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epc_fa2011_lecture_8

epc_fa2011_lecture_8 - Lecture 8

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1 Wastewater Treatment Processes -- Necessary to protect the water quality of receiving surface waterbodies . -- Wastewater treatment processes can be applicable to treat various source wastewaters, however, most typically refers to the municipal wastewater . -- Types of wastewater collection system (=sewer system) 1) Sanitary Sewer System 2) Storm Sewer System 3) Combined Sewer (CS) System (in older infrastructure) 2 Wastewater Collection System (=Sewer System)
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3 Combined Sewers (CS) -- A type of sewer system that collects both sanitary sewage (=normal condition) and stormwater runoff (=wet condition) in a single pipe system, constructed till 50’s in the Northeast and Great Lakes regions -- Tremendous flow variations due to irregular stormwater runoff influxes to sewers Æ Retention time within the treatment plant decreases under high flow, i.e., wastewater is not treated sufficiently, i.e., operational problems. Æ "Strength" of waste is diluted under high flow rate. In biological wastewater treatment systems, this is not favorable since bacteria have acclimated to feeding on a stronger waste, i.e., efficiency suffers. 4 Combined Sewer Overflow (CSO)
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5 Contaminants in Municipal Wastewater -- Suspended solids -- Biodegradable organic matter -- Nutrients, especially N and P -- Pathogens -- Endocrine disruptors 6 Municipal Wastewater Treatment Processes Primary Treatment removal of mostly solid materials in the sewage to protect pumps and other mechanical equipments ( physical treatment) Secondary Treatment removal of dissolved and suspended organics and inorganic particles that were not removed in primary treatment ( biological treatment)
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7 Primary Treatment -- Removal of mostly solid materials in the sewage to protect pumps and other mechanical equipments ( physical treatment) 1) Screen/Bar Racks & Comminutors and Barminutors 2) Grit Chambers 3) Equalization tank 4) Primary Clarifier (Primary Sedimentation Basin) Raw Sewage Bar Rack Screen Comminutor Barminutor Grit Chamber Primary Tank/ Clarifier Equalization Basin Large solids Small, settleable solids Regulate flow rate (=surge protector) Settling basin Secondary Treatment Primary Treatment 8 Primary Treatment 1) Screen/Bar Racks -- Intercept large solids (2 to 3 inches screen opening) -- Consist of a series of parallel bars -- Solids removed referred to as “screenings”
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9 Primary Treatment 1) Comminutors and Barminutors -- The “Teeth” or “Shredder” or “Grinder” -- Genuinely grind and shred large solids into smaller pieces. -- Barminutor is similar to screens with additional mechanical cutter -- Used right after screens, -- Ground-up solids are removed in following grit chamber . 10 Primary Treatment 3) Grit Chambers -- Remove abrasive, largely inorganic "settleable" particles. -- Based on settling of particles due to velocity slowdown caused by helical flow pattern , and subsequent by gravitational pull-down.
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