7.0 MICROBIAL ASPECTS

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door ALEJANDRO DEHESA DELGADO

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PATHOGENS

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EMERGING ISSUES

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

zoonatic pathogen make up 75% of the emerging pathogens.

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

PUBLIC HEALTH ASPECTS

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

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

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

TABLE TO REFER

Table 7.2 (pg 121)

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

Table 7.1 (pg 119)

Characteristics, behavior, resistance of pathogens

TREATMENT OF PATHOGEN

HOUSEHOLD TREATMENT

Combination (multiple-barrier) treatment approaches

Flocculation plus disinfection systems

e.g. commercial powder sachets or tablets

Coagulation, precipitation and / or sedimentation

Simple sedimentation

Thermal (heat) technologies

Boiling

UV light technologies using lamps

UV irradiation

Solar disinfection

Solar UV radiation + thermal effects

Granular media filter

Household-level intermittently operated slow sand fi ltration

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

Membrane, porous ceramic or composite filters

Fiber and fabric filtration

Membrane filtration

Reverse osmosis

Ultrafiltration

Nanofiltration

Microfiltration

Porous ceramic and carbon block filtration

Chemical disinfection

Free chlorine disinfection

CENTRAL TREATMENT

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

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

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

disinfection

filtration

sendimentation

flocculation

coagulation

Water treatment required to remove or destroy pathogenic microorganism

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

OCCURANCE

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

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

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

To provide treatment so that ensure health within water safety plan

To determine the pathogen concentration in source water

PERSISTANCE AND GROWTH IN WATER

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

persistence is affected by several factors such as temperature.

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

IDENTIFYING LOCAL ACTIONS IN RESPONSE TO MICROBIAL WATER QUALITY PROBLEMS AND EMERGENCIES

Actions following an incident

Boil water advisories

METHODS OF DETECTION OF FAECAL INDICATOR ORGANISMS

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.

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

MICROBIAL MONITORING

Helminths

Microscopy

Protozoa parasites

Immunomagnetic separation in combination with immunofluorescence microscopy

Virus

Polymerase Chain Reaction (PCR)

Cell culture

Bacteria (E.coli)

Culture-based method

Solid media

Broth cultures

Included in

surveillance

operational

verification

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

QUANTITATIVE MICROBIAL RISK ASSESSMENT

Risk Assessment Paradigm For Pathogen Health Risks

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

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

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

Identify all possible hazards and their pathways from sources to recipients

Systemically combines information on exposure and dose-response models

REFERENCE PATHOGENS

PROTOZOA

Source of protozoa: Cryptospotidium and Balantidium

Least sensitive to inactivation by chemical disinfection

BACTERIA

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

Legionella and non-tuberculous mycobacteria can grow in water environment

Most sensitive to inactivation by disinfection

VIRUSES

Example: Rotaviruses, enteroviruses, and noroviruses

Can persist in a long period inn water

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

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