Waste Treatment

ENVR 421

Mark Sobsey

Household Human Wastes and Wastewaters

Excreta and Graywater– Definitions and Properties

Excreta: Human feces and urineManaged in different ways:

Direct disposal on land or in waterDirect use as fertilizer, soil conditioner and for aquaculturePre-treatment prior to use Dilution with water to convey (sewage) for disposal or use

Direct use of untreated (raw) sewageTreatment and discharge to land or waterTreatment and reuse (agriculture, aquaculture, horticulture,

industrial and civil useGraywater: Other wastewater from human activity

Not directly from human fecs and urineWastewater 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?

Nitrogen (N) 4.5Phosphorous (P) 0.6Potassium 1.0Organic matter(as BOD)

35

• 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

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.

0

20

Organicskg COD/ (Person·year)

12.3

3.6

14.1

VolumeLiter / (Person·year)

10.0

00 –

200

.00

0 l

500 l 50 l

sour

ce:

Ott

erpo

hl

0

6

Nutrient contentkg N,P,K / (Person·year)

N

P

K

0.8

5.3

1.0

Composition of Household Waste and Wastewater

greywater urine faeces

• 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

• less hygienically critical (less risk)• contains the largest proportion of nutrients

available to plants• may contain hormones or medical residues

2. urine

• hygienically critical (high risk)• consists of organics, nutrients and trace elements• improves soil quality and increase its water

retention capacity

1. feces

characteristicfraction

Characteristics of Human Wastes

sour

ce:

Dra

nger

t, 1

998

Fertilizer Equivalence of Yearly per Capita Excreted Nutrients and Fertiliser Requirements for Producing

250 kg of Cereals

0

1

2

3

4

5

6

N N P P K K

Nu

trie

nt

(kg

)

cerealrequirements

faeces

urine

Fertilizer Potential of Human Excreta

treatment

utilisation

substances faeces(brownwater)

anaerobic digestion,

drying, composting

biogas, soil

improvement

constructedwetlands, gardening,

wastewater ponds, biol.treatment, membrane-

technology

greywater (shower,

washing, etc.)

irrigation,

groundwater- recharge ordirect reuse

urine (yellowwater)

liquid or dry fertiliser

hygienisation by storage or

drying

Options for Excreta and Greywater Utilization

Wastewater Impacts to Natural Receiving Waters

Treated wastewater is often discharged to nearby natural waters

BODChemicals (N,P)Synthetic ChemicalsAntibioticsMicrobial Pathogens

Conventional Wastewater Treatment – Developed World

Water Use Cycle

Water SourceWater Treatment

Plant

Water Distribution

System

WaterUse

WastewaterCollection

WastewaterTreatment

Plant

Dischargeto 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 TreatmentPrimary Treatment Secondary Treatment Tertiary Treatment

Anaerobic Digestion

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 non-edible 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 solidsPFRPs:• 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 % REMOVAL

Fecal indicators Primary sed. 0‑60%

E. coli Primary sed. 32 and 50%

Fecal indicators Trickling filt. 20‑80%

Fecal indicators Activated sludge 40‑95%

Fecal indicators Stab. ponds, 1 mo. >99.9999% @ high temp.

Salmonellae Primary sed. 79%, 6‑7 hrs.

Salmonellae " 73%, 6‑7 hrs.

Salmenellae Trickling filt. 92%

Salmonellae Activated sludge ca. 99%

Entamoeba histolytica Reduction by Sewage Treatment

ORGANISM PROCESS % REMOVALE. histolytica Primary Sed. 50%E. histolytica Primary Sed., 2 hr. 64%E. histolytica Primary sed., 1 hr. 27%E. histolytica Primary sed. + Trickl. Filt. 25%E. histolytica " 74%E. histolytica " 91%E. histolytica Primary sed. + Act. Sludge 83%E. histolytica Oxidation ditch + Sedimentation 91%E. histolytica Stabilization ponds + sedimentation 100%E. histolytica " 100, 94, 87E. histolytica " 100E. histolytica 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

Coliphage 82 99.98 90 90 99.99997

Entero-virus

98 84 96 91 99.999

Giardia 93 99 78 50 99.9993

Crypto-sporidium

93 98 61 <10 99.95

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

110

1001000

10000100000

100000010000000

100000000

110

1001000

10000100000

100000010000000

100000000

F. col. E. coli Ent. C. p. F+ phg.

Num

ber/

100

ml

RawTreated (geom. mean values of 24 biweekly samples)

Estimated Pathogen Reductions by Sewage Treatment Processes: An Example

Sewage Treatment Rx: % Reduction Total % Reduction

• Primary settling 50 50• 2o biological treatment 99

99.5• Granular medium filtration 90

99.95• Disinfection 99 99.9995