Technology Selection Reflections
Getting rid of all the muck
Biggest bang for the buck
Reliability, no need for luck
Monroe L. Weber-Shirk
School of Civil and
Environmental Engineering
Selecting a Treatment Process
Input
Water
characteristics
Resources
(Capacities)
Institutional
Economic
Labor force
Infrastructure
Scale
Algorithm
Decision
Output
Treatment
Process
Education
Treatment Choice
Decision Quality
Decision Quality as f(Data Quantity)
optimal
More data, but no
design change!
Amount of Data
Better default!
How could you increase the y intercept? ____________
Identify critical data!
How could you increase the slope? _________________
Optimal Water Treatment Decision
Sustainable
Improvement in
Public health (risk reduction)
Labor savings
Individual and community empowerment
At a cost/benefit ratio that is commensurate
with competing expenditures and
interventions
An Optimization Problem with
Many Options
 Technology
 Water sources
 Water treatment processes
 Water storage
 Water distribution
 Separate drinking water from other uses (bottled water)
 Scale (household to municipal)
 Staging (order of implementation)
 Sustainable Staged Space
Data Quality
Many of the choices are discrete (either
process A or B or C)
Thus there are regions with additional data
that don’t cause any improvement in design
How can we choose which data to gather to
maximize the rate of approach to the
optimal design?
We will return to this question after we review our options
What are our Choices?
Clean Water Combos
Water Source
1
10
Scale, type, characteristics
Treatment
Ithaca
100
1k
meters
Scale, capacity
100k
1
10
100
1k
people
10k
100k
1
10
100
1k
people
10k
100k
1
10
1
10 Liters 100
Scale, capacity, processes, automation
Storage
10k
Distribution resolution
Scale, capacity
capacity
100
1k
meters
person day
1k
10k
100k
Water Characteristics: Source
Rain
Treat as if it were surface water
Groundwater
If “under the influence,” then treat as if it were
surface water
Surface
Ocean
Water Treatment Objectives
Microbiological Safety
1  Particle removal
 Get turbidity below
 30 NTU (WHO limit
for disinfection only
treatments)
 5 NTU (Particle
removal technologies
should exceed this goal)
2  Pathogen
inactivation/removal
Chemical Safety
 Hazardous chemical
removal
 Naturally occurring
WHO is working
 Arsenic
on guidance for
 Fluoride
these contaminants
 Nitrate/nitrite
 Anthropogenic
contamination
Particle Removal: Big Scale
1
10
SSF Contact
100
1k
people
10k
100k
Direct Conventional
1
Operator Skill*
low
medium
advanced
10
NTU
100
Approximate turbidity range
*EPA’s opinion,
not WHO’s
opinion!
Particle Removal: Small Scale
1
1
10
100
1k
people
10k
100k
SSF Floc/Sed PuR Cartridge Bag
Pot Candle
10
NTU
100
$
cap  yr
$0
sand?
1000
alum
$10
Consumables?
PuR
filters
$1
WHO on Particle Removal for POU
 There is a need to investigate, characterize and implement
physical and physical-chemical technologies for practical
and low cost pre-treatment
 Some physical or physical-chemical methods may be
highly effective for treatment of stored household water on
their own. (i.e., won’t need disinfection)
 Particle removal technologies include:




Settling or plain sedimentation
Fiber, cloth or membrane filters
Granular media filters
Slow sand filter
WHO on SSF as POU
 Slow sand filtration is the least likely to be sustainable at
the household level.
 the preferred filter designs and installations often are larger and
capable of treating more water than needed by individual
households
Need a good small-scale design!
 because of their relatively large size (surface area)
 and the needs for
 proper construction and operation,
 regular maintenance (especially sand scraping, replacement and
cleaning) by trained individuals.
 Such demands for achieving good performance are
unrealistic because they are beyond the capacities and
capabilities of most households
Need a simple cleaning technique!
What was WHO thinking about
SSF?
 How much water
will this system
produce?
0.1 m/hr
 _____
 _____
2.4 m/d
 _____
0.38 m3
 Why won’t this
system work well?
0.45 m
SSF Design Flaws…
Flow control (“floating weir”)
Can’t handle much head loss
Scour when head loss is low
Requires a hill side
3 200 L drums
Expensive
Takes up lots of space
Siphon riskTop layer of
sand can dewater
if supply water
stops or if head
loss is low
Flow Control Failure
 A floating weir (that can be made
of a bowl, two small tubes and a
hose) in the supply tank
maintains a constant flow of
water to the top of the filter tank
 Environmental Health Project
(WASH ) concludes that the close
attention and frequent adjustment
required to operate demonstration
models has resulted in early
abandonment
Why doesn’t this work well?
