Transcript Excreta and Household Wastewaters - Introduction Global Water, Sanitation and Hygiene ENVR 890-2

Excreta and Household
Wastewaters - Introduction
Global Water, Sanitation and Hygiene
ENVR 890-2
Mark D. Sobsey
February, 2009
Household Human Wastes and
Wastewaters
Feces - Composition
Note: This number may be too low;
live bacteria are shed in large quantity
Feces, Microbes and Microbial Pathogens
Besides nutrients and organic matter, human and animal fecal wastes
contain large numbers of microbes (>100 billion/gram).
 Constitute ~1/3rd the mass of human fecal matter
 Most are beneficial or essential in the gut; they are NOT pathogens
 Some gut microbes ARE human pathogens; can cause disease
– Humans and animals harbor pathogens some of the time
– Pathogen colonization and infection is common
– In some food animals (poultry, beef and swine)
– In people with poor sanitation and hygiene
– Esp. in developing world; carriage rates are high
– Human pathogens are typically shed in human and animal feces
– Enteric pathogens can be transmitted by the fecal-oral route; often
106-109 pathogens/gram of feces of an infected person
– Ingested with fecally contaminated water, food, objects,
or by direct and indirect personal contact
Excreta and Graywater– Definitions and Properties
Excreta: Human feces and urine
Managed in different ways:
Direct disposal on land or in water
Direct use as fertilizer, soil conditioner and for aquaculture
Pre-treatment prior to use
Dilution with water to convey (sewage) for disposal or use
Direct use of untreated (raw) sewage
Treatment and discharge to land or water
Treatment and reuse (agriculture, aquaculture, horticulture,
industrial and civil use
Graywater: Other wastewater from human activity
Not directly from human fecs and urine
Wastewater from washing, bathing, etc
Contains human wastes and exudates
Managing Human Excreta - Options
• “Dry” Collection:
– Open defecation
– Collect in a container
• e.g., chamber pot
– Discharge to the
environment w/ or w/o Rx
• Latrines – several kinds
– Treat or dispose of or both
– Separate feces and urine;
• Then, treat/store, use,
dispose to the
environment
Managing Human Excreta - Options
• Semi-wet (or semi-dry)
• Use some water
• Pour-flush toilets and
other low water use
systems
NO! Hanging Toilet/Latrine
Managing Human Excreta - Options
• Wet Systems
Septic tank - soil absorption system
– On-site Septic Systems
– Other On-site systems
• Soak pits
– Sewerage
– Sewage treatment systems
Human Excreta – Resource or Risk?
• Human excreta as a potential resource
• Contains nutrients (N, P, K, and organic
matter)
• Nutrients and organic matter are:
•Detrimental in water, esp. surface water
•Eutrophication, anoxia, fish kills
• Beneficial on land
•Fertilizer, soil conditioner, land stabilizer
• Widely used as a fertilizer and soil
amendment in both developed and developing
countries
• Potential for excreta misuse and
environmental pollution is great without proper
attention to management plans and human
behavior considerations
Nitrogen (N)
Phosphorous (P)
Potassium
Organic matter
(as BOD)
4.5
0.6
1.0
35
Annual Amounts/Person, Kg
Nutrient Content of Human Excreta
• Rich source of inorganic plant nutrients: N, P K and organic matter
• Daily human excretion: ~30 g of C (90 g of organic matter), ~ 10-12 g
N, ~ 2 g of P and 3 g of K.
• Most organic matter in feces most N and P (70-80 %) in urine. K
equally distributed between urine and feces.
Composition of Household
Waste and Wastewater
20
14.1
12.3
5.3
6
3.6
K
Organics
P
kg COD/ (Person·year)
0
N
0.8
1.0
Nutrient content
500 l
50 l
Volume
Liter / (Person·year)
greywater
urine
faeces
source: Otterpohl
kg N,P,K / (Person·year)
0
Characteristics of Human Wastes
fraction
characteristic
1. feces
• hygienically critical (high risk)
• consists of organics, nutrients and trace elements
• improves soil quality and increase its water
retention capacity
2. urine
• less hygienically critical (less risk)
• contains the largest proportion of nutrients
available to plants
• may contain hormones or medical residues
• of no major (or less) hygienic concern/risk
• volumetrically the largest portion of wastewater
• contains almost no (or less) nutrients (simpler
treatment)
• may contain spent washing powders etc.
