To view the article abstracts from this months research update follow this link: July 2019 RESEARCH UPDATE.
I am just recovering from a summer cold. Not particularly severe; lots of sneezes for a day or two. And, this was not related to my work with municipal biosolids. The cold did, however, remind me of the fear mongers who take every new pandemic and attempt to stoke panic or inspire a new disaster movie by suggesting that it could be spread through our sewer system. In anticipation of this summer’s blockbuster movies, a library devoted to the topic is high time.
The first article goes way back, back to the glory days, when people still got vaccinated for measles and just two short years after the Ebola virus was first discovered. The article is here in part to remind us all about why we have wastewater treatment in the first place: to control waterborne diseases. The article, written in 1978, is a review of the potential for disease outbreaks to occur as a result of land application of biosolids (then sewage sludge). The authors note that while treated sludge can have some levels of residual pathogenic viruses, bacteria, cysts and ova, the vast majority of sewage-related disease comes from the UN-treated stuff. Night soil, raw wastewater and raw sewage are the stuff that diseases come from, not the treated or composted materials. The paper is interesting in that it discusses historic outbreaks of illnesses related to contamination of water and crops by insufficiently treated human and animal wastes and wastewaters. It has a nice table showing classes of pathogens and associated diseases:
There is also a table with likely survival times of different organisms in soils and crops. That table is likely out of date. A discussion of ways to kill pathogens in wastewater treatment includes factors like temperature, liming, and composting. The main point here is that wastewater treatment exists for a reason and it is working well. Waterborne illness in nations with advanced wastewater treatment is an oddity, no longer the norm.
But what about all those new and terrifying diseases? For those we start with paper #2. This paper explicitly focuses on the potential for new pandemics to be spread through the wastewater treatment system. The authors state that much research has focused on the potential spread of enteric viruses. Enteric viruses can replicate in your intestines and consist of a DNA fragment protected by a protein shell. They are tough and don’t degrade with heat, acids and oxidants. An outer shell added to that structure gives you an enveloped viruses; this category includes influenza, coronaviruses (SARS and MERS) and Ebola. These typically don’t spread through the fecal route and had been thought to be easier to kill in aqueous systems. If you are a hypochondriac, don’t look at the table below. If you are a fan of disaster films, the table contains a list of viruses, their associated illness, family, structure and concentrations in wastewater.
The article then goes into detail on different types of viruses and their likely means of transmission, starting with influenza. I love our business; the article discusses concentrations of non-fecal spread human influenza viruses in fecal matter. Turns out the way they get there is by swallowing infected snot. Don’t swallow!! Use that Kleenex!! Despite detection in fecal material, the primary transmission mechanism for human influenza remains getting sneezed on by someone who is infected. The route of infection is a different story for bird flu. A vian influenza can be transmitted through the fecal-oral route, at least for birds. That also suggests that the fecal-oral route may be effective for humans, too. The authors suggest that this would be a threat for wastewater transmission. They go on to coronaviruses such as SARS. SARS is spread primarily by sneezing but is also in fecal matter. SARS is just one type of coronavirus. Add these to your check list of things to worry about.
So, they get in your poop. How long would they last in the wastewater system? Take a look at Table 3.
The length of time and the chance of survival is both virus dependent and treatment process dependent, and a full data set for each type of virus and each type of treatment does not exist. The general principles for solids is this: thermophilic treatment kills more and faster than mesophilic treatment. Composting and heat palletization also kill effectively. The authors also discuss persistence in water after treatment. One of the critical problems here is adequate methods of detection. It turns out with some of these viruses that the saying ‘if you can’t find it, it can’t hurt you’ (is that a saying?) may not hold true. This paper provides a lot of good basic information and makes me glad that I’m a fan of romantic comedies, not disaster movies. Dustin Hoffman may have been a star in Outbreak (ranked first in a list of movies on pandemics), but I’d go for Tootsie any day.
Paper #3 is from Pepper and Gerba at the University of Arizona. These guys thankfully look at the potential for a range of trendy diseases to spread through biosolids. The answers are generally a reassuring ‘no’. This one focuses on coronaviruses in water and wastewater. You can relax. The experts say that coronaviruses die off in wastewater (T99.9) in 2-4 days. They note that the viruses last longer in primary effluent than in secondary, likely due to partitioning to solids in the primary. But that survival was still significantly lower than the enteric viruses (those passed primarily through the fecal-oral route) that have been well studied.
Paper # 4 is a more recent look at viruses in wastewater systems prompted by the 2014 Ebola outbreak. The authors studied an unenveloped virus (remember above discussion of enteric viruses and their protein shell and those others with the additional outer shell?) and an enveloped virus. They looked at behavior of each with liquids, solids, porcelain (toilets) and PVC, polypropylene and concrete. They tested them with real and synthetic sludge. The authors generally found that the vast majority of both types of virus partition to the liquid and not the solids, so don’t breathe deeply at the treatment plant. They also note that the behavior of Ebola may vary, as it has a different shape from the viruses used in the study.
For the last paper in the library we again give thanks to Pepper and Gerba. The paper looks at the survival of viruses in thermophilic and mesophilic digestion. One of the viruses they tested is a surrogate for the Ebola virus. You’ve been patient reading if you’ve made it this far. I’ll reward that patience with the point of this paper: both mesophilic and thermophilic digestion reduced to below detection the populations of the virus that was the surrogate for Ebola.
The important points are there are different types of viruses. Those that are spread via the fecal-oral route are most likely to be a concern for wastewater and have been extensively studied. Now we are concerned about versions that don’t typically transmit this way. There is so far a very reduced potential for these to be an issue.
The researchers so far say we are fine. It is summer. Get your pandemic thrills from the movies, not the wastewater system. Remember to get your flu shot and spend the summer enjoying some sun and sand.
PS: I also have a Pepper and Gerba paper on fate of prions if you are interested
Sally Brown, University of Washington