes the notion of a circular economy as it pertains to food systems and applies it directly to wastewater and nutrient recovery.  The authors have calculated how far the nutrients from wastewater have to travel to satisfy agricultural needs in cities across the world.  They consider form and density of the nutrients.  Reclaimed water does not store easily and is very low in nutrient density and so does not lend well to long distance transport.  Vertical farming near the treatment facility would be a perfect end use!  They talk about the ratios of N, P, and K and what crops would be best to grow to take advantage of the balance.  Olives in Rome are an example of a crop with high nutrient demand that would make sense to grow near the city to take advantage of the proximity of nutrients.  The authors also talk about nutrient dense areas like New England where metropolitan areas overlap making citing of appropriate agricultural lands challenging.  The authors address crystal products from wastewater such as struvite as a potential way to make it easier to transport nutrients to farmland.  They mention potassium struvite in addition to ammonium struvite.  Potassium, while rich in urine, is so soluble that it typically exists the plant with effluent.  As a result, biosolids are low in potassium and reliance on biosolids for fertility will require supplemental fertilization with potassium over time.  This is a fascinating well done study.  The conclusion is that our wastes can meet a significant portion of our fertilizer needs.  Distances to do so in the US and Australia are typically greater than in Europe and Asia.  There is also supporting information which I am happy to send if asked.

The concept of potassium struvite as a way to capture the potassium before it exists the plant got my attention and that is the topic of the 4th paper.  It focuses on how you can make potassium struvite from urine.  If I let my husband see this one, I’ll be peeing into a jar for the rest of my days.  

The final paper in the library focuses on animal manure in addition to human manure. In understanding a circular economy it is critical to realize that we eat a fair amount of meat. The first and second papers in the library have some discussion of the energy intensity of producing meat and how eating less of it is better for the environment.  Do you have meatless Mondays in your house? In the meantime there is the rest of the week and lots of animal manure.  On a per capita basis a cow makes about 10x as much poop as a person.  The paper looks at whether the manure that we produce would be sufficient to meet the fertilizer requirements of the corn belt.  It turns out that only 37% of the P that we poop would be required to grow the corn: ‘Seventy-four percent of corn P demand could be met by recyclable P sources in the same county. Surplus recyclable P sources within-counties would then need to travel on average 302 km to meet the largest demand in and around the center of the ‘Corn Belt’ region where ~ 50% of national corn P demand is located. We find that distances between recyclable sources and crop demands are surprisingly short for most of the country, and that this recycling potential is mostly related to manure’.

I don’t know about you but this circular economy thing is sounding pretty good to me.