3. greywater
Fertilizer Potential of Human Excreta
Fertilizer Equivalence of Yearly per Capita Excreted
Nutrients and Fertiliser Requirements for Producing
250 kg of Cereals
6
cereal
requirements
4
faeces
3
2
urine
1
0
N
N
P
P
K
K
source: Drangert, 1998
Nutrient (kg)
5
Options for Excreta and Greywater Utilization
urine
(yellowwater)
faeces
(brownwater)
treatment
hygienisation by
storage or
drying
anaerobic
digestion,
drying,
composting
utilisation
liquid or dry
fertiliser
substances
biogas,
soil
improvement
greywater
(shower,
washing, etc.)
constructed
wetlands, gardening,
wastewater ponds, biol.
treatment, membranetechnology
irrigation,
groundwaterrecharge or
direct reuse
Primary Treatment or Primary Sedimentation
Settle solids for 2-3 hours in a
static, unmixed tank or basin.
• ~75-90% of particles and 5075% of organics settle out as
“primary sludge”
– enteric microbe levels in 1o
sludge are sometimes ~10X
higher than in raw sewage
• enriched by solids
accumulation
• Overall, little removal of
many enteric microbes:
– typically ~50% for viruses
and bacteria
– >50% for parasites,
depending on their size
Enteric Microbe/Pathogen Reductions in
Secondary or Biological Treatment
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Aerobic biological treatment: typically,
activated sludge (AS) or trickling filtration
(TF)
Then, settle out the biological solids
produced (2o sludge)
~90-99% enteric microbe/pathogen
reductions from the liquid phase
Enteric microbe retention by the biologically
active solids: accumulation in AS flocs or TF
biofilms
Biodegradation of enteric microbes by
proteolytic enzymes and other degradative
enzymes/chemicals
Predation by treatment microbes/plankton
(amoeba, ciliates, rotifers, etc.
Aerobic microbes utililize carbon and other
nutrients to form a healthy activated sludge
AS biomass (floc)
The biomass floc is allowed to settle out in
the next reactor; some AS is recycled
Waste Solids (Sludge) Treatment
• Treatment of settled solids from 1o and 2o sewage treatment
• Biological “digestion” to biologically stabilize the sludge solids
– Anaerobic digestion (anaerobic biodegradation)
– Aerobic digestion (aerobic biodegradation)
– Mesophilic digestion: ambient temp. to ~40oC; 3-6 weeks
– Thermophilic digestion: 40-60oC; 2-3 weeks
• Produce digested (biologically stabilized) sludge solids for further
treatment and/or disposal (often by land application)
– “Thickening” or “dewatering”
– drying or “curing”
• Waste liquids from sludge treatment are recycled through the sewage
treatment plant
• Waste gases from sludge treatment are released
(or burned if from anaerobic digestion: methane, hydrogen, etc.)
Enteric Microbe/Pathogen Reductions by Sludge
Treatment Processes
• Anaerobic and aerobic digestion processes
– Moderate reductions (90-99%) by mesophilic processes
– High reductions (>99%) by thermophilic processes
• Thermal processes
– Reductions depend on temperature
• Greater reductions at higher temperatures
• Temperatures >55oC usually produce appreciable pathogen reductions.
