Simmons 1 ENVR 430-1 Microbial Control Measures by Wastewater Processes Suggested Reading: BrockChapter 28- Wastewater Treatment, Water Purification, and.

Simmons 1

ENVR 430-1Microbial Control Measures by

Wastewater Processes

Suggested Reading:

Brock Chapter 28- Wastewater Treatment, Water Purification, and Waterborne Microbial Diseases pp. 934-942 (posted as .PDF file on website)

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Wastewater Impacts to Natural Receiving Waters

Treated wastewater is often discharged to nearby natural waters

BODChemicals (N,P)Synthetic ChemicalsAntibioticsMicrobial Pathogens

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Water Use Cycle

Water SourceWater Treatment

Plant

Water Distribution

System

WaterUse

WastewaterCollection

WastewaterTreatment

Plant

Dischargeto Receiving

Water

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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.

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Conventional Sewage Treatment

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Microbial Reductions in Wastewater Treatment

• Treatment designed for reduction of solids and organics (TSS, BOD, NOT pathogens)

• Typical overall pathogen reductions: ~ 90‑99%.

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 ~10X higher than in

raw sewage– Little removal of enteric microbes: typically ~50%

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Trickling Filter and Aeration Basin for Wastewater Treatment

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Microbial Reductions in Wastewater Treatment

Secondary or Biological Treatment: • aerobic biological treatment: typically, activated

sludge or trickling filtration • 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– Biodegradation of enteric microbes

• proteolytic enzymes and other degradative enzymes/chemicals• Predation by treatment microbes/plankton (amoeba, ciliates,

rotifers, etc.)

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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.)

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“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)

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Land Application of Treated Wastewater: Alternative Disposal Option

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Facultative Oxidation (Waste Stabilization) Pond

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On-site Septic Tank-Soil Absorption System

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20th Annual On-Site Wastewater Treatment Conference Planning, Implementing and Managing Decentralized Wastewater

October 11-13, 2004 McKimmon Center, North Carolina State University To register or see complete conference details: www.soil.ncsu.edu/swetc/onsiteconf/2004/main04.htm

Our conference objectives are to give you:

•A better understanding of how various planning, permitting and management processes can affect your job, community and environment. •Essential information regarding the use of GPS/GIS in your job. •An in-depth look at how failures can be avoided through proper planning and post permit inspections. •Methods to work with homeowners to improve system understanding. •Greater knowledge about the applicability and legal issues of Time-of-Sale inspections. •Up-to-date information on how local, state and national certifications are obtained. •A chance to interact with colleagues and manufacturers within the on-site community and understand how each member of the community can help with your job.

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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

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ReCip: Reciprocating Wastewater Technology

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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

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Microbiological water quality in a large in-building, water recycling facility

R. Birks*, J. Colbourne**, S. Hills* and R. Hobson** Thames Water Innovation and Development, Manor Farm Road, Reading, RG2 0JN, UK** UK Drinking Water Inspectorate, Floor 2/D1, Ashdown House, 123 Victoria Street, London, SW1E 6DE, UK

Abstract The Thames Water recycling plant at the Millennium Dome, London, reclaimed three sources of water: greywater from the washbasins, rainwater from the Dome roof and groundwater from a borehole onsite. These were pre-treated separately, and the mixed stream filtered using ultrafiltration and reverse osmosis membranes. Monitoring for indicator microorganisms was undertaken throughout the plant and in the reclaimed water distribution system, as well as ad-hoc monitoring for the presence of pathogens in the raw waters. Treatment to the level of ultrafiltration was more than adequate to produce a water quality meeting existing worldwide reclaimed water guidelines for toilet flushing. Owing to the excellent quality of the water leaving the plant, no significant microbiological growth was observed in the reclaimed water distribution system during the year. The raw greywater exhibited a higher faecal bacterial load than the rainwater and groundwater, as predicted from more human contact (i.e. hand washing). Environmental strains of Legionella were observed in the three raw greywater samples analysed for pathogens, as was Cryptosporidium, Giardia and faecal enterococci. The rainwater had relatively high levels of faecal bacteria, probably of avian origin. Giardia was detected in one rainwater sample confirming the potential for this water source to contain pathogens.

