NEW PROPERTY FOUND FOR TiO2

Investigation Into Marine Concrete Anti-Fouling Coatings

Long term ecologically sound answer to organic growth remains unsolved, however the use of titanium dioxide (TiO2) particles within coatings for concrete pavements have received considerable attention in recent years.

By Peter Hughes, Contributing Writer

Published April 1, 2013

                                                       

    

 

Marine Coatings

Marine Coatings

Marine Fig 1

Marine Fig 2

Marine Fig 3

Marine Fig 4

Marine Fig 5

Marine Fig 6

Marine Fig 7

Marine Fig 8

 

Our civil engineers  involved  in  the  construction  or  maintenance  of  marine  concrete structures  are  faced  with  the problem of preventing unwelcome microbial growth in an environmentally friendly  way.  A long term ecologically sound answer to organic growth remains unsolved, however the use of titanium dioxide (TiO2) particles within coatings for concrete pavements have received considerable attention in recent years as these particles can trap and decompose organic and inorganic air pollutants by a photocatalytic process (1). In spite of these promising benefits, the durability and resistance to wear of TiO2 surface coatings upon fibre reinforced marine concrete has not been evaluated. In this article, the development of fundamental research on the application of TiO2-based photocatalysis in a marine environment will be introduced. The problems encountered at a UK study site restricting a larger scale application of the technology are discussed.

Photocatalytic coatings are successfully used with many other building materials and have been shown to retard algal growth on concrete (2). In spite of these promising benefits, applications of this technology are currently limited. The durability of this technology in a marine application needs to be established before large-scale practical implementation is undertaken. Titanium dioxide (TiO2) is a white inorganic substance that is thermally stable, non-flammable and insoluble. TiO2, the oxide of the metal titanium, which is the ninth most abundant element in the earth’s crust, occurs in many rocks and mineral sands, the most economically important being ilmenite and rutile deposits. Ultra-fine (nano-scale) titanium dioxide (Anatase) was used in this research for surface treatments. The potential of titanium dioxide as a photocatalyst was discovered by (3). This process, which is similar to plant photosynthesis, allows the decomposition of water into oxygen and hydrogen in the presence of light, by means of a TiO2-anode (1). Based on this heterogeneous photocatalytic oxidation process, nitrogen oxides are oxidized into water-soluble nitrates while sulfur dioxide is oxidized into water-soluble sulfates; these substances can be washed away by moisture in the form of rainfall or seawater. The overall aim of this research, is to advance the understanding of how a photocatalytic (TiO2) coatings responds in a marine environment. This phase of work, carried out in the northwest of England, has recorded anti-fouling performance and intends to progress towards a non-toxic, environmentally-benign strategy for future industrial applications.

The ‘Development’ Tio2 Coating Used In This Research

Primary particles of ultrafine TiO2 within the development coating used was typically in the range of size from 10 to 60 nm, not only as existing discreet primary particles but as aggregates, with secondary particle sizes typically >100 nm. The coating was a stable aqueous dispersion (sol) of ultrafine TiO2 particles. Key features included an anatase crystal form with a 10 wt% of TiO2 content. The coating had a neutral pH of 8.5, with a high surface area (dry) of 300 m²/g, it dried clear, and was UV light activated with limited fluorescent light activity.  It is marketed for architectural applications.

Tio2 Coating Application In This Study

The coating procedure consisted of three independently applied layers brushed (concrete tiles) or roller applied (static site) onto the surface of concrete specimens, as per the manufacturer’s recommendation. The primer layer was applied to lower the viscosity of the material. This assisted in generating a good seal in the priming process through the filling of cracks and blowholes in the concrete surface. The primer formed a coating layer with a dry film thickness of 10µm. On top of the dried primer, an undercoat was applied after a drying time of 24h. Then, three separate topcoats were applied, each 10µm and a further 24h drying time, thus, bringing the overall thickness of the photocatalytic coating to 50µm. Although the coating was composed of a number of different layers, the comparatively short time between applications ensured that the finished complete layer did not show any distinct separate layers, but can be treated for all intents and purposes in this research as a single layer, see figure 1.