 Where is constant head?
 Where is head loss
element?
 How is flow adjusted?
 What is the role of the
nylon string?
 What happens when you
add a pebble?
 How flexible is a rubber
tube?
The Proctor and Gamble
Solution: PuR
 The PuR product uses ferric sulfate, bentonite, sodium carbonate,
chitosan, polyacrylamide, potassium permanganate, and calcium
hypochlorite
 A small sachet of powdered product visibly separates the cleaned water
from the murky masses
 Initial efforts are underway to develop a sustainable market-based
approach for delivery and to learn how to best make POU products
available. Three separate complementary models are being explored:
 a social model led by non-profit organizations
 a commercial model led by the private sector
 an emergency relief model led by relief organization
 One small sachet, costing about US $0.10 in the commercial model,
will treat 10 liters of water (enough drinking water for an average
family for two days)
PuR: Directions
 Add 1 sachet to 10 litres of water and stir to begin
process of separating the cleaned water from the
murky masses
 Stir water for 5 minutes until clear No sedimentation?
 Filter water through a cloth and dispose of
separated floc in the latrine
 Let clear water stand for 20 minutes to allow for
complete disinfection
 Store in a suitable container to prevent
recontamination
PuR: Microorganisms and
Arsenic Removal
 PuR is expected to provide excellent disinfection (>7-log
bacterial, >4-log viral and >3-log parasite reductions)
across a variety of water types and under conditions that
stress less effective purification products including solar or
chlorine treatment alone
 No E. coli were detected post-treatment in any of 320
samples of drinking water sources collected in developing
countries
 The POU treatment was also effective in removing arsenic
from water artificially contaminated with arsenic and from
water with naturally occurring arsenic contamination
 In Bangladesh tests, arsenic decreased by a mean of (85%)
88% of treated samples were <50 ppb
PuR Turbidity Range
Turbidities in the samples were reduced
significantly, pre-treatment ranged from 0 to
1850 NTU (mean 19 NTU) and final values
were generally less than 1 NTU (average
0.25 NTU).
The highest final turbidity observed was 3.2
NTU for a water source whose starting
turbidity had 1850 NTU
PuR Critique
 This is not sustainable or in the interests of people in rural
areas.
 It becomes a product that has to be purchased on a regular
basis from a foreign country.
 I think the analogy to the scandalous infant formula
problems of a couple of decades ago should be kept in
mind where people were encouraged to abandon breast
feeding in favor of a foreign infant formula.
 Getting people “hooked” on a product that will require as
much as 10% of their income instead of trying to develop
sustainable solutions that don’t have recurrent cost and that
the villagers have control over is exploitive in the worst of
ways
--Humphrey Blackburn*
*Okay, he designs and sells slow sand filters…
Particle Removal: Small Scale
1
1
10
100
1k
people
10k
100k
SSF Floc/Sed PuR Cartridge Bag
Pot Candle
10
NTU
100
$
cap  yr
$0
sand?
1000
alum
$10
Consumables?
PuR
filters
$1
Minimal Data Requirements for
Surface Water Treatment
What would you need to know before you
would be willing to recommend a water
treatment technology for a community of
250 that is currently relying on an untreated
surface water source?
Minimal Data…
 Turbidity
 Pathogens
 Chemicals
Will determine treatment technology
Assume pathogens are present!
 Determine if naturally occurring contaminants are
present in region
 Assess watershed exposure risk to agricultural and
industrial contamination
 Economic, Institutional, Educational Capacity
1
The Choice of Scale
100k
My long held assumption that only
centralized systems made sense
Remember creativity: vary parameters over
the full range of possibilities
Vary number of customers per treatment plant!
Are there situations where decentralized is
better?
