Technology Selection Reflections

1
Technology Selection Reflections

• Getting rid of all the muck
• Biggest bang for the buck
• Reliability, no need for luck

2
Selecting a Treatment Process
Input
Algorithm
Output
Water characteristics
Treatment Process
Resources (Capacities)
Decision
Institutional
Economic
Labor force
Education
Infrastructure
Scale
3
Decision Quality as f(Data Quantity)
optimal
Treatment Choice Decision Quality
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?
_________________
4
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

5
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

6
Data Quality

• Many of the choices are discrete (either process
  A or B or C)
• Thus there are regions with additional data that
  dont 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
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What are our Choices?Clean Water Combos
Ithaca

• Water Source
• Scale, type, characteristics
• Treatment
• Scale, capacity, processes, automation
• Storage
• Scale, capacity
• Distribution resolution
• Scale, capacity

capacity
8
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

9
Water Treatment Objectives
Microbiological Safety
Chemical Safety
1

• Particle removal
• Get turbidity below
• 30 NTU (WHO limit for disinfection only
  treatments)
• 5 NTU (Particle removal technologies should
  exceed this goal)
• Pathogen inactivation/removal

• Hazardous chemical removal
• Naturally occurring
• Arsenic
• Fluoride
• Nitrate/nitrite
• Anthropogenic contamination

WHO is working on guidance for these contaminants
2
10
Particle Removal Big Scale
SSF
Contact
Direct
Conventional
Operator Skill
low
medium
advanced
EPAs opinion, not WHOs opinion!
Approximate turbidity range
11
Particle Removal Small Scale
SSF
PuR
Cartridge
Bag
Floc/Sed
Pot
Candle
Consumables?
0
10
1
filters
sand?
alum
PuR
12
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., wont need
  disinfection)
• Particle removal technologies include
• Settling or plain sedimentation
• Fiber, cloth or membrane filters
• Granular media filters
• Slow sand filter

13
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
• 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 good small-scale design!
Need a simple cleaning technique!
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What was WHO thinking about SSF?

• How much water will this system produce?
• _____ m/hr
• _____ m/d
• _____ m3
• Why wont this system work well?

0.45 m
0.1
2.4
0.38
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SSF Design Flaws
Flow control (floating weir)
Cant handle much head loss
Scour when head loss is low
Requires a hill side
Siphon risk- Top layer of sand can dewater if
supply water stops or if head loss is low
3 200 L drums
Expensive
Takes up lots of space
16
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

17
Why doesnt 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?

18
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)

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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
• 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

No sedimentation?
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PuR Microorganisms andArsenic Removal

• PuR is expected to provide excellent disinfection
  (gt7-log bacterial, gt4-log viral and gt3-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 lt50 ppb

21
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

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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
  dont 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
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Particle Removal Small Scale
SSF
PuR
Cartridge
Bag
Floc/Sed
Pot
Candle
Consumables?
0
10
1
filters
sand?
alum
PuR
24
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?

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Minimal Data
Will determine treatment technology

• Turbidity
• Pathogens
• Chemicals
• Determine if naturally occurring contaminants are
  present in region
• Assess watershed exposure risk to agricultural
  and industrial contamination
• Economic, Institutional, Educational Capacity

Assume pathogens are present!
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The Choice of Scale

• 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?

27
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

28
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 homeowners initiative
• Example Household wells

29
EPAs 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-Of-Use 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 immuno-compromised,
  receive safe drinking water

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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

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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?
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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)

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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?

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Water Quantity and Access for Health
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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

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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

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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.

38
HACCP for Household Water Storage Vessels
39
HACCP for Filtration/Chlorination
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HACCP for Boiling and SODIS
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Reflections

• We need better solutions for
• Particle removal
• Chemical removal
• Existing designs are too expensive, dont 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)
• Can we outperform PuR?
• We need better guidance for technology selection
  based on turbidity (or other easily monitored
  parameters)

Two meanings!
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Monitoring Capabilities

• Chlorine disinfection measure residual
• Hach 0.27 to 1.25 per test
• Too expensive for POU applications
• Reasonable for community systems

43
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)

44
Testing for Coliform BacteriaPresence/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.

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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

46
Membrane Filtration
Add 2 mL of m-endo broth (selective media)
Place membrane filter in the petri dish on top of
the nutrient pad
Petri dish with sterile absorbent nutrient pad
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Membrane FiltrationIncubation and Results

• Incubate for 24 hours at 35C
• Coliform bacteria grow into colonies with a green
  metallic sheen
• Non-coliform bacteria may grow into red colonies
• Coliform concentration is __________________

2
1
4
3
6
5
8
7
8 coliform/100 mL
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Monitoring Turbidity

• Hach portable Turbidimeter 837.00
• Sechi disk (great for lakes)
• SODIS technique

49
Turbidity Measurements
lens
90 detector
lamp
0 detector
sample cell
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Cheap Turbidity Measurements
eye

• What is our cheap detector?
• What is the detector measuring?
• How could you make a cheap method of measuring
  turbidity

Transmission
Refraction
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