Results And Discussion

The biological complexity of the phenomenon, part of a larger study (4), referred to as marine biofouling, is enormous. It has been shown here and in previous research (5) that it is an ecological community with entities originating from all that we call life. Also, each organism has its own solution for how to find and attach on a surface, evolved during millions of years. It is the author’s view, it is impossible to invent new antifouling coatings without restricting the problem, meaning that several antifouling strategies have to be part of a holistic approach, leading to a bigger solution.

There are however several obstacles to be cleared before titanium dioxide photocatalyst technology can be adopted in the control of marine biofouling. Not only the fact that the applicability of this technology is limited considerably because the catalyst works only where there is light, but the application of a coating to composite materials such as concrete has limitations, as shown in figure 2.

The performance of the coating was observed to be heavily dependent on the underlying composite material. First of all, due to differences in intrinsic properties the synthetic fibres, in abundance at the surface of the concrete samples, inhibited a satisfactory bond between coating and substrate. The thermal coefficients of the coating were different from that of the concrete and its constituents. Thermal expansion and movement, referred to as ‘fibre pop out’, of exposed fibres instigated a cracking of the coating, as seen in figure 3, resulting in not only reduced photocatalytic activity but also structure and strength destructions.

Furthermore, the attachment of filamentous algae to the surface of the coating, seen in figure 4, was also observed to be detrimental to its long term durability. Diatoms, illustrated in figure 5, form another component of marine biofilms and act a settlement mediator for larger fouling. The diatom attachment to coatings examined showed that this single algae cell accelerated coating degradation.

Filamentous bacterial growth from within the matrix of the new concrete, as observed in figure 6, also played its part in the eventual cracking and delamination of the coating from its foundation. This previously unreported phenomena is discussed in more detail elsewhere (6). Coatings for marine concrete structures are subject to harsh environments, dynamic loads, continuous expansion and contraction by heat, rain/seawater splash, impacts from debris, erosion, micro-organisms etc. In this condition, most coatings deteriorate in a short period of time in the form of cracking, blistering, disbanding or chalking. The application of the TiO2 based coating tested in this research was not designed to defend from microbial growth from ‘within’ the concrete, effectively a living substratum, observed in figure 7. The occurrence of a bacterial biofilm formation under the coating has significantly effected the performance of the coating. A  study into the addition of TiO2 powder with an average size 21 nm (30% rutile and 70% anatase) into a bacterial colony, showed that 60–120 min were sufficient to destroy all the bacteria (7). Other workers also confirm that using lower dimension TiO2 particles leads to a faster bacterial destruction (8). These new observations of bacterial growth seen in figure 6 are detrimental to the long term durability of the coating and requires further investigation. This newly observed degradation mechanism, see figure 8, reported here, of a coating has implications for not only the construction sector.

Conclusions

Based on the analysis conducted, the following conclusions may be drawn that macro and micro synthetic fibres at the surface of concrete inhibit a strong and durable bond between the coating and the substratum, accelerating cracking and the eventual breakdown of the coating. Algal filamentous growth including diatoms attached to the surface of the coatings, applies further pressure on the integrity of the coating. Bacterial filamentous growth from within the matrix of the concrete, grows at the coating/concrete interface. This growth disrupts the bond between coating and substratum, leading to the de-lamination of the coating. Based on the results presented, further research is recommended to consider factors such as microbial growth under a coating, application methods and variation, coating composition, and long term durability. Furthermore, research in this field, needs to be developed to determine if any coatings have the potential to be effective in the long term strategy against marine biofouling.

Peter Hughes is a final year PhD student at the University of Central Lancashire, UK, investigating marine biofouling and its implications for the durability of marine concrete.

