Download The Biological Process in Wastewater Treatment

Bioscience, Inc.
Allentown, PA
www.bioscienceinc.com
The Biological Process of
Wastewater Treatment
Jay Hill
Product Manager
Typical Wastewater Treatment
Steps
• Coarse Physical Treatment
• Settling of Suspended Solids/Floatables
• Biological Treatment of Dissolved/ Fine
Solids
• Recovery of Biomass
• Removal of Inorganics
• Disinfection
• Excess Biomass Removal
Primary Treatment
• Bar Screen
• Clarifier
– Primary sludge
• Sand/grit
• Coarse organic matter
– Floatables
• FOG
• DAF or API Separator
– FOG, petroleum HC, light solids
Activated Sludge Systems
O2 CO2
Untreated
Discharge
Clean Water
Aeration Tank
Clarifier
Recycled Sludge
Biomass (Secondary
Sludge)
Secondary Clarification
• Clarifier
– Secondary sludge
• Fine organic matter
– Floatables
• FOG
Solids Processing
• Sludge Thickening
• Aerobic or Anaerobic Digestion
• Centrifuge
• Belt Press
• Incineration, Land Application, Fertilizer, Landfill
Aerobic Microbial
Respiration
C,H + O2
*
CO2
+ H2O
+ protein
* bacteria, N, P, pH, temperature
Composition of Wastewater

Inorganics





Ammonia
Nitrate
Phosphate
Carbonate
Minerals




Calcium
Magnesium
Iron
Etc.

Organics

Biodegradable (BOD)




Carbohydrates
Proteins (TKN)
FOG
Non-Biodegradable
(COD-BOD)





Large particles
Complex polymers
(plastics, lignin)
Surfactants (some)
Pesticides (some)
Pharmaceuticals (some)
Requirements for Growth of
Microbes





Temperature
pH
Water activity
Energy source
Nutrients





Carbon
Nitrogen
Phosphorus
Minerals
Vitamins/growth factors
Temperature

Thermophiles


Mesophiles


40°C to >100°C
10°C to ~45°C
Psychrophiles

<5°C to ~35°C
pH

Acidophiles


pH 0-6
Alkaliphiles

pH 8-13
Most bacteria prefer pH 6-8
 Most fungi prefer pH 4-7

Water Activity

Salt content of water





Fresh water <1% NaCl (most bacteria)
Brackish water ~1-3% NaCl (limits some species)
Seawater ~3.5% NaCl (salt tolerant only)
Saline water up to 30+% (saturated NaCl)- (only
few species)
Soils (moisture content and salts)


50-100% FMC (most bacteria)
Fungi tolerate lower moisture content
Energy Sources

Oxygen (aerobes) C6H12O6+ 6 O26 CO2+6 H2O

Autotrophs







NH4++ 2 O2 NO3-+ H2O + 2 H+ (Nitrifiers)
H2S + 2 O2 SO4 - - + 2 H+ (sulfur oxidizers)
H2S + 0.5 O2 S0 + H2O (sulfur oxidizers)
Nitrate (facultative) C6H12O6 + 6 H2O 6 CO2+ 12 H2
/ 5 H2 +2 NO3 - + 2 H+  N2 + 6 H2O (denitrifiers)
Sulfate (anaerobes) C2H4O2CO2 / SO4 -- H2S
(sulfate reducers)
Carbon dioxide (anaerobes) CO2+ 4 H2 CH4 +2 H2O
(methanogens)
Fermentation C6H12O62 CO2+2 C2H5OH
Nutrients Required for Growth







Carbon
 Usually from food source or CO2
Nitrogen
 Usually from ammonia, nitrate or
simple organics (amino acids)
Phosphorus
 Inorganic phosphate
Sulfur
 Inorganic sulfate or simple organics
Minerals (Ca, Mg, K, Na, Fe)
Trace elements (Ni, Co, Cu, Mo, Zn)
Growth factors/vitamins
Operation Limits

pH 6-9
<4: Most bacteria dead or inactive
<6: Bacteria activity drops, fungi
may create settling problem
<6.5: Nitrification very poor
7.5: optimum for hydrocarbons,
fog, nitrification, sulfide
>9: Bacteria activity drops

