Bacterial Removal From Water
• Objectives
To understand the theory and practice of monitoring the bacteriological
quality of water.
To know the typical bacteriological standards required for Raw and
Treated Water.
References
Water Supply - Twort et al
Examination of Water for Pollution Control (Vol 3) - M.J. Suess
Report 71 - The microbiology of water 1994 Part 1 - Drinking Water ,HMSO
UK Water Supply (Water Quality) Regulations 2000 (SI 3184)
http://www.dwi.gov.uk/regs/si3184/3184.htm
http:// www.dwi.gov.uk/regs/pdf/Interim2003.pdf (Guidance for SI 3184)
EC Directives
(98/83/EC) Drinking Water - Official Journal L 330
(80/778/EEC) Drinking Water - Official Journal L229
(75/440/EEC) Abstraction - Official Journal L 194
Water Supply Bacteriology
useful for:
(1) Detection of faecal pollution in potential water supply (very sensitive test).
(2) Assessment of water treatment plant performance.
(3) Confirmation of hygienic safety of final water entering supply.
(4) Surveillance of water quality throughout distribution.
(5) Indicator bacteria: give Quantitative results therefore used as basis for these
standards:
(1) Raw Water Quality
(2) Treated Water Quality
(3) Distribution System Water Quality
(4) Bathing Water Quality
(5) Quality of Water for shellfish growing
(6) Quality of water for re-use in irrigation.
Typical Bacterial Concentrations in
Water Samples
Coliform/100 ml
Underground water
<100 (<10)
Upland stream
500
Lowland river
104 (Tyne typically 20,000/100ml)
Industrialised river
105
Raw sewage
107
“Royal Commission” effluent
105
Tap Water
0
Bacterial Examination of Water
(1) Can easily distinguish faecal from other sources of contamination.
(2) Extremely sensitive tests.
107 E.coli/100 ml raw sewage
Can detect 1 E.coli/100 ml
Therefore can dilute sewage x 10-6 and still detect it
Much more sensitive than many chemical tests.
(3) Simple, reliable tests
Dehydrated media, pre-sterilised materials available.
Consistent monitoring across Europe (World!)
(4) Quantitative result therefore can define microbiological standards for different
water uses.
Indicator Organisms
• 1. Suitable for analysis from all sources
– tap, river, sea, industrial.
• 2. Present wherever enteric pathogens exist
• 3. Should survive longer than hardiest enteric pathogen
• 4. Should not reproduce in the water
• 5. Easy and Specific Assay
• 6. Harmless to humans
• 7. numbers should reflect (correlate with) degree of faecal pollution
Bacterial Examination of Water
Some important Definitions:(1) Coliforms:-
Gram -ve, non-spore forming rods.
Aerobic/facultative anaerobes
Lactose
Acid + Gas, 48 hr. 35C (37C)
Oxidase negative.
Tolerant of bile salts (and synthetic detergents, SDS)
(2) Thermotolerant Coliforms:(TTC)
(a) Faecal Coliforms:- As above but at 44C.
(but not all 44 C + orgs.are faecal in origin)
(b) Escherichia coli:- Thermotolerant Coliforms (44 C)
which give Acid + Gas in 24 hrs.
And form Indole from Tryptophan
(MR +; VP -; Citrate -)
(3) Faecal Streptococci S. faecalis S. faecium S. bovis etc.
Gram positive cocci, chain forming.
Possess Lancefields Group D antigen
Grow in presence of Bile, Salt and Sodium azide, at 45oC.
In animals, are as numerous as E.coli
In humans are less numerous than E.coli (FC/FS > 4)
has been used to
identify source
of pollution
F.S. Survive in seawater better than E.coli.
Rapid death at 20oC but prolonged survival < 10oC.
More resistant to chlorination than Coliforms + E.coli.
(4) Sulphite-reducing Clostridia and Clostridium perfringens
Gram positive, spore forming rods. Anaerobic.
Spores survive much longer than vegetative cells of other indicators.
Much more resistant to chlorination.