Acknowledgement
The author thanks his supervisors for their guidance. D. Fairhurst, Professor I. Sherrington, Dr. N. Renevier, Professor L.H.G. Morton, Professor P. C. Robery and Dr. L. Cunningham.
Further discussions are invited at: PHughes1@uclan.ac.uk

References
1. Fujishima, A., Rao, T., Tryk, D. Titanium dioxide photocatalysis. Journal of Photochemistry and Photobiology. 1, 2000, 1-21.
2. Peller, JR, Whitman, RL, Griffith, S, Harris, P, Peller, C, Scalziatti, J. TiO2 as a photocatalyst for control of the aquatic invasive alga, Cladophora, under natural and artificial light. Photoch. Photobio. A. 186, 2007, 212-217.
3. Fujishima, A., Honda, K. Electrochemical photolysis of water at a semiconductor electrode. Nature. 238, 1972, 8-37.
4. Hughes, P., Fairhurst, D., Sherrington, I., Renevier, N., Morton., L.H.G., Robbery, P., Cunningham, L. Microscopic examination of a new mechanism for accelerated degradation of synthetic fibre reinforced marine concrete. Construction and Building Materials. 41, 2013, 498-504.
5. Hughes, P. A new mechanism for accelerated degradation of synthetic-fibre-reinforced marine concrete. Concrete. 9, 2012, Vol. 46, 18-20.
6. Hughes, P. A study into the microbial growth within new marine concrete. Concrete. 1, 2013, Vol. 47, 34-36.
7. Saito, T, Iwase J, Horic J, Morioka T. Mode of photocatalytic bactericidal action of powdered semiconductor TiO2 on mutans streptococci. Journal of Photochem Photobio B Bio. 14, 1992, 369-379.
8. Huang, Z, Maness P, Blakem D, Wolfrum E, Smolinski S, Jacoby W. Bactericidal mode of titanium dioxide photocatalysis. J Photochem Photobio A Chem. 130, 2000, 163-170.

ADHESIVE FOR SURGERY

 

 

Mussels can be a delicious meal, but the chemistry that lets mussels stick to underwater surfaces may also provide a highly adhesive wound closure and more effective healing from surgery. In recent decades, bioadhesives, tissue sealants and hemostatic agents became the favored products to control bleeding and promote tissue healing after surgery. However, many of them have side effects or other problems, including an inability to perform well on wet tissue.

“To solve this medical problem, we looked at nature,” said Jian Yang, associate professor of bioengineering at Penn State. “There are sea creatures, like the mussel, that can stick on rocks and on ships in the ocean. They can hold on tightly without getting flushed away by the waves because the mussel can make a very powerful adhesive protein. We looked at the chemical structure of that kind of adhesive protein.”

Yang, along with University of Texas-Arlington researchers Mohammadreza Mehdizadeh, Hong Weng, Dipendra Gyawali and Liping Tang, took the biological information and developed a wholly synthetic family of adhesives. They incorporated the chemical structure from the mussel’s adhesive protein into the design of an injectable synthetic polymer. The bioadhesives, called iCMBAs, adhere well in wet environments, have controlled degradability, improved biocompatibility and lower manufacturing costs, putting them a step above current products such as fibrin glue and cyanoacrylate adhesives.

Fibrin glues are fast acting and biodegradable but have relatively poor adhesion strength. They may also carry the risk of blood-borne disease transmission and have the potential for allergic reactions due to animal-based ingredients. Cyanoacrylate adhesives offer strong adhesion, rapid setting time and strong adhesion to tissue, but they degrade slowly and may cause toxicity, often limiting their use to external applications. In addition, neither product is effective when used on wet tissue, a requirement of internal organ surgery, nor are there any current commercially available tissue adhesives or sealants appropriate for both external and internal use.

The researchers tested the newly developed iCMBAs on rats, using the adhesive and finger clamping to close three wounds for two minutes. Three other wounds were closed using sutures. The researchers reported their findings in a recent issue of Biomaterials.¹

The iCMBAs provided 2.5 to 8.0 times stronger adhesion in wet tissue conditions compared to fibrin glue. They also stopped bleeding instantly, facilitated wound healing, closed wounds without the use of sutures and offered controllable degradation.

“If you want the material to stay there for one week, we can control the polymer to degrade in one week,” said Yang. “If you want the material to stay in the wound for more than a month, we can control the synthesis to make the materials degrade in one month.”

