Treated effluent sterilisation
Secondary Sewage Treatment
Secondary Sewage Treatment, such as in package plants, only reduces the level of micro-organisms by about 90%. ‘Sterilisation’ provides a much higher level of reduction and is in particular used to reduce the level of pathogenic (harmful) organisms.
- Sterilisation of treated wastewater / sewage effluent is required in a number of different applications.
- Where effluent is used to irrigate grass where people play, or on food crops.
- Sterilisation is also required in some applications where effluent is discharged into the sea or small bodies of water where there may be contact with people.
- In some areas sterilisation may be required where there is serious groundwater contamination and where this water is used for public drinking water supply.
- Sterilisation is required as a matter of course in some tropical and developing countries.
Three methods of sterilisation are available.
Biodigester Ozonisation systems use an Ozone Generator, a small air pump and diffuser to sterilise the treated sewage effluent in a special chamber or final settlement tank where there is no recycling system in use.
See diagram above for a six person system (Ref: BDOZ6).
Biodigester ‘Ozonisation systems’ are available for a wide range of populations. Please ask for details.
Even after sterilisation it is still inadvisable to spray the effluent and create an aerosol because fine droplets in the air can be ingested.
The use of chlorination systems for sterilising treated wastewater/sewage effluent has been banned in Europe for many years. This is because chlorination of protein derived compounds creates by-products that can be significantly damaging in the environment.
The discharge of free chlorine into a watercourse is also unsatisfactory.
BES advises and promotes the use of low maintenance Ozonisation systems as an alternative to chlorination. See above. However BES is aware that Chlorination is standard practice in many developing countries.
Ultra Violet (UV) Sterilisation
UV light used for the sterilisation of treated sewage / waste water effluent has the disadvantage that a biological slime grows on the tube(s) even with the best quality effluents. Consequently the tubes have to be cleaned on a very frequent basis to avoid any deterioration in performance.
BES advises and promotes the use of low maintenance Ozonisation systems to avoid the cleaning problem and to provide reliable operation and performance.
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