Useful test for water supplies which can only be sampled occasionally and which
may have intermittent pollution (e.g. shallow wells/springs)
Also useful for examining marine sediments to detect zone affected by sewage
outfall. (Range > 10 km)
Raw Water (Abstraction) Standards
1962 WHO (Omitted 1973 and 1984)
Coliform/100ml
0-50
50-5,000
5,000-50,000
>50,000
I
II
III
IV
Classification
Needs Disinfection only
Needs Conventional treatment
Needs Extensive treatment
Unacceptable - only use if
nothing else
1975 EEC
A1
Coliforms/100 ml
50
Faecal Coliforms/100 ml 20
Faecal Streps./100 ml
20
Salmonellae
Nil/5 l
A2
5,000
2,000
1,000
Nil/5 l
A3
50,000
20,000
10,000
DisinfectionConventional Intensive
Only
Treatment
Treatment
Conventional Treatment
- flocculation, coagulation, decantation,
filtration, chlorination
Intensive Treatment
- breakpoint chlorination, flocculation, coagulation,
decantation, filtration, carbon adsorption, disinfection (ozone, final chlorination)
Typical Bacterial Counts for River
Thames at Water Intake
Total ‘aquatic’ bacteria (20 C)1.2 x 106 /100 ml
Total ‘Coliform’ bacteria (37 C)
1.6 x 105 /100 ml
Faecal Coliforms
E.coli
Salmonellae
Typical pattern -
2.5 x 103 /100 ml
8 x 102 /100 ml
3/litre
Highest counts in winter
High counts after heavy rainfall
High counts when river flow high
No: fluctuates widely.
Problems -
(1) Aftergrowth/regrowth
(2) Slime formation
(3) Contamination of Distribution System
(4) Resistance of viruses
WHO Guidelines 1984
Bacteriological Quality Treated Water
Piped supplies
CFU/100 ml
Treated water entering
distribution
Faecal coliforms - 0
Coliforms
0
Untreated water entering
distribution
Faecal coliforms - 0
Coliforms 3 in occ. sample
not in consecutive samples
0 in 98% yearly samples
Water in distribution
system
Faecal coliforms 0
Coliforms 3 in occ. sample
not in consecutive samples
0 in 95% yearly samples
Unpiped supplies
Faecal coliforms - 0
Coliforms 10
Bottled drinking water
Faecal coliforms - 0
Coliforms 0
< 1 NTU
pH < 8
0.2 - 0.5 Cl2
1980 EEC Drinking Water Directive
(80/778/EEC)
Treated water leaving WTP
Sample
Total Coliforms
100 ml
Faecal Coliforms
100 ml
Feacal Streptococci
100 ml
Sulphite reducing Clostridia 20 ml
(M.F.)
0
0
0
-
(MPN)
<1
<1
<1
<1
Tap Water
(guide level)
37C Plate count <10 /ml
22C Plate count <100 /ml
Bottled Water
(MAC)
37C Plate count <20 /ml
22C Plate count <100 /ml
Amended by 1998 Council Directive (98/83/EC)
essentially the same as above and implemented in UK as Water Supply (Water
Quality) Regulations 2000.
Sampling Frequency
At consumers Taps
WHO (1984)
• 1 per month per 5000 population (up to 100,000 pop)
• plus 1 per month per additional 10,000 population
EC Directive (80/778/EEC)
• same rate as to WHO (but up to 300,000 pop)
• no increments above 300,000 pop
At Treatment Works
WHO (1984)
daily testing for total coliforms
EC Directive (80/778/EEC)
no requirements
Sampling Frequency
1998 Drinking Water Directive (98/83/EC)
At consumers taps
Volume (m3/day)
Check Monitoring
(No per Year)
Audit Monitoring
(No per Year)
< 100
100 - 1000
1000 – 10,000
10,000 – 100,000
> 100,000
Member state sets
Member state sets
4
4
+ 3 for every 1000m3/d
Assume 200L (0.2 m3) per person per day
(1 m3 = 5 people)
1
1 (+1 per 3000 m3/d)
3 (+1 per 10,000 m3/d)
10 (+1 per 25,000 m3/d)
UK Regulations, Water Supply Regulations 2000
Directive and National Requirements
Concept of Supply Zones, fixed annually, ideally linked to a Supply Point
(i.e.WTW, pumping station, blending point, service reservoir).
