Enhancement of SODIS for safe drinking water supply from collected

Report
Water Safety
Conference 2010
M.T. Amin, H. Kim, M.Y. Han
Enhancing SODIS for safe drinking water supplies
from collected rainwater
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
1
Contents
1
Introduction
2
Materials and Methods
3
Results and Discussion
4
Conclusions
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
2
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
3
Background
< Tailand >
•
•
•
< Uganda >
Lots of countries have water shortage problems over the world
Rainwater harvesting (RWH) can be alternative water resource to
these countries
Because RWH system is simple to install and manage, this system has
been spread to water shortage areas.
Sited from “ELLIAS SAIDIN and AMINUDDIN BAKI, RAINWATER HARVESTING: POTENTIAL ALTERNATIVE WATER RESOURCES IN MALAYSIA,
WATER MALAYSIA 2009”
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
4
What is rainwater harvesting system?
Uses
Catchment
Cleaning
Gardening
Emergency
Toilet
Storage
drain pipe
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
5
Rainwater as drinking water?
- Rainwater can’t be used
as drinking water for the
possibility of microbial
contamination.
-At least one-third of the
population in developing
countries has no access
to safe drinking water
Simple disinfection method can make and supply
safe drinking water by rainwater
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
6
Solar Disinfection (SODIS)
•
•
•
Inactivation of microorganisms by UV-A-radiation and thermal
treatment
Suited for providing safe drinking water in rural and semi-urban
communities in developing countries
Promoted by the World Health Organization (WHO)
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
7
Limitation of SODIS
•
•
Few scientific and engineering data for rainwater disinfection
Only strong sunlight radiation for about 6~8 h daily is adequate for
the complete disinfection
SOCO-DIS (Solar Collector Disinfection) system
• Improving SODIS to achieve more
concentrated sunlight radiation and
temperature effects
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
8
Objectives
• To compare the efficiency of SOCO-DIS with that of SODIS
• To optimize the developed SOCO-DIS system by investigating
the effects of a variety of factors.
- base surface
- box angles
- pH
- turbidity
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
9
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
10
Sample collection site
Completion date
2005.10
Roof area
3,892 ㎡
Green roof area
935 ㎡
residence
about 1,000
persons
RWH
Beginning
date
2006. 4
A kind of
catchment
concrete, terrace,
green roof
Catchment
area
3,652㎡
Tank
volume
250 ton
Consumed
60~90 ton/day
Uses
toilet
* RWH : Rainwater harvesting system
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
11
The quality of rainwater samples
PHYSIOCHEMICAL PARAMETERS
Initial Temp. 0C
pH
EC
μS/cm
DO
mg/l
23-25
7-9
150-500
5-9
MICROBIAL PARAMETERS
Turbidity
TC
FC
E-Coli
NTU
CFU/100ml CFU/100ml CFU/100ml
1-5
880-1100
400-450
200-250
HPC
CFU/ml
1500-2000
Main target
•
•
•
Samples were always collected from the same outlet point, about 1.35
m from the base of the tank
The reason for the different initial values of all the parameters is the
effect of the season and residential time in the tank
These are used as the standard initial values for the rainwater samples
in this study.
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
12
Weather conditions
Weather conditions
Weak sunlight
Moderate sunlight
Strong sunlight
Irradiance range (avg.), W/m2
200-450 (300)
450-700 (580)
650-1000 (880)
•
•
•
Disinfection System
SOCO-DIS
SODIS
SOCO-DIS
SODIS
SOCO-DIS
SODIS
Max. Water Temp., 0C
39
35
46
44
52
48
Weather conditions are categorized into three different types,
depending upon low, medium and high sunlight radiations.
The temperature difference is about 2~4 0C, with the great temperature
rise in the SOCO-DIS system.
Effective temperature about 50OC observed only under strong weather
conditions in SOCO-DIS
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
13
Outline of experiment
W
L
θ
ø
Reflective PET bottle (SODIS)
SOCO-DIS system
SOCO-DIS
SODIS
• Consist of five wooden components
covered by aluminum
• A maximum theoretical
concentration of three times the
solar radiation is achieved
• 1.7 L rainwater sample was
contained to 2 L PET bottle.
• Aluminum foil is placed under the
PET bottle for reflection
TC, FC, E-Coli, HPC was observed
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
14
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
15
1- The effects of weather condition
2- The effects of base surfaces
3- The effects of box angles
4- The effects of initial pH
5- The effects of initial turbidity
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
16
The effects of weather condition
• Disinfection exhibited three stages of treatment depending upon the
sunlight intensity with middle stage being critical.