From 2004 Water Science and Technology Vol 50 No 2 pp 165–172

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Disinfection• Disinfection is any process to destroy or prevent the growth

of microbes• Many disinfection processes are intended to inactivate

(destroy the infectivity of) the microbes by physical, chemical or biological processes

• Inactivation is achieved by altering or destroying essential structures or functions within the microbe

Inactivation processes include denaturation of:– proteins (structural proteins, enzymes, transport

proteins)– nucleic acids (genomic DNA or RNA, mRNA, tRNA, etc)– lipids (lipid bilayer membranes, other lipids)

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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

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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 discharge

• Often 200-1,000 per 100 ml geometric mean as permitted discharge limit

• Less effective for viruses and parasites: typically, 90% reduction

Toxicity of chlorine and its by‑products to aquatic life now limits wastewater chlorination - may need to:

– Dechlorinate– Use an alternative, less toxic chemical disinfectant– Use an alternative treatment process to reduce enteric

microbes• granular medium filtration or membrane filtration

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Estimated Pathogen Reductions by Sewage Treatment Processes: An Example

Treatment Rx: Reduction Cumulative Conc.

(%) Reduction (%) (#/L)

None 0 0 10,000

Primary settling 50 50 5,000

2o biological treatment 99 99.5 50

Granular med. filtration 90 99.95 5

Disinfection 99 99.9995 0.05

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Calculating Microbial Reductions by Treatment Processes: Log10 vs. Percent

• Microbial reductions are computed to “normalize” the raw data on treatment efficacy of different systems or at different sites

• Reductions provide a uniform way to compare different treatment processes or systems

Examples:

FC Coliphage FC Coliphage FC Coliphage

1 influent 2.00E+07 1.10E+04 1.96 1.38 99% 96%1 effluent 2.20E+05 4.60E+022 influent 4.39E+06 1.60E+06 1.52 0.65 97% 78%2 effluent 1.32E+05 3.60E+05

Log10 reduction = [Log10(influent) - Log10(effluent)]

Percent reduction = [(influent - effluent) / influent] * 100

Raw Data (cfu or pfu/ml) Log10 Reduction Percent ReductionSite Location

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Disinfection: Kinetics

Disinfection is a kinetic process:

increased inactivation with increased exposure or contact time

Chick's Law: disinfection is a first‑order reaction. (Nt/No = e-kT)

(NOT IN PRACTICE!) Assumes :• all organisms are identical• death (inactivation) results from a first-order or “single-

hit” or exponential reaction.

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Disinfection Activity and the CT ConceptDisinfection activity can be expressed as the product of

disinfection concentration (C) and contact time (T)– Assumes first order kinetics (Chick’s Law) such that disinfectant

concentration and contact time have the same “weight” or contribution in disinfection activity and in contributing to CT

• Example: If CT = 100 mg/l-minutes, then– If C = 10 mg/l, T must = 10 min. for CT = 100 mg/l-min.– If C = 1 mg/l, then T must = 100 min. for CT = 100 mg/l-min.– If C = 50 mg/l, then T must = 2 min. for CT = 100 mg/l-min.

So, any combination of C and T giving a product of 100 is acceptable because C and T are interchangeable

The CT concept fails if disinfection kinetics do not follow Chick’s Law (are not first-order or exponential)

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DISINFECTION AND MICROBIAL

INACTIVATION KINETICS

Contact Time

MultihitFirstOrder

Retardant

Log

Sur

vivo

rs

Nt/N0

Retardant Kinetics:1.persistent fraction; 2.mixed populations; 3.different

susceptibilities of microbes to inactivation;

4.aggregation

Declining rate or “Shoulder” Curve Kinetics:

1. decline in disinfectant concentration over time;

2.multi-hit kinetics; 3.aggregation

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Properties of an Ideal Disinfectant

1. Broad spectrum: active against all microbes

2. Fast acting: produces rapid inactivation

3. Effective in the presence of organic matter, suspended solids and other matrix or sample constituents

4. Nontoxic; soluble; non-flammable; non-explosive

5. Compatible with various materials/surfaces

6. Stable or persistent for the intended exposure period

7. Provides a residual (sometimes this is undesirable)

8. Easy to generate and apply

9. Economical

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Common Disinfectants in Water and Wastewater Treatment

• Free Chlorine• Monochloramine • Ozone • Chlorine Dioxide• UV Light

• Low pressure mercury lamp (monochromatic) • Medium pressure mercury lamp

(polychromatic)• Pulsed broadband radiation