The iCMBAs are also non-toxic, and because they are fully synthetic, they are unlikely to cause allergic reactions. Side effects were limited to mild inflammation. “If you put any synthetic materials into your body, the body will generate some inflammation,” Yang said.

The researchers are now working on improving the formula. “We are still optimizing our formulation,” he said. “We are trying to make the adhesion strength even stronger” to expand its use for things like broken bones where strong adhesion is tremendously important. The researchers are also looking at adding components that could control infection.

“We can introduce another component with anti-microbial properties, so it can do two functions at once,” said Yang.

The iCMBAs could eventually be used in a wide range of surgical disciplines from suture and staple replacement to tissue grafts to treat hernias, ulcers and burns. “There are so many applications that you can use this glue for to help in surgery,” he said.

---

NEW SAFETY DAYTA SHEETS FOR CHEMICALS, GLOBALIZED

By MAUREEN BRADY,
Managing Editor
OSHA’s updated Hazard
Communication Standard (HCS),
which conforms to the United
Nations’ Globally Harmonized System of
Classification and Labeling of Chemicals
(GHS), aims to provide a common and coherent approach to classifying chemicals and
communicating hazard information on labels
and safety data sheets. According to former
U.S. Secretary of Labor Hilda Solis, the
revised standard will “improve the quality and
consistency of hazard information, making it
safer for workers to do their jobs and easier
for employers to stay competitive.”
The three major areas of change are in
hazard classification, labels and safety data
sheets.
Hazard classification: The definitions
of hazard have been changed to provide specific
criteria for classification of health and physical
hazards, as well as classification of mixtures.
These specific criteria will help to ensure that
evaluations of hazardous effects are consistent
across manufacturers, and that labels and safety
data sheets (SDS) are more accurate as a result.
Labels: Chemical manufacturers and
importers will be required to provide a label
that includes a harmonized signal word, pictogram and hazard statement for each hazard
class and category. Precautionary statements
must also be provided.
Safety Data Sheets: Will now
have a specified 16-section format.
 While full compliance with the rule
will begin in 2015, OSHA is requiring that
employees are trained on the new label
elements (i.e., pictograms, hazard statements, precautionary statements and signal
words) and SDS format by December 1,
2013. Is your company on track to meet this
December deadline?
Why train now?
Many American and foreign chemical
manufacturers have already begun to produce
HazCom 2012/GHS-compliant labels and
SDSs. OSHA says it is important to ensure that
when employees begin to see the new labels and
SDSs in their workplaces, they will be familiar
with them, understand how to use them, and
access the information effectively. The sooner
you start training your workers, the more prepared your workers will be for these changes.
The updated HCS also stipulates that
employers must provide additional employee
training for newly identified physical or
health hazards by June 1, 2016.
Who should be trained?
The GHS states in Chapter 1.4, Section
1.4.9, the importance of training all target
audiences to recognize and interpret label
and/or SDS information, and to take appropriate action in response to chemical hazards.
Training requirements should be appropriate
for and commensurate with the nature of
the work or exposure. Key target audiences
include workers, emergency responders and
also those responsible for developing labels
and SDSs. To varying degrees, the training
needs of additional target audiences have to
be addressed. These should include training
for persons involved in transport and strategies required for educating consumers in
interpreting label information on products that
they use.
What are the GHS label
elements?
Some GHS label elements have been standardized (identical with no variation) and are
directly related to the endpoints and hazard
level. Other label elements are harmonized
with common definitions and/or principles.
(See Figure to the right.)
Symbols (hazard pictograms), signal words
and hazard statements have all been standardized and assigned to specific hazard categories and classes, as appropriate. This approach
makes it easier for countries to implement the
system and should make it easier for companies to comply with regulations based on
the GHS. Prescribed symbols, signal words
and hazard statements can be readily selected
from Annex 1 of the GHS “Purple Book.”
These standardized elements are not subject
to variation and should appear on the GHS
label as indicated in the GHS for each hazard
category/class in the system.
What is the GHS Safety
Data Sheet (SDS)?
The (Material) Safety Data Sheet (SDS)
provides comprehensive information for
use in workplace chemical management.
Employers and workers use SDSs as
sources of information about hazards and to
obtain advice on safety precautions.
The SDS should contain 16 headings.
The GHS MSDS headings, sequence and
content are similar to the ISO, EU and
Data sheets,
pictograms &
signal words
OSHA GHS training must be
completed by December 1, 2013
The Section numbers refer to the sections
in the GHS Document or "Purple Book".

