water treatment technologies in low income regions · entamoeba histolitica dysentery trophohzoid...

Water Treatment Technologies in Low Income Water Treatment Technologies in Low Income RegionsRegions

Lecture Lecture ““Water Resources and Drinking WaterWater Resources and Drinking Water””

Michael Berg and Stephan Hug

Swiss Federal Inst. of AquaticScience and Technology

Water treatment in low income regions

Water treatment in low income regions

Surface water (biological contamination)- boiling- ceramic filters- chlorine treatment- UV irradiation (SODIS)

Reduced groundwater (chemical contamination)- Fe, As

Alternative- rain water harvesting

Surface water and groundwater- Fluoride

Boiling of water

R. Meierhofer, Eawag

• Contaminated water is filled in a heat-resistant vessel (cooking pot, steel drum) and brought to boil.

• At sea level, the boiling point is at 100° C. Rule-of-thumb: keep water boiling for 1 Minute at sea level, add 1 minute of boiling time for every 1000 meter of elevation.

• Ideally, the water is cooled and stored in the same vessel in order to minimise chances of re-contamination.

Boiling time of water


Advantages:• Complete disinfection of

pathogens

• Simple to set up, operate, and maintain

• Common technology

• Can be combined with cooking and tea boiling

Limitations:• Boiling water is expensive!

(fuel, fire wood, gas, etc.)

• Method is time consuming (presence needed during the heating process, long time for cooling down)

Water boiling


• energy is scarce and expensive

• electricity or kerosenare generally not available

Reality:

Boiling of water


Ceramic filters

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Purpose: • Removal of solid particles and some pathogens

(depending on the pore size of the filter)

Method: • Water is filtered through this porous material, usually

unglazed ceramic pots or candles coated with colloidal silver

• The filter retains the solid materials as well as some of the pathogens, depending on the size of the pores.

• Ceramic filters can be produced locally but usually are mass-produced in factories.

Ceramic filters

How does it work?

1. A specially constructed clay/ceramic pot is placed inside the top of a larger water storage container.2. Contaminated water is poured into the ceramic pot. 3. As the water seeps through the porous pot, nearly all of the impurities are removed.4. Pure drinkable water is collected in the large water container. 5. Drink up!

Local production of eramic filters

the pots are stamped, cleaned and then air dried.

pots are fired in a traditional kiln

testing of flow rate

pots are coated with colloidal silver

Advantages:• Handling for users very

simple

• Removes parasites such as worm eggs and protozoa

• Maintenance easy

• Works with both rain water and surface water

Limitations:• Purifies max. 2 liters per

hour

• Filter candles can easily be damaged

• Supply chain for new filters must be in place

Ceramic filters

Chlorine disinfection

0.5% hypochlorite solution (stable for 1 year)

- 100 mL solution cost some 0.40 CHF (can treat 1500 liters)- used in the ratio of 3 drops per liter of waterwater is shaken and allowed to stand for 30 min- the free reactive chlorine contents is usually between 0.2–0.5 mg/L- applied in areas of water borne outbreaks or flood disasters


Local production and distribution

Chlorine

Strong taste ?

Advantages:

• Simple

• Inexpensive

• Excellent bacterial/viral removal

• Residual chlorine prevents recontamination to a certain degree

• No energy required at the household level

Limitations:

• Strong taste of the treated water

• By-products of the chemical reactions may be harmful

• Effective only for low turbidity

• Strength of different disinfectants may vary over time


Sunlight has a strong disinfecting effect and can be used for the disinfection of drinking water

Research on SODIS „Solar Water Disinfection“ has been taken up by Eawag/ SANDEC in 1991.

The method has extensively been tested for more than 10 years inthe laboratory and in the field.

Water irradiation in PET bottle

1. The Method

2. How to apply

3. Scientific Aspects

4. Advantages andLimitations

SODIS - Solar Disinfection

How does SODIS Work?

• plastic bottles filled with contaminated water and are exposed to sunlight for 6 hours

• sunlight disinfects the water by the UV-A radiation

• a synergy occurs if the water temperature rises above 50 ºC

• SODIS kills 99.99% of diarrhoea causing pathogens (Bacteria, Viruses, Cryptosporidium and Giardia)

1. The Method

2. How to apply



How do I use SODIS?