Nutrients
BOD:N:P = 100:5:1
Effluent ammonium-N <2 mg/L
may limit BOD removal or slow
response to slug loading
Effluent ammonium-N <0.5 mg/L
probably deficient unless
nitrifying (nitrate provides N)
Effluent ortho-phosphate <1 mg/L
may limit BOD removal or slow
response to slug loading
Effluent ortho-phosphate <0.2
mg/L probably deficient
Operation Limits

Temperature
<5°C Few bacteria are active
<15°C Nitrification and most
bacteria growth very slow
20-35°C Optimum for most bacteria
39-45°C Bacteria activity drops,
death rate increases
>45°C Only adapted or
thermophilic processes occur

Biomass
MLSS normally 1500-6000 mg/L
<1500 poor settling, dispersed
>6000 oxygen limited?; may
overflow clarifier weir
MLSS/MLVSS 80-90%
<80% low viable percentage,
possible accumulation of inert
<70% may occur in aerobically
digested sludge
>90% light (poor settling) floc
Operation Limits

Sludge Age/MCRT
<3 days Poor settling/COD
removal/high sludge production
<8 days May have poor nitrification
>20 days May have filament
problems or pin floc; good for
exotic chemical degradation and
sludge digestion

SOUR
Complete mix system 3-15 mg
O2/g MLSS per hour
<3 Inhibition or severe underload
>15 Slug load/ possible overloading
Staged aeration –1st Stage
30-100 mg O2/g MLSS per hour
<20 Inhibition
<30 Insoluble waste `
>100 Overloading
Operation Limits

Dissolved Oxygen
2-7 mg/L normal range
<0.5 Anaerobic
<1 General BOD removal slows
<2 Nitrification slows
>7 Slow growth (inhibition) or
underloaded
>9 Bacteria dead or inactive

Sludge Blanket
Normal range 3-7 ft below surface
<3 feet(1 meter) poor settling or
compaction; biomass may
washout with flow increase
>7 feet (2 meters) Rapid settling
may leave dispersed solids in
effluent
Heavy Organic Load
Typical Upsets
Increased Growth/Respiration
Reduced Dissolved Oxygen
More Sludge to Clarifier
Reduced Growth/Respiration
Inadequate Removal
Poor Settling
Worse Effluent
Deflocculation of the Biomass
Elevated BOD/COD
High Effluent Suspended Solids
Common Wastewater
Problems