• Synergistic effects of radiations and temp. are evident under strong
weather conditions where rainwater is disinfected completely.
1200
Weak Sunlight
Moderate Sunlight
Strong Sunlight
800
600
400
400
300
200
200
100
0
0
250
2000
E-Coli (CFU/100ml)
200
HPC (CFU/ml)
TC (CFU/100ml)
1000
FC (CFU/100ml)
500
150
100
50
0
1500
1000
500
0
0
2
4
6
Time (hr)
8
0
2
4
6
Time (hr)
8
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
The effects of weather condition
1.0
0.9
SOCO-DIS
SODIS
0.8
TC
FC
E-Coli
HPC
-1
k (h )
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
200200 400
600
5002 800
850 Avg. Irradiance (W/m )
1000
200200 400
600
5002 800
850 Avg. Irradiance (W/m )
1000
• In case of SODIS, no parameter met the potable guideline values
• SOCO-DIS system proved ineffective under weak weather conditions mostly
because the synergistic effects of radiations and temperatures are absent
• The difference of disinfection efficiency of SOCO-DIS system is about 2030% with that of simple SODIS mostly because of the enhanced effects of
concentrated radiations
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
The effects of base surfaces
•
1000
250
E-Coli (CFU/100ml)
•
Disinfection efficiency of SOCO-DIS system with different base surfaces including
reflective, absorptive, and transmissive (Trans.) is evaluated and compared
under moderate sunlight conditions.
The thermal effects have not significantly contributed by comparing the results of
absorptive base surface with that of reflective base surface where disinfection
efficiency is more.
With insignificant thermal or synergistic effects because of low temperature, it can
be concluded that UV radiation effects are prominent under moderate sunlight
conditions.
800
TC (CFU/100ml)
•
600
400
Ref. (SODIS)
Reflective
Absorptive
Transmissive
200
0
0
2
4
Time (hr)
200
150
100
50
0
6
8
0
2
4
6
Time (hr)
8
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
The effects of box angles
•
1200
250
E-Coli (CFU/100ml)
•
To improve the amount of radiation reaching the water, the solar box is kept an
angle of 370 (Latitude of the location=mid-day position of sun) .
Solar box with continuous changing of direction with respect to the sun’s
position is the best choice due to minimized shading effects of open wings of
box, but it would require more labor work.
The best selection, thus, would be the inclined position of box for
optimum disinfection efficiency.
1000
TC (CFU/100ml)
•
800
600
Hz. (SODIS)
Horizontal
Inclined
Changing
400
200
0
0
2
4
6
Time (hr)
8
200
150
100
50
0
0
2
4
6
Time (hr)
8
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
The effects of initial pH
•
•
•
Rainwater with acidic pH offered best disinfection efficiency for SOCO-DIS system for
all microbial parameters without any exception.
TC and HPC, which were not removed under standard sampling conditions of neutral
pH, are also inactivated completely at low pH values.
Overall disinfection efficiency increased from 10 to 20% by decreasing pH values
from basic to neutral and then acidic states, respectively.
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
The effects of initial turbidity
• SODIS showed poor performance for all microbial parameters at higher turbidity
and disinfection efficiency decreased by almost 10-20%.
• Low turbidity sample show better results although this difference is insignificant
up to may be 20NTU.
• This could be due to the loss of UV due to scattering & absorption by
particles
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
23
Conclusions
• Disinfection efficiency of the SOCO-DIS is 20~30 % better than SODIS
and it managed complete disinfection under strong and even moderate
weather condition
• Optimized SOCO-DIS design and operation conditions
- Reflective base: 10~15 % better than absorptive and transmissive
surface
- Inclined position: 10% better than horizontal position
- low pH: improving the efficiency from 10 to 20 %
- low turbidity: decrease the efficiency by 10 to 15 %
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
24
Further study
Social acceptability of rainwater as drinking water
• Even though there is excellent technology, it has no meaning without social
acceptability.
• Therefore, effort to change unwelcome attitude should be followed to use
rainwater as drinking water.
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
25
Rainwater challenge
• Water tasting event was held with tap
water, bottled water and treated rainwater
• People vote there sticker to the most
acceptable water as drinking water
Tap water
Rainwater
Bottled water
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
26
Water Safety Conference
November 2-4 2010, Kuching, Malaysia
27

similar documents