UV to the rescue

New York City is about to open the world’s largest UV disinfection plant in a couple of months, which will treat roughly 5 billion gallons per day.  That’s a lot of water.  That’s also a prime reason why I always found the evil plot at the heart of Batman Begins very difficult to swallow: the bad guys lace the water supply with a toxin that induces psychosis, but assuming that Gotham City is basically New York City, they’d have to be dumping at least 500,000 gallons per day for 100 ppm toxin in the water supply — some 9100 55-gallon barrels.  That’s quite a logistical headache to hide, deliver, and dispose of that many barrels.  I won’t go into the details of pipe networks that also make this improbable — the work of fiction did get people to ask me questions about water supply, which is never a bad thing.

I have digressed.  The NYC UV disinfection plant will be the second treatment step for New York’s water supply, besides chlorination.  Given the reports from Wisconsin about the necessity for UV disinfection to prevent viral gastroenteritis, New Yorkers could soon be a lot healthier.  Turns out the EPA has been quietly requiring a secondary step for water treatment on top of chlorination, whether it be filtration or UV disinfection.  EPA has been worried about standard water-borne pathogens like Giardia, Cryptosporidium, and Adenovirus, but this rule has preempted the latest research on the role of viruses in water-borne illness.  Good job, EPA!

how good are our regs?

Some recent studies on viruses and microbes in our water and wastewater treatment systems should give us all pause.  First, researchers in Wisconsin conducted a very clever study that correlated concentrations of viruses in tap water with rates of illness in the local community.  When chlorine or UV disinfection, which inactivates viruses, was added to those communities’ water treatment systems, the illness rates declined.  The results were conclusive enough that even before the study was formally published, the Wisconsin legislature mandated chlorine or UV disinfection for all water treatment systems in the state.  Of course, the politicians have since interfered, as the newly elected Republican caucus repealed that law last year.  The study suggested that the source of the pertinent viruses was leaking sewer pipes.

A second study came out last year in Minnesota, showing that even a top-of-the-line wastewater treatment plant is ineffective at removing DNA fragments that could confer antibiotic resistance to new microbes.  The treatment plant in question, in Duluth, MN, uses tertiary treatment estimated to be better than 95% of US wastewater treatment plants, and yet genes for antibiotic resistance were found in the effluent and in the pristine water bodies that the plant discharges into.  Even if the microbes have been killed, the DNA can “live on” to spread to other cells.

If our treated wastewater is a potential source of viruses and antibiotic-resistant genes to the environment, then we must ask ourselves if our regulations are sufficient to protect human health and the environment.  Should we measure our drinking water and treated wastewater in a more holistic manner to assess their safety?  Right now, the standard is fecal coliform bacteria as an indicator for all microbiological activity.  Do regular DNA assays need to be included in our standards?

I would argue that adding UV disinfection (quaternary treatment) to wastewater treatment merits consideration.  Although it is costly in energy, the spread of viruses and antibiotic resistance should not be taken lightly, and adding UV treatment to water treatment (already a trend among the facilities that can afford it) does not impact the pathway from the wastewater to the environment.  This is also something to keep in mind for water recycling purposes — you don’t want to drink water if that stuff’s still in there…