DIRTY CARPETS ??

Disinfecting and Sanitizing Carpet

By William R. Griffin

OCTOBER 24, 2012

 

Those familiar with the Institute of Inspection, Cleaning and Restoration Certification (IICRC) water damage and remediation standards will quote portions of the standard that say if you have a "Level 3" black water contamination, you can't clean the carpet and/or cushion. It must be replaced.

In those cases, you often have sewage, bodily fluids or infectious materials or bio-waste in or on the carpet; of course, the realistic procedure is to remove the carpet and replace it.

Where this becomes less clear is when the spill or contamination is small, such as less than one square foot in size and is not extensive, or is primarily located on the surface of the carpet.

Can this be saturated with a disinfectant or sanitizer, for the required dwell time, and then extracted? Would it then be considered acceptable?

That's a question often debated by the experts and often a reality faced on the job by cleaning professionals.

It's not always sewage

What about the homeowner who has children and pets and wants to the have the carpet sanitized during cleaning?

What about an apartment, hotel or condo building manager who has had a tenant that had pets and wants to remove pet odors and stains?

What about a day care center where multiple children play and sleep on the carpet and occasionally vomit or have an accident involving urine or feces?

What about a carpeted hospital or nursing home that smells of urine, or the carpet on a locker room floor of a health club that smells like dirty, stale socks? Is there a way to effectively and legally disinfect or sanitize these areas?

Disinfect versus sanitize

Here's the reality: You can use a disinfectant product or solution on carpet, but that won't — according to U.S. Environmental Protection Agency (EPA) definitions — allow you to legally claim on a product label or in your advertising that you have or can disinfect carpet.

Depending on the carpet manufacturer, using a disinfectant or sanitizing product may void any warranty in existence. Some disinfectant and sanitizing products may leave a residue that can attract soil, and some products affect the performance of mill-applied stain resistance properties.

Lastly, there is no realistic "on the job" way to test, verify or validate that what you have done to disinfect or sanitize carpeting has actually been effective. There are protocols to test the effectiveness of a sanitizing chemical when used on carpet, but the tests are expensive and done only in a lab.

What the experts say

Cliff Zlotnik, former owner of Unsmoke Systems, which produced the Microban line of products that are now sold by Legend Brands, has strong feelings about disinfection.

"I do not believe that a product will be approved by the EPA to disinfect a carpet. My understanding is that the EPA's position is that only hard surfaces can be disinfected," Zlotnik said. "I also believe the EPA's current testing protocol for carpet sanitizers is flawed."

Zlotnik added that there are a number of sanitizers on the market that are approved for use on carpeting. "Most are quaternary (quat)-based, but there are also phenolic-based products on the market."

Ann Kowalecki, the product manager for Legend Brands, said this: "The most important thing is to read and follow the instructions on the label. That will tell you how to use the product, its limitations and what it can properly be used for."

Kowalecki said that this will include such things as whether the carpet needs to be cleaned first, how to dilute the product, and if it needs to be flushed after application.

"From the EPA's standpoint, you can't disinfect a carpet. That terminology relates to hard surfaces, not carpeting," Kowalecki emphasized. "But you can, if you follow the label directions, say that you will sanitize or decontaminate a carpet. From a practical standpoint, it depends on how far gone the carpet is, what it's soiled with and how much of it there is on the surface and in the backing of the carpet."

Patrick Moffett, president of Environmental Management and Engineering Inc., said that disinfecting and sanitizing carpet are two different things. "In clean and gray water losses, carpet is expected to be able to be cleaned and restored with no appreciable increase in the biological load of the carpet," he said. "If you look at chemical manufacturer disinfectant claims, they are for hard surfaces and seldom for fabrics."

