Transcript Waste Treatment ENVR 421 Mark Sobsey

Waste Treatment
ENVR 421
Mark Sobsey
Household Human Wastes and
Wastewaters
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
Managing Human Excreta - Options
• Wet Systems
– 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
Conventional
Wastewater
Wastewater
Impacts to Natural
Receiving Waters
Treatment – Developed World
BOD
Chemicals (N,P)
Synthetic Chemicals
Antibiotics
Microbial Pathogens
Treated wastewater is often discharged to nearby natural waters
Water Use Cycle
Water Source
Water
Use
Water Treatment
Plant
Wastewater
Collection
Wastewater
Treatment
Plant
Water
Distribution
System
Discharge
to Receiving
Water
Pathogen Concentrations in Raw Sewage
• Highly variable and influenced by many
factors:
– Types and prevalence of enteric infections in the
population
– Geographic, seasonal, and climatological factors
• "Strength" and age of the sewage.
– More water use, weaker sewage.
"Guesstimated Worst-case" Pathogen
Concentrations in U.S. Raw Sewage (No./L):
– Enteric Viruses and Protozoan Cysts: ~ 10,000 of
Each Group/Liter.
– Enteric Bacteria: ~100,000/Liter.
Municipal Wastewater Collection
(Chapel Hill, NC)
•Generally, a gravity flow system
•Includes pump stations and “Force Main” sewers
Conventional Sewage Treatment
Conventional Sewage Treatment
Primary Treatment
Anaerobic Digestion
Secondary Treatment
Tertiary Treatment
Trickling Filter and Aeration Basin for
Wastewater Treatment
Treating Separated Sewage Solids
or Sludge
Waste Solids (Sludge) Treatment
• Treatment of the 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
• 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.)
“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
• thermal (high temperature) processes (incl. thermophilic
digestion); hold sludge at 50oC or more for specified times
• lime (alkaline) stabilization; raise pH 12 for 2 or more hours
• composting: additional aerobic treatment at elevated
temperature
Class A sludge or “biosolids” can be disposed by a variety of
options (marketed and distributed as soil conditioner for use on nonedible plants)
Land Application of Treated Wastewater:
Alternative Disposal Option
Facultative Oxidation (Waste
Stabilization) Pond
On-site Septic Tank-Soil Absorption System
Modular Wastewater Treatment Systems
electrochemical metals removal
process, pH adjustment, coagulation,
clarification, multi-media filtration, air
stripping, activated carbon adsorption,
final pH adjustment, sludge dewatering
Wastewater Reuse
Wastewater is sometimes reused for beneficial, non-potable
purposes in arid and other water-short regions
Often use advanced or additional treatment processes,
sometimes referred to as “reclamation”
1. Biological treatment in “polishing” ponds and constructed
wetlands
2. Physical-chemical treatment processes as used for
drinking water:
– Coagulation-flocculation and sedimentation
– Filtration: granular medium filters; membrane filters
– Granular Activated Carbon
– Disinfection
Primary Treatment or Primary
Sedimentation
Settle solids for 2-3 hours in a static, unmixed tank
or basin.
• ~75-90% of particles and 50-75% 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
• 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 of the 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 microbe reductions
• Constructed Wetlands
– aerobic systems containing biologically active, oxidizing
microbes and emergent aquatic plants
• Lagoons and constructed wetlands are practical and
economical sewage treatment alternatives when land is
available at reasonable cost
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 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% in single ponds and by
multiples of 90% for ponds in series.
• Microbe removal may be quite variable depending upon pond
design, operating conditions and climate.
– Reduction efficiency lower in colder weather and 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
• Used where there are no sewers and 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 located 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
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:
– near 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.
• Often uses advanced or additional treatment processes,
sometimes referred to as “reclamation”
• Biological treatment in “polishing” ponds and constructed
wetlands
• Physical-chemical treatment processes as used for drinking
water:
– Coagulation-flocculation and sedimentation
– Filtration: granular medium filters; membrane filters
– Granular Activated Carbon adsorption
– Disinfection
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
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
99.9995
% Reduction
50
99
90
99
Total %
50
99.5
99.95