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Wastewater Characterization

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)

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Wastewater Characterization

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  1. Wastewater Characterization NC Subsurface Operator School

  2. 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?

  3. 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

  4. 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

  5. What is Wastewater? • Used water and water-carried solids Industrial Wastewater Domestic Wastewater

  6. Domestic Wastewater • Commercial • Schools • Restaurants • Other businesses

  7. 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

  8. 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

  9. Any source can be high strength Can predict strength of some sources…

  10. 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

  11. Average = 70% of Design Average = 90% of Design

  12. 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

  13. Hourly variation in use Homes: Morning water usage, evening water usage, laundry day water usage

  14. Hourly variation in use Restaurants: dishwashing and food prep Schools: lunch time Grocery Stores: nighttime cleaning activities, monthly floor stripping and cleaning activities

  15. Number of sources • Household • Wastewater produced by one household • Components vary day to day • Community • Wastewater produced by multiple households • Higher values • More constant

  16. Use by fixture

  17. What’s in Wastewater? • Pollutants or constituents of concern • Organics/inorganics • Solids • Pathogens • Nutrients • Metals • Persistent organic chemicals • Fats, oils, grease

  18. 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

  19. 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

  20. 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.

  21. Pathogens • 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

  22. Nutrients • Elements essential for plant growth Macronutrients Micronutrients Nitrogen (N) Phosphorus (P) Potassium (K) Boron Chlorine Copper Iron Manganese Molybdenum Nickel Zinc Primary Calcium (Ca) Magnesium (Mg) Sulfur (Su) Secondary

  23. 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

  24. Forms of Nitrogen Organic N NH4+ NO3- /NO2- Total Kjeldahl Nitrogen Total Nitrogen • TKN: Amount already mineralized to NH4 + PLUS nitrogen that is still bound in organics

  25. 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 N N Urea

  26. Inorganic (mineral) nitrogen • Ammonium (NH4+) • Nitrate (NO3-) Inorganic N Organic N NH4+ Mineralization NO3- Lysine

  27. NH4+ NO3- Inorganic Nitrogen • 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” • Available for plant uptake • Positive charge: binds to soil particles • Volatilizes to atmosphere as NH3 • Converted to NO3- in aerobic conditions • “Nitrification” • Ammonium N (NH4+) NH3

  28. 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

  29. 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

  30. 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

  31. 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

  32. 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?

  33. Methods ofmeasurement • Solids analyses (TSS) • Biochemical oxygen demand (BOD) • Chemical oxygen demand (COD) • Dissolved oxygen (DO) • Pathogens • pH • Nutrients

  34. 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

  35. 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

  36. 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

  37. 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

  38. Dissolved Oxygen (DO) • Adequate levels • Allow biological treatment • Minimize objectionable odors • Low levels can indicate • Inadequate aeration • Excessive amounts of organic material (BOD)

  39. 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

  40. pH • pH of domestic wastewater ranges from 6.5 to 7.5 • rapid changes can kill bacteria • Measures acid or base quality of water

  41. Questions?

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