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Bacterial Removal From Water

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

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Bacterial Removal From Water

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  1. 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) (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

  2. 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.

  3. Typical Bacterial Concentrations inWater 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

  4. Bacterial Examination of Water (1) Can easily distinguish faecal from other sources of contamination. (2) Extremely sensitive tests. 107E.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.

  5. 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

  6. 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 44C + orgs.are faecal in origin) (b) Escherichia coli:- Thermotolerant Coliforms (44C) which give Acid + Gas in 24 hrs. And form Indole from Tryptophan (MR +; VP -; Citrate -)

  7. (3) Faecal StreptococciS. 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.colihas been used to In humans are less numerous than E.coli (FC/FS > 4) 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)

  8. Raw Water (Abstraction) Standards 1962 WHO (Omitted 1973 and 1984) Coliform/100mlClassification 0-50 I Needs Disinfection only 50-5,000 II Needs Conventional treatment 5,000-50,000 III Needs Extensive treatment >50,000 IV Unacceptable - only use if nothing else 1975 EEC A1 A2 A3 Coliforms/100 ml 50 5,000 50,000 Faecal Coliforms/100 ml 20 2,000 20,000 Faecal Streps./100 ml 20 1,000 10,000 Salmonellae Nil/5 l Nil/5 l 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)

  9. Typical Bacterial Counts for RiverThames at Water Intake Total ‘aquatic’ bacteria (20C) 1.2 x 106 /100 ml Total ‘Coliform’ bacteria (37C) 1.6 x 105 /100 ml Faecal Coliforms 2.5 x 103 /100 ml E.coli 8 x 102 /100 ml Salmonellae 3/litre Typical pattern - 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

  10. WHO Guidelines 1984Bacteriological Quality Treated Water < 1 NTU pH < 8 0.2 - 0.5 Cl2 Piped suppliesCFU/100 ml Treated water entering Faecal coliforms - 0 distribution Coliforms 0 Untreated water entering Faecal coliforms - 0 distribution Coliforms - 3 in occ. sample not in consecutive samples 0 in 98% yearly samples Water in distribution Faecal coliforms 0 system 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

  11. 1980 EEC Drinking Water Directive(80/778/EEC) Treated water leaving WTP Sample (M.F.) (MPN) Total Coliforms 100 ml 0 <1 Faecal Coliforms 100 ml 0 <1 Feacal Streptococci 100 ml 0 <1 Sulphite reducing Clostridia 20 ml - <1 Tap Water 37C Plate count <10 /ml (guide level) 22C Plate count <100 /ml Bottled Water 37C Plate count <20 /ml (MAC) 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.

  12. 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

  13. Sampling Frequency 1998 Drinking Water Directive (98/83/EC) At consumers taps Assume 200L (0.2 m3) per person per day (1 m3 = 5 people)

  14. 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.) PCV Total Coliforms 100 ml 0 Escherichia coli 100 ml 0 Enterococci 100 ml 0 Clostridium perfringens 100 ml 0 Colony count - at 22C and 37C (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 (0/250ml) Pseudomonas aeruginosa (0/250ml) Colony count (22C < 100/ml; 37C < 20/ml)

  15. 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 1 per month per 5000 population (zones of 100,000 pop) • Enterococci - 1 to 8 per year • Clostridium perfingens* 1 to 8 per year (2 to 76 per year if surface water source) • Colony count* 2 to 76 per year • At works, and service reservoirs (no: per zone) • TC, E. coli , 4 -365 per year • Clostridium perfringens* 1 to 48, or 2 to 2190 (if surface water source) • Colony count* 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.

  16. Bacterial Removal 100 10 1 0.1 37C Plate Count Storage Reservoir % surviving E. coli 12C 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 E. coli 16C 10 20 30 40 time (d)

  17. 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.

  18. 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

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