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Wastewater Characteristics

Wastewater Characteristics

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Wastewater Characteristics

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  1. Wastewater Characteristics Shihwu Sung, Ph.D., PE Department of Civil, Construction & Environmental Engineering Iowa State University

  2. What is Wastewater? = 99+% water + impurities Impurities include: • Insoluble Particulates = Suspended Solids (SS) Inorganic SS or Fixed SS, e.g., silt Organic SS, or Volatile SS, e.g., cell mass • Soluble Solutes Soluble Inorganics, e.g., salts Soluble Organics, e.g., sugars Nutrients:N and P Could be organic/inorganic or particulate/soluble Could cause eutrophication in receiving water body Organic nutrients plus ammonia (NH4+) have oxygen demand Oxygen Demand

  3. Wastewater Characteristics Analysis • 1% = 10 g pollutants / Kg of water = 10,000 mg/L • All pollutants can be measured in Solid Matrix Tests

  4. particulate soluble organic 550oC in Temp. inorganic 1μm in size Solid Matrix TS = TSS + TDS ║ ║║ VS = VSS + VDS +++ TFS = FSS + FDS particulate organic soluble organic particulate inorganic soluble inorganic sand, silt salts T : Total S : Solids or Suspended D : Dissolved V : Volatile F : Fixed

  5. Example:A water sample contains: Sugar: 100 mg/L Fine sand: 60 mg/L Bacteria: 25 mg/L Salts e.g., NaCl, KHCO3: 125 mg/L What is the TDS and VS/TS of this sample? T : Total S : Solids or Suspended D : Dissolved V : Volatile F : Fixed TS = TSS + TDS ║ ║ ║ VS = VSS + VDS + + + TFS = FSS + FDS 310 85 225 125 25 100 185 60 125

  6. Raw Sewage Bar Rack Pretreatment Grit Chamber Primary Treatment Equalization Basin Pump Secondary Treatment Tertiary Treatment Primary Settling Biological Treatment Secondary Settling Advanced Waste Treatment e.g., Nutrient removal Receiving Body

  7. Organic content in wastewater • Organics can be subdivided into: • Carbohydrate, Protein, Lipid (Oil & Fat) • Biodegradability: • Carbohydrate>Protein>Lipid • As a “rule of thumb” in Anaerobic Digestion • Higher protein generates more alkalinity • Maximum 30% of COD from Lipid • Thermophilic digestion preferred in lipid digestion • due to higher lipid solubility in higher temperature

  8. (BODult / BOD5) = 1.5 – 2.0 Biodegradable COD (BCOD) Estimation: 1. BCOD = BOD5 * (BODult / BOD5) 2. BCOD (Oil & Grease) = FOG * 2.88 3. BCOD (Protein) = ( TKN – NH3-N) * 6.29 * 1.50 4. BCOD (Carbohydrate) = (1) – (2) – (3) Grease: C8H16O C8H16O + 23/2 O2→ 8 CO2 + 8 H2O 2.88 g COD / g grease Protein: C16H24O5N4 (12x16 + 24 + 16x5 + 14x4) / (14x4) = 6.29 1.50 g COD / g protein BODult = Ultimate BOD ~ BCOD FOG = Fat, Oil & Grease TKN = Total Kjeldahl Nitrogen = organic-N + ammonia-N See Handout: Table 3.1 COD Mass Equivalents of Some Common Constituents

  9. COD / BOD5 ratio => Biodegradability Lower ratio => Higher biodegradability Typical value of raw wastewater = 1.5 – 2.0 Typical value of biologically treated effluent = 4 - 8 NH4-N / TKN ratio => Freshness Lower ratio => Fresh sample pH issues: chemical usage, VFA production, etc.

  10. Wastewater Treatment Options • aerobic treatment for soluble chemical oxygen demand (COD) in 50 - 40,000 mg/L range • anaerobic treatment for high CODs (4000 - 50,000 traditionally) • alternative processes for CODs < 50 mg/L (e.g., carbon adsorption, ion exchange) and > 50,000 mg/L (e.g., evaporation and incineration)

  11. See examples in handout