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CE 356: Fundamentals of Environmental Engineering
Wastewater Characteristics
Ricardo B. Jacquez
Professor, CAGE Department
New Mexico State University
Teaching Assistant: M. T. Myint
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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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Sources of Wastewater (Major Components)
1. Domestic: food, soap and detergents, bathroom (fecal and urine), and paper.
2. Commercial: bathroom and food from restaurants and other “stores.”
3. Industrial: highly variable, dependent on industry, controlled by pre-treatment regulations.
4. Runoff from streets: sand and petroleum and tire residues (infiltration, not a direct discharge).
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Wastewater Characteristics
Characteristics are categorized as:
- Physical
- Chemical
- Biological
Concentrations characterize wastewater as:
weak, medium, and strong.
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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).
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“SEWAGE”
• Domestic wastewater is the ideal mixture of biodegradable nutrients and microorganisms:
– BOD (organics)– Nitrogen (N)– Phosphorus (P)– Miscellaneous Micronutrients (S, Fe, Ca, . . . )– Bacteria
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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
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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
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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
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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
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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
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Biological Characteristics
“Most” microorganisms known to microbiologists can be found in domestic wastewater.
- Bacteria
- Protozoa
- Viruses
- Algae (limited)
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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)
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Population Equivalents cont.
For 100 gpcd and consider for one person:
BOD0.17 lb
100gal
1
8.34 lb
106 galmg
L
BOD 204mg
L
SS0.2 lb
100gal
1
8.34 lb
106 galmg
L
SS 240
mg
L
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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.
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Find the BOD and flow equivalent for an industrial waste with the following characteristics:
Q 0.1MGDMGDMGD BOD 450mg
L
Flow: 0.1MGD
100gal
person day
1000peoplepeoplepeople
BOD: 0.1MGD 450 mg
L
8.34 lb
MGDmg
L
0.17 lb BOD
person day
2208peoplepeoplepeople
BOD equivalent is 2.2 times greater than flow equivalent.