Centralized Models in the Global
North
 Centralized (Municipal)




Water source (possibly multiple sources)
Treatment (possibly multiple facilities)
Storage (usually multiple tanks in sprawling communities)
Distribution (one network with redundancy)
 Governance
 Federal or State regulations
 City department, Commission
 Ownership
 Private or Public
Decentralized Models in the Global
North
Single source, treated as needed, stored
(often in a pressure tank in the basement)
Owned and maintained by the homeowner
Initial local health department inspection
Additional testing at homeowner’s initiative
Example… Household wells
EPA’s case for POU/POE
 Public water supply consumers may not always possess the
financial resources, technical ability, or physical space to
own and operate custom-built treatment plants
 Small drinking water treatment systems, such as Point-OfUse and Point-Of-Entry (POU/POE) units, may be the best
solution for providing safe drinking water to individual
homes, businesses, apartment buildings, and even small
towns
 These small system alternatives can be used for not only
treating some raw water problems, but they are excellent
for treating finished water that may have degraded in
distribution or storage or to ensure that susceptible
consumers, such as the very young, very old, or immunocompromised, receive safe drinking water
POU/POE Concerns
 The problem of monitoring treatment performance so that
it is comparable to central treatment
 POU devices only treat water at an individual tap (usually
the kitchen faucet) and therefore raise the possibility of
potential exposure at other faucets. Also, they do not treat
contaminants introduced by the shower (breathing) and
skin contact (bathing)
 These devices are generally not affordable by large
metropolitan water systems
 POU devices are only considered acceptable for use as
interim measures, such as a condition of obtaining a
variance or exemption to avoid unreasonable risks to
health before full compliance can be achieved
POE Solutions
 The 1996 regulations required the POU/POE units to be
 owned, controlled, and maintained by the PWS or by a person
under contract with the PWS operator to ensure
 proper operation and maintenance
 compliance with the MCLs or treatment technique
 equipped with mechanical warnings to ensure that customers are
automatically notified of operational problems
 Under this rule, POE devices are considered an acceptable
means of compliance because POE can provide water that
meets MCLs at all points in the home
Could each community in the Global South have a
designated person who maintains the POU devices?
POU wins over Centralized
Treatment when…
 The distance between houses is large (order 1 km)
then POU supplies are common
 The centralized system is unreliable (low
institutional capacity, poor infrastructure)
 The cost of POU treatment is less than the cost of
a centralized treatment facility (small
communities)
 POU only treats water for human consumption
(with savings in capital, operation, and
maintenance costs)
Opening Question
You live in a small community that
chlorinates a surface water with turbidities
that range between 5 and occasionally 200
NTU
Give 2 reasons why a POU SSF might not
be a good solution
What research would you like to conduct to
determine how serious these problems are?
Water Quantity and Access for
Health
Service level
Access measure
Needs met
Level
of
health
risk
No access
(quantity
collected often
below 5 l/c/d)
More than 1000m or 30
minutes total collection
time
Consumption cannot be assured
Hygiene - not possible (unless practiced at
source)
Very
high
Basic access
(average
quantity unlikely
to exceed 20
l/c/d)
Between 100 and 1000m
or 5 to 20 minutes total
collection time
Consumption - should be assured
Hygiene - handwashing and basic food hygiene
possible, laundry/bathing difficult to assure
unless carried out at source
High
Intermediate
access (average
quantity about
50 l/c/d)
Water delivered through 1
tap on-plot or within
100m or 5 minutes total
collection time
Consumption assured
Hygiene - all basic personal and food hygiene
assured; laundry and bathing should also be
assured
Low
Optimal access
(average
quantity 100
l/c/d and above)
Water supplied through
multiple taps continuously
Consumption - all needs met
Hygiene - all needs should be met
Very
low
Reactor Challenges for POU
Flow rate control
Batch vs. continuous flow
Quantity of water to treat
Operation and Maintenance
Monitoring (or the lack thereof)
is there any indication of whether the POU
device is working?
Failure modes… HACCP
Water Safety Plan
 Risk assessment to define potential health
outcomes of water supply
 System assessment to determine the ability of the
water supply system to remove pathogens and
achieve defined water quality targets (remember
the chlorinator assignment?)
 Process control using HACCP
 Process/system documentation for both steady
state and incident-based (e.g., failure or fault
event) management
Hazard Analysis at Critical Control
Points (HACCP)
It is recommended that HACCP for
household water collection, treatment and
storage be applied in the context of a Water
Safety Plan that addresses source water
quality, water collection, water treatment,
water storage and water use.