• Alkaline processes: lime or other alkaline material
– Reductions depend on pH; greater reductions at higher pHs
• pH >11 produces extensive pathogen reductions
• Composting: high temperature, aerobic biological process
– Reductions extensive (>99.99%) when temperatures high and waste
uniformly exposed to high temperature
• Drying and curing
– Variable and often only moderate pathogen reductions
“Processes to Further Reduce Pathogens” “PFRP”: Class A
Sludge
Class A sludge:
• <1 virus per 4 grams dried sludge solids
• <1 viable helminth ovum per 4 grams dried sludge solids
• <3 Salmonella per 4 grams of dried sludge solids
• <1,000 fecal coliforms per gram dry sludge solids
PFRPs:
• Thermal (high temperature) processes (incl. thermophilic
digestion); hold sludge at 50oC or more for specified times
• lime (alkaline) stabilization; raise pH 12for 2 or more hours
• composting: additional aerobic treatment at elevated
temperature
• Class A sludge or “biosolids” disposal by a variety of options or
used as a soil conditioner
– Class A biosolids can be marketed/distributed as soil
conditioner for use on non-edible plants
Alternative Biological Treatment of Wastewater:
Alternatives for Small and Rural Communities
• Lagoons, Ponds and Ditches
– aerobic, anaerobic and facultative
– for smaller communities and farms
– enteric microbes are reduced by ~90-99% per pond
• multiple ponds in series increases overall microbe reductions
• Constructed Wetlands
– aerobic systems containing biologically active, oxidizing
microbes and emergent aquatic plants
– Microbial reductions comparable to or greater than ponds or
lagoons.
• Lagoons and constructed wetlands are practical and
economical sewage treatment alternatives when land is
available at reasonable cost
Facultative Oxidation (Waste Stabilization) Pond
Pathogen reductions of 90-99%, depending on design, operation and conditions
Two or more ponds in series achieve 90-99% reduction per pond, giving 99-99.99%
reduction in 2 ponds and 99.9-99.9999% reduction in 3 ponds in series, etc,
Stabilization Ponds or Lagoons
• Aerobic and Facultative Ponds:
• Biologically Rx by complementary activity of algae and bacteria.
• Used for raw sewage as well as primary- or secondary-Rx’d.
effluent.
• Bacteria and other heterotrophs convert organic matter to carbon
dioxide, inorganic nutrients, water and microbial biomass.
• Algae use CO2 and inorganic nutrients, primarily N and P, in
photosynthesis to produce oxygen and algal biomass.
• Many different pond designs have been used to treat sewage:
• facultative ponds: upper, aerobic zone and a lower anaerobic
zone.
• Aerobic heterotrophics and algae proliferate in the upper zone.
• Biomass from upper zone settles into the anaerobic, bottom zone.
• Bottom solids digested by anaerobic bacteria.
Enteric Microbe/Pathogen Reductions in Stabilization Ponds
• BOD (a measure of biodegradable organic matter) and enteric
microbe/pathogen reductions of 90%, esp. in warm, sunny climates
• Even greater enteric microbe/pathogen reductions by using two or
more ponds in series
• Better BOD and enteric microbe/pathogen reductions if detention
(residence) times are sufficiently long (several weeks to months)
• Enteric microbes reduced by 90-99% in single ponds and by
multiples of 90-99% for ponds in series.
• Microbe removal often quite variable, depending upon pond design,
operating conditions and climate.
– Reduction efficiency lower in colder weather and with shorter
retention times
Constructed Wetlands and Enteric Microbe
Reductions
• Surface flow (SF) wetlands reduce enteric microbes
by ~90%
• Subsurface flow (SSF) wetlands reduce enteric
microbes by ~99%
• Greater reduction in SSF may be due to greater
biological activity in wetland bed media (porous
gravel) and longer retention times
• Multiple wetlands in series incrementally increase
microbial reductions, with 90-99% reduction per
wetland cell.
Septic Tank-Soil Absorption Systems for On-Site Sewage Rx
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Used where no sewers or community sewage treatment facilities: ex.: rural homes
Septic tank: solids settle and are digested
Septic tank effluent (STE) is similar to primary sewage effluent
Distribute STE to soil via a sub-surface, porous pipe in a trench
Absorption System: Distribution lines and drainfield
Septic tank effluent flows through perforated pipes 2-3 feet below the land surface
in a trenches filled with gravel, preferably in the unsaturated (vadose) zone.
– Effluent discharges from perforated pipes into trench gravel and then into
unsaturated soil, where it is biologically treated aerobically.
– Enteric microbes are removed and retained by the soil and biodegraded along with STE
organic matter; extensive enteric microbe reductions are possible
– But, viruses and other pathogens can migrate through the soil and reach ground water
if the soil is too porous (sand) and the water table is high
Ecological Sanitation (Eco-San):
Circular Flow/Recycling of Nutrients and Other Materials
Basis and Approach:
Considers urine, feces and water as resources in an
ecological loop.