How we clean and sanitize clothing is to use detergents and proper rinsing, Moffett said. "Hot water must be 140 degrees Fahrenheit and, in hospital settings, hot water must be above 160 degrees Fahrenheit. When we get carpet adhesives above 120 degrees Fahrenheit, they tend to liquefy and break apart." Using hot water is not practical in salvaging an entire sewage-soaked carpet, he said.

Also, according to Moffett, some people are promoting enzymes for disinfecting purposes. "They work to a degree, but I've not seen a product manufacturer step up to the plate and guarantee that their product killed 99.99 percent of coliform bacteria, viruses, mold and parasites in carpeting."

Rick Hoverson of Advanced Vapor Technologies Inc. said that disinfection and sanitization of carpet is difficult because of the mass and irregularity of the surface. That's why he promotes his dry vapor system.

"With dry vapor, we can get a reduction in the number of microorganisms present in a carpet and the process is quite effective against odors, dust mites and their allergens, but we can't make claims or guarantee disinfection or sanitization," Hoverson said. "Our tests prove that repeated passes and extended exposure to dry vapor are more effective than a single pass. We have found that dry vapor is more effective on thin fabrics such as cubical curtains, than thick fabrics such as carpeting."

Another issue cited by Hoverson is the fact that there are no definitive or easy ways to test the effectiveness of the results of any attempt at disinfection or sanitization of carpeting.

The botanical side

The latest advancements in botanical disinfecting technology have made it possible for products to kill micro-organisms without endangering human health, according to Sam DeAth, president of Benefect Corp. "The technology continues to advance and in 2012 we will be seeing botanical carpet sanitizers registered by the EPA — the first of their kind."

DeAth said the market is quickly becoming educated on issues regarding indoor air quality and unnecessary chemical toxicity. "Today, we have a choice to use safer, botanical products while still achieving the same results, even for carpet."

In the past, DeAth said, it was assumed that disinfectants had to be toxic to humans to do their job. He's excited that the botanical option has emerged as a viable solution. "While it's true that traditional hard surface disinfectants will likely kill any organisms that they come into contact with, antimicrobial products that are EPA registered as carpet sanitizers are specifically formulated for penetrating into porous carpet materials and to avoid binding with soils or the carpet fibers themselves, which is what quats do. So they are still a better choice."

Keep it clean, healthy and safe

If you use products or processes to sanitize carpet, the most important thing to remember is the health and well-being of yourself, your workers and your customers.

Do what is best for everyone. Keep everything clean, healthy and safe.

---

Bill Griffin is an industry consultant and trainer, and the owner of Cleaning Consultant Services Inc. He is also president of ICAN, a non-profit association comprised of industry professionals providing free consultation services through Cleaning Management Institute (CMI). Comments and questions about bidding and estimating are encouraged: (206) 849-0179;WGriffin@CleaningConsultants.com.

PROBLEMS WITH THE WATER YOU DRINK ??

 

Waste Water Processing Industry Topics

 

Water/Waste Processing

 

          Waterborne microbial disease still the greatest risk to     water supplies

 

By Joseph Cotruvo

April 01, 2013

No Comments

KEYWORDS cryptosporidium / waterborne disease / legionella / cotruvo

Email / Print / Reprints /

Share on facebook Share on twitter Share on linkedin | More

/ Text Size+

Larger Smaller

[X]

Traditionally, most microbial waterborne diseases in the United States are gastrointestinal and short-term, self-resolving infections. They can include bacterial pathogens, enterovirus, rotavirus, norovirus and hepatitis A virus, or protozoa like Cryptosporidium and giardia.
Although detecting waterborne disease outbreaks is difficult, and numbers are underestimates, reported waterborne disease outbreaks in the United States have declined since implementation of the 1974 Safe Drinking Water Act. The range is from a high of 90 reported outbreaks in 1979-1982 to fewer than 10 in 2002, out of about 60,000 community water systems. In addition, surveillance for outbreaks is today better than in the past, and identification of the causative microbial pathogens has significantly improved.
The reduced outbreak incidence is probably attributable to EPA requirements for microbial quality monitoring and increased water treatment that involves filtration and disinfection of surface water and disinfection of groundwaters. However, while the number of waterborne outbreaks has declined, the portion attributable to distribution system contamination has increased.