Poor Settling
Effluent Violation (TSS or BOD)
Filamentous Forms
Poor Nitrification
Toxicity
Odors
Aerobic Microbial
Respiration
C,H + O2
*
CO2
+ H2O
+ protein
* bacteria, N, P, pH, temperature
Chemical Characterization of
VISC 25
Parameter
Result
Comments
pH of 10% solution
10.5
Alkalinity
37 meq/100 g
Ammonium-Nitrogen
400 mg/L
Nitrite-Nitrogen
5 mg/L
Color fades rapidly
Nitrate-Nitrogen
<5mg/L
Turns yellow after cadmium addition
Phosphate-Phosphorus
30 mg/L
Chemical Oxygen Demand
71,000 mg/L
Titrated to pH 7 w/HCl
Wastewater Treatment Plant
Performance Testing
Process control tests or performance evaluation tests to determine overall treatment
process efficiency, identify or investigate problems, or evaluate specific ability to
treat target compounds. Process control tests generally must be quick turnaround
tests usually performed on-site to allow process adjustment in response to
problems. However, some longer time-frame tests may be set up to predict or
determine the effect of process changes or identify trends in process efficiency.
Some of the investigations performed by Bioscience have been designed to:
1.
evaluate foam or settling problems
2.
measure nitrification rates or nitrification potential
3.
measure FOG degradation rates or potential
4.
measure permissible loading rates for potentially toxic waste streams or septage
5.
measure effectiveness of bioaugmentation
6.
measure biomass kinetic constants for process design.
Wastewater Treatment Plant
Performance Testing
Available methods include:
Standard Methods 5210D Biochemical Oxygen Demand
Respirometric Method (Respirometric Oxygen Uptake)
Standard Methods 2710B Oxygen-Consumption Rate (Specific Oxygen
Uptake Rate; Dissolved Oxygen Probe Method)
OECD 209 Activated Sludge, Respiration Inhibition Test
ASTM D5120 Standard test Method for Inhibition of Respiration in the
Activated Sludge Process
Short-Term BOD Test (EZ-BOD instrument test for influent or effluent
BOD-5 estimation)
Suspended Solids (Photometric Method)
CONTRAL Biodegradation Kinetics
Microscopic Evaluation of Biomass (Higher Forms and Filaments)
Wastewater Treatment Problems (AS)
Problem
Cause
Cure
FOG in collection
Various
DNT-RF/GEL
Odor/H2S
Anaerobic condition
DNT-RF/ANL
FOG in aeration basin
Slow digestion
DNT-RF/SXM/NPN/TM
High temperature/low
activity
Hot process water
HT
No or partial nitrification
Toxicity/low temp/low
SRT/nutrients
XNC/XNL/TM
Low COD or specific
compound removal
Low temp
/various/industry specific
HX, XR, XP, etc.
Excessive filaments
various
XF, SXM, nutrients
Excessive sludge
FOG/cellulose/etc
accumulation in sludge
SR
Poor sludge digestion
Nutrient imbalance/FOG
AD, SXM, TM
Wastewater Treatment Problems (Lagoon)
Problem
Cause
Cure
Odor/H2S
Odor/NH3
Anaerobic condition
High NH3 /High pH
ANL/TN and/or aeration
ECL
FOG in aeration basin
Slow digestion
DNT-RF/SXM/NPN/TM
High temperature/low
activity
Hot process water
HT
No or partial nitrification
Toxicity/low temp/low
SRT/nutrients
XNC/XNL/TM
Low COD or specific
compound removal
Low temp
/various/industry specific
LF, HX, XR, XP, etc.
Excessive sludge
FOG/cellulose/etc
accumulation in sludge
SR
Animal waste consistency
High solids
DL
Algae
High nutrients (N,P)
AL/ALN
Poor denitrification
Low facultative population
DEN
Bioaugmentation
How Does Bioaugmentation Work?
• Numbers – By adding cultures regularly the
minor cultures (but important cultures) gain a
survival advantage (against the dominant
cultures) .
• Natural Genetic Interchange – Recent work
indicates the possibility of transfer to the
biomass of desirable and needed
characteristics (but not permanently),
particularly capabilities controlled by the
plasmids in the cells and demanded by the
conditions in the system.
Activated SludgeCulture Selector
The biomass is comprised of thousands of
cultures of bacteria, fungi, protozoans, etc.
The system “selects” cultures with both
major/dominant populations and minor
counts. Both populations are important in
obtaining good effluent quality.
The combination of cultures in the biomass
continuously changes and adapts to
changes in ambient conditions.
Major Versus Minor Cultures
• Major Cultures
Grow rapidly
settle well
control the general nature of the biomass
• Minor Cultures
Produce important results
Are more difficult to maintain in the biomass
The Transfer of Plasmids
a
b
c
Scientific American, January 1998, p. 68
d
Bioaugmentation Benefits
Benefits for Wastewater Treatment:
 Reduce Effluent Peaks (NPDES outages)
 Reduce Effects of Toxic Compounds
 Improve Settling Thru Filament Control
 Enhance Process Stability
 Reduce Sludge Production
 Minimize Downtime/Reduce Labor
Filamentous Populations
Individual microbes do
the work
Microbes flocculate and
form particles that settle
But the filamentous
forms inhibit settling
Nitrification
2NH4+ + 3O2
2NO2- + O2
2NO2- + 4H+ + 2H2O
2NO3-
NH3 Treatment System
Removal of
insolubles
Removal of
BOD
Clarifier
Recycle of Sludge
Discharge of Sludge Removal of NOD
Clarifier
Recycle of Sludge
Discharge of Sludge