Presentation on theme: "CEE 421, Lecture #1. Municipal WW Management Systems Sources of Wastewater Processing at the Source Wastewater Collection Transmission and Pumping Treatment."— Presentation transcript:
1972: Federal Water Pollution Control Act u PL 92-500 subsequently amended and now called the Clean Water Act –established water quality goals “fishable & swimmable” and timetable –established National Pollution Discharge Elimination System (NPDES) –construction grants for WW treatment u required secondary treatment (30/30) –30 mg/L BOD 5 –30 mg/L TSS
TYPICAL AERIAL VIEW OF A WASTEWATER TREATMENT PLANT
Wastewater Treatment u Primary – Removes Solids u Physical Operations – Screening, Sedimentation u Secondary – Removes Organics u Biological and Chemical Operations u Tertiary – Removes Nutrients u Biological and Chemical Operations
Wastewater Characteristics (Table 3-1) u Physical –Temperature, Odor, Taste, Solids u Chemical –Organics, Inorganics u Biological –Animals, Plants, Microorganisms
Solids: significance u TDS: used as a measure of inorganic salt content in drinking waters and natural waters u TSS: used to assess clarifier performance u VSS: used to estimate bacterial populations in wastewater treatment systems
ODORS u Gases produced by decomposition of organic matter (Hydrogen Sulfide) u Effect of odors: psychological stress, nausea, vomiting, headaches, poor appetite, deterioration of community, lower socio- economic status etc. u Classification of odors: See Table 3-5
Odor Characterization and Measurement u Factors: Intensity, Character, Hedonics, Detectability u Methods: Sensory Method –Olfactometer (Human Errors), Electronic Nose u TON- Threshold Odor Number u MDTOC – Minimum Detectable Threshold Odor Concentration
Temperature u Higher in wastewater than waster supply u Mean annual temperature 10-21.1 o C u Effects reaction rates, chemical reactions, suitability of the water for beneficial reuse, solubility
Chemical Characteristics u Organics and Inorganics u Organic Matter 75% of Suspended Solids and 40% of the filterable solids are organic in nature u Principal groups – proteins, carbohydrates, fats and oils, surfactants, VOCs, Pesticides u Priority Pollutants – 129 Compounds controlled by USEPA
Oxygen Demand u It is a measure of the amount of “reduced” organic matter in a water u Relates to oxygen consumption in a river or lake as a result of a pollution discharge u Measured in several ways –BOD - Biochemical Oxygen Demand –COD - Chemical Oxygen Demand –ThOD - Theoretical Oxygen Demand
ThOD This is the total amount of oxygen required to completely oxidize a known compound to CO 2 and H 2 O. It is a theoretical calculation that depends on simple stoichiometric principles. It can only be calculated on compounds of known composition. C 6 H 12 O 6 + 6O 2 = 6CO 2 + 6H 2 O If you have 100 mg/L of Glucose what is the ThOD in mg/L ?
BOD: A Bioassay Briefly, the BOD test employs a bacterial seed to catalyze the oxidation of 300 mL of full-strength or diluted wastewater. The strength of the un-diluted wastewater is then determined from the dilution factor and the difference between the initial D.O. and the final D.O. BOD Bottle
BOD with dilution Where BOD t =biochemical oxygen demand at t days, [mg/L] DO i =initial dissolved oxygen in the sample bottle, [mg/L] DO f =final dissolved oxygen in the sample bottle, [mg/L] V b =sample bottle volume, usually 300 or 250 mL, [mL] V s =sample volume, [mL] When BOD>8mg/L
BOD - Oxygen Consumption L=oxidizable carbonaceous material remaining to be oxidized
BOD - loss of biodegradable organic matter (oxygen demand) LoLo LtLt L or BOD remaining Time L o -L t = BOD t BOD Bottle BOD Bottle BOD Bottle BOD Bottle BOD Bottle
BOD Modeling "L" is modelled as a simple 1st order decay: Which leads to: We get: And combining with:
Temperature Effects Temperature Dependence Chemist's Approach: Arrhenius Equation Engineer's Approach:
NBOD Nitrogeneous BOD (NBOD) 2 moles oxygen/1 mole of ammonia 4.57 grams oxygen/gram ammonia-nitrogen Like CBOD, the NBOD can be modeled as a simple 1st order decay:
COD: A chemical test The chemical oxygen demand (COD) of a waste is measured in terms of the amount of potassium dichromate (K 2 Cr 2 O 7 ) reduced by the sample during 2 hr of reflux in a medium of boiling, 50% H 2 SO 4 and in the presence of a Ag 2 SO 4 catalyst.
COD (cont.) The stoichiometry of the reaction between dichromate and organic matter is: COD test is faster than BOD analysis: used for quick assessment of wastewater strength and treatment performanceCOD test is faster than BOD analysis: used for quick assessment of wastewater strength and treatment performance Like the BOD, it does not measure oxidant demand due to nitrogeneous speciesLike the BOD, it does not measure oxidant demand due to nitrogeneous species It does not distinguish between biodegradable and non- biodegradable organic matter. As a result COD's are always higher than BOD's.It does not distinguish between biodegradable and non- biodegradable organic matter. As a result COD's are always higher than BOD's. Where:
Organic Content u TOC: total organic carbon –measured with a TOC analyzer –related to oxygen demand, but does not reflect the oxidation state of the organic matter u other group parameters –oil & grease u specific organic compounds
TOC Total organic carbon analysis is a determination of organic carbon in a sample regardless of its oxidation state or biodegradability. Other measures of total organic matter (e.g., COD, BOD) may respond differently to solutions of equal carbon concentration depending on the oxygen content or the bidegradation kinetics. For the measurement of total organic carbon, the sample is exposed to an oxidizing environment often at very high temperatures. With complete oxidation all carbon is converted to carbon dioxide and swept into a detector by the carrier gas. The oxidation process is based on the following stoichiometry:
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