The following question-and-answer session occurred following the WEF webcast titled "Updates on Novel Coronavirus for Water Professionals" held on Feb. 25.

Question: There was some discussion of free chlorine residual required to inactive the virus. What about combined chlorine – chloramines?

Answer: Dr. Mark Sobsey (Gillings Schools of Global Public Health, UNC-Chapel Hill): What we know is that chloramines are effective in inactivating microbes, it’s just that the rate of inactivation is slower. And in other terminology, the CTs for chloramines are bigger numbers than they are for free chlorine so I think with proper chloramine dosing and sufficient contact time, the CTs that may be targeted should be adequate to deal with a virus like this. As Dr. Arduino mentioned these viruses are sort of at the bottom of the resistance list when it comes to resistance to chlorine disinfection. So, we know from lots of work, particularly with non-enveloped viruses, that chloramines do work. It’s just that it takes a higher dose, longer contact time, and therefore I think we can rely on that for controlling these viruses should they, in fact, ever get into things like drinking water supplies or even into wastewater treatment systems where, again, we may be using combined disinfection rather than free chlorine disinfection.  And remember, that in most situations, especially where you’re using chloramines you do have some initial free chlorine residual which is, of course, helpful.

Q: What’s the current level of log-inactivation for viruses achieved by conventional wastewater treatment? For some context, surface drinking water facilities are designed to provide 4-log inactivation of viruses.

A: Dr. Sobsey (UNC-Chapel Hill): What we should be trying to achieve are extensive virus reductions in wastewater just as we are wanting to achieve in drinking water supplies.  And, of course, the disinfection process is applied after some initial treatment by other physical and chemical and biological processes where again under appropriate operations conditions we should be able to get a couple log reductions of viruses under most circumstances for primary, secondary treatment.  For disinfection, if we do this right, we should be able to get perhaps another 4-logs reduction so that the overall reduction in a conventional wastewater treatment plant, if properly managed, could be as high as 6-logs reduction.  Now remember that, not all the time are we able to optimize treatment so sometimes we’re going to get less performance but we should be guided by the extent to which we can achieve NPDES permit requirements for fecal coliform bacteria where you have to get down to no more than several hundred fecal coliforms per 100ml.  Remember, you’re starting with really high concentrations of those bacteria. So if you’re starting with 107, 108 fecal coliforms per 100ml and you can get down to 102, or 103, you’re achieving a comparable reduction of those bacteria, which again, if properly managed and operated, you should be able to get about the same for a virus like this. That’s not to say that some of the non-enveloped viruses might be more resistant which is one of the reasons why there’s a greater focus now on how to better address viruses in wastewater in terms of achieving low levels in wastewater effluent discharges especially in things like recreational waters. 

Q: Do you believe the PFRP processes for treating Biosolids will be adequate to assure pathogen reduction where biosolids products may be distributed to the public? So basically, are the current class A biosolids requirements sufficiently protective in light of coronavirus?

A: Dr. Sobsey (UNC-Chapel Hill): My sense is that class A biosolids requirements do indeed require extensive reductions of pathogens including viruses. There is a requirement for no detectable virus presence in a certain unit quantity of biosolids dry weight. Which means, again, you could have started with a rather high concentration of viruses and now you’re getting down to the point of little or no detection in class A biosolids. So, if your processes are operating properly and you can achieve class A performance for viruses, again, the risk should be very low in general for viruses and in particular for a virus like this. Obviously, class B biosolids, another issue, another ball game because class B biosolids do allow more fecal bacteria to be present and there are no specific requirements for the log-term reduction of viruses. So obviously we should be moving more and more towards class A biosolids for more widespread in terms of the environment.

Q: Really focusing on the research as research is being conducted for coronavirus and the assumption is that this would be most squarely with CDC, do we need special experimental studies and does that need to be in secure lab facilities?

A: Dr. Matt Arduino (Environmental Hygiene and Infection Prevention, Office of the Director, Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention (CDC)): I think the studies will probably have to be at BSL 2+ to BSL 3 until we figure how safely to handle the virus in certain situations.  Most of the lab work right now is not based on culture. So, all the diagnostics that are being performed are all molecular assays. So that we can move most of those assays out to as many laboratories as we can. But at some point, some of these studies will have to occur and we’re probably going to have to move to those that have a BSL 2+ to 3 capacity.   We have up to BSL 4 laboratories which are the high containment laboratories.  CDC does and BSL 3 laboratories actually even occur in academia. There are laboratories throughout the country who have BSL 3 and then there are a number of facilities who are even higher that have the BSL 4 capability as well. So, there are research laboratories who would be able to do this type of work.

Q: Moderator asked: As we stand right now, is COVID-19 considered a bloodborne pathogen under the OSHA standard?

A: Dr. Christopher Brown (Occupational Safety and Health Administration (OSHA), Department of Labor): The OSHA standard doesn’t necessarily apply based on the type of pathogen.  It applies based on the occupational exposure and if the exposure is to blood, the list of covered body fluids to which the standard applies or other potentially infectious materials as defined in the standard, then the standard applies. Generally speaking, however, the bloodborne pathogen standard does not apply to the most common routes of transmission of COVID-19. So, when we’re talking about airborne transmission or transmission from respiratory secretions to a person’s facial mucosa, those types of exposures are not covered under bloodborne pathogens but would be covered by the personal protective equipment standards including the respiratory protection.

Q: Do you think there was airborne transmission through the ventilation system in the Diamond Princess cruise ship docked in Yokohama, Japan, where approximately 550 people became infected, understanding that there may be some opinion involved here?

