22 ENVIRONMENT and ENERGY
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Risk management approaches to control legionella
This document describes risk management approaches and technologies for controlling legionella growth in premise plumbing systems . The information presented is based on the references reviewed during the preparation of this document .
By the Environmental Protection Agency
In general , technologies for controlling legionella have been shown to offer some degree of effectiveness against legionella . However , the long-term eradication of legionella from a premise plumbing system has not been demonstrated consistently with any of these technologies . Complex plumbing systems , such as those found in a multi-storey building , might have areas where there is less exposure to disinfectants and heat , which could provide opportunities for bacteria to grow . Legionella bacteria may be found in biofilms or in sections of the plumbing system with long water residence times , depending on the pipe materials , water temperature and other system-specific factors . The effectiveness of a technology against legionella growth in biofilm or legionella ingested by amoebae is often cited as a concern . Other studies suggest that disinfectants , disinfection byproducts and other environmental pollutants may induce an increase in antimicrobial resistance of bacteria , including pathogens such as L . pneumophila ( Ashbolt et al ., 2013 ).
The retention of viable legionella in amoebae cysts is an important factor for risk management of water distribution and premise plumbing systems . Springthorpe et al . ( 2014 ) discusses the importance of the association between opportunistic pathogens , such as legionella , and free-living protozoa ( which include amoebae ), and how the protozoa might lead to long-term persistence of the pathogens by allowing them to relocate and / or avoid interventions , such as disinfection . Wang et al . ( 2013 ) suggest that natural systems may provide conditions , such as an abundance of beneficial microbial diversity , which may help prevent and potentially control the growth of opportunistic pathogens that can be found in engineered environments .
Establishing and maintaining a disinfectant residual throughout the system is critical for the effectiveness of chlorine , monochloramine , chlorine dioxide and CSI treatments . Maintaining a disinfectant residual provides increased protection in the event legionella is released into the premise plumbing system ( for example , sloughing off of biofilm material containing legionella ) or enters a premise plumbing system through the PWS distribution system . Ozone and UV disinfection do not produce a disinfectant residual ( USEPA , 2007 ). Therefore , water treated with only these methods , in some cases , may be susceptible to subsequent contamination unless treatment is at the point of use or supplemental treatment is provided . For these reasons , more than one type of treatment or control measure may be necessary to inhibit legionella growth in a premise plumbing system ( VHA , 2014 ).
The effectiveness of a particular technology is dependent upon building-specific characteristics , such as pipe material , age and condition ; water usage rates and water age ; and water quality parameters ( for example , pH , hardness , organic contaminants , inorganic contaminants , and types of waterborne pathogens ). Therefore , decisionmakers may want to consider the specific conditions of each premise plumbing system before making a decision and ensure that the conditions are adequate for the selected approach .
The physical and chemical characteristics of the finished water from water treatment plants
March 2017 Volume 23 I Number 1 www . plumbingafrica . co . za