Microbiological Quality
(at Consumers taps)
Sample
(M.F.)
Total Coliforms
100 ml
Escherichia coli
100 ml
Enterococci
100 ml
Clostridium perfringens
100 ml
Colony count - at 22C and 37C
PCV
0
0
0
0
(no abnormal change)
(at works, Service reservoirs)
TC, E. coli, Clostridium, Colony counts – (quality requirement as above)
Cryptosporidium
(< 1 per 10 litres daily monitoring)
( in Bottled water)
Enterococci and E. coli
Pseudomonas aeruginosa
Colony count
(0/250ml)
(0/250ml)
(22C < 100/ml; 37C < 20/ml)
UK Regulations, Water Supply Regulations 2000
Frequency of monitoring
Audit and Check monitoring, Standard and Reduced (where deterioration is negligible)
Frequencies . Therefore frequency varies widely, sliding scales based on:
• Output of WTW (m3/day)
• Size of Supply Zone (<100 to 100,000 p.e)
At Taps (no: per zone unless stated otherwise)
TC, E. coli
Enterococci Clostridium perfingens*
Colony count*
1 per month per 5000 population (zones of 100,000 pop)
1 to 8 per year
1 to 8 per year (2 to 76 per year if surface water source)
2 to 76 per year
At works, and service reservoirs (no: per zone)
TC, E. coli ,
Clostridium perfringens*
Colony count*
4 -365 per year
1 to 48, or 2 to 2190 (if surface water source)
4 -365 per year
* these termed “Indicator Parameters” (Schedule 2), any failures require further
investigation. Rest are “Prescribed Concentration or Value (PCV)” , (Schedule 1).
Note ; residual disinfectant monitored at taps and works at the same frequency as TC.
% surviving
Bacterial Removal
100
37C Plate Count
10
Storage
Reservoir
E. coli 12C
1
E. coli 16C
0.1
10
20
30
time (d)
40
Storage
After 30 days, assume 90% removal E.coli
Coagulation, Sedimentation & Filtration
Assume 99% removal
Disinfection (Cl2)
Assume further 99% removal
Therefore 4-5 log removal of bacteria in water treatment process.
i.e. 100,000 E.coli /100 ml
< 1 E.coli /100 ml
Supplies at risk from
Microbiological Problems:
Lowland waters with the following characteristics:-
(1)
Plate counts from distribution
> 103/ml (22oC 7 day YEA)
(2)
Total Organic Carbon, as C
> 2 mg/l in final water
> 0.5 mg/l change in distribution system.
(3)
Dissolved oxygen
10-15% average fall in distribution system.
(4)
Disinfectant
Failure to maintain residual throughout the distribution system.
Enforcement of Standards:
•
Drinking Water Inspectorate (DWI)
– formed 1990
– monitors water undertakers’ performance
•
Water Undertaker
– analyse samples and keep records
– Produce reports
– Investigate outbreaks (+ inform DWI)
• Identify source (e.g. consumer’s installations or supplies?)
•
Possible failure
TC but not FC in supply
– Possible Causes: sludge in pipes, nutrients in water, dead-ends (low chlorine
residual)
•
Solutions
–
–
–
–
distribution system checks
flush network
switch raw water source
increase disinfectant strength
Health guidelines for the use of wastewater in agriculture and aquaculture.
Technical Report Series 778, WHO, Geneva, 1989
This standard is based on epidemiological studies.
Category Reuse conditions
Faecal coliforms (geometric mean /100ml)
A. Unrestricted Irrigation (crops likely to be
eaten raw, Salad crops)
Less than 1000 faecal coliforms/100 ml
B . Restricted Irrigation. (Only crops which are
not eaten or not eaten raw, cereals, fodder
crops, pasture and trees
No faecal coliform standard
Category Reuse conditions
Parasites
A. Unrestricted Irrigation (crops likely to be
eaten raw, Salad crops)
1 or less helminth egg per litre
B. Restricted Irrigation. (Only crops which are
not eaten or not eaten raw, cereals, fodder
crops, pasture and trees)
1 or less helminth egg per litre
.