methods of water treatment
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Methods of water
treatment
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SAND FILTRATION
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Sand filtration
Filtration material: silicate sand ofdifferent granulation
Applications for removal of: Aggregates originally present in water
Flocs after flocculation, iron removal of limesoftening
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Types of sand filters
Slow
Rapid gravity
Rapid pressure
Self cleaning
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Slow filter
Open to gravity Filtration velocity 0.1 0.2 m/h Easy to operate Maintenance and cleaning: Automated or
manual scraping the impurities from the
upper layer of the filter
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Slow filter
Not economically feasible due to highinvestment
Better filtration efficiency Good in removing parasites and bacteria
Protozoan ParasiteGiardia
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Slow filter
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Maintenance of slowfilter
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Rapid gravity filter
Usually for bigger utilities Filtration velocity around 5 m/h
Sand bed layer height around 2 m
Water depth above sand 0.5 m Sand mesh size 0.8-1.5 mm
Bottom layer sand mesh size 4-6 mm
Cleaning in counter-current backwashwith water and compressed air (airscourging reduce consumption ofwater for backwashing)
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Rapid gravity
sand filter
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Pressure rapid sand filter
Sand layer depth up to 3 m
Filtration velocity up to 18 m/h
Mesh size:
Filtering layer 1-2 mm
Bottom layer 4-6 mm
Maximum operating pressure 0.5 0.6
bara
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Sand filters overview
Slow
Best filtration efficiency
Low feasibility
Rapid gravity
Backwash: water + air
Rapid pressure
High filtration velocity Backwash: water + air
Self-cleaning
No control needed
No valves or pumps
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Disinfection
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Disinfection of water Removal of pathogens in water
Prevention of epidemics
Fulfilment of law requirement for drinking water
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Methods of disinfection
Chemica
l
Chlorine
Cl2
Ozone
O3
Silverand
copper
Ag, Cu
Physical
TermicoC
UVFiltration
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Chlorine (Cl2)
Yellow-green gas
Toxic
Oxidizing agent
Disinfection time 30 min
Cl2
+ H2O HCl + HClO
HClO HCl + O
Purchased in steelcontainers
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Chlorine based disinfectants
Chlorine Cl2
Chlorine dioxideClO2
Sodium hypochloriteNaClO
Calcium hypochlorite
Ca(ClO)2
Trichloramines NCl3
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Disinfection chlorine basedchemicals
1. Liquid chlorine (Cl2), usually available in pressurized containers
inexpensive
highly toxic and should be used only by appropriately trained individuals withthe proper chlorinators and ejectors.
2. Sodium hypochlorite (NaOCl)
liquid
more expensive and bulky than liquid chlorine
safer to handle.
5-15 % chlorine
finite shelf life.
3. Calcium hypochlorite (Ca(OCl)2)
solid
approximately 65 percent chlorine
easy to handle in either tablets or granular form
relatively expensive
must be kept dry to prevent degradation
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Disinfection with silver
Inactivates bacteria above 0,015mg/L
Used for cooling water in hospitals
Pools Fisheries (Fish is sensitive to
chlorine)
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Copper and silver disinfection
Positively charged copper ions (Cu2+
) in the water bindto the particles of opposite polarity, such as bacteria,viruses and fungi and disturb cell wall permeability andcause nutrient uptake to fail. Copper ions penetrate thecell wall and as a result they will create an entrance forsilver ions (Ag+). Silver ions bond to various parts ofthe cell, such as the DNA and RNA, cellular proteins and
respiratory enzymes.
Applications of copper-silver disinfection:
Swimming pools
Cooling towers Legionella in hospitals and nursing homes
Drinking water
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Disinfection with UV
irradiation
UV mercury lamps are immersed in water or
placed above the surface of water No chemical addition
It doesnt change chemical composition ofwater,
Simple operation and maintenance Disadvantage: no residual to prevent bacterial
regrowth
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Disinfectionwith UV
irradiation
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Coagulation and flocculation
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Aggregates Colloidal matterMolecules
100 nm 1 nm
Minerals
Turbidity GasesAluminosilicates
OrganicsClay
Size of particles in water
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Floc formation andsedimentation
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Floc formation and flotation
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Flocs separation from water
SedimentationLonger time necessary
Big reactor
Flotation
Usually enhanced by introduction of micro bubbles ofair
Fast (smaller reactor and shorter time necessary)
More expensive due to energy for aeration
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