7.0 MICROBIAL ASPECTS

Inhalation of water droplets

Contact with water (dermal)

Ingestion of the eggs in food
contaminated with faeces or
faecally contaminated

Patients undergoing immunosuppressive
therapy or those with acquired
immunodeficiency syndrome (AIDS)

VIRUSES

Smallest pathogen and difficult to remove by physical process (filtration)

Can persist in a long period inn water

Example: Rotaviruses, enteroviruses, and noroviruses

BACTERIA

Most sensitive to inactivation by disinfection

Legionella and non-tuberculous mycobacteria can grow in water environment

Example: Vibrio, Campylobacter, E.coli O157, Salmonella and Shigella

PROTOZOA

Least sensitive to inactivation by chemical disinfection

Source of protozoa: Cryptospotidium and Balantidium

Systemically combines information on exposure and dose-response models

Identify all possible hazards and their pathways from sources to recipients

Risk Assessment Paradigm For Pathogen Health Risks

Exposure Assessment: Estimation of number of pathogen that is exposed to an individual through ingestion

Dose-Response Assessment: To derive the probability of an adverse effect following exposure to one or more pathogenic organisms

Risk Characterization: Data collection on exposure, dose-response and incidence and severity of disease

To determine whether a treatment or other process is effective in removing target organisms.

Included in

verification

operational

surveillance

Bacteria (E.coli)

Culture-based method

Broth cultures

Solid media

Virus

Cell culture

Polymerase Chain Reaction (PCR)

Protozoa parasites

Immunomagnetic separation in combination with immunofluorescence microscopy

Helminths

Microscopy

Analysis for faecal indicator organisms provides a sensitive, although not the most rapid, indication of pollution of drinking-water supplies.

The standardization of methods and of laboratory procedures is of great importance if criteria for the microbial quality of water are to be uniform in different laboratories and internationally.

Boil water advisories

Actions following an incident

pathogen with low persistence are more likely to be spread by person to person contact or poor personal hygiene.

persistence is affected by several factors such as temperature.

high amount of biodegradable organic carbon together with warm water can permit growth of waterborne pathogen.

To determine the pathogen concentration in source water

To provide treatment so that ensure health within water safety plan

The concentration of pathogen in raw water can be estimated from concentration of pathogens in waste water

Faecel indicator bacteria, such as E.Coli always present at high concentration in waste water

Discharge water is diluted in receiving surface water leading to reduce pathogen number with the dilution factor

CENTRAL TREATMENT

Validation is important in ensuring that treatment will achieve the desired goals

Water treatment required to remove or destroy pathogenic microorganism

For example : poor quality surface water require multiple treatments stages.

coagulation

flocculation

sendimentation

filtration

disinfection

The case that efficacy for microbial reduction differ among the microbial groups so different treatment process are needed.

There are positive and negative interactions occur between multiple steps and these can affect the overall of water quality.

HOUSEHOLD TREATMENT

Chemical disinfection

Free chlorine disinfection

Membrane, porous ceramic or composite filters

Porous ceramic and carbon block filtration

Membrane filtration

Microfiltration

Nanofiltration

Ultrafiltration

Reverse osmosis

Fiber and fabric filtration

Granular media filter

Rapid granular, diatomaceous earth, biomass and fossil fuel - based filter

Household-level intermittently operated slow sand fi ltration

Solar disinfection

Solar UV radiation + thermal effects

UV light technologies using lamps

UV irradiation

Thermal (heat) technologies

Boiling

Coagulation, precipitation and / or sedimentation

Simple sedimentation

Combination (multiple-barrier) treatment approaches

Flocculation plus disinfection systems

e.g. commercial powder sachets or tablets

Table 7.1 (pg 119)

Characteristics, behavior, resistance of pathogens

Table 7.2 (pg 121)

Microorganisms for which transmission through drinking
water has been proposed but evidence is lacking

developing and applying control on drinking water quality should be control such a outbreaks.

waterborne pathogen that contaminated through drinking water can lead to severe and life threatening. Eg: cholera, hepatitis, thyphoid.

effects and exposure to pathogens are not the same for all individuals . Not all infected individuals will develop symptomatic infections.

global changes, human development, population growth and climate change influence water disease risk

zoonatic pathogen make up 75% of the emerging pathogens.

zoonatic pathogen pose the greatest challenge to ensure the safety of drinking water and ambient water