We Stink at Controlling Biosolids Odors

If you actually track the news clippings in this email from week to week, you might find yourself skipping those coming out of Marilla, NY, and Fort Meade, FL. You will likely recognize these, each and every week, as a kind of “Groundhog Day” story. Once a community’s ire has been raised, and anger over biosolids has set in, the heat takes a long time to dissipate. More often than not, that anger is tied to odor nuisances caused by biosolids.

I had a call from a MABA member this week, an alert in case a reporter was on the job, of a particularly egregious series of events involving “sludges” from aerobic digesters with serious winter problems. The events involved a teacher alarmed by odors, concerns for the safety of her students, and calls to 9-1-1. So far, the media has been quiet. Phew! Dodged that bullet!

You can’t justify this kind of situation.

Haven’t we learned that odors can undo so much good work? Why can’t we get equipment that works and not let us down with our stabilization needs? Why don’t we have a back-up plan when things go wrong? And why, despite 20 years of concerted research, are most commonly deployed biosolids treatment systems in the U.S. not yet able to produce a nuisance-free biosolids?

The answer is: because it is difficult and costly.

I also believe the answer is because we have stopped trying hard enough.

WERF has spent a lot of time and money supporting research into the mechanisms of odor production and its control. I was part of that effort. We searched hopefully and hard for a neat prescription for process changes we could make and technologies we could adopt that would dependably produce nuisance-free biosolids. We didn’t get there.

We did get some notable WERF publication. For example, we got Identifying & Controlling Odor in the Municipal Wastewater Environment Phase 3: Biosolids Processing Modifications for Cake. And there is another report, apparently still not yet released, that sounds as though it will be helpful: Wastewater Treatment Plant Design and Operations Modifications to Improve Management of Biosolids Odors and Sudden Increases in Indicator Organisms.

Some of the research initiatives spawned by WERF studies may still bear fruit. Findings are winding their way through the innovation cycle. One example is a recent patent application for the strategic use of metal-salt conditioners.

In the end, I, for one, was disappointed. I had expected a more triumphant conclusion than we have reached. I imagine others were disappointed, too, though we haven’t spoken truthfully about it among ourselves.

The bottom line in 2015 seems to be that research to fix biosolids odors is mostly done with. For those agencies and companies who contribute to WERF and who today set its policies, a low/no odor biosolids still seems a “nice idea.” A few agencies, notably DC Water, are even planning to achieve that goal.


DC Water may well lead the way, which would be fabulous, because the need to solve the odor problem is no less urgent than it was 20 years ago.

We cannot presume that in the future the “right-to-farm” principle, which in many regions has protected some odorous operations from shut down, will be available, as it is not free of its own threats. We have seen the challenge to right-to-farm arise in Pennsylvania, where odors from CAFOs (confined animal feedlot operations) and, more recently, the debate over “fracking," has called state pre-emption of local environmental controls into a fresh and substantive debate. There may be no “right-to-farm with biosolids” in the future.

Nor should we rely upon Part 503 for giving us a pass on odors. We may wish that 503 compliance were tantamount to our practices posing no risk of adverse human and environmental health. But this may not be adequate in the future. In my 2007 paper, Biosolids as a Cause of Somatic Disease, I argued for the importance of our responding properly to “idiopathic environmental intolerance” as a health consequence of malodors, particularly biosolids malodors. One of my main sources for this paper, Philadelphia-based odor psychologist Pamela Dalton, authored a 2014 paper “Asthma and odors: The role of risk perception in asthma exacerbation.” In it she says, “Expectations elicited by smelling a perceived harmful odor may affect airway physiology and impact asthma exacerbations.” This is important to understand, as biosolids are a classic example of a “perceived harmful odor.”

To check myself on this notion that our odor research effort is not substantive today, I did a science literature search. (http://scholar.google.com/ is an amazing site; so is MyEndNote.) Some great research about reducing nuisance risks in biosolids was published in 2014 and 2015, just not in the United States. It may well prove true that future breakthroughs will come from research done abroad, where a focus on “high quality biosolids” has been more sustained.

Let me give you a flavor to some of the significant journal articles from the past year.

Hygienization performances of innovative sludge treatment solutions to assure safe land spreading. “…two digestion pretreatments (sonication and thermal hydrolysis) and two sequential biological processes (mesophilic/thermophilic and anaerobic/aerobic digestion) were compared to the mesophilic (MAD) and thermophilic anaerobic digestion (TAD)…. The microbial quality limits for the unrestricted use of sludge in agriculture (no Salmonella in 50 g wet weight (WW) and E. coli <500 CFU/g) were always met when thermal digestion or pretreatment was applied… The anaerobic/aerobic digestion process increased the removal of E. coli and somatic coliphages compared to the simple MAD and always achieved the hygienization requirement … for the use of treated sludges in agriculture with restriction on their application.”

Bacterial pathogen indicators regrowth and reduced sulphur compounds’ emissions during storage of electro-dewatered biosolids. “Electro-dewatering (ED) increases biosolids dryness from 10–15 to 30–50%, which helps wastewater treatment facilities control disposal costs…. [U]nder anaerobic conditions, odorous reduced sulphur compounds (methanethiol, dimethyl sulphide and dimethyl disulphide) were produced by untreated and heat-treated biosolids, but were not detected in the headspaces above ED samples. The data demonstrate that ED provides advantages not only as a dewatering technique, but also for producing biosolids with lower microbial counts and odour levels….”

Combined Mesophilic Anaerobic and Thermophilic Aerobic Digestion Process: Effect on Sludge Degradation and Variation of Sludge Property. “One-stage autothermal thermophilic aerobic digestion (ATAD) is effective for the reduction of volatile solids (VSs) and pathogen in sewage sludges. A novel process of combining mesophilic (<35 °C) anaerobic digestion with a thermophilic (55 °C) aerobic digestion process (AN/TAD) occurred in a one-stage digester, which was designed for aeration energy savings.”

This next research project was published by 11 European scientists in search of robust digestion technologies, illustrating the commitment to advancing the state-of-the-art “across the pond.”

Quality assessment of digested sludges produced by advanced stabilization processes. “Removals of conventional and emerging organic pollutants were greatly enhanced by performing double-stage digestion (UMT and AA treatment) compared to a single-stage process as TT; the same trend was found as regards toxicity reduction.” [TT is thermal hydrolysis with thermophilic digestion. UMT is mesophilic digestion. AA is sequential anaerobic / aerobic treatment.]

Europe and Asia researchers are demonstrating an inventiveness and urgency to developing new approaches to biosolids stabilization that may someday produce results of the kind we in the United States had hoped in 1994 we would be achieving. I, for one, would urge us to rejoin the creative endeavor to achieve a nuisance-free, pathogen-free biosolids product. But as it stands....

Our commitment to biosolids odor control stinks.