ASTM D6734 Coliphage Detection Testing in Water
ASTM D6734 determines coliphages infective for E. coli C in water. The test procedure is easy, affordable, and results in less than 6.5 hours. This coliphage technique can detect coliphages in water with a detection limit of 1 coliphage per volume analyzed. The values are considered as a standard when expressed in SI units.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM D6734 is a standard test method for detecting low levels of coliphages in water samples. Coliphages are bacteriophages (viruses that infect coliform bacteria, particularly Escherichia coli) and are used as indicators of fecal contamination and the potential presence of enteric human viruses in water supplies.
Because human enteric viruses are present at very low concentrations and are difficult to culture directly, coliphages serve as practical surrogate indicators for virus monitoring. This method is used in drinking water quality monitoring, recreational water assessment, and wastewater treatment efficiency evaluation.
Scope, Applications, and Benefits
Scope
ASTM D6734 evaluates:
- Detection and enumeration of somatic coliphages and/or male-specific (F+) coliphages
- Applicability to low-turbidity drinking water and treated wastewater
- Sample concentration and host bacteria plaque assay procedures
- Coliphage presence/absence or quantitative plaque-forming unit (PFU) counts
Applications
- Drinking water quality monitoring and regulatory compliance
- Recreational water safety assessment
- Wastewater treatment plant effluent monitoring
- Virus removal efficiency evaluation of water treatment processes
- Groundwater and surface water contamination assessment
Benefits
- Provides a practical viral contamination indicator in water
- More conservative fecal indicator than total/fecal coliforms alone
- Supports multi-barrier water treatment performance monitoring
- Aligns with EPA and WHO guidance on viral indicators
- Enables early detection of treatment failures or source contamination
Test Process
Sample Collection & Concentration
The water sample is collected and, if needed, concentrated to achieve adequate detection sensitivity.
1Host Bacteria Preparation
E. coli host culture is grown to log-phase under specified conditions for plaque assay susceptibility.
2Plaque Assay
The sample is mixed with host bacteria in soft agar, plated, and incubated for plaque formation.
3Coliphage Enumeration
After incubation, plaques are counted and coliphage concentration (PFU per 100 mL or liter) is calculated and reported.
4Technical Specifications
| Parameter | Details |
|---|---|
| Standard | ASTM D6734 |
| Test Principle | Plaque assay using E. coli host bacterium |
| Applicable Matrices | Drinking water, treated wastewater, recreational water |
| Measured Output | Coliphage concentration (PFU/100 mL or PFU/L) |
| Incubation Temperature | 37°C (E. coli host) |
| Detection Limit | 1 PFU per sample volume analyzed |
Instrumentation Used for Testing
- Microbiological safety cabinet and incubator
- E. coli host strain cultures and growth media
- Agar plates and soft agar overlay materials
- Colony/plaque counter or manual counting equipment
- Sample concentration apparatus
- Autoclave and sterile sampling equipment
Results and Deliverables
- Coliphage count (PFU/100 mL or PFU/L)
- Presence/absence determination for regulatory compliance
- Plaque assay plates (documented photographically)
- Treatment efficiency data (log removal values)
- Water quality monitoring and regulatory compliance reports
Frequently Asked Questions
Coliphages are viruses that infect E. coli bacteria. They are used as indicators because they are present alongside human enteric viruses during fecal contamination, are easier and safer to detect, and survive similarly in aquatic environments.
Somatic coliphages infect through the bacterial cell wall and are more abundant; F+ coliphages infect through the F-pili and are considered closer indicators of human enteric virus presence. ASTM D6734 may address one or both groups.
Drinking water typically contains very low coliphage levels (potentially <1 PFU/L). Concentrating large volumes (10–1000 L) is necessary to reliably detect such low concentrations.
The EPA Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) references coliphages for source water monitoring. Their broader regulatory use continues to evolve at state and federal levels.
No. Absence of coliphages indicates low fecal contamination risk but does not guarantee virus-free water. They are indicators, not direct measures of pathogenic human viruses.
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