The dark path of this Biosolids TOPICS started unexpectedly with one of my regular podcasts, On the Media, with host Brooke Gladstone, a podcast I started listening to during last year’s election. Her podcast from the first week of July, ominouslytitled Apocalypse, Now, consists of a set of interviews with novelists interpreting theAnthropocene, specifically climate change. Stanley Robinson spoke in the segment titled Our Future City, and of his new book New York 2140, which imagines the effect of a 200 foot rise in ocean level on NYC (a MABA member in need of some timely advice?). The Desert Reasserts Itself is the podcast segment discussing Claire Vaye Watkins' most recent book, Gold Fame Citrus, about extreme drought in California caused by climate change. "Solastalgia," and Other Words for Our Changing World is an interview with Robert Macfarlane who argues we need new words if we are to come to grips with the subtle and not-so-subtle ways humans are altering the environment (isn’t this what we did with the word “biosolids” some two decades ago?).
My new insight from the podcast was the overarching observation that the seriousness of the climate change issue involves scales of time and space that are nearly impossible for human beings to perceive, but for an artistic interpretation, partially explaining our political confusion.
I asked myself, in view of humanity’s very large challenge, what role do we play as environmental stewards, engaged in our own modest segment of the world?
There is no end to websites willing to offer you crystal-clear assessments of priority environmental issues facing humanity. A conservative, cautious approach is offered by Bjorn Lomborg, an environmental skeptic who established the Copenhagen Consensus Center. This Center sorts out priorities using a rigorous cost-effectiveness approach. Its four top priorities: Tackling malnutrition and hunger; Health and disease; Green R&D (climate change and agricultural productivity); and Trade and Development (free trade, no protectionism).
More likely your web search will unveil compelling urgencies at the other extreme. One such example is a new “must-read” essay The Uninhabitable Earth, by New York Magazine’s David Wallace-Wells, positing “What climate change could wreak – sooner than you think.” The essay sets out its depressing arguments with nine foreboding headings: I. ‘Doomsday’, II. ‘Heat Death’, III. The End of Food, IV. Climate Plagues, V. Unbreathable Air, VI. Perpetual War, VII. Permanent Economic Collapse, VIII. Poisoned Oceans, IX. The Great Filter. This last one is mass extinction. The essay introduced me to Amitav Ghosh, who, in his book The Great Derangement, wonders why global warming and natural disaster haven’t become major subjects of contemporary fiction. I was introduced, too, to Peter Ward, a charismatic paleontologist, who says that, due to hydrogen sulfide emissions, the “mass extinction we are now living through has only just begun; so much more dying is coming.” Yes, dark, indeed.
In response, I put on a mantle of optimism, and look for a worthy challenge for us biosolids managers. After all, biosolids management is at the nexus of water, waste, soil, and human health, and we have tools to ameliorate crop failures, plagues, drought, and toxic emissions. The threat of a re-emergence of epidemic diseases are among the very horrifying calamities. How might biosolids managers help stave off this threat? We could help stop the spread of antibiotic residues and antibiotic resistant genes, or ARGs.
Several years ago, an article indicted wastewater treatment for the spread of antibiotic resistant microbes. The article, “Wastewater a source of antibiotic-resistant bacteria: study,” was based on a study of “extended-spectrum β-lactamase–producing Escherichia coli,” or ESBLEC. This study (Wastewater Treatment Plants Release Large Amounts of Extended-Spectrum β-Lactamase–Producing Escherichia coli Into the Environment) reported: “The treatment at the WWTP led to the relative enrichment of ESBLEC. We estimated that >600 billion of ESBLEC are released into the river Doubs daily and the sludge produced by the WWTP, used as fertilizer, contains 2.6 × 10(5) ESBLEC per gram.” That’s per gram! That would be 10(11) per metric ton.
Why is this a problem? As explained in Antibiotics and antibiotic resistance: A bitter fight against evolution, “recent research has raised awareness that sub-lethal concentrations of antibiotics can also foster resistance as an undesirable side-effect…. subinhibitory concentrations of antimicrobials may increase, even more, the mutagenic effect of antibiotics.” Other current research, such as Occurrence of antibiotics and antibiotic resistance genes in a sewage treatment plant and its effluent-receiving river, confirmed that “sewage was an important repository of the resistance genes, which need to be effectively treated before discharge into the natural water body.” In cities with major health care centers, this concern could be exacerbated by the higher probable incidence of wastewater-borne pathogens and aggressive antibiotic use. The report Occurrence of antibiotics and antibiotic resistance genes (ARGs) in hospital and urban wastewaters and their impact on the receiving river found “widespread occurrence of antibiotics and ARGs in urban and hospital wastewater and how these effluents, even after treatment, contribute to the spread of these emerging pollutants in the aquatic environment.” This doesn’t sound good.
