# 274
Yesterday, Cornell University released a study, which I posted about here, where they issued vague assurances that the H5N1 avian flu virus would be rendered inactive through standard wastewater treatment protocols. They used the far less pathogenic H5N2 virus as a stand in for the bird flu virus, and determined that UV treatment, chlorination, and bacterial digesters killed the microbes.
This report was designed to assuage the fears of waste treatment plant operators who might be exposed in the course of their duties, and the general public who might be concerned about cross contamination of the public water supply.
While I viewed this report as potentially good news, I also have concerns over how well these results would be achieved in the real world.
The USGS maintains a website where they provide a simplified explanation of how wastewater treatment plants operate. There are, according to the USGS, six basic steps to treating raw sewage. Excerpts from this site are in blue. My comments are in red.
The Primary Treatment Process
1. Screening:
Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals. Unless they are removed, they could cause problems later in the treatment process. Most of these materials are sent to a landfill.
At this point, anything screened and removed would have to be considered contaminated and possibly a level 3 biohazard.
2. Pumping:
The wastewater system relies on the force of gravity to move sewage from your home to the treatment plant. So wastewater-treatment plants are located on low ground, often near a river into which treated water can be released. If the plant is built above the ground level, the wastewater has to be pumped up to the aeration tanks (item 3). From here on, gravity takes over to move the wastewater through the treatment process.
Sewage at this point is still untreated, and still potentially laden with the H5N1 virus. Maintenance work on equipment, pumps, and lines would risk exposure to the virus.
In some areas, during times of heavy rains, untreated sewage is ocasionally released into local waterways when the system cannot handle the load. Many municipalities have simply decided it is easier to pay a fine than to upgrade their facilities.
3. Aerating:
One of the first steps that a water treatment facility can do is to just shake up the sewage and expose it to air. This causes some of the dissolved gases (such as hydrogen sulfide, which smells like rotten eggs) that taste and smell bad to be released from the water. Wastewater enters a series of long, parallel concrete tanks. Each tank is divided into two sections. In the first section, air is pumped through the water.
Pumping air through the sewage, to increase bacterial digestion, also increases the possibility of the aerosolizing of the virus. Some plants use sprayer systems, while others use bubbler systems. Some use both. How likely this aerosolization would be, I can’t say, but it seems possible.
4. Removing sludge
Wastewater then enters the second section or sedimentation tanks. Here, the sludge (the organic portion of the sewage) settles out of the wastewater and is pumped out of the tanks. Some of the water is removed in a step called thickening and then the sludge is processed in large tanks called digesters.
5. Removing scum:
As sludge is settling to the bottom of the sedimentation tanks, lighter materials are floating to the surface. This 'scum' includes grease, oils, plastics, and soap. Slow-moving rakes skim the scum off the surface of the wastewater. Scum is thickened and pumped to the digesters along with the sludge.
6. Killing bacteria:
Finally, the wastewater flows into a 'chlorine contact' tank, where the chemical chlorine is added to kill bacteria, which could pose a health risk, just as is done in swimming pools. The chlorine is mostly eliminated as the bacteria are destroyed, but sometimes it must be neutralized by adding other chemicals. This protects fish and other marine organisms, which can be harmed by the smallest amounts of chlorine.
The treated water (called effluent) is then discharged to a local river or the ocean.
This final step, the killing of the bacteria with chlorine, assumes that chlorine deliveries will continue during a pandemic. Most waste treatment plants, and water treatment plants, only have a couple of week’s worth of chlorine on hand due to the volatile nature of the chemical. They are dependent upon timely deliveries.
If everything works as it should, and there are no mechanical breakdowns, or disruptions in deliveries of essential chemicals, and no `accidental’ or uncontrolled spills of untreated sewage, then perhaps all of these concerns are overblown. I have to assume the folks at Cornell used due diligence in their study, and have solid scientific rationale behind their conclusions.
But in the real world, as we know, sewage happens.
Systems break. People may fail to show up for work, or make mistakes when they do. And with 50,000 waste treatment plants in operation (all built by the lowest bidder), there are 50,000 opportunities for problems.
On the water treatment side of the equation, the delivery of chlorine will also be essential, as will the continued oversight by qualified water plant operators.
Most small `package’ plants that service small communities, both water and sewer, are fairly well automated. They rely on visits by licensed operators several times a week to check the machinery, take samples, and make adjustments. Thousands of communities will be dependent upon these operators doing their jobs, and having the chemicals required, for their safe operation.
If a pandemic results in 40% absenteeism nationwide (possibly an optimistic number), then the number of qualified operators available to do this important work will be dramatically reduced, at least for a period of time. If deliveries of chlorine are compromised, then even if operators show up, water treatment problems could still ensue.
Exactly how big a problem any of this will actually be in a pandemic is unknown. We know that studies have shown that the H5N1 virus can remain alive in bird feces for days, depending upon the temperature. Much will depend upon how much virus is shed from the body through the fecal route.
Not addressed in this study was what would happen if the power goes out for any length of time. Again, something we can’t know whether it will happen or not during a pandemic, but there are concerns in the industry. If the power goes out, not only do treatment plants cease operating, so do lift stations that move raw sewage along the sewer system to the plants.
Anytime you take 40% or more of the workforce out of the equation, and disrupt critical deliveries, you run the risk of major system failures.
The study admits at least one large `gap', and that is in the effectiveness of chlorine in killing the virus. There have been previous reports out of Vietnam calling into question how well chlorine works. The Cornell study stated:
For chlorine, which is mostly ubiquitous in U.S. drinking water, the results were less definitive. Inactivation of H5N2 depends on both chlorine concentrations and time of exposure. On average, U.S. treatment plants treat drinking water with chlorine concentrations of 1 milligram per liter for 237 minutes. Under these conditions, the researchers found that H5N2 (and probably H5N1) would be mostly inactivated, but further studies are needed to see if the viruses stay active when they come out of feces or are at different pH and salinity levels.
Given that chlorination is the primary method of water treatment here in the US, this little caveat gives me pause.
Yesterday I said I regarded this report as potential good news. I still do.
But I recognize that laboratory experiments don’t always mimic life in the real world, and so I take these pronouncements with a large grain of salt.
