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Legionnaires' Bacteria Reemerges In Previously Disinfected Cooling Towers
schwit1 writes with the New York Times' unsettling report that 15 water-cooling towers in the Bronx that this week tested positive for Legionnaires' disease had been disinfected less than two months ago.
From the NYT: After an outbreak of the disease killed 12 people in July and August in the South Bronx, the city required every building with cooling towers, a common source of the Legionella bacteria that cause the disease, to be cleaned within two weeks. ... [The] city found this week that bacteria had regrown in at least 15 towers that had been cleaned recently in the Morris Park section of the Bronx. The testing occurred after a fresh outbreak in that area that has killed one person and sickened at least 12, and spurred an order from health officials for the towers to be disinfected again.
I work in legionella management in the UK, cooling towers must be disinfected every 6 months, no shit the legionella came back, it's present everywhere in the environment. The US has very lax laws for public water safety, see also New York's hideous water towers/roof tanks
What exactly do these cool? Do they cool water or act like an AC?
I've been managing facilities and staff to maintain cooling towers for years. I've personally cleaned them, I've personally maintained them, and I've personally been responsible for the water treatment/chemistry as part of their operational and preventive maintenance.
The answer to your question is, they technically cool water, which is then piped back into a building(s) and used as a "heat sink" for any air conditioning/refrigeration equipment inside the building. In your home air conditioner, you have the box with the fan that sits outside. This box is called the"condenser". The condenser's job is to release any heat that is removed from inside the house. In that type of mechanical refrigeration, the refrigerant (R-22, colloquially called Freon) is compressed to allow for a controlled evaporation cycle inside the indoor unit (the evaporator). As the refrigerant absorbs heat from inside the home, it is pumped outside to the condenser where it releases the head into the air (in this case, the outside air is the "heat sink"). That is, the fan on the condenser pulls outside air across the coils where the hot refrigerant is being pumped, and the heat transfers to the outside air, cooling your house.
In large commercial applications, it is often more efficient to use water based systems to achieve this. In this method, the refrigerant that has absorbed the heat from inside the facility is dumped into what's called "condenser water". The water absorbs the heat, and the cooled refrigerant goes back to the air conditioning systems in the building to absorb more heat. The condenser water is pumped up to the cooling towers where it is filtered through several screens while large fans pull outside air across them (similar to the home system). The combination of the water flow patterns, air velocity, and evaporation will cool this condenser water, allowing for it to be sent back to the indoor air conditioning systems so that it can absorb more heat and start the cycle again.
I mention all of this to say this: the ONLY reason this type of contamination is happening is because of improper maintenance. Period. Water treatment systems are just about idiot proof. So, while we may not hear about it, I guarantee someone, somewhere took a short cut. Maybe it was the end of the fiscal quarter and someone was under pressure to save money, so they postponed the delivery of the aquastat chemicals for a couple of weeks to make budget. Maybe a maintenance engineer didn't really do his rounds inspection that day and so he didn't see that one of the chemical feeder pumps had tripped out on overload. Maybe the maintenance workers didn't want to spend a few hours inside one of these steamy boxes cleaning out additional algae buildup. It's not a glamorous job to say the least, but not terribly difficult in the grand scheme.
People should not only lose their jobs and licenses for this, people absolutely deserve litigation for this. This is nothing short of negligence.
I'd be curious to know if the design of these cooling towers(unfortunately, results for 'cooling towers' tend to be heavy on the really big ones used by power plants, which aren't terribly relevant except sharing certain basic principles of operation) would allow for UV sterilization.
The idea that you can actually 'disinfect' something in the real world, outside of a cleanroom or high end operating room, for more than a few minutes to hours is mostly a polite fiction. Any sort of real world plumbing arrangment is going to be hosting assorted biofilms and other incredibly durable bacterial reservoirs more or less inevitably. As the massive success of modern sanitation systems has proven, you can get water 'clean enough' for the more-or-less-healthy to stay that way; but if you actually need to exterminate almost all the bacteria, you are picking a whole different fight.
If, though, you only need to ensure that the contents of the droplets emitted by the cooling system in operation are reasonably disinfected, intense UV in the outflow ducts might be able to do that, and UV isn't high energy enough to do too much violence to metal parts(plastics/rubber/etc. can be trouble; but you won't be commiserating with nuclear reactor operators over radiation embrittlement issues.)
Sure, no problem. there are closed type systems, but when you have Cooling Towers, it's an open system. That is, there's a secondary chilled water loop that circulates inside, and it dumps its head into the primary loop through a plate and frame heat exchanger. The primary loop gets pumped out to the cooling towers, where it goes through the cooling tower "fill" which is a scheme of different diverter surfaces to separate the water into thin streams running along flat surfaces. Outside air is then drawn across the fill, and that removes the heat and aids in evaporation of the water. Any water that is evaporated away is replaced with fresh "makeup water".
:-)
As the water is being drawn across the fill, it starts to evaporate and also atomize (meaning that the streams of water break up into tiny droplets that are technically still liquid, but are light enough to be carried away in the moving air stream). As these water droplets are pulled into the outside air, they can be carried anywhere. Often, cooling towers are located on the roof of buildings. The other thing that you'll often see on the roof is the building exhaust fans and the fresh air make up fans. If the fresh air makeup fan inlets are located anywhere near the cooling tower, it is very possible to have those same tiny water droplets get sucked into the intake, and pumped into the building along with the fresh air makeup.
Mechanical Engineers usually design the location of these intakes to be far enough away form the Cooling Towers to prevent infiltration, but wind currents can be a little hard to predict. Also, if the Cooling Tower isn't being operated correctly, there can be more water atomization than there should be. For example, if the Variable Frequency Drives (VFDs) that control the Cooling Tower Fan speed isn't set up right, it can run too fast and pull out more water droplets than it should be (this should ordinarily be kept to a minimum because makeup water isn't cheap, and it's not "green" to use too much water).
Hope that helps.
Or perhaps we understand that quite well. And decide that it's not that big a problem.
Civilian nuclear power deaths in the USA, to date: zero.
Military nuclear power deaths in the USA, to date: four? Basically the people in the room with the test reactor (that fit in a bathtub) when someone pulled the control rod (yes, there was only one) out by hand.
Hmm, 70 years of nuclear power in the USA, with so few casualties. I could wish the highways were that safe. Or Airline travel. Or trains. Or COAL MINING. Or Oil drilling. Or even hydropower dams.
Hell, more people have died just this year installing solar cells than have died in nuclear power accidents in the USA in all of history.....
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