Clearing the air
Cutting-edge technology, and regulatory and industry safeguards have ensured safe methods of treating wastewater and producing biosolids — the solid organic materials recovered from treatment plants for land use. Although numerous studies have shown that biosolids are safe to use as fertilizer, the materials still can have a foul odor, so many people recoil at the thought of having the treatment plants or biosolids-fertilized land anywhere near their homes. That visceral response can block efforts to build or expand wastewater treatment facilities, and to burn, bury or fertilize with biosolids.
“Public perception revolves around this issue,” says Adam Krantz, managing director of government and public affairs for the Washington, D.C.-based Association of Metropolitan Sewerage Agencies (AMSA). “[We need to] move the public away from fear to knowledge. The [disgust] factor needs to be reduced.” Educating people, especially about the benefits of using biosolids to grow crops and restore lands, is the way to do that, Krantz says.
Government and industry need to do a better job of telling and showing people why treatment operations and biosolids are safe and what has been done to control odors. It is just as important for them to talk about current and planned research and development to lessen odors further. People disgusted by the smell and/or fearful that biosolids cause illness need reassurance on that score. Addressing residents’ complaints in that way can help clear the air around the volatile subject.
No piece of cake
Residents’ frustration with odor is tied to antipathy toward building treatment centers or spreading biosolids near them — the not-in-my-backyard syndrome. It can pit bedroom-community residents against utilities and farmers who use the treated biosolids as fertilizer.
At the bottom of the odor problem are the biosolids cakes — the solids produced after sewage sludge goes through treatment — particularly the cakes produced by anaerobic digestion, in which bacteria that do not use oxygen degrade the sludge. The cake is the biggest problem because anaerobic digestion stabilizes a larger total volume of sludge than any other process.
A draft study on biosolids odors by the Alexandria, Va.-based Water Environment Research Foundation (WERF) found that, in general, the more bioavailable protein in the biosolids cake, the worse and longer-lasting the odors. The study also found that incomplete digestion or high shear (friction) on biosolids during dewatering could leave more bioavailable protein in the cake.
High shear can be reduced by using lower-energy methods for dewatering, such as belt filtration. However, the WERF draft study cautioned that attaining more complete anaerobic digestion, or dewatering with lower shear, cannot cut down on odors independent of upstream conditions or the nature of downstream processing equipment or storage conditions. Alternatively, proteins can be destroyed by methods including pre-pasteurization, which ruptures bacterial cell walls, and sonication, which breaks down cell walls with high-frequency sound waves.
“Certainly, there have been a lot of advances in odor control technology that allow for decreasing — to a great degree — the odor generated by a treatment plant,” says Mike Sullivan, supervising engineer for the Los Angeles County Sanitation District. For example, plants can cover a primary sedimentation tank “and pull the air out from underneath to treat it,” Sullivan explains. Or, if biosolids are processed outdoors (e.g., through composting), they can be put in enclosed storage.
Biofiltration, he says, is a popular treatment that uses porous organic material “so that the air you’re treating moves through at a fairly low speed, giving you a natural breakdown of odor compounds.” Chemical and carbon treatments — two other frequently used options — remove specific odor compounds.
However, there’s no such thing as a completely odor-free plant. For instance, biofilter material itself is an odor source. “If it’s wood chips, the air is going to smell like wood chips,” Sullivan says.
Respecting, responding to objections
Because plants cannot completely remove odors from biosolids, local governments must contend with residents who suspect that plant odors cause illness. While the Washington, D.C.-based National Academy of Sciences’ National Research Council (NRC) has found no documented cause-effect link between exposure to biosolids and people becoming ill, the group is calling for new and extensive research to clarify the potential negative health effects of biosolids.
Odor researcher William Cain, of the Chemosensory Perception Laboratory at the University of California, San Diego, also emphasizes the lack of a cause-effect link. “The evidence is, at most, so scant that it’s essentially zero,” he says. “You can have symptoms from odors you don’t like, but this is not illness. Most of these are non-specific symptoms that can have any number of origins.”
Cain notes that some of the most odorous compounds in biosolids — amines, carboxylic acids and mercaptans — create the characteristic taste and smell of fish (amines) and the taste of most cheeses (carboxylic acids) and beers (mercaptans). “If odors [affect health], then which odors, and at what concentration?” he asks. “No one has made any attempt to specify this any more or apply quantification. You’ve got to start dealing with it one odor at a time.”
However, there is a distinction between odor and toxicity. “[Treatment plants can] put out things that are at a toxic concentration, [or] pollute so badly that their emissions could cause health effects,” Cain says. “If things are in this toxic range, beyond the limits imposed by regulations, then we’re not talking about odor. We’re talking about toxicity, so we have to stay below the level where people would become ill.”
Normal emission levels, Cain asserts, are well below the toxicity range. “California, in particular, has been extremely conservative in setting these reference levels, to the point that industry complains that it’s over-regulated. There’s a large margin for error,” he says.
More study needed
The Washington, D.C.-based Environmental Protection Agency (EPA) established rules in 1993 to regulate the use of biosolids in the United States, but the science of assessing risks has changed significantly since then. NRC has called for more scientific work “to reduce persistent uncertainty about the potential for adverse health effects.” NRC primarily wants: improved risk-assessment methods to set better standards for chemical limits and pathogen-reduction; a framework to examine the effect of biosolids exposure on health — including a way to document successes in preventing or lessening exposures to pathogens and toxic elements — and more staff and funding for EPA’s biosolids program.