Further, researchers are looking at how treatment processes effect the formation and release of ARGs. The report Metagenomic Comparison of Antibiotic Resistance Genes Associated with Liquid and Dewatered Biosolids gives rise to concern, still in active research, that “Activated sludge is a hotspot for the accumulation of antibiotics and has been shown to be a selective environment for microorganisms that contain antibiotic resistance genes (ARGs)….” Additionally, anaerobic digesters seem to be a concern. For instance, in Survival of Antibiotic Resistant Bacteria and Horizontal Gene Transfer Control Antibiotic Resistance Gene Content in Anaerobic Digesters, the authors write “Notably, mesophilic digestion was more susceptible to ARG intrusion than thermophilic digestion, which may be attributed to a higher rate of ARB survival and/or horizontal gene transfer between raw sludge bacteria and the digester microbial community.”
Advanced treatment processes may reduce the concern of ARG. In Removal of total and antibiotic resistant bacteria in advanced wastewater treatment by ozonation in combination with different filtering techniques the authors conclude that “advanced wastewater treatment by ozonation plus charcoal or sand filtration after common sewage treatment is an effective tool for further elimination of microorganisms from sewage before discharge in surface waters.”
What about the potential effects of land application of ARG-laden biosolids? To answer that question, we are joined by researchers in microbial risks of manure, which are arguably the greater concern. The results are mixed, but not scary. Environmental Impacts Associated with the Land Application of Municipal Biosolids (MB)reports that “host-specific Bacteroides spp. markers were detected up to one month in soils receiving CP2 MBs, but not in leachate, suggesting their use in source tracking is better suited to recent pollution events or following surface runoff.” The science article Abundance of Antibiotic Resistance Genes in Bacteriophage following Soil Fertilization with Dairy Manure or Municipal Biosolids, and Evidence for Potential Transduction calls for treatment processes that reduce the risks, processes that are familiar to us in wastewater and increasingly looked at by the agricultural industry. This report states: “The results indicate that soil-borne bacteriophage represents a substantial reservoir of antibiotic resistance and that bacteriophage could play a significant role in the horizontal transfer of resistance genes in the context of an agricultural soil microbiome. Overall, our work reinforces the advisability of composting or digesting fecal material prior to field application and suggests that application of some antibiotics at subclinical concentrations can promote bacteriophage-mediated horizontal transfer of ARGs in agricultural soil microbiomes.”
With land application, specific field practices can be deployed to mitigate risks of release of ARG to the environment. Elevation of antibiotic resistance genes at cold temperatures: implications for winter storage of sludge and biosolids discovered increases in “ARGs during biosolids storage and identifies changes in operational protocols that could help reduce ARG loading to the environment when biosolids are land-applied.” Reassuringly, the Part 503 based “waiting periods” following land application prior to crop production is a positive result for ARG reduction, just as it is for human pathogens and for pathogen indicators. The report Impact of Fertilizing with Raw or Anaerobically Digested Sewage Sludge on the Abundance of Antibiotic-Resistant Coliforms, Antibiotic Resistance Genes, and Pathogenic Bacteria in Soil and on Vegetables at Harvest” recommends that “Overall, the results of the present study suggest that producing vegetable crops in ground fertilized with human waste without appropriate delay or pretreatment will result in an additional burden of antibiotic resistance genes on harvested crops. Managing human exposure to antibiotic resistance genes carried in human waste must be undertaken through judicious agricultural practice.”
In the High Quality Biosolids Research Project, of which I am part, the team is not looking at ARG so much as other attributes influencing suitability of biosolids products for residential users. But, simply put, we don’t want consumer products inoculating humans with disease-resistant microbes. So, for that reason, the element of this study that involves “house fly attraction” bears specifically on biosolids product quality, but it would effect ARG management, as well. In our study, Kansas State University professor Ludek Zurek is looking at fly attraction to biosolids, using protocols he deployed in the work reviewed in Insects Represent a Link between Food Animal Farms and the Urban Environment for Antibiotic Resistance Traits.
The state-of-knowledge on wastewater and land treatment effects on ARG transmission is still early. Research today suggests that enhancement of treatment plant and land application practices can provide sound and effective barriers. If you make biosolids products that measure very low in indicator organisms and that attract no flies, you are likely doing well already. So, while climate change may continue to wreak havoc with rising sea levels, sulfide gases, unlivable heat, and crop failures, we can nevertheless be soundly managing our corner of the world. A global dystopia may inevitably descend, but at least we will be maintaining a Biosolids Utopia.