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Water and Wastewater Treatment

CE5WWTa

Storage and Preliminary Treatment

John Bridgeman

j.bridgeman@bham.ac.uk

Objec:ves

To understand the role of preliminary treatment processes and storage of raw water in the overall water treatment process.

To consider the principal processes in common use at surface and groundwater sources.

Preliminary Processes

1. Screens Upland/lowland rivers, reservoirs/lakes (not groundwater)

2. Microstraining Reservoirs/lakes, upland rivers

3. Storage Upland/lowland rivers

4. Aera?on Groundwater, boKom of lakes/reservoirs

5. Chemical pre-treatment When high coliform count, runo water or downstream of

sewage works

Screening

Basic Principles Prevent large debris entering process plant Dierent types choice governed by:

Size of debris to be removed Nature of downstream processes Cleaning mechanisms

Screening

Purpose: To protect downstream processes

Type: Coarse Fine

Type Aperture (mm)

Coarse 75-100 Medium 15 50

Fine 3 15 Milli 0.25 3

Coarse Screens

Provided at river intakes 25mm dia bars @ 75-100mm spacing Angled for raking 0.5 m/s inow velocity

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Provided at river intakes

25mm dia bars at 75-100mm spacing

Angled for raking

0.5 ms-1 inow velocity

Fine Screens

Fine screen mesh 10mm eec:ve aperture Mechanically cleaned

Band or drum Disc screen

Screening (ne)

A_er coarse xed screen Mobile (belt, drum or disc) Debris box Leaves and twigs

Grid spacing 5 x 5 mm apart

Belt screen (ne)

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Band Screen

Bandscreen

hKp://www.youtube.com/watch?v=RIKWqed-k7c

hKp://www.youtube.com/watch?v=htbYLFNPq18&NR=1

Microstraining

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Drum Screen Drum Woven stainless steel mesh (60m) less than a

tea strainer

Fine mesh supported by coarser mesh 2% of strained water used to wash mesh Good for water from reservoirs/lakes i.e. water with liKle suspended maKer

Removes algae

Drum Screen

Spray line

Mesh drum

0.5 m/s

Storage

Lowland rivers (SS >50 mg/l)

Improve quality before treatment

Ensure adequate supply during peak :me

Physico-chemical reac:ons Sedimenta:on UV radia:on Floccula:on (long term storage)

Issues Atmospheric pollu:on and fall out

Birds, algae (>10 days storage)

Land required Thermal stra:ca:on (if large)

Stra:ca:on

Epilimnion 20oC Thermocline

Hypolimnion 4oC

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Aera:on

Groundwater, deep lake/reservoir waters, polluted rivers, i.e. water that has liKle DO

Anaerobic water can adversely aect coagula:on and damage lters.

Add O2 by cascade or fountain Reduces corrosiveness of H2O Precipitates Fe Removes hydrogen sulphide and vola:le organics (taste issue)

Chemical pre-treatment

Chlorine IntermiKent high dose chlorine 5 mg/l Unusual as pre-treatment If high coliform count from surface runo (agriculture, sewage works, oods)

Chlorine oxidises low concentra:ons of Fe, Mn

Chemical pre-treatment

Ac:vated carbon

IntermiKent PAC doses up to 20mg/l Remove algae, reduce colour, odour and organic compounds

Added as slurry before coagula:on Long contact :me adsorp:on Needs removal later (sedimenta:on & ltra:on) Reduces lter life & generates more sludge

Objec:ves

To understand the role of preliminary treatment processes and storage of raw water in the overall water treatment process.

To consider the principal processes in common use at surface and groundwater sources.