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Learning Objectives. Comprehend basic characteristics of domestic wastewater (flow rate, BOD, SS) and apply these characteristics to a preliminary engineering design.Calculate mass loadings within the wastewater treatment system for BOD and SS.Calculate and interpret mass balances for mixtures of wastewaters.Calculate and interpret population equivalents for industrial wastewater..
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1. CE 356: Fundamentals of Environmental Engineering
Wastewater Characteristics
Ricardo B. Jacquez
Professor, CAGE Department
New Mexico State University
Teaching Assistant: M. T. Myint
2. Learning Objectives Comprehend basic characteristics of domestic wastewater (flow rate, BOD, SS) and apply these characteristics to a preliminary engineering design.
Calculate mass loadings within the wastewater treatment system for BOD and SS.
Calculate and interpret mass balances for mixtures of wastewaters.
Calculate and interpret population equivalents for industrial wastewater.
3. Wastewater Characteristics Sources of Wastewater
Physical Characteristics
Sewer Crown Corrosion
Chemical Characteristics
Typical composition of untreated domestic wastewater
Biological Characteristics
Population Equivalents
4. Sources of Wastewater (Major Components) Domestic: food, soap and detergents, bathroom (fecal and urine), and paper.
Commercial: bathroom and food from restaurants and other “stores.”
Industrial: highly variable, dependent on industry, controlled by pre-treatment regulations.
Runoff from streets: sand and petroleum and tire residues (infiltration, not a direct discharge).
5. Wastewater Characteristics Characteristics are categorized as:
Physical
Chemical
Biological
Concentrations characterize wastewater as:
weak, medium, and strong.
6. Physical Characteristics Solids
- Total solids: residue after evaporating all water
(50% volatile and 50% fixed)
(Volatile=organic. Fixed=inorganic mg/L)
- Suspended solids: residue retained on a filter
(75% volatile and 25% fixed).
- Dissolved solids: residue passing through a
filter (40% volatile and 60% fixed).
- Settleable solids: residue after one hour settling in an
Imhoff cone (ml/L) (the indicator of primary sludge).
8. Physical Characteristics cont. Odors: Odors are caused by gases produced by anaerobic decomposition of wastewater (driven by microorganisms and limited oxygen).
Aerobic Respiration: Organics + O2* = CO2 + H2O
Anaerobic Respiration:
Organics + SO4-2 * = H2S + odorous organics
Fermentation:
Organics + Reduced Organics * = odorous organics
* Electron Acceptor
Various odorous compounds result
10. Sewer Crown Corrosion - Organics+SO4-2 =H2S + odorous organics
H2S is volatile, rises to the crown of sewer, and dissolves in water vapor. Crown is aerobic (O2).
H2S + 2O2 = H2SO4 (Bacteria ? sulfuric acid)
Crown caves in, expensive prevention and sewer maintenance / replacement.
water condensation
Aerobic
H2S + 2O2 = H2SO4
SO-2 H2S
Anaerobic
11. “SEWAGE” Domestic wastewater is the ideal mixture of biodegradable nutrients and microorganisms:
BOD (organics)
Nitrogen (N)
Phosphorus (P)
Miscellaneous Micronutrients (S, Fe, Ca, . . . )
Bacteria
12. Chemical Characteristics Organics: Predominant biodegradable fraction, BOD
-Protein -Fats, Oils, and Greases
-Carbohydrates -Surfactants (detergents)
-Urea
Priority pollutants
Industrial solvents, pesticides, etc.
Pre-treatment standards control concentrations to trace levels
13. Chemical Characteristics cont. Inorganic Matter
Nitrogen: from protein and urea.
NH2, NH3, NH4+ forms ammonia and organics.
An essential nutrient for growth of bacteria.
Oxygen Demand:
NH4+ + 2O2 = NO3- + 2 H+ + H2O
14. Chemical Characteristics cont. Phosphorous: phosphate (PO4-3)
Inorganic-detergents
organic-food and metabolic wastes
Trace nutrients: S, Fe, Mn, Mg, Ca, K, Zn, Mo, etc. . . . . . plentiful
20. Mass Loading Calculations Mass = Conc x Flow Rate
= mg/L x MGD x 8.34 x 1/24
= lbs/hr
Mass = Conc x Flow Rate
= mg/L x ft3/sec x 0.22
= lb/hr
21. Mass Balance Calculations Fundamental Law: Massin = Massout
Massin = Q1 x Conc1 + Q2 x Conc2 (knowns)
Massout = QT x ConcT
(unit constants cancel out)
QT = Q1 + Q2
ConcT = unknown
22. Biological Characteristics “Most” microorganisms known to microbiologists can be found in domestic wastewater.
Bacteria
Protozoa
Viruses
Algae (limited)
23. Population Equivalents 1. Wastewater discharge: 100 -120 gpcd
- 70 gpcd domestic
- 10 gpcd industrial/commercial
- 20 to 40 gpcd infiltration
2. Suspended Solids and BOD
SS = 0.2 lb pcd (without kitchen grinder)
SS = 0.22 lb pcd (with kitchen grinder)
BOD = 0.17 lb BOD pcd
BOD = 0.26 lb BOD pcd (with kitchen grinder)
24. Population Equivalents cont.
26. Population Equivalents cont. Used to
Establish population equivalency of an industrial waste.
Establish charge for treating industrial waste based on BOD or SS rather than flow.
28. Summary Domestic wastewater is a well balanced, nutrient rich medium for bacterial decomposition.
After primary treatment, biodegradation is the most cost effective secondary treatment.
- Effective biodegradation requires
BOD:N:P = 100:5:1
- Domestic wastewater contains 100:20:5.
- Organics (BOD) limits N and P reduction.
Advanced treatment is required to
remove excessive N and P.