Microbiology of Drinking Water

Production and Distribution

Gabriel Bitton

• Éditeur: Wiley-Blackwell
• Année: 2014
• ISBN:
  9781118743911
• Édition: 1
• Sujet: Biological Sciences
• Sous-sujet: Microbiology

Microbiology of Drinking Water Production and Distribution addresses the public health aspects of drinking water treatment and distribution. It explains the different water treatment processes, such as pretreatment, coagulation, flocculation, sedimentation, filtration, disinfection, and their impacts on waterborne microbial pathogens and parasites. Drinking water quality may be degraded in water distribution systems—microorganisms form biofilms within distribution systems that allow them to flourish. Various methodologies have been proposed to assess the bacterial growth potential in water distribution systems. Microbiology of Drinking Water Production and Distribution also places drinking water quality and public health issues in context; it addresses the effect of bioterrorism on drinking water safety, particularly safeguards that are in place to protect consumers against the microbial agents involved. In addition, the text delves into research on drinking water quality in developing countries and the low-cost treatment technologies that could save lives. The text also examines the microbiological water quality of bottled water, often misunderstood by the public at large.

1
MICROBIAL CONTAMINANTS IN DRINKING WATER

1.1 INTRODUCTION

In water treatment plants, the goal is to produce pathogen- and parasite-free drinking water, not necessarily sterile water. There are, however, several sources of contamination in a potable water system (Percival et al., 2000):

• Drinking water source (see Chapter 2).
• Inadequate treatment in the water treatment plant.
• Water distribution system (WDS): Treated water quality may deteriorate in the distribution system. Pathogens and parasites may be introduced into treated water through cracks in the water pipes, back-siphonage or cross-contamination.
• Biofilm development which may alter water quality.

This chapter surveys the major microbial pathogens and parasites which may contaminate drinking water.

1.2 TRANSMISSION ROUTES OF PATHOGENS AND PARASITES

Transmission involves the transport of an infectious agent from the reservoir to a host. It is the most important link in the chain of infection. Pathogens can be transmitted from the reservoir to a susceptible host by various routes. The transmission pathways of water-related pathogens are summarized in Figure 1.1 (WHO, 2011c).

Figure 1.1 Transmission pathways for water-related pathogens and parasites. Adapted from WHO (2011c). Guidelines for Drinking-Water Quality. 4^th Ed. World Health Organization, Geneva, Switzerland.

1.2.1 Person-to-Person Transmission

The most common route of transmission of infectious agents is from person to person. Examples of direct contact transmission are the sexually transmitted diseases such as syphilis, gonorrhea, herpes, or acquired immunodeficiency syndrome (AIDS). Coughing and sneezing discharge very small droplets containing pathogens within a few feet of the host (droplet infection).

1.2.2 Waterborne Transmission

Water is essential to life on Planet Earth. Humans generally consume from 2 to 4 L water/day. The composition of drinking water has positive (e.g., iron, fluoride) and, sometimes, negative effects on human health because it may contain microbiological, chemical, and radiological contaminants. When contaminated with human and animal wastes, water contributes to (Mintz et al., 2001)

• Waterborne diseases: Infections with microbial pathogens may result in gastrointestinal problems (e.g., diarrhea) or in systemic illnesses (e.g., hepatitis caused by viruses; kidney failure resulting from infection with Escherichia coli O157:H7) (Krewski et al., 2002).
• Water-washed diseases (e.g., trachoma, lice, tick-borne disease) linked to poor hygiene resulting from poor access to safe water.
• Water-based diseases such as schistosomiasis caused by parasitic worms (e.g., Schistosoma mansoni) that live inside freshwater snails. The infectious form of the worm, called cercariae, contaminates the water and causes infection following contact with the skin. The parasite causes damages in several organs such as the intestines, skin, liver, and the brain.
• Water-related diseases caused by insect vectors that breed in water (e.g., malaria, Dengue fever, yellow fever).

In 1854, John Snow, an English physician and epidemiologist, first established the waterborne transmission of pathogens. Following a cholera epidemics that resulted in 500 deaths, he noted a relationship between the cholera epidemics and consumption of water from the Broad Street well in London. In 1893, Robert Koch, isolated the bacterium that causes cholera, establishing the link between drinking water contamination and the onset of cholera. At the beginning of the twentieth century, cholera and typhoid fever were the major waterborne diseases of concern to public health officials (more details are given by Medena et al., 2003). Other pathogens and parasites have emerged since and include, among others, Cryptosporidium, Giardia, E. coli O157:H7, and enteric viruses.

In 1996, diarrheal diseases contracted worldwide mainly via contaminated water or food, killed 3.1 million people, most of ...