5 Wastewater Characteristics
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Transcript of 5 Wastewater Characteristics
CE 356: Fundamentals of Environmental Engineering
Wastewater Characteristics
Ricardo B. Jacquez
Professor, CAGE Department
New Mexico State University
Teaching Assistant: M. T. Myint
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.
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).
Wastewater Characteristics
Characteristics are categorized as:
- Physical
- Chemical
- Biological
Concentrations characterize wastewater as:
weak, medium, and strong.
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).
“SEWAGE”
• Domestic wastewater is the ideal mixture of biodegradable nutrients and microorganisms:
– BOD (organics)– Nitrogen (N)– Phosphorus (P)– Miscellaneous Micronutrients (S, Fe, Ca, . . . )– Bacteria
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
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
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
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
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
Biological Characteristics
“Most” microorganisms known to microbiologists can be found in domestic wastewater.
- Bacteria
- Protozoa
- Viruses
- Algae (limited)
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)
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
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.
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.