Topic 5: Disinfection
Description
Disinfection is a key process in drinking water treatment and essential for protecting public health. Its purpose is to inactivate or destroy disease-causing microorganisms such as bacteria, viruses, and protozoa.
Even when source protection and filtration are effective, disinfection is often used as a final safety barrier to ensure microbiological security.
It is therefore considered the final barrier in a multi-barrier water safety concept.
Common disinfection technologies include:
- UV disinfection
- Chlorination
- Ozonation
Each method differs in performance, operational requirements, and network behavior.
UV Disinfection
How It Works
UV disinfection uses ultraviolet light to damage the DNA of microorganisms, preventing them from reproducing and causing infection.
The process is physical, not chemical, and works instantly as water flows through the reactor.
It is effective against:
- bacteria
- viruses
- protozoa (e.g. Giardia, Cryptosporidium)
Advantages
- no chemicals required
- no change in taste or odor
- highly effective against many pathogens
- immediate action
- no disinfection by-products
- environmentally friendly
- effective against chlorine-resistant organisms
Disadvantages
- no residual protection in the network
- risk of recontamination after treatment
- requires low turbidity water
- lamp maintenance required
- needs reliable electricity supply
Typical Applications
- groundwater systems
- spring water supplies
- small and medium treatment plants
- mountain and rural systems
- bottled water production
Chlorination
How It Works
Chlorination involves adding chlorine-based compounds to water to destroy microorganisms.
A key feature is the presence of a residual disinfectant, which remains active in the distribution system and continues to protect the water after treatment.
This makes chlorination effective not only in the plant but also throughout the network.
Advantages
- provides residual protection in distribution systems
- proven and widely used technology
- effective against most bacteria and viruses
- low infrastructure requirements
- easy monitoring and control
- suitable for large networks
- protects against secondary contamination
Disadvantages
- possible taste and odor effects
- requires careful dosing control
- formation of disinfection by-products possible
- limited effectiveness against some protozoa
- chemical handling required
Typical Applications
- municipal water supply systems
- long distribution networks
- warm climate regions
- storage tanks and reservoirs
- emergency disinfection
- systems requiring network protection
Ozonation
How It Works
Ozonation uses ozone (O₃), a strong oxidant, to disinfect water and oxidize contaminants.
Ozone is generated on-site and reacts quickly with microorganisms and dissolved substances.
In addition to disinfection, it can also:
- oxidize iron and manganese
- improve taste and odor
- reduce color
- break down organic compounds
Advantages
- very strong disinfection performance
- rapid microbial inactivation
- improves taste, odor, and color
- oxidizes a wide range of contaminants
- no chemical storage required
- enhances downstream treatment processes
Disadvantages
- no residual protection in the network
- high energy demand
- complex system and operation
- requires on-site generation
- trained operators needed
Typical Applications
- large municipal treatment plants
- surface water treatment systems
- challenging raw water sources
- taste and odor problems
- advanced multi-barrier systems
Key Difference
| Parameter | UV | Chlorination | Ozonation |
|---|---|---|---|
| Microbial removal | Excellent | Excellent | Excellent |
| Residual effect | No | Yes | No |
| Chemicals added | No | Yes | No residual |
| Taste/odor impact | None | Possible | Improvement |
| Complexity | Low | Low–medium | High |
| Energy demand | Medium | Low | High |
Key Takeaway
Disinfection is the final and critical barrier in drinking water treatment.
UV disinfection provides strong microbial safety without chemicals, chlorination ensures long-term protection within the distribution system, and ozonation offers powerful disinfection combined with water quality improvement.
The right choice depends on raw water quality, system design, and whether residual protection in the network is required.