Wastewater Characterization

NC Subsurface Operator School

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?

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

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

What is Wastewater?

Used water and water-carried solids

Industrial WastewaterDomestic Wastewater

Domestic Wastewater

Commercial Schools Restaurants Other businesses

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

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

Any source can be high strength

Can predict strength of some sources…

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

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

Hourly variation in use Homes: Morning water usage, evening

water usage, laundry day water usage

Hourly variation in use

Restaurants: dishwashing and food prep Schools: lunch time Grocery Stores: nighttime cleaning

activities, monthly floor stripping and cleaning activities

Number of sources

Household Wastewater produced by one

household Components vary day to day

Community Wastewater produced by

multiple households Higher values More constant

Use by fixture

What’s in Wastewater?

Pollutants or constituents of concern Organics/inorganics Solids Pathogens Nutrients Metals Persistent organic chemicals Fats, oils, grease

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

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

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.

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

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

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

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

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

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

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

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

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

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?

Methods ofmeasurement

Solids analyses (TSS) Biochemical oxygen demand (BOD) Chemical oxygen demand (COD) Dissolved oxygen (DO) Pathogens pH Nutrients

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

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

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

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)

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

pH

pH of domestic wastewater ranges from 6.5 to 7.5

rapid changes can kill bacteria

• Measures acid or base quality of water

Questions?