1. The Method

2. How to apply



What kind of bottles do I need?

In order to successfully make use of SODIS, the following bottles are needed.

• PET-bottles (All PET bottles up to 3 liter volumeexcept; colored, damaged, heavily scratched or PVC )

1. The Method

2. How to apply



What if the water is turbid (cloudy)?

SODIS does NOT work if the water is very turbid (more than 30 NTU*) as it scatters the sunlight and therefore shields the pathogens.

• In order to determine whether the turbidity is higher than allowed the following test can be made:

– Place the SODIS logo or a newspaper headline (15cm by 4cm) below the open PET-bottle

– Look through the mouth of the bottle towards the logo or headline– If one can still read the logo, the water is suitable for the SODIS

process, if not one must perform a filtration.

1. The Method

2. How to apply



* NTU: Nephelometric Turbidity Unit

The water has a turbidity of higher than 30 NTU, what do I have to do?

If the SODIS logo test has resulted negatively, the following methods can be used to remove the turbidity.

• Let the bottles stand still until the particles settle to theground and then carefully pour into PET-bottle

or• Filter the water through a folded piece of cloth

1. The Method

2. How to apply



SODIS

* CGI: Corrugated Galvanized Iron = “Wellblech”

Research on the material

Can PET bottles be used for SODIS without concern?

1. Eawag study about photooxidation of PET bottles:

-> Photoproducts are formed at the outer side of the bottle.

-> There is no diffusion of Formaldehyde or Acetaldehyde into the water

2. Study on the diffusion of Phthalates and Aliphatic compounds in collaboration with EMPA:

-> The maximum concentration of plasticizers (DEHA, DEHP) is much lower than WHO guidelines for drinking water

1. The Method

2. How to apply



* DEHA: Di(2-ethyl hexyl) adipate; DEHP: di-2-ethyl hexyl phthalate

Pathogen Illness

Reduction through SODIS ** at water temperatures of 40°C and solar exposure of 6 hours

Bakteria E.coli Indikator for Water

Quality & Enteritis

3-4 log (99.9 -99.99%)

Vibrio cholera Cholera 3-4 log Salmonella spp. Thyphoid 3-4 log Shigella spp. Dysentery 3-4 log Viruses Rotavirus Diarrhoea, Dysentery 3-4 log Polio Virus Polio inactivated, results not yet

published Hepatitis Virus Hepatitis Reduction of cases of SODIS

users Protozoa Giardia spp Giardiasis 3-4 log (Infectivity of Cysts) Cryptosporidium spp. Cryptosporidiasis 2-3 log (Infectivity of Cysts) Entamoeba histolitica Dysentery trophohzoid stage inactivated

Which microorganisms areinactivated by SODIS?

1. The Method

2. How to apply



Advantages SODIS

• SODIS improves the microbiological quality of drinking water

• SODIS is easy to understand and applicable at low cost

• Only Sunlight and PET-bottles are needed

• SODIS improves the health!

1. The Method

2. How to apply



Limitations of SODIS

• SODIS requires sufficient sunlight. -> Under a cloud cover of more than 50% the bottles have to be exposed for 2 days.

• SODIS requires a turbidity of less than 30 NTU.

• SODIS does not improve the chemical water quality.

• SODIS is not ideal to treat large quantities of water. (The UV-A radiation is reduced by 50% at a water depth of 10cm and a turbidity of 26 NTU)

1. The Method

2. How to apply



SODIS

Education Promotion

Comparison of biological inactivation

Reduced groundwater (chemical contamination)

Reduced groundwaters are often exceeding drinking water guidelines of Fe, Mn and As

Conc. range WHO guideline Major problemsFe <0.01-150 mg/L no guideline

recommendation<0.3 mg/L

taste and odour, colour stains onlaundry, clogging of pipes andfilters

Mn <0.01-20 mg/L 0.4 mg/L neurotoxic effects in children,chlorosis and necrosis inplantstaste and odour, colour stains

As <0.1-1000 µg/L 10 µg/L chronic poisoning of people

Reduced groundwater (chemical contamination)