HACCP for Household Water
Storage Vessels
Hazard Vessel Type Vessel Integrity
Intact or not intact,
Appropriate based on visible
Critical or not
damage (e.g.,
Control appropriate, cracks, scratches),
Point(s) based on
broken or missing
design
parts (e.g., cap) and
leaks
Vessel Sanitation
Sanitary or nor
sanitary, based on
frequency of
cleaning and
cleaning method
HACCP for Filtration/Chlorination
Type of
Treatment
Source Water
Hazards
Source Water
Critical Control
Point(s)
Treatment
Hazards
Treatment Critical
Control Points
Filtration
methods
Contaminated or Choose best
uncontaminated? available source,
Turbid?
with low turbidity
Poor filtration
and turbidity
reduction
Observe (monitor)
for adequate
turbidity
(cloudiness)
reduction
Chlorination or
mixed oxidants
from electrolysis
of brine (NaCl)
Contaminated or
uncontaminated?
Turbid? Chlorinedemanding
solutes?
Poor
chlorination due
to inadequate
dose and
contact time
Observe (monitor)
for chlorine residual
(C) and for adequate
contact time (T),
i.e., adequate CT
Choose best
available source,
with low turbidity
and low chlorine
demand
HACCP for Boiling and SODIS
Source Water
Critical Control
Point(s)
Type of
Treatment
Source Water
Hazards
Heating to
boiling with fuel
Contaminated or Choose best
uncontaminated? available source
Solar Radiation
in clear plastic
bottles (heat +
UV radiation or
heat only)
Contaminated or
uncontaminated?
Turbid? UVabsorbing
solutes?
Choose best
available source,
with low turbidity
and low UVabsorbing solutes
Treatment
Hazards
Treatment Critical
Control Points
Inadequate
temperature
achieved
Heat to a visible
rolling boil
Inadequate
sunlight to
achieve target
temperature
and UV dose
Target temperature
sensor (thermometer
or melting wax);
elapsed exposure
time (timer, clock,
sun position, etc.);
monitor/observe
weather (sunny, part
sun or cloudy)
Reflections…
 We need better solutions for
 Particle removal
 Chemical removal
 Existing designs are too expensive, don’t work well
enough, or require advanced operator skills
 We need easy to use and cheap monitoring devices
 Remove particles before disinfection (unless you are
using heat)
Two meanings!
 Can we outperform PuR?
 We need better guidance for technology selection based
on turbidity (or other easily monitored parameters)
Monitoring Capabilities
Chlorine disinfection – measure residual
Hach $0.27 to $1.25 per test
Too expensive for POU applications
Reasonable for community systems
Monitoring Capabilities: Coliform
 Current cost is several dollars per sample for membrane
filtration (enumeration)
 Absolutely prohibitive for POU monitoring
 Difficult for small communities
 MIT Design that matters is exploring cheaper methods of
measuring coliform concentrations
 Melted wax incubator
 More economical filtration apparatus
 Coliform removal is still one of the best ways to evaluate
filter performance (remember bacteria are hard to remove)
Testing for Coliform Bacteria:
Presence/Absence Tests
 Colisure allows testing for coliform bacteria
and/or E. coli in 24 - 28 hours.
 The detection limit of ColiSure is 1 colony
forming unit (CFU) of coliform bacteria or E.
coli per 100 mL of medium.
 If coliform bacteria are present, the medium
changes color from yellow to a distinct red or
magenta.
 If E. coli are present, the medium will emit a
bright blue fluorescence when subjected to a
long wave (366 nm) ultraviolet (UV) light.
Testing for Coliform Bacteria:
Membrane Filtration
Membrane filter
0.45 μm pores
47 mm in diameter
Filter 100 mL of
water to be tested
through the
membrane filter
Membrane Filtration
Petri dish with
sterile absorbent
nutrient pad
Add 2 mL of mendo broth
(selective
media)
Place membrane
filter in the petri
dish on top of
the nutrient pad
Membrane Filtration:
Incubation and Results
 Incubate for 24 hours at
35°C
 Coliform bacteria grow
into colonies with a
green metallic sheen
 Non-coliform bacteria
may grow into red
colonies
 Coliform concentration
is __________________
8 coliform/100 mL
2
1
5
3
7
4
6
8
Monitoring: Turbidity
Hach portable Turbidimeter: $837.00
Sechi disk (great for lakes…)
SODIS technique
Turbidity Measurements
lens
90° detector
lamp
0° detector
sample cell
10° detector
LED
Turbidity Sensors
(approximate turbidity measurement)
sample cell
Cheap Turbidity Measurements
What is our cheap detector? eye
What is the detector measuring?
Refraction
Transmission
How could you make a cheap method of
measuring turbidity
1
10
1
100
1k
people
10
100 Liters 1k
person day
1
10 Liters 100
person day
1k
10k
10k
100k
100k