EPA’s response to the NRC recommendations is a strategy that would conduct priority research to update scientific support for its rules governing biosolids, combine results of intra- and extra-EPA research to strengthen the sewage sludge program, and continue to increase partnerships and communication with the public and other interested parties. In the next two fiscal years, EPA hopes to implement the strategy in several ways, including determining if any additional pollutants should be regulated, surveying the published evidence of pollution occurrence and its effects, and creating a dialogue with other health-related federal agencies to consider tracking incident reports and investigating whether exposure to biosolids can be linked to health problems.
Meanwhile, stakeholders in the biosolids debate are trying to resolve their differences. For example, EPA and WERF met with representatives of organizations concerned about land application of biosolids to discuss issues and find some common ground at a Biosolids Research Summit in July. EPA also is thinking of conducting research and tracking field studies by other parties to learn more about what happens to pathogens in the soil and air after sewage sludge has been land-applied. From that, EPA could determine if changes to its biosolids regulations are necessary to safeguard public health.
On a parallel track, EPA, the U.S. Department of Agriculture and Pennsylvania are collaborating on studies to measure the exposure levels for pathogens, odors, particulates and endotoxins in and around the sites where biosolids are land-applied. The trio also combined to form an Information Sharing Group, which includes individuals who discuss their environmental concerns with researchers to help shape how research studies are conducted.
Conflict resolution
While studies about biosolids safety are ongoing, some local governments are wrestling with the idea of land application bans. In some states — notably Virginia, California and Florida — some local governments have banned or are considering a ban on Class B biosolids because they contain some pathogens. (Class A biosolids are pathogen-free, but most farmers prefer nutrient-rich and inexpensive Class B biosolids.)
But Class B land application is controlled by techniques that further reduce pathogen levels before crops are harvested or people are exposed to the biosolids. Additionally, biosolids, which are regulated, are applied to only 1 percent of all agricultural land in the U.S., “whereas the majority of soil amendments, like manure and commercial fertilizers, are unregulated,” says Sam Hadeed, technical and communications director for the Alexandria, Va.-based National Biosolids Partnership, an alliance between EPA, AMSA and the Water Environment Federation that helps local governments improve biosolids management.
Conversely, the Denver Metro Wastewater Reclamation District has been building public trust in the land application of biosolids at its Deer Trail, Colo., farm. While buying the land, Metro faced opposition from neighbors who complained about land application practices, truck traffic to and from the site, and soil erosion. By 1997, when Metro announced that it would accept treated groundwater from a Superfund site, it was hit with a barrage of angry criticism, culminating in a cease-and-desist order from Elbert County — where 60 percent of Metro land lies — that stopped biosolid application.
“The choice was, ‘Do we want to go to court and fight these guys or do we want to live with them?’ and we decided on the second course,” says Steve Frank, Metro’s public information officer. Metro began a dialogue with opponents and ultimately joined Elbert and Arapahoe counties in contracting with the U.S. Geological Survey (USGS), in Reston, Va., to conduct a monitoring program that analyzed the biosolids and the soil at the farm to determine whether surrounding property, groundwater or surface waters had been contaminated. Each year, USGS meets with the community to report on the program.
The change in public opinion has been slow but steady. In 2000, the year after the program began, Metro surveyed the farm’s neighbors, elected officials, residents and community leaders to determine their level of satisfaction with its efforts. Metro received a “D” grade from the still-skeptical populace in 2000, but, three years later, it received a “B” grade.
“There are probably a few people who will go to their graves saying, ‘I just want you guys to leave’, but, by and large, there has been greater acceptance because of our consultations with everyone,” Frank says. “We’re getting there.”
Like Metro, other local government agencies are allaying residents’ fears by going beyond the regulatory minimums to achieve credibility. The National Biosolids Partnership’s Environmental Management System (EMS), a voluntary demonstration program, is helping public utilities gain acceptance for biosolids use. “We knew that to gain and maintain public acceptance for biosolids programs, [we] had to have good performances in environmental protection, regulatory compliance, public participation and quality environmental practices,” says Peter Machno, EMS manager.
Orange County, Calif., became the first of 53 participating agencies to meet the five requirements for gaining certification as an EMS program in August. It documented its responsibilities from biosolids pre-treatment to final treatment; adopted the Partnership’s Code of Good Practice, which specifies goals and commitments for system practice and management; and operated its program according to 17 principles concerned with critical control points. It also conducted a third-party audit of its performance, and it pledged continual system improvements on regulatory compliance, public participation, quality management practices and environmental protection.
Los Angeles also has received its certification, and NBP expects that another 20 agencies will complete audits by mid-2004. But the Partnership emphasizes that EMS certification signifies the beginning, not the end, of a continuous commitment to quality.
Agencies must be proactive, Frank concludes. “You need to get involved as early as you can with people who believe they have a stake in what you’re about to do,” he says. “They want to be involved. They want to have some control over it instead of just sitting there waiting for something to happen.”
Ray Pelosi is an Atlanta-based freelance writer.