Relevant species

Reduced species Oxidised species Oxidation with O2 at pH 7Fe [Fe2+]aq (cation) {Fe3+OOH}s (solid) fast (minutes)

Mn [Mn2+]aq (cation) {Mn4+OxHy}s (solid) very slow (month to years)

As [As(III)O33-]aq (anion) [As(V)O4

3-]aq (anion) slow (days to month)

Oxyanions (like PO43-)

Tubewells

Hanoi

Arsenic in Rural AreasVietnam

Berg et al., ES&T 2001, 35, 2621–2626

Hanoi

Berg et al., ES&T 2001, 35, 2621–2626

Arsenic in Rural AreasVietnam

Spatial Variation within Short Distance

Van Phuc village, July 2002

2.2

540

43

Top view

Spatial Variation within Short Distance

Van Phuc village, schematic side view

Red River

aquifer

Concentrations very heterogeneous !!

Core no. 3 (20m deep)

Core no. 4 (37m deep)

Sediment Cores

silt clay peat clay sand with clay clay

2 4 5 10 17

clay sand clay

5 27 37 m

20 m

As Concentrations in Pore Water

dissolved Arsenic org. Carbon

• reductive dissolution of As

•As concentration in sediment plays minor role

As Vietnam

<10 µg/L10-50 µg/L50-200 µg/L>200 µg/L

As concentration

Fe concentration

<1 mg/L1–10 mg/L10–20 mg/L>20 mg/L

Fe Vietnam

Color of FeOOH precipitates in water

after one hour of contact with air

Groundwater pumped in rural household

City of Hanoi

Aeration for iron precipitation

[Fe2+]aq --> {Fe3+OOH}s

Public water supply of Hanoi

Fe removal

Aeration / Fe-Precipitation

Fe-Sedimentationand Filtration

raw groundwater

drinking water

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Ph¸p

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ai

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g Yª

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Total FeFe3+

Fe c

once

ntra

tion

Fe raw waterFe treated water

water treatment plant

As removal

Aeration / Fe-Precipitation

Fe-Sedimentationand Filtration

raw groundwater

drinking water

Sand Filter for household treatment

Sand filter – top view

Mechanism of arsenic removal

In sand filterFe oxidation

Fe precipitation on sand

As oxidation

As co-precipitation (-> mainly adsorption to FeOOH)

As(III), As(V) = Oxyanions

As(V) adsorbs 10–100 times better than As(III)

Sand filter As removal efficiencyA

s co

nc. (

µg/L

)

Raw groundwater

Filtered water

50 µg/L

10 µg/L

tested sand filters

80% average As removal

As removal dependent on Fe concentration

Phosphate >2.5 mg/L

more Fe

Phosphate >2.5 mg/L

As

rem

oval

Fe concentration (mg/L)

more Asremoval

Fe/As ratio

resi

dual

As

(µg/

L)

Fe / As ratio

Fe/As >50

Fe/As >250

Enhanced aeration

a) cascade b) sprinkler

Enhanced aeration

Sand filter in use

Filter on roof

Filter on roof for running tap water

Applicability of sand filters in other countries

Advantages:

• As removal related to observable improvement of water quality (iron removal)

• treatment is very fast (minutes)

• can easily be constructed by villagers (neighbor to neighbor knowledge transfer)

• low construction and operation cost, materials locally available

Limitations:

• groundwater iron concentration must be sufficient,i.e. Fe/As ratio >50

• Phosphate >2.5 mg/L lowers efficiency

Passive Arsenic Co-precipitation

Fe settling tanks

Mechanism of arsenic removal

Co-precipitationFe oxidation

Fe precipitation on sand

As oxidation

As co-precipitation (-> mainly adsorption to FeOOH)

arse

nic

rem

oval

by

sand

filte

r

Both systems similar As removal efficiency

arsenic removal by co-precipitation

Comparison of co-precipitation vs. sand filterne

eds

3 to

5m

ins

needs 8 to 24 hours

Sand filter much faster and less turbid water

Passive Arsenic Co-precipitation

Advantages:

• Very simple

• As removal is related to observable iron removal

• low construction and operation cost, materials locally available

Limitations:

• slow process

• water still turbid after 2 days

• turbidity contains arsenic

• open tank prone to biological contamination

Rainwater harvesting

Rainwater tank

Rainwater harvesting

Advantages:

• Acceptable quality for domestic purposes

• Few natural chemical contamination

• Low microbial contamination

Limitations:

• Limited supply and uncertainty of rainfall

• storage over several month

• Some roofs not suitable (e.g. straw, copper)

Questions

?

