Chapter 11 Wastewater Treatment. On-Site Disposal Systems Septic Tanks Pit Toilets.
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Transcript of Chapter 11 Wastewater Treatment. On-Site Disposal Systems Septic Tanks Pit Toilets.
Chapter 11Chapter 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
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)
Treatment Levels
Bar Rack
removes large solids such as rags and debris
helps protect pumps, valves, pipelines Communitor
shreds material w/o removing from flow
Bar Screen
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
Grit Chamber
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
Preliminary Clarifier (Settling Tank)
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
Trickling Filter
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
Activated Sludge
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)
Secondary Clarifier (Final Settling in Text)
Chlorination/dechlorination
UV disinfection
Disinfection