technology selection reflections
DESCRIPTION
Technology Selection Reflections. Getting rid of all the muck Biggest bang for the buck Reliability, no need for luck. Selecting a Treatment Process. Input. Algorithm. Output. Water characteristics. Treatment Process. Resources (Capacities). Decision. Institutional. Economic. - PowerPoint PPT PresentationTRANSCRIPT
Monroe L. Weber-Shirk
School of Civil and
Environmental Engineering
Technology Selection ReflectionsTechnology Selection Reflections
Getting rid of all the muck
Biggest bang for the buck
Reliability, no need for luck
Selecting a Treatment ProcessSelecting a Treatment Process
Water characteristics
Resources (Capacities)
Institutional
Economic
Labor force
Infrastructure
Decision
Input Algorithm Output
TreatmentProcess
Education
Scale
Decision Quality as f(Data Quantity)Decision Quality as f(Data Quantity)T
reat
men
t Cho
ice
Dec
isio
n Q
uali
ty
Amount of Data
optimal
More data, but no design change!
How could you increase the y intercept? ____________Better default!
How could you increase the slope? _________________Identify critical data!
Optimal Water Treatment DecisionOptimal Water Treatment Decision
SustainableImprovement in
Public health (risk reduction)Labor savingsIndividual and community empowerment
At a cost/benefit ratio that is commensurate with competing expenditures and interventions
An Optimization Problem with Many Options
An Optimization Problem with Many Options
TechnologyWater sourcesWater treatment processesWater storageWater distributionSeparate drinking water from other uses (bottled water)
Scale (household to municipal) Staging (order of implementation)
Sustainable Staged Space
Data QualityData 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
What are our Choices?Clean Water Combos
Water SourceScale, type, characteristics
TreatmentScale, capacity, processes, automation
StorageScale, capacity
Distribution resolutionScale, capacity
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1 10 100 1k 10kmeters
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Ithaca
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person day
1 10 100 1kLiters
person daycapacity
Water Characteristics: SourceWater Characteristics: Source
RainTreat as if it were surface water
GroundwaterIf “under the influence,” then treat as if it were
surface water
SurfaceOcean
Water Treatment ObjectivesWater Treatment Objectives
Particle removalGet turbidity below
30 NTU (WHO limit for disinfection only treatments)
5 NTU (Particle removal technologies should exceed this goal)
Pathogen inactivation/removal
Hazardous chemical removalNaturally occurring
ArsenicFluorideNitrate/nitrite
Anthropogenic contamination
Microbiological Safety Chemical Safety
WHO is working on guidance for these contaminants
1
2
Particle Removal: Big ScaleParticle Removal: Big Scale
1000
NTU
1
10
100
SSF Contact Direct Conventional
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Approximate turbidity range
Operator Skill*low
mediumadvanced
*EPA’s opinion, not WHO’s opinion!
Particle Removal: Small ScaleParticle Removal: Small Scale
1000
NTU
1
10
100
SSF
1 10 100 1k 10kpeople
100k1 10 100 1k 10kpeople
100k
PuR Cartridge BagFloc/Sed
Consumables?
Pot Candle
sand? alum PuR filters
$0 $10$
cap yr$1
WHO on Particle Removal for POUWHO 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 POUWHO 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!
What was WHO thinking about SSF?
What was WHO thinking about SSF?
How much water will this system produce?_____ m/hr_____ m/d_____ m3
Why won’t this system work well?
0.45 m
0.12.4
0.38
SSF Design Flaws…SSF Design Flaws…
Scour when head loss is lowRequires a hill side
3 200 L drumsSiphon risk-Top layer of sand can dewater if supply water stops or if head loss is low
Expensive
Takes up lots of space
Flow control (“floating weir”)
Can’t handle much head loss
Flow Control FailureFlow 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?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 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: DirectionsPuR: 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?
