Restorative Faith in Biosolids!
New work on restoration with biosolids is the focus of the Research Update this month.
One of the first end uses for biosolids and other residuals was for the restoration of disturbed lands. This was tried on coal-mined lands in VA and PA way back in the 1970s and 1980s. It worked well, so well in fact that it became the cornerstone of many biosolids programs.
Much of the biosolids in the late 1970s and early 1980s produced by the City of Philadelphia went into ‘mine mix’. A significant portion of the biosolids produced west of the Cascades in Washington State went to the coal mine in Centralia, WA. The MWRDGC (Chicago biosolids) sent most of its material to strip mine lands in Fulton County.
Back in those days, the standard approach was to spread the biosolids deep. Concerns with metals focused on metals added by the biosolids and not the metals in the wastes. This was before the pre-treatment and Part 503 regulations fundamentally improved the quality of the cake. The classic text on mine reclamation with biosolids that sums up the research for this approach is by Penn State's Bill Sopper, ‘Municipal Sludge Use in Land Reclamation’. You can get it used on Amazon. I have two copies but I am not sharing.
Restoration is still a great end use for biosolids and other residuals. Much has changed since the early days. We have gotten more sophisticated in how the biosolids are applied, generally lower application rates and often in mixtures with other materials. While in the past we worried about metals added with the biosolids, now we have realized that the biosolids can be used to cure metal toxicity on metal contaminated sites. The requirements to restore sites have also gotten more complicated. More and more, restoration of a plant cover is not sufficient. It is important to show that you have restored a ‘functional ecosystem’ and that you have also reduced the toxicity of any contaminants that are present. Finally, we are realizing that biosolids can be used to restore a wide variety of sites, including disturbed lands within urban boundaries. And that is how the library starts, with two articles that describe how biosolids were used to restore a steel mill slag site in Chicago.
The first article is pretty basic. It gives the basic information on the site, a 230-hectare brownfield site. Different rates of biosolids, alone and in combination with dredged sediment were added to replicated field plots and sown in turfgrass. Metals in the soils were tested and found, but all at relatively low levels. Grass grew well with the biosolids. Lysimeters were used to monitor for nutrient movement, and no impact was observed. In short, biosolids worked well, and the article even has pictures that prove it.
The second article takes the first article one step further. Also based on research done in Chicago, the second article focuses on ecosystem services that will be restored when amendments are used to bring a plant cover back to disturbed soils. Again, the site is holds steel mill waste, and this time plots were set up on the grounds of the wastewater plant. Two rates of biosolids, an USCC STA-approved compost and a mixture of biosolids, water treatment residuals and char were tested. Here the variables measured reflect a more sophisticated understanding of the complexities of a functional ecosystem. Soil quality was measured, including nutrient availability and total carbon and nitrogen. Microbial diversity and function were measured through enzyme assays. Earthworm survival and reproduction studies were carried out. Finally, natives were seeded in the plots, and a plant diversity index was measured. All treatments worked great, but biosolids were the best. In addition, pharmaceuticals were measured in runoff, and a few were found, all at nanogram per liter concentrations.
The next two papers take us to mine sites, but here metal mining instead of coal mining. The first takes a look at soil microbial populations on copper mine tailings restored with biosolids in Arizona. Ian Pepper is the first author here and this means that we are given an in depth look at microbial diversity. Short version is that the biosolids-amended tailings showed similar microbial diversity as non- disturbed soils. Long version, I’ll send you the paper.
The next paper is one of mine. Here it is focused on long-term efficacy of biosolids or compost on Pb and Zn tailings at a Superfund site in Missouri. We looked at worms, plants, soil, and mammals and all look good. What we also did was calculate how long it would have taken to form that soil that we built naturally, about 1,875 years. We also looked at what the carbon balance would be if the biosolids that are currently incinerated in Missouri were instead used to restore the remainder of that site, a savings of about 400 tons of CO2 per hectare.
I also wrote the last paper in this month’s library. It is a review paper of the different metal contaminated sites that have been restored with organic amendments and the different tools used to show that these amendments are effective in restoring plants and ecosystem function to the sites. It is truly a wonderful thing to have a tool that brings these barren areas back to life.