In the public eye
Beginning in 2001 Legionaires disease was added to the surveillance and reporting system, and incidences of water-related legionellosis are being reported with some regularity worldwide. Legionellosis is a consequence of inhalation of aerosols contaminated with Legionella pneumophila and perhaps other related species.
Legionaires disease gets its name from a 1976 outbreak among attendees at an American Legion convention in Philadelphia staying at a particular hotel. There were 221 reported cases and 34 deaths from pneumonia. It required about six months of intense microbiological and chemical investigations to identify the causal bacterial agent because there was no known culturing technique available for the then unknown strain of bacteria.
The origin of exposure was blow-down inhaled aerosols from an air-conditioning system. The cases indicated that smokers were at greater risk than non-smokers. Speculation as to origin was rampant, and it even included a supposed “theory” involving a relatively exotic chemical that might have been pyrolyzed while smoking cigarettes. I recall hearing a report from a U.S. Senate committee that undertook its own assessment and announced that supposed chemical cause, shortly before the true microbial agent was identified. Apparently politics and science don’t mix very well.
Retrospective investigations revealed that in fact numerous “legionnaires” cases had occurred previously and had not been identified, and that a milder form of respiratory infection called Pontiac fever was not uncommon. Many outbreaks and deaths have been reported since then, especially in hospitals. The U.S. Centers for Disease Control has estimated up to 18,000 legionellosis deaths in the U.S. each year.
What actually happens
Since 1976 it has been determined that Legionella pneumophila are fairly common soil and water bacteria and pathogenic when inhaled, not from ingestion. They grow under low nutrient warm water conditions at temperatures in the range of 25 C to 50 C. So, they can be present in warm to hot water systems, showerheads, humidifiers, misting and cooling water for air conditioning systems and hot tubs. In distribution systems and plumbing they can colonize biofilms where they may be protected from normal disinfectant residuals.
The at-risk populations are predominantly those who are elderly and also persons with impaired immune systems. Hospital environments have been the source of numerous cases of outbreaks and deaths related to Legionella. However, it is apparent that there are high-risk people in the general population; for them even a typical house or building environment could be a risk, and specific diagnoses and determinations of causal origin will be less likely.
There are water system management techniques for reducing patient risks used by many hospitals. They include monitoring their plumbing systems, additional disinfection and periodic shock disinfection or heating. Chlorine, chlorine dioxide and even peroxides and silver and copper are being used, but with some controversy for the latter two. There are several studies that indicate that systems with chloramine residuals have a much lower risk of a Legionella related outbreak than those with free chlorine residuals. The rationale is that although chloramines are less potent than free chlorine, their lower chemical reactivity allows them to more effectively penetrate biofilms that may harbor the Legionella.
Other recommendations include maintaining hot water systems above 50 C to reduce growth of the microorganisms, but the dilemma is that temperatures in the 55 C to 60 C range introduce a scalding risk, especially for children and seniors.

Moral of story
The law of unanticipated consequences is still functioning. The benefits of modern warm controlled housing environments, air conditioning and indoor hot water plumbing can have downside consequences. Even those beneficial societal technological advances can provide an opportunity for otherwise innocuous microbes to proliferate and cause disease and death.
The moral of the story is that nature is always evolving, and there are perverse unidentified microbes out there that can harm us. Water treatment to control many microorganisms, not just E. coli, is essential, and waterborne microbial disease is still, and always will be, the greatest risk from public drinking water supplies. Aging water distribution systems require aggressive rehabilitation to prevent leaks and breaks where inoculation by microorganisms and accumulation in biofilms can occur. Replacing that aging infrastructure is a much greater national priority than the hypothetical risks of trace chemical contaminants that get a lot of publicity and lead people to spend money on bottled water because they think it is safer.