Seeks to protect public health, prevent pollution and
return nutrients and humus to the soil.
Nutrient recycling to ensure food security.
Separate urine and feces at source;
Do not mixed with water.
- avoid contaminating large volumes of water
with pathogens.
- separation make it easier to recover and
recycle nutrients
After dilution and/or processing, separated urine can
be applied to the soil as a hygienic fertilizer.
Feces can be safely composted to allow
incorporation of its organic matter into food
production.
Ecological Sanitation - EcoSan
Advantages and options:
• Affordable, flexible sanitation
options for all
• Wide range of toilet designs
• Different ways to collect/treat
urine/feces.
• Low- and high-technology
solutions for rural and urban
settings.
• Allows for central and/or
decentralized management
• Dry and/or waterborne systems
Log10 Reduction of Pathogens by Wastewater Rx Processes
Log10 Reduction of Pathogens by Wastewater Rx Processes
REMOVAL OF ENTERIC BACTERIA BY
SEWAGE TREATMENT PROCESSES
ORGANISM
PROCESS
Fecal indicators Primary sed.
E. coli
Primary sed.
Fecal indicators
Fecal indicators
Fecal indicators
Salmonellae
Salmonellae
Salmenellae
Salmonellae
% REMOVAL
0-60%
32 and 50%
Trickling filt.
20-80%
Activated sludge
40-95%
Stab. ponds, 1 mo. >99.9999% @ high temp.
Primary sed.
79%, 6-7 hrs.
"
73%, 6-7 hrs.
Trickling filt.
92%
Activated sludge
ca. 99%
Entamoeba histolytica Reduction by Sewage Treatment
ORGANISM
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
E. histolytica
PROCESS
% REMOVAL
Primary Sed.
50%
Primary Sed., 2 hr.
64%
Primary sed., 1 hr.
27%
Primary sed. + Trickl. Filt.
25%
"
74%
"
91%
Primary sed. + Act. Sludge
83%
Oxidation ditch + Sedimentation
91%
Stabilization ponds + sedimentation 100%
"
100, 94, 87
"
100
Aerated lagoon (no settling)
84%
Microbial Reductions by Wastewater Treatment
% Reduction
Microbe 1o&2o Filt. Disinfect. Store Total Rx.
Tot. colif.
98
69
99.99
75
99.99999
Fec. colif.
99
10
99.998
57
99.999996
99.98
90
90
99.99997
98
84
96
91
99.999
93
99
78
50
99.9993
Crypto- 93
sporidium
98
61
<10
99.95
Coliphage 82
Enterovirus
Giardia
Disinfection of Wastewater
• Intended to reduce microbes in 1o or 2o treated effluent
– Typically chlorination
– Alternatives: UV radiation, ozone and chlorine dioxide
• Good enteric bacterial reductions: typically, 99.99+%
– Meet fecal coliform limits for effluent dicharge
• Often 200-1,000 per 100 ml geometric mean as permitted
discharge limit
• Less effective for viruses and parasites: typically, 90-99% reduction
• Toxicity of chlorine and its by-products to aquatic life now limits
wastewater chlorination; may have to:
– Dechlorinate
– Use an alternative, less toxic chemical disinfectant or
– Use an alternative treatment process to reduce enteric microbes
• granular medium (e.g., sand) filtration
• membrane filtration
When Wastewater Disinfection is
Recommended or Required
• Discharge to surface waters:
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near drinking water supply intakes
used for primary contact recreation
used for shellfish harvesting
used for irrigation of crops and greenspace
other direct and indirect reuse and reclamation
purposes
• Discharge to ground waters waters:
– used as a water supply source
– used for irrigation of crops and greenspace
– other direct and indirect reuse and reclamation purposes
Wastewater Reuse
• Wastewater is sometimes reused for beneficial, non-potable
purposes in arid and other water-short regions.
