Additional perspective on using biosolids in Nova Scotia
There has been ongoing discussion of biosolids use on soils in Nova Scotia. Several commentaries back and forth, including one from Dr. Murray McBride of Cornell Waste Management Institute, triggered a response Op-Ed piece submitted to The Chronicle Herald (Halifax) by Ned Beecher of NEBRA.
July 28, 2009
Treating wastewater is a modern necessity. Two years ago, sanitation was identified by a BMJ (formerly British Medical Journal) survey as the greatest single medical advance since 1840. In recent years, Halifax Regional Municipality (HRM) has made great advances in wastewater treatment. The current setback is unfortunate. Still, HRM and its communities should be proud of the progress.
Wastewater treatment (whether at a centralized treatment plant or in a septic system) produces sewage sludge. It has to be managed. There are only three options: landfilling, incineration, or recycling to soils. Each option has its impacts on the environment, its pros and cons. Landfill disposal and incineration waste the abundant nutrients and organic matter in sewage sludge and can generate significant greenhouse gas emissions. Incineration consumes net fossil fuel energy (even if heat is recovered) and has air emissions issues. Land application of treated sewage sludge – biosolids – like that conducted by N-Viro Canada for HRM – raises questions about trace chemicals and heavy metals.
In a recent column, Murray McBride, PhD, focused on that tiny fraction of potentially harmful constituents in biosolids applied to land. He is not the first to do so. Research scientists around the world have published thousands of papers over the past three decades regarding the potential impacts of traces of contaminants in biosolids. They are not finding significant negative impacts when biosolids are applied in accordance with modern standards.
At a 2004 once-a-decade “state of biosolids science” conference that Dr. McBride also attended, the large majority of biosolids researchers I spoke to believe that biosolids applied to soils according to modern regulations present minimal risk. A 1996 U. S. National Academy of Sciences (NAS) review of biosolids use on food crops found “While no disposal or reuse option can guarantee complete safety, the use of these materials in the production of crops for human consumption, when practiced in accordance with existing federal guidelines and regulations, present negligible risk to the consumer, to crop production, and to the environment." A subsequent 2002 NAS review found “no documented scientific evidence” that U. S. federal regulations– have failed to protect public health. And U. S. federal regulations are less stringent than Nova Scotia’s guidelines.
What exists is uncertainty, said the 2002 NAS report. Many people don’t know about biosolids recycling to soils, and it is natural to raise questions. Research is ongoing. But that research is not dealing with major risks (such as extremely high levels of heavy metals in some sludges used 30+ years ago). Today, research is examining much smaller potential risks. Because of control of what goes into sewers, metals and many of the most commonly-known toxic chemicals are no longer a significant issue in modern biosolids.
For example, Dr. McBride raised concern about potential molybdenum (Mo) impacts. He fails to note that farmers rigorously manage the pH of the total soil mass, to ensure good crop growth. It is the pH of the total soil mass that makes the difference in Mo availability. Also, guidelines restrict the Mo in biosolids to levels that present minimal risk.
The same is true with other regulated metals – there are regulatory limits, and those limits cannot be exceeded if the biosolids are to be applied to soils. The other “toxic metals that are not being monitored” have not been ignored, as Dr. McBride implies. Rather, the risks they present were assessed by U. S. EPA and university scientists and no need was found to regulate them – they just do not show up in high enough concentrations to present risk.
Dr. McBride also failed to note that biosolids must be applied at a controlled rate, providing only as much lime or nitrogen as the soil/crop system requires. This means that any trace contaminants (measured in parts-per-million or less) are being applied in tiny amounts. He also fails to mention that the reason those trace contaminants are in biosolids is because they are not water soluble and they mostly bind with solids – in the biosolids and in the soil. They are persistent, he notes, which means that most are not bioavailable – thus, plants and animals do not absorb them in any significant quantities.
The fact is, persistent chemicals in biosolids are uncommon. Most contaminants entering wastewater treatment systems are broken down by the diverse physical, chemical, and biological processes of a wastewater treatment plant, the biosolids treatment process, and/or the biologically rich soil. Research by Agriculture & Agri-Food Canada (AAFC) has demonstrated this for some of the “new” contaminants of concern mentioned by Dr. McBride.
Speaking of trace chemicals in biosolids, Dr. McBride says “it is reasonable to conclude” that they “will increasingly enter the human food chain… with continued sewage sludge application to land.” This is misleading. Miniscule traces may do so, but human exposure to these chemicals is far greater through daily use of products that contain them! Biosolids applied to land is not a significant pathway for human exposure.
For more than a decade, Dr. McBride has been insisting that a level of safety be applied to biosolids recycling that is not applied to other risks. Animal manures contain metals and pathogens and have caused significant documented outbreaks of illness, but they are less regulated than biosolids. Animal manures contain some of the same or similar trace chemicals, and there is far more animal manure being land applied than biosolids.
Science has documented many benefits to soils and crops from proper biosolids (and manure) use: improved tilth, better capacity to absorb and hold water (reducing runoff), improved crop yields, and improved crop nutritional value. Biosolids have been widely used for restoring barren lands to productive uses (some of the Halifax N-Viro biosolids are destined for such use). And when compared to landfill disposal and incineration, biosolids recycling to soils has lower net carbon dioxide equivalent emissions.
For sustainability, we need to continue to return the nutrients and organic matter in biosolids to soils not too far from the wastewater treatment plant. At the same time, I expect Dr. McBride and I can agree that society should continue to restrict the use of known toxic metals and chemicals, so that wastewater and biosolids quality will further improve.
But right now, the N-Viro Halifax biosolids land application program is one of many across the continent that are safely serving to close the loop of recycling while protecting public health and the environment.
Ned Beecher, Executive Director
North East Biosolids and Residuals Association
The North East Biosolids and Residuals Association is a 501(c)(3) non-profit professional association dedicated to advancing the recycling of biosolids and other organic residuals in New England and eastern Canada. NEBRA membership includes most of the environmental professionals and organizations that produce, treat, test, consult on, and manage the beneficial uses of biosolids and other large volume recyclable organic residuals in this region. NEBRA is funded by membership fees, donations, and project grants. It is directed by a volunteer Board of Directors from MA, ME, NH, VT, and New Brunswick. NEBRA’s financial statements and other information are open for public inspection during normal business hours.