Effective management of microbial fouling to reduce health-related risk from industrial water has become a business priority. The most important -- but not the only -- industrial water health-related issue today is the risk of legionellosis.
This is the condition of being infected by bacteria in the genus Legionella. It can result in the pneumonia known as Legionnaires' Disease or the flu-like symptoms known as Pontiac Fever. This disease is the second or third most frequent cause of sporadic community-acquired pneumonia in the United States. Worldwide, hundreds of thousands of people are affected by legionellosis each year, but mostly exposure on this massive scale is from domestic water systems, not from industrial water systems. In susceptible people, the disease can be devastating. Even for those who recover, it is now established that permanent damage to the lungs can occur.
Legionella proliferation is always associated with its protozoan hosts and in biofilms from water or soil. Industrial water systems are prone to conditions that can amplify the concentration of pathogen to dangerous levels. Specifications for controlling health-related risk from legionellosis have now appeared in guidance from industrial associations and governments all over the world.
In the United States, guidance has been published by the Occupational Safety & Health Administration (1998), American Society of Heating, Refrigerating and Air-Conditioning Engineers (2000), Cooling Technology Institute (2000), Centers for Disease Control and Prevention (2001), American Society of Testing and Materials (2002), and others. Taken together, this guidance should be thought of as the code, or standard, of practice in the United States. In a litigious society, motive to comply with this code of practice should be extremely compelling.
But, legionellosis is not the only health-related risk from industrial water about which the public has become aware. Recently, nontuberculosis mycobacterial (NTM) pneumonia has been increasingly associated with aerosol-generating water systems. The causative bacterial agents are found ubiquitously in the environment especially associated with biofilms in aquatic and soil habitats. Sixteen species of bacteria in the genus Mycobacterium are known to be potential human pathogens. Public concern about the disease appears to be increasing.
Also of growing concern, especially in tropical regions of the world, is disease caused by pathogenic amoebae such as Naegleria fowleri and also in the genus Acanthamoeba. Primary amoebic meningoencephalitis, granulomatious amoebic encephalitis and acanthamoebic keratitis (amoebic infections of the eye) all are potentially serious afflictions. Although disease-causing infections by these common water-borne protozoa are rare, mortality rates among the ill can be high.
Managing the Microbial Fouling ProcessMost industrial water is in systems open to the environment. Microbial inoculation usually occurs continuously. By a very large margin, most viable and productive microorganisms in industrial water systems are found on surfaces in biofilms and in cell aggregates -- not found floating around alone in the recirculating water. Biofilms and the nutrients that fuel them are the root cause of most microbial fouling problems in industrial water systems.
It turns out that common water-borne protozoa such as amoebae in the genus Acanthamoeba are much more important in biofilms than anyone believed just a few years ago. As is well known, protozoa graze upon the bacteria in biofilms for food. They can be easily observed (with a microscope) voraciously devouring biofilms in industrial water systems (figure 1).
But, it is now more recently known that, while Legionella and Mycobacterium are consumed for food by protozoa along with other bacteria in biofilms instead of being devoured by phagocytosis, as are the others, these bacteria infect their hosts and exponentially multiply within them. Their virulent, prolific intracellular progeny destroy the protozoan host and are then released in vast numbers back into the environment wherein new susceptible protozoan hosts are insidiously infected. Unfortunately for us, certain human white blood cells (macrophage) are sufficiently similar to protozoa. Infection of macrophage in our respiratory system by Legionella and Mycobacterium can lead to severe disease in susceptible people if enough pathogen is inhaled.
Simply applying chemical sufficient to eliminate biofilms and the protozoa that graze upon them is usually not successful. Protozoa form cysts that are highly resistant to chemicals, heat and drying. Pathogenic Legionella can survive inside these cysts and can thereby also survive massive doses of chemical. Control of microbial fouling, therefore, requires the systematic application of a fouling process management strategy (table 1).
Often surprising to those unfamiliar with the microbial world, this last category of practice, regulation of remedy, is the key to long-term technical success. Microbial fouling deposits are communities of living microorganisms. Completely eliminating them or sterilizing them is almost never practical. Adaptation to antimicrobial treatments can rapidly occur, especially in stable, microbiologically diverse biofilms. Unvarying application of remedy will become progressively less effective because surviving microorganisms in biofilms predominate to build ever more resistant microbial communities. This is an undisputed fact in nature and industry. Failure to heed its significance has lead to many spectacular industrial failures.
Controlling and Managing RiskAssessing risk is the essential first step in minimizing it. A formal risk assessment always results in a document that links discovery of problem root-causes with specifically recommended corrective action and assigns responsible personnel to action. The risk assessment document helps establish value and provides motive to get the risk management job done properly.
While risk assessment is the necessary first step, it most certainly is not the only step in a risk management plan. Typically, service recommendations derived from the risk assessment are for analytical work to locate and quantify pathogens in the system, monitoring, control, and disinfection.
Risk management in microbial fouling control for industrial water is tremendously valuable. Today, users of industrial water obtain this value most consistently, safely, cost-effectively and conveniently when they take full advantage of professional specialists trained in hygiene services.