• Widespread in developing countries;
– often done poorly with inadequate reduction of pathogens/toxins
• Often uses advanced or additional treatment processes,
sometimes referred to as “reclamation”
• Biological treatment in “polishing” ponds, constructed wetlands
and other “natural” systems
• Physical-chemical treatment processes used for drinking water:
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–
–
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Coagulation-flocculation and sedimentation
Filtration: granular medium filters; membrane filters
Granular Activated Carbon adsorption
Disinfection
(Details of these water treatment process to presented in
lectures on water treatment)
Indicator Microbe Levels in Raw and Treated
Municipal Sewage: Sewage Treatment Efficacy
Number/100 ml
100000000
10000000
1000000
100000
10000
1000
100
10
1
F. col. E. coli Ent.
C. p. F+ phg.
Raw
(-------------Bacteria--------- Bact. spores Viruses)
Treated
(geom. mean values of 24 biweekly samples)
Estimated Pathogen Reductions by Sewage
Treatment Processes: An Example
Sewage Treatment Rx:
Reduction
•
•
•
•
Primary settling
2o biological treatment
Granular medium filtration
Disinfection
% Reduction
50
99
90
99
Total %
50
99.5
99.95
99.9995
Effect of Sanitation on Health
Fewtrell, L. and J.M. Colford, Jr. (2004) Water, Sanitation and
Hygiene: Interventions and Diarrhoea. A Systematic
Review and Meta-analysis. World Bank, Washington.
Effect of Sanitation on Health
• Only 2 of 4 available studies could be included in the meta-analysis
• Not possible to extract data from Kumar et al. (1970) or calculate CIs for Gross et al.(1989)
• Children (i.e. ≤ 60 months): random effects pooled estimate = 0.678 (95% CI: 0.529 – 0.868)
Fewtrell L, Kaufmann RB, Kay D, Enanoria W, Haller L, Colford JM Jr. (2005) Water, sanitation, and hygiene interventions to
reduce diarrhoea in less developed countries: a systematic review and meta-analysis. Lancet Infect Dis. 2005 Jan;5(1):42-52.
Effect of Sanitation on Health (Diarrhea) - Recent Data
Barreto ML Et al., Effect of city-wide sanitation programme on reduction in rate of childhood
diarrhoea in northeast Brazil: assessment by two cohort studies. Lancet 2007;370:1622–28
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A city-wide sanitation intervention was started in Salvador, Brazil, in 1997 to improve
sewerage coverage from 26% of households to 80%.
The effect of this programme on diarrhea morbidity in children less than 3 years of age was
studied
Two longitudinal studies: 1997–98 before the intervention & 2003–04 after the intervention.
Each study consisted of a cohort of children (841 in the preintervention study and 1007 in
the postintervention study; age 0–36 months at baseline); followed up to 8 months.
Children were sampled from 24 sentinel areas randomly chosen to represent the range of
environmental conditions in the study site. Individual or household questionnaires were
initially applied by trained fieldworkers; an environmental survey was done in each area
before and after the sanitation programme to assess basic neighborhood and household
sanitation conditions.
Daily diarrhoea data were obtained during home visits twice/week.
The effect of the intervention was estimated by a hierarchical modelling approach fitting a
sequence of multivariate regression models.
Diarrhea prevalence fell by 21% (95% CI 18–25%), from 9·2 (9·0–9·5) days per child-year
before the intervention to 7·3 (7·0–7·5) days per child-year afterwards.
– After adjusting for baseline sewerage coverage and potential confounding variables, the
overall prevalence reduction was 22% (19–26%).
Conclusion: urban sanitation is a highly effective health measure
Effect of Sanitation on Health (Diarrhea) - Recent Data
Genser Et al.. (2008) Impact of a city-wide sanitation intervention in a large urban centre on social, environmental
and behavioural determinants of childhood diarrhoea: analysis of two cohort studies. Int J Epidemiol. 37(4):831-40.
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Poor socioeconomic status (SES) increases diarrhea risk
– mostly via lack of sanitation, poor infrastructure and living conditions.
The effectiveness of a city-wide sanitation intervention on diarrhea in a large urban
site in Northeast Brazil was recently demonstrated.
The intervention altered the magnitude of relative and attributable risks of diarrhea
determinants and the pathways by which those factors affect diarrhea risk.
Determinants of prevalence of diarrhea were determined in two cohort studies
conducted before & after the intervention; in pre-school children followed for 8 mos.
