wastewater characterization nc subsurface operator school
TRANSCRIPT
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Wastewater Characterization
NC Subsurface Operator School
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Wastewater Characterization
Why is this important? What is wastewater? Where does it come from? How much is there? What’s in it? How can we measure it?
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Why is this important?
Influent wastewater (raw sewage) Inform treatment system design
STE and pretreatment effluent Inform treatment system design Inform drainfield sizing Determine compliance
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Why is this important?
Pretreatment unit mixed liquor Process monitoring and control
Ground/surface water discharge (after soil dispersal/treatment) Determine risk and inform design Determine compliance
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What is Wastewater?
Used water and water-carried solids
Industrial WastewaterDomestic Wastewater
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Domestic Wastewater
Commercial Schools Restaurants Other businesses
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Domestic Wastewater
Food preparation Restroom (sinks, toilets) Laundry
uniform in color and composition gray in color and musty smelling unusual colors or odors indicate abnormal
discharges
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Industrial Wastewater
Manufacturing processes Car wash facilities
Variable in composition May contain high levels of
chemicals or toxic substances Pretreatment & industrial
inputs can affect color/odor
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Any source can be high strength
Can predict strength of some sources…
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How much is there?
Prescriptive codes Unit flow rates for different facilities Predict usage based upon past experience Design flow
Actual measurement captures peak usage Hourly Daily Monthly
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Actual average flow
Varies considerably Hourly variation
Fewer facilities, higher peaking factor Daily variation
Schools, churches, businesses Weekly
Variable use facilities: vacation rentals, etc. Seasonal
Long periods of inactivity
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Hourly variation in use Homes: Morning water usage, evening
water usage, laundry day water usage
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Hourly variation in use
Restaurants: dishwashing and food prep Schools: lunch time Grocery Stores: nighttime cleaning
activities, monthly floor stripping and cleaning activities
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Number of sources
Household Wastewater produced by one
household Components vary day to day
Community Wastewater produced by
multiple households Higher values More constant
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Use by fixture
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What’s in Wastewater?
Pollutants or constituents of concern Organics/inorganics Solids Pathogens Nutrients Metals Persistent organic chemicals Fats, oils, grease
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Organic constituents Waste from plant or animal sources Can be consumed by microbes
Anaerobic and aerobic processes Expressed as biochemical oxygen
demand (BOD) or chemical oxygen demand (COD) A commonly-used indicator of wastewater
strength. Biological growth
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Metals: Inorganic chemical compounds
Often found in industrial discharges Stable and resistant to decomposition Some essential for animal & plant nutrition At higher levels some metals can be
highly toxic Especially in soil with low pH More mobile
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Solids
Organic and inorganic materials Fractions:
Total Solids Total dissolved solids (TDS) Total suspended solids (TSS)* Total settleable solids
Solids removal is a major goal of wastewater treatment
Can clog treatment/dispersal components
*TSS is another commonly-used expression of wastewater strength.
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Disease-causing organisms Helminths (worms), protozoa, bacteria, viruses
Comfortable in human digestive system Conditioned to living in low oxygen Difficulty surviving in air-filled environments Many pathogens are removed when solids
are removed
Pathogens
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Nutrients
Elements essential for plant growth
Nitrogen (N)Phosphorus (P)Potassium (K)
Calcium (Ca)Magnesium (Mg)Sulfur (Su)
Primary
Secondary
BoronChlorineCopperIronManganeseMolybdenumNickelZinc
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Nutrients
N and P are a major concern in wastewater Can affect water quality
Nitrogen – more detrimental to marine environments
Can also cause methemoglobinemia and other problems
Phosphorous – more of an effect on freshwater
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Forms of Nitrogen
Organic N
NH4+
NO3- /NO2
-
Total Kjeldahl Nitrogen
TKN: Amount already mineralized to NH4
+ PLUS nitrogen that is still bound in organics
Total Nitrogen
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Organic nitrogen Found in cells of all
living things (proteins, peptides, amino acids)
Principle compound in feces and urine
Not available to plants until bacterial conversion to inorganic form through MINERALIZATION
Urea
NN
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Inorganic (mineral) nitrogen
Ammonium (NH4+)
Nitrate (NO3-)
Mineralization
NH4+
NO3-
Organic N Inorganic N
Lysine
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Inorganic Nitrogen Ammonium N (NH4
+) Nitrate N (NO3-)
Available for plant uptake
Negative charge: not held by soil
High potential for leaching to groundwater
Can be converted to N2 if:
Low O2 with C or S present
“Denitrification”NO3
-
NH4+
Available for plant uptake
Positive charge: binds to soil particles
Volatilizes to atmosphere as NH3
Converted to NO3
- in aerobic conditions
“Nitrification”
NH3
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Phosphorous Found in body wastes, food residues,
fertilizers, detergents, industrial discharges Some forms available to plants P in soil often forms insoluble compounds
“Precipitation” Rarely mobile in soil, but can move with soil
particles during erosion Can promote algal growth in P-limited
waters Mainly inland
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Fats, Oils, and Grease(FOG)
Animal or vegetable-based FOG Residential/Commercial kitchens
Degradable by microorganisms
Petroleum-based FOG Industry/automotive repair Personal care products
NOT readily broken down by microorganisms
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Persistent organic chemicals - Stable organic compounds
Slow to decompose Can persist in soil and groundwater for
years Many are synthetic compounds
Industrial discharges Solvents & household cleansers Paint Medical products Personal care products
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Inorganic constituents
Minerals, metals, dissolved salts Sand, silt, cadmium, copper, lead, zinc,
sodium Stormwater, inflow and infiltration
Cracked pipes, leaky manhole covers
Residential, commercial, industrial sources Stable compounds
Not easily broken down by microorganisms
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Measuring wastewater strength
How much treatment is required? What is the effluent quality at different
stages of treatment? Has wastewater been successfully
treated? Are we compliant with regulations?
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Methods ofmeasurement
Solids analyses (TSS) Biochemical oxygen demand (BOD) Chemical oxygen demand (COD) Dissolved oxygen (DO) Pathogens pH Nutrients
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Solids analyses
Total suspended solids (TSS) Sample filtered through pre-weighed filter Filter and residue dried at 103-105 degrees C Increase in weight of filter represents TSS
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Biochemical oxygen demand (BOD)
Amount of oxygen consumed by microbes during decomposition of organic matter Test performed over 5 day period: BOD5
High BOD means high levels of organics
Domestic wastewater ranges from 100 to 300 mg/L BOD
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Chemical oxygen demand (COD)
Amount of organic matter oxidized by a strong chemical oxidant
Measures additional compounds that microorganisms don’t decompose COD will be higher than BOD
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Dissolved oxygen (DO)
Concentration of O2 dissolved in water Most wastewater treatment processes
Require aerobic conditions Cannot occur in anaerobic conditions
Measure with meter and probe or colorimetric kit An indication of treatment efficacy
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Dissolved Oxygen (DO)
Adequate levels Allow biological treatment Minimize objectionable odors
Low levels can indicate Inadequate aeration Excessive amounts of organic material
(BOD)
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Pathogens
Testing for all pathogens is impractical
Fecal coliform used as indicator organism Present in digestive system
of warm blooded animals High levels in wastewater
indicate high levels of pathogens
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pH
pH of domestic wastewater ranges from 6.5 to 7.5
rapid changes can kill bacteria
• Measures acid or base quality of water
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Questions?