Aim: Assessment of point of use water purifiers (ZERO B) for removal of bacteria
Approach: The global population which did not have access to safe drinking water in the
year 2012 was around 700 million. With household treatment of water, it has been reported
that diarrhoeal illnesses could be reduced by 30–40%. In India, it has been observed that 70%
of the surface water and 33% of ground water is microbiologically and chemically
contaminated. In rural areas due to the dispersed settlements, drinking water sources are
usually decentralised in the form of dug wells, hand pumps or tube wells. Even in urban
areas, despite the existence of centralised water supply, marginal communities may lack the
access to such utilities through such centralised systems as they may be prone to get
contaminated. In such scenarios, household point-of-use water purifiers become important.
A point-of-use water filter is a type of water filtration system that treats the water at
a single tap. These types of filters are most commonly installed under a kitchen sink in order
to provide high-quality, clean and healthy drinking water at the kitchen tap. The point of use
purifiers have been categorised into thermal- or light-based treatment techniques, physical
removal methods, chemical treatment techniques and integrated water purification.
1. Thermal or light based treatment techniques
a) Boiling- One minute of boiling at a temperature 100°C (at mean sea level) ensures
neutralisation of faecal and thermo-tolerant coliforms, protozoan cysts and viruses.
b) Thermal pasteurisation-In thermal pasteurisation, temperature usually does not go
beyond 75°C which is suitable to eliminate E.coli. It has been reported faecal coliform
and viruses could be removed.
c) Solar disinfection (SODIS)-For low volumes of filtered water with less turbidity,
water can be filled in transparent polyethylene terephthalate (PET) bottles and kept
under sunlight for at least six hours after forceful shaking for aeration. SODIS can be
an effective way to use heat and UV radiations from the sun to targets microbes.
d) Ultraviolet (UV) treatment-For low turbid water UV treatment could be effective even
on Crypto Giardia lamblia cysts and Cryptosporidium parvum oocysts.
2. Chemical treatment techniques
a) Chlorination-Chlorination is a simple, affordable and scalable method of water
disinfection through the use of sodium hypochlorite NaOCl (liquid), NaDCC (solid)
and calcium hypochlorite (Ca(OCl)2) (solid). With a dosage of 2 mg/L for about 0.5 h,
chlorination could eliminate the enteric bacteria.
b)
Combined flocculation/coagulation and disinfection (CFD/CCD)- For a reduction in
turbidity as
well
as
microbial
disinfection, combined methods
such as
coagulant/flocculant as well as chemical disinfectant powders/tablets are used. These
products combine calcium hypochlorite (or bleach) with coagulating agents like
sodium carbonate and oxidisers like potassium permanganate. The method could
eliminate bacteria, viruses, protozoa.
3. Physical methods
a) Sedimentation or clarification-Clarifiers like alum, lime, iron, seeds of Moringa
oleifera (drumstick) etc. have been used to reduce turbidity through sedimentation.
There are also claims that Strychnos potatorum and aluminium salts (alum) and iron
salts could help in reduction in microbial contamination.
b) Membrane based treatment methods- In these methods, filtration occurs across a
semi-permeable membrane. Depending on the pore size, microfiltration (0.1–1 µm)
can retain only bacteria, ultrafiltration (0.005–0.1 µm) can remove both bacteria and
viruses, nanofiltration (0.5–5 nm) cannot retain salts, while reverse osmosis (0.15–
0.5 nm) can even filter out salts.
Reverse osmosis (RO)-RO with pore size of < 1 nm and high water pressure filters
i.
out all types of pathogens and waterborne impurities.
ii.
In forward osmosis, a bag made of semi-permeable membrane is filled with
concentrated sugar solution and then dipped in impure water. Due to the osmotic
potential, water enters the pouch and contaminants get trapped outside the bag.
iii.
Paper, fabric and fibre filters-Considering the pore size of paper and fabric filters,
only pathogens like Vibrio cholerae can be filtered to a extent of 95–99%.
4. Integrated water purification- These water purifiers combine multiple types of water
treatment techniques for example RO systems generally are supported by
microfiltration, ultrafiltration and ultraviolet treatment techniques.
5. Adsorpive media for Arsenic and Selenium- adsorptive media includes activated
alumina, granular ferric hydroxide or other iron based media often used for fluoride
removal but also for arsenic and selenium removal. Source water pH is adjusted to
achieve optimum contaminant removal.
6. IX for various IOCs, Radium and Uranium- IX can consist of anion and cation
exchange. IX achieves the removal of charged inorganic species from water using an
ion-specific resin.
I
The point of use water purifiers are easy to use, cost effective, odour and taste
will improve as well as remove harmful toxins from the water. However, they do not
promise to offer full protection that is not all germs and contaminants may be
removed from the water. All the cartridges must be properly disposed as they contain
harmful toxins and if they are thrown anyhow they can pollute the environment.
NSF protocol mandates that water purifiers need to be evaluated to assess
the capabilities of the treatment device to remove the target microbiological
contaminant over the define life of the treatment device. The treatment devices are
tested for their performance by challenging them with target bacteria and virus. The
test challenge organisms used are E. coli ATCC 10536/Klebsiella terragena; through
evaluation of bacteria and viruses can be done with a pooled challenge.
In this experiment, the spike water is produced by adding test organism
of the count 105-106 CFU/ ml to test water. Then the conditioning is carried out where
the flow rate is measured. The challenge spike cycle is carried out where the effluent
and influent sample is collected. These samples are then treated with 10 % sodium
thioglycolate. Then the analysis of these samples is carried out by pour plate method
on ENDO ager or MacConkeys agar plate. The count before filtration and after
filtration of sample is compared and the log bacterial reduction in the number of cells
is determined and compare with EPA acceptance criteria. The log reduction criteria
for this protocol should be atleast 6 log reduction of bacteria, 4 log reduction of virus.
Requirements
1) Test water
2) Endo agar
3) 10% sodium thioglycolate
4) 14.6% sodium thio-sulphate
5) Sterile TSB agar plates
6) Saline
7) Tarson Carboy
PROCEDURE
1. Devices: At least two sealed units of the water treatment device are to be tested under
the evaluation study
2. Test water :
Physical parameters of the water to be used for testing are as follows:

Free from chlorine and disinfectant

pH 6.5 to 8.5

total organic carbon 0.5mg/mL

turbidity 1,0 NTU

temperature 20+/-5℃

total dissolved solids 500 mg/mL
3. Spike water
Spike water challenge is prepared by adding test organism to test water. The treatment
devices are challenged with bacteria and virus at the same time by adding adequate
quantities of suspension of Escherichia coli ATCC10536
4. Bacterial challenge suspension- Escherichia coli ATCC 10536 is used as test
organism.
1. Make a saline suspension of overnight grown test organism to get an OD of about
0.1 at 621nm which will give viable count of 108 CFU/ml
2. Use this suspension in appropriate quantities to get final count between 105/ ml
and 106/ ml in the challenges water.
TEST PROCEDURES
1. Conditioning –
i.
Install and condition a minimum of 2 units in accordance with manufacturers
instructions.
ii.
Allow about 2 litre of test water to pass through ZERO B filter measure and
record the flow rate; confirm that it is as specified by the manufacturers.
iii.
Drain out water completely and then allow the challenged water to pass
through it.
2. Challenge (spike) cycles
i.
Allow about 2 litre of spiked water to pass through the ZERO B filter.
ii.
Make sure to retain 200mL of the influenced spike water for analysis .
iii.
Allow the device to run in a normal and collect the effluent sample as
specified. The treatment device is to be challenged at different time points
during the life time study. They are

Start of test

25%

50%

75%

100%
3. Sample collection:
i.
Neutralizer; a neutralizer containing sodium thioglycolate is used to neutralize
the residual disinfectant and metal ions in test sample.
ii.
Add 1 mL of the neutralizer for every 100 mL of the sample collected in the
testing protocol.
iii.
Make sure that the neutralizer is added immediately as soon as the sample is
collected or the neutralizer is added to the sampling cup prior to sample
collection
Quantity of sample:
i.
All the samples will be collected in duplicate (2100 mL) and stored under
refrigeration at 4-10℃ till they are analyzed.
ii.
The time between sample collection and analysis ( plating) should not exceed 3 hrs.
4. Analysis of sample :
Analyse all the influent and effluent samples by the method of analysis is given
below.
Pour plate method and membrane filtration method is carried out to enumerate
bacteria in samples
Analysis of bacteria
A. Standard Pour Plate method (For influent and effluent samples)
I.
II.
Prepare serial dilution of the test/input sample in saline
Influent samples: influent samples are analysed by pour plate method
only. Plate 1 mL of 1:100, 1:1000, 1:1000 dilution in ENDO agar/
MacConkey agar as per standard pour plate method and incubate at
37℃ for 24-48 hrs. for effluent samples plate undiluted, 1:100,1:1000
dilution and process as for influents
III.
Appropriate positive control (plating untreated E.coli suspension) and
negative controls ( medium and saline controls ) must be kept during
each challenge experiment to eliminate errors due to problems
occurring due to bacterial strain, media or diluent.
Reporting results: Report log Bacterial Reduction and compare with log 6.0 log reduction
EPA acceptance criteria.
Results:
Conclusion:
References :
1. 2016. Advantages and Disadvantages of Water Filtration. BIOTECH.
2. 2006. Point-of-use or point-of-entry treatment options for small drinking water
systems. U.S. Environmental Protection Agency, Office of WaterWashington,
DC.
3. Venkatesha R, Rao AB, Kedare SB. 2020. Appropriate household point-of-use water
purifier selection template considering a rural case study in western India. Applied
Water Science 10.
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