A: Dr. Arduino (CDC): Well, from what I understand just from some second-hand reports, on the Diamond Princess there was a lot of mixing of individuals. So, there wasn’t effective isolation going on of infected individuals. So, there were still places where there was some mixing of infected and susceptible individuals on the cruise, while they were in quarantine. So that is part of it. The other part of that is to try to understand what those ships’ ventilation systems are like. I have no clue what the ventilation systems are like. But they are not really designed to handle, at least on the older cruise lines, not really designed to handle somebody with an airborne infection.  And if you look, historically, if you look at tb on board ship, there have been outbreaks of tuberculosis onboard naval vessels in the United States Navy, and some of the other navies from Europe as well.

Q: In the absence of a workplace policy regarding precautionary action when employees are returning from travels to areas where there’s been infection, should organizations impose voluntary quarantine or other preventative measures?

Dr. Brown (OSHA):  I think this may require some tag teaming from CDC as well because OSHA does not have authority over quarantine. That generally falls under CDC’s lane.  Having said that however though, given that individuals coming back into the country are being screened by CDC personnel in conjunction with Custom and Border Protection, we’re not recommending any specific additional quarantine measures.  When we’ve gotten this question in the past, we do tend to remind employers that you have discretion and flexibility in implementing workplace flexibilities as you see fit. It’s your workplace, you can do that. If the type of work that your worker does can be accomplished through voluntary telework or remote work options and you think that that’s appropriate and it’s a mutually agreeable situation between the employer and the worker, then there is certainly nothing wrong with doing that. 

Q: Please clarify some of the numbers of infections and just how the numbers work, the statement that there’s been about 80,000 cases including 2,700 deaths, but then 2,000 - 3,000 recoveries? What about the other about 75,000 people?

A: Dr. Sobsey (UNC-Chapel Hill): Well, the reports show that there are about 75,000, closer to 80.000, reported cases. The problem is that while these cases can get logged in, not everyone has the same criteria for declaring what’s a case and when that gets logged in and where, not a lot of information in terms of follow up. It’s assumed that many people who were infected and perhaps even became ill did recover but we’re not necessarily at a point where those who were maybe released and went back into the population after treatment or maybe otherwise got recorded as a case but perhaps never went into hospital, the extent to which, you know, they’re still well and what their outcomes were is still rather incomplete. So, the number for recovered people is just a small subset probably of all those people who were infected and perhaps have recovered.

Q: What is the contact time associated with free chlorine concentration in the .2 - .5 ppm range for inactivating SARS?

A: Dr. Sobsey (UNC-Chapel Hill): Its relatively short. I don’t remember the exact number but I think the goal was to achieve extensive disinfection of several orders of magnitude within even a minute or just a few minutes so the CT would have been relatively short down in the range of maybe 10 – 30 minutes. There are references on this and there have been at least a few published papers in which the CTs are reported and those are the references that probably should be consulted to get a better idea of what the allowable contact times, of what the usable contact times are as well as the residuals. There’ve been reports where even at somewhat lower free chlorine concentration, even down around .1 to .16, rapid and extensive inactivation was possible in reasonably short time periods, consistent with, you know, the residence time in a chlorine contactor.


Q: With the level of uncertainty that we’re currently dealing with, with the bioaerosols, is there any clarity that you can provide around what should be done with collection system workers versus more in the plant around, say, aeration basins where they’re going to encounter bioaerosols?

A: Dr. Brown (OSHA):  The key word is uncertainty. We’ve worked through this issue with other pathogens in the past and I think what our determinations based on looking at available  literature and what’s kind of known about hazard assessment in these type of water treatment workplace environment is that sites around mixing basins and where streams of water come together or where aerosols are most heavily generated, in the past we’ve recommended to the extent that workers are exposed to those bioaerosols that employers consider using respirators to protect the workers.  I think we should keep in mind that using respirators just for the sake of using respirators if there’s not actually a hazard may not be the best ideal. In general, that’s the case because respirators can also pose additional hazards themselves, particularly if workers are not able to tolerate them for a long term or are getting a false sense of protection by wearing them where they are not being worn properly. Things like that. But especially in this case, where we’re also dealing with the potential for supply chain availability issues given the amount of supply that is in the demand for health care and other sectors as well as the fact the supply chain comes out of China and may not be as routinely available as it generally is. Those are some concerns there. I think really this goes back to employers doing a hazard assessment and we’ll probably, as we learn more about the persistence of this pathogen in wastewater know more about whether coronavirus is a specific concern.  Happy to hear others take on that, but I think from our position generally we default back to employers doing a hazard assessment and identifying what types of controls are most effective. When, there was some uncertainty around this during Ebola, we also tried to recommend employers really emphasize the hierarchy of control so that if there were particular areas within a treatment plant or within the collection system where they were worried that workers might have exposure to bioaerosols that they were either limiting access to those areas or using enclosures to isolate workers from the potential hazard before we immediately jump to using respirators. And then, one other thing to note. I think in this situation, given that we’re dealing with a potentially wet environment, a discussion around respirators may not center around disposable filtering facepiece N95 respirators. It might be more appropriate to use elastomerics with cartridges that are going to be able to stand up to the wet mist environments that these workers are working in.


Title: Updates on Novel Coronavirus
for Water Professionals



  • Mark Sobsey, Gillings Schools of Global Public Health, UNC Chapel Hill
  • Matt Arduino, Environmental Hygiene and Infection Prevention, Office of the Director, Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention
  • Christopher Brown, Occupational Safety and Health Administration, Department of Labor
  • Christine Tomlinson, CBRN Consequence Management Advisory Division, Office of Emergency Management, U.S. Environmental Protection Agency
  • Rasha Maal-Bared, EPCOR Water, WEF DPHC Waterborne Infectious Disease Outbreak Control (WIDOC) Chair
  • Scott Schaefer, A2ES, WEF DPHC Chair (Moderator)