What is in Biosolids?

A New Valuation of Biosolids

At the top of my long list of emails on Monday morning was one from Brett, a spirited entrepreneur and social media networker. His note: “Hi Bill: How can the biosolids industry leverage this?” He had picked up on a provocative title in Business Insider e-zine “Feces contain gold worth millions.” Business Finder apparently responded to an article in the technology newsletter Science Daily entitled: “Sewage could be a source of valuable metals and critical elements.” Based on the report, the metals in biosolids in our Mid Atlantic Biosolids Association region are worth $360,000,000. Brett knows enough about MABA’s finances to wonder if these metals were a better source of funds for MABA than membership dues.

I wrote back a flippant reply, balking at the reasonableness of the assertion that the biosolids from a million people contained elements worth $13,000,000. How could the “stuff” passing through a human gut shed so much gold and silver?

Still I figured I ought to give the story a second glance. I am glad I did. The article quoted a researcher from the USGS, and the report was one of highly-featured news items from among nearly 11,000 presentations at the annual meeting of the American Chemical Society, of which I am proud member. After reading through the original article in Environmental Science and Technology, I wrote Brett a retraction. This is a meaningful piece of research, and one we all could benefit from reading.

The article is “Characterization, Recovery Opportunities, and Valuation of Metals in Municipal Sludges from U.S. Wastewater Treatment Plants Nationwide.” The report is one of a series of studies on biosolids undertaken by a laboratory at Arizona State University which Paul Westerhoff and Rolf U. Halden, two names that may be familiar to you, are heading.

If this is the first you are hearing of the National Sewage Sludge Repository, I am sure it won’t be the last. “[O]ur research team at the Biodesign Institute has created the National Sewage Sludge Repository (NSSR), a large repository of digested MSSs [municipal sewage sludge] from 164 wastewater treatment plants from across the USA, as part of the Human Health Observatory (H2O) at Arizona State University (ASU).” The samples were acquired from the US EPA when it concluded its two national sewage sludge surveys. Some very important data characterizing biosolids in the United States is coming about as a result of the “repository.”

The project at ASU examined 58 elements, many of which had never before been analyzed in biosolids. Samples were drawn from the repository and made into a “mega composite” sample, but also biosolids were sampled at local wastewater plants in Phoenix.

Several features of the project report fascinated me. First, it arrayed concentrations of all metals on a single bar chart where the “Y-axis” was a logarithmic scale in scientific notation, ranging from E+01 to E+07 and the terms were in “micrograms per kilogram dry solids”. It was hard to get my mind to recognized that a zinc concentration of 500 mg/Kg dry weight was expressed as 5.E+05 ug/Kg (I am something of a math nerd, so sorry for my fascination with this). But the importance was that all 58 elements could be easily arrayed on a single bar graph for the entire span of concentrations, highest to lowest, i.e., from Calcium 3.5E+07 to Rhenium 0.8E+00, ug/Kg dry weight.

A second feature that impressed me was the use of the term “EF,” meaning enrichment factor. The researchers used as a reference profile for concentrations in biosolids the concentration of elements in the Earth’s crust. In this way, a value of “1.0” indicated that the element in the biosolids was in equivalent concentration to that found in soil and dust, meaning the biosolids gave no evidence of having an anthropogenic source. Most elements have some human contributions, and some elements derived from human products would have ratios of, say, 5.0. I had never seen this so well laid out.

The third feature, the one that caused Business Insider to get excited, was the valuation of the element constituents. The researchers used a model of concentration, partitioning, and commodity pricing to rank the elements to potential value for extraction from the biosolids matrix. This led to the finding that: “For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually. A model incorporating a parameter (KD - EF- $Value) to capture the relative potential for economic value from biosolids revealed the identity of the 13 most lucrative elements ([in order of value]Ag, Cu, Au, P, Fe, Pd, Mn, Zn, Ir, Al, Cd, Ti, Ga, and Cr) with a combined value of US $280/ton of sludge.”

This is not the first, and not the final, result from research on samples drawn from the National repository. We now have quite an array of journal articles. Here are a few, and they all have value to answering the question, so what is in biosolids?

Validation of mega composite sampling and nationwide mass inventories for 26 previously unmonitored contaminants in archived biosolids from the U.S National Biosolids Repository,author Bipin P.Chari and Rolf U. Halden. One finding: “Using a mass balance approach, the total loading of these 26 pharmaceuticals to U.S soils from biosolids land application was estimated at 5-15 tons year-1”.

Occurrence and loss over three years of 72 pharmaceuticals and personal care products from biosolids–soil mixtures in outdoor mesocosms, authors Evelyn Walters, Kristin McClellan, and Rolf U. Halden. One finding is: “Study results suggest that PPCPs shown in the laboratory to be readily biotransformable can persist in soils for extended periods of time when applied in biosolids.”

Pharmaceuticals and personal care products in archived U.S. biosolids from the 2001 EPA national sewage sludge survey, authors Kristin McClellan, and Rolf U. Halden. Findings, similar to the previous one, include: “The loading to U.S. soils from nationwide biosolids recycling was estimated at 210–250 metric tons per year for the sum of the 72 PPCPs investigated… This demonstrates that PPCP releases in U.S. biosolids have been ongoing for many years and the most abundant PPCPs appear to show limited fluctuations in mass over time when assessed on a nationwide basis.”

National inventory of alkylphenol ethoxylate compounds in U.S. sewage sludges and chemical fate in outdoor soil mesocosms, authors Arjun Vankatesan and Rolf U. Halden. One finding is: “Surfactant levels in U.S. sewage sludge ten-times in excess of European regulations, substantial releases to U.S. soils, and prolonged half-lives found under field conditions, all argue for the U.S. to follow Europe's move from 20 years ago to regulate these chemicals.”

Nanomaterial Transformation and Association with Fresh and Freeze-Dried Wastewater Activated Sludge: Implications for Testing Protocol and Environmental Fate, authors Mehlika A. Kiser, David A. LadnerKiril D. Hristovski and Paul K. Westerhoff. One finding: “This study indicates that natural or engineered processes (e.g., anaerobic digestion, biosolids decomposition in soils) that result in cellular degradation and matrices rich in surfactant-like materials (natural organic matter, proteins, phospholipids, etc.) may transform nanoparticle surfaces and significantly alter their fate in the environment.

Good news, we are learning what is in biosolids. Bad news, we are learning what is in biosolids. At least we will be able to answer that oft-heard charge: “no one knows what is in sludge; it is just a toxic soup.” We know now. Clearly, the analyses coming out of the National Sewage Sludge Repository are neither good nor bad, it is “what’s so.” The Repository is as thoughtful a source for a “mega composite” sample of U.S. biosolids as can be created, and it does provide a snapshot of what conventionally prepared biosolids traps in its organic-mineral complex. What those elements and compounds mean for ecological and human health is still down the road to be understood.

In the meantime, I will use the “factoid” published widely this week from the ACS convention whenever I can. I can say that scientists report that the elements flushed to the treatment plants each year has a value of $13 per person.

This reaffirms what I already knew: biosolids has real value.