By Sally Brown, University of Washington
Abstracts of these resources are available in the searchable Information Portal offered to Northwest Biosolids members.
Greener gas? Impact of biosolids on carbon intensity of switchgrass ethanol
Carbon accounting for compost use in urban areas
Creating topsoils and soil conditioners from biosolids and urban residuals
Municipal biosolids — A resource for sustainable communities
Biosolids and ecosystem services: Making the connection explicit
Sometimes it is good to remind yourself of what you get when you invest in research and researchers. As NW Biosolids is coming up to its annual budget process, this seems like a good time to see where those research dollars have gone. It also helps that I’ve had a good year in terms of publications. The library this month is all about benefits associated with the use of biosolids. The two main things that all of the publications have in common is that the work they present was supported in part by NW Biosolids and that I’m one of the authors. You will also note there are no mentions of COVID-19 or PFAS.
One of the things that I’ve focused on over the years is the carbon balance for different uses of biosolids. The first paper presents data from a multi-year field trial where we compared biosolids and synthetic fertilizers for growing switchgrass. Switchgrass has been touted as a ‘green’ source of feedstocks for ethanol. There are a number of papers that have shown that corn-based ethanol is not the answer- with high nutrient requirements, water requirements, and energy requirements to make fuel. Switchgrass, as a perennial crop with lower nutrient requirements, can be used to produce ethanol that has a much lower carbon intensity. Put this in your engine and you can really feel good. An aside here- this research was started before anyone knew who Elon Musk was and before the Model S Tesla had been released. We tested biosolids to see if we could make that ethanol even greener. We measured plant yield, chemical composition, and potential ethanol yield per acre. We also measured nitrous oxide emissions- the potential Achilles heel due to the high CO2e of N2O. Answer is- worked great, much better than using synthetic fertilizers. So if you are looking for a non-food chain crop - here is one option.
The 2nd paper also focuses on carbon accounting. Here we are going in the opposite direction of non-food chain crop; urban uses of biosolids composts. There are lots of ways to use composts in cities. In this paper, we considered using the biosolids composts for growing grass, trees, and vegetables. We also considered the less glamorous but also important use to control erosion and flooding on roadside right of ways. If you land-apply your biosolids, carbon accounting is a way to show how you are doing good for the planet- whether or not your crop is switchgrass. Composting with use by your actual ratepayers has its own benefits. If you’ve ever used biosolids compost to grow fruits or flowers, you know what I mean. Question is do you still sequester carbon? The short answer is yes - the longer answer is how much depends on who and how it is being used. It turns out that your most loyal customer, who regularly comes and picks up their own, applies it to their lovingly tended lawn, gives you the least benefit. The new developer, who gets it delivered by the truckload and puts it on the soil they nearly destroyed building those townhouses, will give you the most. An easy to read version of this article is also available in Biocycle, "Urban Compost Math - Calculating Carbon Offsets."
Taking urban use one step further, the third article reports on the work by Ryan Batjiaka who used biosolids from San Francisco and a range of residuals -based materials from the Bay area to make different biosolids based potting soils and topdress products. Class A biosolids are great but are typically not the product you want to distribute locally in a ‘cake’ form. Modeling his work on the success of the TAGRO program, Ryan set to mixing. He had panelists look and smell the mixes. He tested a range of soil chemical properties. He tried to germinate seedlings. And he grew petunias. Some of those petunias were lovely, others not so much.
He generally found that mixing the biosolids 50:50 by volume with a range of urban wood waste gave you a product that smelled good, looked good and grew pretty flowers. The woody material he used as low in contaminants, something that had been a big concern. A range of chars were too strong in the quantities he tested, up to 25% by volume. But these materials have potential for use at lower rates and even for making composts. Again - a version of this paper is also out in Biocycle, "Connections: What's Cooking."
The last two papers are more general, focusing on the benefits of biosolids. There was a special issue of a journal coming out with a focus on biosolids. Rolf Halden, University of Arizona, and not a known fan of the material was the editor. Somehow we managed to get two in there. The first is a general article on benefits of biosolids with a focus on use in the US. We talk about biosolids for agronomic crops and urban uses. It is a good, short, summary of benefits. The final paper takes a broader look at benefits. It considers biosolids and global sanitation in the context of the wide range of ecosystem services. We talk about soil health and how fundamental using wastes such as biosolids is to restoring soil health and the range of ecosystem services that provides.
I love what I do and really appreciate the support from NW Biosolids and other agencies. Hopefully you’ll love some of what that support gets you.