by Sally Brown, University of Washington

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

1. The characterization of feces and urine: A review of the literature to inform advanced treatment technology

2. Systematic review of greenhouse gas emissions for different fresh food categories

3.Plant-based diets add to the wastewater phosphorus burden

4.Review of black soldier fly (Hermetia illucens) as animal feed and human food

5.Reducing climate impacts of beef production: A synthesis of life cycle assessments across management systems and global regions

We are about to embark on eating season.  Halloween and candy followed by Thanksgiving and with the bird and the sides and then the holidays with potato pancakes if those are you passion and/ or holiday cookies, roasts and cakes.  The expression ‘you are what you eat’ is well known.  Well, this month we address our own special version of that saying: ‘We are what we pass’.  I just made that up in case you were wondering. 

The library this month is in honor of the upcoming eating season and focuses on our own contributions to the wastewater system and how what we eat impacts our urine, feces, the wastewater process and the planet.  Call this light reading for a highly specialized audience. 

The first article is a general review of the characteristics of our pee and poop.  It turns out that quantity and moisture content of poop is as varied as the different poop emojis. 

poop

The average person in a well off country produces 126 g of poop per day (wet weight) with quantities ranging from 51- 796 g.  The dry weight of that is 28 g with about 50% of that dry weight consisting of dead and living microbial biomass.  If you are from a low income country your daily production is higher- a mean of 250 g per person per day with a range of 75-520 g.  The dry weight also increases with a mean of 38 g and a range of 18- 62 g per person per day.  The difference is fiber.  People in low income countries eat more fiber than we do and so poop more and wetter.  For those with constipation concerns this quote from the paper may be of help : Non-degradable fiber undergoes minimal changes in the digestive tract as it is relatively un-fermentable and shortens colonic transit time (Bijkerk et al., 2004).  Another bit on fiber is that digestable fiber such as oat bran and cabbage will increase fecal weight and moisture content.  There is also a discussion of how many movements per day are normal. 

The paper also has a table with reported nutrient and metal content of feces.  For example the reported P content ranges from 0.35- 2.7 g per capita per day.  Average compositon on a wet weight basis also includes 5% C and 0.7% N.  The paper further details urine quantity and composition.  Fascinating reading.

From there we take a step back to a much wider lens.  The paper gives approximate values for the carbon intensity of different types of food.  As more and more of us become aware and concerned about climate change, changing our diets is a tool that each and every one of us can embrace now.  No need to build a wind turbine in your front yard.  Just eat less meat and more nuts.  Or legumes.  If you do eat meat make it pork or chicken, not beef or lamb.  This is a paper that gives you the numbers behind Meatless Mondays (https://www.mondaycampaigns.org/meatless-monday).  I myself have not given up on beef.  Those steaks are just too good to let them go completely.  I just eat them less frequently and don’t have as much when I do.  That puts me in the flexitarian category.  Here is a glimpse of one of the many tables with a ton of data. 

table4

So think about fish over filets.  Tastes good, helps the planet and is potentially even better for you.

novfish

It turns out for those that go the whole way to strict vegetarians, their diet can have an impact on wastewater treatment.  Paper #3 discusses this impact.  If you skip the meat, vegetarian diets can increase the P load in wastewater influent.  The authors here focus on P loadings in the UK.  Peak P intake for people was in 1963 (1599 mg P pp-1 d-1) and has since decreased (1354 mg P pp-1 d-1).  Processed foods account for about 50% of this P.  If people adopt a low meat or vegan diet, the scenerio modeled in this study, P into treatment plants would increse by 17-35% over baseline.  That isn’t so good now is it.=

So how about we go really crazy?  Article #4 discusses what we know about using black soldier flies as a component of human and animal diets.  You can also use these little bugs to treat the wastewater to begin with.  Talk about having your cake and eating it too….

larva

I just happened to have some of the larvae in my freezer.  I’ve tasted these and they are no match for a good NY strip.  Not sure if we are ready to talk about eating them directly but as food for Fido- I am all in.  I say this as a dog owner and lover, not as a way to pass the larvae.  These critters are voracious and not at all picky eaters and can offer a great alternative for both waste treatment and for production of a high protein and fat food source (just not for my supper right now).

The library ends with an article on beef production and how to lower its carbon footprint.  There is a long way to go here so plenty of room.  One of the ways is through better use of manures and compost in field/ pastures that cattle are allowed to graze on.  The authors include Rebecca Ryals from UC Merced who did some of the seminal work on the Marin Carbon project.  She is now working on biosolids and one of her students presented this work in our on line Biofest a month ago.  Appropriate soil management and giving cattle access to soils and pastures can significantly reduce the impact of beef production.  And organics is a critical tool in that formula.

So enjoy the beginnings of this holiday season and remember ‘You are what you pass’. 

novsteak