MICROBIOLOGICAL EFFICIENCY OF WATER TREATMENT
Report No FR0219
To review the available literature on the removal of bacteria, viruses and cysts by water treatment processes. To identify circumstances in which breakthrough of different groups of micro-organisms could occur and the subsequent treatments which could be used to protect public health.
The microbiological safety of drinking waters must be ensured to protect public health. Investigations in 90/91 on the assessment of drinking water disinfectants (F-0501A) have demonstrated that "natural" populations of micro-organisms may be more resistant to treatment than is predicted by studies with laboratory cultures. Although slow sand filtration has been demonstrated to be an effective barrier to microbiological challenges there are doubts whether rapid gravity filters are equally effective and the use of granular activated carbon is known to pose some potential microbiological problems. Recent outbreaks of Cryptosporidiosis have demonstrated the vulnerability of certain aspects of some treatment strategies.
The literature reviewed quotes high micro-organism removal efficiencies by water treatment processes. However, outbreaks of waterborne disease do occur which demonstrate that conventional water treatment cannot guarantee the safety of drinking water sup plies at all times. The report highlights certain water treatment practices that are susceptible to the passage of micro-organisms into supply.
The report highlights the failure of current bacteriological monitoring to ensure that water supplies are free of viruses and protozoan cysts. The use of alternate indicators of water treatment efficiency such as coliphages and clostridia are proposed by several authors.
The objectives of future work can be summarised as follows :
V RESUME OF CONTENTS
This review discusses waterborne pathogens and their removal by conventional water treatment processes. Outbreaks of waterborne disease and their possible causes are reported. Water treatment practices that could lead to the passage of pathogens into supply are highlighted.
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