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Chapter 11

Chapter 11. Wastewater Treatment. On-Site Disposal Systems. Septic Tanks Pit Toilets. Flow Schematic for a Wastewater Treatment Plant. Flow Schematic for a Wastewater Treatment Plant. Treatment Levels. Preliminary Treatment Bar screen (bar rack) and/or comminutor Flow measurement Pump

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Chapter 11

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  1. Chapter 11 Wastewater Treatment

  2. On-Site Disposal Systems • Septic Tanks • Pit Toilets

  3. Flow Schematic for a Wastewater Treatment Plant

  4. Flow Schematic for a Wastewater Treatment Plant

  5. Treatment Levels • Preliminary Treatment • Bar screen (bar rack) and/or comminutor • Flow measurement • Pump • Grit chamber • Primary Treatment • sedimentation tank or clarifier • Secondary Treatment • Aeration (activated sludge) tank or trickling filter • secondary clarifier (sedimentation)

  6. Bar Screen • Bar Rack • removes large solids such as rags and debris • helps protect pumps, valves, pipelines • Communitor • shreds material w/o removing from flow

  7. Grit Chamber • Removes dense grit w/o removing less-dense organic solids • Grit: sand, gravel, other inorganic material, and minimally putresible organics (egg shells, coffee grounds, seeds) • Purpose: • prevent excessive wear; abrasion of equipment • prevent deposition of grit in pipes/channels • prevent accumulation of grit in tanks

  8. Preliminary Clarifier (Settling Tank) • Included in many treatment plants • Removes much of the settleable solids (grit is usually removed first in grit chamber) • reduces solids flowing to the remaining units • reduces BOD since the solids removed in the tank are organic and have a BOD

  9. Trickling Filter • Liquid wastewater sprayed over bed of rocks or plastic • Microorganisms attached to rocks/plastic accomplish biodegradation of waste in flowstream • Air circulates through rock/plastic bed

  10. Activated Sludge • Microorganisms that accomplish biodegradation of waste in flowstream are suspended in the liquid contents of the tank • Air is supplied to the tank for survival of aerobic microorganisms

  11. Secondary Clarifier (Final Settling in Text) • Microorganisms from activated sludge (or trickling filter) settle, producing a clarified effluent leaving the tank • Settled microorganisms in activated sludge are recycled to activated sludge tank • Some microorganisms are “wasted” from the system (to sludge treatment)

  12. Disinfection • Chlorination/dechlorination • UV disinfection

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