biological treatment 1 jae k. (jim) park, professor dept. of civil and environmental engineering...
DESCRIPTION
Minimum National Standards for Secondary Treatment 3 ParametersUnits30-day ave. conc.7-day ave. conc. BOD 5 mg/L30/45 a 45/65 Suspended solidsmg/L30/45 a 45/65 Hydrogen-ion conc.pH units6~9 b 6~9 b Carbonaceous BOD 5 c mg/L2540 a Average removal 85% b Only enforced if caused by industrial wastewater or by in-plant chemical addition c May be substituted for BOD 5 at the option of the National Pollution Discharge Elimination System (NPDES) permitting authorityNational Pollution Discharge Elimination SystemTRANSCRIPT
Biological Treatment
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Jae K. (Jim) Park, Professor
Dept. of Civil and Environmental Engineering
University of Wisconsin-Madison
Treatment Objectives
1980 to 2000Removal of toxic compounds and nutrients (N & P)
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Early 1970s to 1980Based on aesthetic and environmental
concernsBegan to address nutrient removalImproved treatment efficiency and
widespread treatment of wastewater
1900 to early 1970s Removal of suspended and floatable materialTreatment of biodegradable organicsElimination of pathogenic organisms
21st CenturyEndocrine disrupting chemicals (EDCs) and
other synthetic compounds, emerging pathogens, etc.
Minimum National Standardsfor Secondary Treatment
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Parameters Units 30-day ave. conc. 7-day ave. conc. BOD5 mg/L 30/45a 45/65 Suspended solids mg/L 30/45a 45/65 Hydrogen-ion conc. pH units 6~9b 6~9b
Carbonaceous BOD5c mg/L 25 40
a Average removal 85%b Only enforced if caused by industrial wastewater or by in-plant
chemical additionc May be substituted for BOD5 at the option of the
National Pollution Discharge Elimination System (NPDES) permitting authority
Kinetics of Biological Growth
Lagphase
log (# ofcells)
Log (exponential)growth phase
Stationary(declining)
phase Death (endogenousdecay) phase
t
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Dispersed growthCause: Microorganisms do not form but are dispersed, forming only small clumps or single cells.
Effect: Turbid effluent. No zone settling of sludge.Slime (jelly) viscous bulking; or non-filamentous bulking Cause: Microorganisms are present in large amounts of exocellular slime. In severe cases, slime imparts a jelly-like consistency to the activated sludge.
Effect: Reduced settling and compaction rates. Virtually no solids separation in severe cases resulting in overflow of sludge blanket from secondary clarifier. In less severe cases a viscous foam often is present.
BulkingCause: Filamentous organisms extend from flocs into the bulk solution and interfere with compaction and settling of activated sludge.
Effect: High SVI - very clear supernatant. Low RAS and WAS solids concentration. In severe cases, overflow of sludge blanket occurs. Solids handling processes become hydraulically overloaded.
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Activated Sludge Separation Problems (1)
Settling Problem in Activated Sludge Processes
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Activated Sludge Separation Problems (2)
Pin floc or pinpoint flocCause: Small, compact, weak, roughly spherical flocs are formed, the larger of which settle rapidly. Smaller aggregates settle slowly.
Effect: Low SVI - a cloudy, turbid effluentBlanket rising Cause: Denitrification in secondary clarifier releases poorly soluble N2 gas which attaches to activated sludge flocs and floats them to the secondary clarifier surface.
Effect: A scum of activated sludge forms on surface of secondary clarifier.Foaming/scum formationCause: Caused by non-degradable surfactants and by the presence of Nocardia spp. and sometimes by presence of Microthrix parvicellar.
Effect: Foams float large amounts of activated sludge solids to surface of treatment units. Nocardia and Microthrix foams are persistent and difficult to break mechanically. Foams accumulate and can putrefy. Solids can overflow into secondary effluent or overflow tank free-board on to walkways.
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Floc Formers
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Foaming
Nocardia spp.
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Life
1. Matter: H, O, C, N, P, S and minor elements
2. Energy• Solar radiation: Photo-synthetic autotrophs• Organics: Heterotrophs• Inorganics: Chemoautotrophs
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More plant-like(producer)
More animal-like(consumer)
Gets carbon from atmosphere
Gets carbon from organic materials
Autotroph Heterotroph
Classification of Microorganisms
AnimalsRotifers
Crustaceans
PlantsMossesFerns
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Eucaryotes: multi-cellular
Algae
Procaryotes: “before nucleus”, unicellularBlue green algae
Fungi Protozoa
Bacteria
Mic
roor
gani
sms
Redox Reaction
Organic molecule (C+H+O+N+S+P)(wastewater, hazardous chemicals,
etc.)
CO2, H+, and e-
A molecule
Oxidized
Reduced
Electron donor
Electron acceptor
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Aerobic Condition
Aerobic respirationO2 presentElectron acceptor: O2 (→ H2O)Good for large volumes of dilute
wastewater (< 500 mg BOD5/L)High growth rates, thus high
sludge production (0.3~1 lb VSS/lb BOD5)
Produce a more stable end product
O
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Anoxic Condition
Anaerobic respiration (denitrification)
No dissolved oxygenNO3
- and NO2- present
Electron acceptor: NO2- and NO3
- (→ N2 + H2O)
Relatively high sludge productionShould be avoided in the clarifier
AX
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Fermentation No O2, NO3
-, NO2-, or SO4
2- present Electron acceptor: endogenously generated
by the microorganism Good for concentrated wastes (> 1000 mg
BOD5/L) Low sludge production
Complex organic compounds
Low molecular weight fatty acids
CH4, CO2, and H2O
Anaerobic Condition AN
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Biological Treatment: Conditions Required to Remove Target
Compounds
Organics (carbonaceous energy)Aerobic, heterotrophs (aerobic oxidation)
Ammonia (nitrogenous energy)Aerobic, chemoautotrophs (nitrification)
Nitrite/nitrate (nitrogenous energy)Anoxic, heterotrophs (denitrification)
Phosphorus (nutrient)Anaerobic, heterotrophs (luxury uptake)
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SVI MeasurementOne-liter graduated cylinder30 minute settling periodSVI = (mL/L)/(g/L) = mL/g, i.e., volume
occupied by one gram of settled solids
1-L
mL
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SVI Example CalculationSettled sludge vol.: 260 mL/LMixed liquor Suspended Solids (MLSS): 2,000 mg
TSS/L = 2 g/LmL/L 130
Lg 2
LmL 260
SVI
< 75 Excellent75 < SVI < 120 Good120 < SVI < 250 Poor
> 250 Bad, bulking
t = 0 10 min 20 min 30 min
260 mL
Bulking
sludge
Well settled sludge
Aeration basin