Relative, attributable and mediated risks of diarrhea determinants were estimated.
The intervention reduced diarrhea and also changed attributable and relative risks of
diarrhea determinants by altering the pathways of mediation.
Before the intervention SES was a major distal diarrhea determinant (attributable risk:
24%) with 90% of risk mediated by other factors, mostly by lack of sanitation and poor
infrastructure (53%).
After the intervention, only 13% of risk was attributed to SES, with only 42% mediated
by other factors (18% by lack of sanitation and poor infrastructure).
The intervention reduced diarrhea risk by reducing direct exposure to unfavurable
sanitation conditions.
It also altered the effect and mediation pathways of most distal diarrhea determinants,
especially SES.
The importance of public sanitation measures in reducing the impact of poverty on
diarrhea was corroborated.
Impact of Improved Sanitation on Health
• Improved sanitation reduces infectious
diseases in developing world settings
• Evidence from intervention studies, casecontrol studies and other epid. studies.
• Data are limited; few studies; poor quality
• Estimate of effect: in the 25-45% range for
reduction of diarrheal disease in children
• Similar to the magnitude of the effect of
improved water quality (or quantity)
Community Led Total Sanitation (CLTS)
• An approach to facilitate the process of empowering local
communities to stop open defecation and to build and use latrines
or other effective sanitation without the support of any external
hardware (construction materials) subsidy
• Focuses on creating change in sanitation behavior through
community participation rather than just constructing toilets.
• Done through a process of social participation; behavior focus
• Focuses on the whole community not individual behaviors
• Emphasizing the collective benefit from stopping open
defecation by encouraging a more cooperative approach
• People decide together how they will create a clean and hygienic
environment that benefits everyone.
• Encourages local communities to visit the dirtiest and filthiest
areas in the community, appraise and analyze their practices, to
shock, disgust and shame people.
• The approach is provocative and entertaining, and participatory,
leaving decisions and action to the community.
10 Principles of CLTS
1. Aim/Target: 100% Total Sanitation
2. Based on creating Genuine Demand but not Charity
3. Thrives through aggressive Awareness but not through Subsidies
4. Recognizes a Wide Range of Technology Options
5. Technology Choice Based on Affordability, Appropriateness and
acceptability
6. Lowest Requirement: Contain or Restrict Excreta (no open defecation)
7. Communities (Villagers) Plan, Implement Monitor their own progress
8. Government to support Long Term Sustainability of initiatives
9. Facilitation is done by an indigenous organiaations – CBO or NGO
- Bottom Up approach
10. Hygiene Promotion is provided for an Initial Period of about 2 years
Key Steps in CLTS
1ST Step: Realization of Unhygienic Sanitary
Practices Through Analysis of Community Feces
• Community Led Participatory Rural Appraisal (PRA)
• A Walk of Shame – see actual situation on ground
• Ground Mapping of Feces – where are they/whose
are they!
• Calculation of Feces amounts - varies
• Raising Flag of Feces (Flagging) – where they are
• Village Commitment - no open defecation!
• Community sanitation policing
Key Steps in CLTS
2nd Step: Organizing and Mobilizing the Community
• Have Commitment towards No Open Defecation
(NOD) Followed by Hygiene Promotion
• Form Village Sub-committees – for Effective
Implementation and Monitoring
• Use existing community groups –child club, women
and local cultural groups
• Monitoring/Information using an open Board
• Looking at future – community vision & dream
• Family Monitoring Chart
• Exchange Visits
• NOD Declaration - (perhaps within 3 months)
• Recognize well performing communities
Sanitation Policy Issues
• Sanitation policy is a challenge
• Sanitation lags far behind water in coverage and
effective sustained use
• Sanitation intervention hardware (latrines, other
toilets, sewerage and sewage treatment) is usually a
major infrastructure change and investment
• Sanitation requires a personal and community
behavior commitment to use the sanitation facilities
• The drivers for behavior change in sanitation are
complex and require considerable time and effort at
the personal, household and community levels
• Existing sanitation infrastructure is often poor and
poorly maintained
• Sanitation remains one of the biggest unmet global
needs; new strategies and approaches needed