Collection and Preliminary Treatment Flashcards
Specific Gravity of Grit, Sand and Gravel
2.6
Grit Removed from Wastewater Contains
Inorganic: Sand, Silt, Small Gravel, Shells
Organic: Rice, Corn, Coffee Grounds
Combined Sewers handle what kind of flow?
Domestic Sewage and Storm Water
- these are no longer made; storms can increase hydraulic loading to the point they are diverted into rivers and streams
What problems can inadequate grit removal from raw sewage cause?
- Wear on Pumps and Mechanical Equipment
- Affect downstream treatment process
effectiveness/efficiency :- build up in primary treatment/ aeration basins
- accumulate in digesters
Units that shred, cut or grind rags and large solids in raw wastewater and return shredded solids to the wastewater flow
- Comminutor
- Barminutor
- Muffin Monster
Most common flow measuring device installed where influent enters the WWTP
Parshall Flume
What occurs when the velocity in the grit channel is too slow?
Light organics settle with the grit. The organics then putrify. This can cause odors due to producing hydrogen sulfide.
Putrification is the decomposition of matter in the absence of oxygen
Pre-aeration of raw sewage can produce this benefit to later treatment.
Primary clarifier settling is significantly improved
Why pre-chlorination of raw sewage is not recommended or practiced
Pre-Chlorination of raw or untreated sewage can produce undesirable chlorinated organic compounds that are suspected carcinogens (cancer causing)
The minimum design velocity in a gravity sewer
Minimum design velocity is 2 feet per second (fps)
The optimum velocity of sewage flow in a grit channel.
Optimum velocity is 0.8 - 1.2 feet per second (fps)
Term for typical variation in domestic sewage flow to a treatment plant.
□ Diurnal Flow :
Sewage flow reflects the water use of a community
and typically has two “peaks” and two “valleys”
during each 24 hour period.
Common velocity control devices used at the end of grit channels.
□ Parshall flume
□ Proportional weir
Used to remove rags and large debris from wastewater.
□ Bar screen
□ Trash rack
Terms used to describe storm water and groundwater flow into a sanitary sewer during wet weather conditions
□ Inflow
□ Infiltration
Stormwater flow into a wastewater treatment plant can cause this
Hydraulic overload of the treatment plant
Sewer that flows as a result of the slope of the pipe.
Gravity sewer
Sewer discharge pipe from a sewage pumping station.
Force main
Methods used to determine the condition of a sanitary sewer.
□ TV camera inspection
□ Sewage flow monitoring at manholes
□ Visual inspection of manholes
Treatment plant problems that can occur if shredding equipment is not operating properly.
□ Plugging of pumps
□ Fouling of aeration equipment
□ Plugging of trickling Filter (distributor arm openings and
media)
□ Build-up in digesters
Typical operating mode for two identical pumps in a sewage pumping station.
The “lead” - “lag” status of the pumps should be switched automatically after each pumping cycle.
Component parts of a pre-cast manhole,
□ Base
□ Riser section(s)
□ Cone
Terminology used to describe sewer lines:
Lateral
Main
Trunk or Outfall
□ Lateral sewer receives no flow from other sewer lines
□ Main sewer receives sewage flow from laterals
□ Truck or outfall sewer carries the sewage flow from an entire area. The pipe that directly discharges into the treatment plant
Bottom of sewer pipe.
Sewer invert
Function of storm sewer catch basin
Settle out grit and sand from storm water flows