Iron, Arsenic & Manganese

Iron in anoxic groundwater supplies is a common problem: its concentration level ranges from 0 to 150 mg/L while WHO recommended level is <0.3 mg/L. The iron occurs naturally in the aquifer but levels in groundwater can be increased by dissolution of ferrous borehole and handpump components. Iron-bearing groundwater is often noticeably orange in colour, causing discoloration of laundry, and has an unpleasant taste, which is apparent in drinking and food preparation.

Arsenic. Inorganic arsenic can occur in the environment in several forms but in natural waters, and thus in drinking-water, it is mostly found as trivalent arsenate (As(III)) or pentavalent arsenate (As (V)). Organic arsenic species, abundant in seafood, are very much less harmful to health, and are readily eliminated by the body.

Manganese is known to block calcium channels and with chronic exposure results in dopamine depletion, causing diminished intellectual function in children.

Mobilization of Fe and As in groundwater

Buried organic matter is the key to reduced groundwater.Deposition of sediment in deltas happens in numerous parts of the world. Whensediment is buried, the iron oxide and its arsenic are often quite stable. As rainwaterpercolates downward through them from the surface, it carries in it small amounts ofoxygen dissolved from the air through which the rain fell. Small though theseamounts are, they are enough to remind the iron oxide of the conditions under whichit traveled from the mountains, which was in river water containing small amounts ofdissolved oxygen. It is this oxygen that maintains the iron oxide in a stable state.

Buried organic matter upset that stability. The vegetation in the buried swamps isslowly rotting, just like silage on a farm or grass cuttings in the garden compost-heap.The decomposition occurs because bac teria are eating the organic matter and turningit into carbon dioxide and body material. To make this process work they needoxygen. Humans survive the same way, but we take our organic matter in a morepalatable form, such as rice, fish, or meat, and we take oxygen in through our lungs todrive our metabolism of this food. We get our body weight from these processes andalso the energy for work and play. The bacteria in the ground are entirely natural andpose no threat to health - they are firmly attached to their source of food (buried peat)and on it they stay, reluctant to let go and be carried away to starvation by the slowpercolation of the surrounding water in the sediment, rather like beggars at a banquet,who have no intention of leaving while there is food on the table.

Bacterial decay causes mobilization of arsenic, iron and manganese.The bacteria that are decomposing the subsurface vegetation come in many differentforms. Some can survive by eat organic matter only if, like humans, they have freeoxygen from the atmosphere available to drive the process; these live very close to thesediment surface, where atmospheric oxygen can penetrate from the overlying air andwhere small amounts of oxygen d issolved in rainfall are also available. But thesebacteria consume all the atmospheric oxygen that comes their way; their cousins thatlive deeper in the sediment must live without atmospheric oxygen. These deep-dwelling bacteria have grown so used to being deprived of atmospheric oxygen thatthey have even come to dislike it as being too rich a dietary supplement. They nowprefer to take their oxygen from other sources, and therein lies another part of theproblem.

The only other ready source of oxygen available to the deep-dwelling bacteria in thedelta sediments is the oxygen tied up chemically in iron oxide. Despite the fact thatthe oxygen is chemically combined with the iron, they wrench the oxygen out of theiron oxide and use the it to drive their metabolism as they consume the peat - althoughthey do that rather slowly because fighting iron for its oxygen is not a very rewardingway to live. The bacteria have no use for the iron, nor for the accompanying arsenicthat is in the iron oxide, so both are ejected from the bacterial cell as waste, only toaccumulate in the water and poison its unsuspecting consumers. Which is whyreduced groundwater can be rich in both dissolved iron and dissolved arsenic. Arsenicis particularly present in Holocene groundwater where sediments are less than 10’000years old, poorly weathered and not ye t flushed enough.

J.M. McArthur, UCL, London, UK

water treatment technologies in low income regions · entamoeba histolitica dysentery trophohzoid...

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