PuR: Microorganisms andArsenic 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 RangePuR 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 CritiquePuR 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 ScaleParticle Removal: Small Scale
1000
NTU
1
10
100
SSF
1 10 100 1k 10kpeople
100k1 10 100 1k 10kpeople
100k
PuR Cartridge BagFloc/Sed
Consumables?
Pot Candle
sand? alum PuR filters
$0 $10$
cap yr$1
Minimal Data Requirements for Surface Water Treatment
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…Minimal Data…
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
Will determine treatment technology
Assume pathogens are present!
The Choice of ScaleThe Choice of Scale
My long held assumption that only centralized systems made sense
Remember creativity: vary parameters over the full range of possibilitiesVary number of customers per treatment plant!
Are there situations where decentralized is better?
1 100k
Centralized Models in the Global North
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
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 homeownerInitial local health department inspection Additional testing at homeowner’s initiativeExample… Household wells
EPA’s case for POU/POEEPA’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-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
POU/POE ConcernsPOU/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 SolutionsPOE 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…
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 QuestionOpening 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
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 POUReactor Challenges for POU
Flow rate controlBatch vs. continuous flowQuantity of water to treatOperation and MaintenanceMonitoring (or the lack thereof)
is there any indication of whether the POU device is working?
Failure modes… HACCP
Water Safety PlanWater 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)
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
HACCP for Household Water Storage Vessels
Hazard Vessel Type Vessel Integrity Vessel Sanitation
Critical Control Point(s)
Appropriate or not appropriate, based on design
Intact or not intact, based on visible damage (e.g., cracks, scratches), broken or missing parts (e.g., cap) and leaks
Sanitary or nor sanitary, based on frequency of cleaning and cleaning method
HACCP for Filtration/ChlorinationHACCP 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 uncontaminated? Turbid?
Choose best available source, 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? Chlorine-demanding solutes?
Choose best available source, with low turbidity and low chlorine demand
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
HACCP for Boiling and SODISHACCP for Boiling and SODIS
Type of Treatment
Source Water Hazards
Source Water Critical Control Point(s)
Treatment Hazards
Treatment Critical Control Points
Heating to boiling with fuel
Contaminated or uncontaminated?
Choose best available source
Inadequate temperature achieved
Heat to a visible rolling boil
Solar Radiation in clear plastic bottles (heat + UV radiation or heat only)
Contaminated or uncontaminated?Turbid? UV-absorbing solutes?
Choose best available source, with low turbidity and low UV-absorbing solutes
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…Reflections…
We need better solutions for Particle removalChemical 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) Can we outperform PuR? We need better guidance for technology selection based
on turbidity (or other easily monitored parameters)
Two meanings!
Monitoring CapabilitiesMonitoring Capabilities
Chlorine disinfection – measure residualHach $0.27 to $1.25 per test
Too expensive for POU applicationsReasonable for community systems
Monitoring Capabilities: Coliform 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
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
Testing for Coliform Bacteria: Membrane Filtration
Membrane filter0.45 μm pores47 mm in diameter
Filter 100 mL of water to be tested through the membrane filter
Membrane FiltrationMembrane Filtration
Petri dish with sterile
absorbent nutrient pad
Add 2 mL of m-endo broth
(selective media)
Place membrane filter in the
petri dish on top of the
nutrient pad
Membrane Filtration:Incubation and ResultsMembrane 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 __________________
12
34
5 6
78
8 coliform/100 mL
Monitoring: TurbidityMonitoring: Turbidity
Hach portable Turbidimeter: $837.00Sechi disk (great for lakes…)SODIS technique
Turbidity MeasurementsTurbidity Measurements
90° detector
lamp
lens
sample cell
0° detector
LED
sample cell
10° detector
Turbidity Sensors (approximate turbidity measurement)
Cheap Turbidity MeasurementsCheap Turbidity Measurements
What is our cheap detector?What is the detector measuring?
How could you make a cheap method of measuring turbidity
eye
Refraction Transmission
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