Disinfection Cheat Sheet
Summary
A quick cheat sheet when selecting a disinfection method for a design. Bookmark this page so you have current access to the most current information as things do change.
Standard Disinfection Doses
| Method | Standard Dose |
|---|---|
| UV | 20-40 mJ/cm2 |
| Chlorine | CT 15-60 mg·min/L (0.5-1 mg/L free chlorine for 30-60 min, pH 7-8, 20°C) |
| Ozone | CT 5-20 mg·min/L (1-2 mg/L for 5-10 min) |
Disinfection Efficacy Ratings Key
| Rating | Description | Meaning | Example |
|---|---|---|---|
| Effective | ≥3-4 log inactivation (99.9-99.99% kill rate) at standard dose. | Reliable pathogen control; safe for discharge/reuse with minimal risk. | Method "works" - e.g., UV at 20-40 mJ/cm2 fully inactivates E. coli. |
| Limited | 1-3 log inactivation (90-99.9% kill rate) or variable (depends on conditions like pH/turbidity). | Partial control; reduces but doesn't eliminate risk - needs backups like multi-barriers. | Method "half-works" - e.g., chlorine on norovirus lowers spread but may not prevent outbreaks alone. |
| Ineffective | <2 log inactivation (<99% kill rate) at standard dose. | Fails to control; high residual risk - requires alternatives or higher doses (noted where applicable). | Method "doesn't work" - e.g., chlorine on Cryptosporidium leaves viable oocysts. |
| Higher Dose Note | "Ineffective (effective at >X)" means standard fails but increased dose succeeds. | Option for upgrades - e.g., boost UV to >150 mJ/cm2 for adenovirus. Use for resilient pathogens like spores; combines with filtration for best results. | Use for resilient pathogens like spores; combines with filtration for best results. |
Disinfection Efficacy Against Common Waterborne Pathogens
| Pathogen (Type) | UV (20-40 mJ/cm²) | Chlorine (CT 15-60) | Ozone (CT 5-20) |
|---|---|---|---|
| E. coli (Bacteria) | Effective [1] [2] | Effective [3] [4] | Effective [5] [6] |
| Salmonella spp. (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Shigella spp. (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Vibrio cholerae (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Campylobacter spp. (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Pseudomonas aeruginosa (Bacteria) | Limited [2] | Limited [4] | Effective [6] |
| Mycobacterium spp. (Bacteria) | Limited [2] | Limited [4] | Limited [6] |
| Leptospira spp. (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Yersinia enterocolitica (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Legionella pneumophila (Bacteria) | Limited [2] | Limited [4] | Effective [6] |
| Helicobacter pylori (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Listeria monocytogenes (Bacteria) | Effective [2] | Limited [4] | Effective [6] |
| Aeromonas hydrophila (Bacteria) | Effective [2] | Effective [4] | Effective [6] |
| Bacillus subtilis spores (Bacteria spore) | Ineffective (effective at >60 mJ/cm²) [1] [2] | Ineffective (effective at >200 mg·min/L) [3] [4] | Ineffective (effective at >50 mg·min/L) [5] [6] |
| Clostridium perfringens spores (Bacteria spore) | Ineffective (effective at >100 mJ/cm²) [1] [2] | Ineffective (effective at >200 mg·min/L) [3] [4] | Ineffective (effective at >50 mg·min/L) [5] [6] |
| Clostridium difficile spores (Bacteria spore) | Ineffective (effective at >100 mJ/cm²) [1] [2] | Ineffective (effective at >200 mg·min/L) [3] [4] | Ineffective (effective at >50 mg·min/L) [5] [6] |
| Poliovirus (Virus) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Coxsackievirus (Virus) | Effective [1] [2] | Limited [3] [4] | Limited [5] [6] |
| Echovirus (Virus) | Effective [1] [2] | Limited [3] [4] | Limited [5] [6] |
| Hepatitis A (Virus) | Effective [1] [2] | Effective [3] [4] | Effective [5] [6] |
| Hepatitis E (Virus) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Rotavirus (Virus) | Effective [1] [2] | Effective [3] [4] | Effective [5] [6] |
| Norovirus (Virus) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Sapovirus (Virus) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Adenovirus (Virus) | Ineffective (effective at >150 mJ/cm²) [1] [2] | Effective [3] [4] | Limited [5] [6] |
| Astrovirus (Virus) | Effective [1] [2] | Effective [3] [4] | Effective [5] [6] |
| Parvovirus (Virus) | Effective [1] [2] | Effective [3] [4] | Effective [5] [6] |
| Cryptosporidium parvum (Protozoa) | Effective [1] [2] | Ineffective (effective at >1,000 mg·min/L) [3] [4] | Effective [5] [6] |
| Giardia lamblia (Protozoa) | Effective [1] [2] | Limited (effective at >230 mg·min/L) [3] [4] | Effective [5] [6] |
| Cyclospora cayetanensis (Protozoa) | Effective [1] [2] | Ineffective [3] [4] | Effective [5] [6] |
| Naegleria fowleri (Protozoa) | Limited [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Entamoeba histolytica (Protozoa) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
| Balantidium coli (Protozoa) | Effective [1] [2] | Limited [3] [4] | Effective [5] [6] |
Glossary
| Term | Definition |
|---|---|
| UV | Ultraviolet disinfection; refers to a physical process using UV-C light (typically at 254 nm wavelength) to damage pathogen DNA/RNA, preventing replication and infection. |
| Chlorine | Chemical disinfection using chlorine compounds (e.g., sodium hypochlorite or chlorine gas) to oxidize pathogen cells, proteins, and nucleic acids. |
| Ozone | Gaseous oxidant (O₃) used for disinfection; rapidly breaks down pathogen cell walls, proteins, and nucleic acids through oxidation. |
| mJ/cm² | Millijoules per square centimeter; unit measuring UV energy dose delivered per unit area to achieve inactivation. |
| CT | Concentration × Time; metric for chemical disinfectant exposure, calculated as disinfectant concentration (mg/L) multiplied by contact time (min). |
| mg·min/L | Milligrams per minute per liter; unit for CT value, indicating the product of concentration and time in chemical disinfection. |
| Log (Reduction) | Logarithmic scale of inactivation; e.g., 1-log = 90% kill, 2-log = 99%, 3-log = 99.9%, 4-log = 99.99%. |
| Disinfection | Process to reduce or eliminate viable pathogens in water to levels safe for discharge or reuse. |
| Inactivation | Rendering pathogens non-viable or unable to replicate/infect, often measured in log reduction without necessarily destroying the structure. |
| pH | Measure of water acidity/alkalinity (scale 0-14); affects disinfectant efficacy (e.g., chlorine works better at lower pH). |
| Turbidity | Cloudiness of water due to suspended particles; reduces UV penetration and chemical disinfectant contact, lowering efficacy. |
| Multi-barrier | Strategy using multiple sequential or overlapping safeguards (e.g., filtration + disinfection) to ensure contaminant removal, providing redundancy if one barrier fails. |
Bibliography
- EPA Ultraviolet Disinfection Guidance Manual
- EPA Water Treatment Manual
- EPA Disinfection Profiling and Benchmarking Guidance Manual
- Chlorine Disinfection and CT Calculations
- Overview of the Main Disinfection Processes for Wastewater and Drinking Water Treatment Plants
- EPA Alternative Disinfectants and Oxidants Guidance Manual
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