Page 385 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch10_333-356.qxd 8/2/10 9:02 PM Page 345

10.7 Treatment and Disposal or Reuse of Wastewater 345
Pretreatment

Air
Scum

Overflow
Trash

Secondary
Primary
Aeration

Dry sludge finishing

Dryer
Sludge digestion
Methane

Figure 10.8 Wastewater Treatment Processes Flow Diagram (Courtesy Wikipedia)
http://en.wikipedia.org/wiki/Image:ESQUEMPEQUE-EN.jpg

populate the slimes utilize the waste matter for growth and energy. Their growth
unfolds large interfaces at which adsorption, absorption, diffusion, and other inter-
facial forces or contact phenomena bring about exchanges between wastewater and
slimes. To remain active and aerobic, the biomasses are supplied with air. They are
either supported on beds of granular material, such as broken stone over which the
wastewater trickles more or less continuously, or they are generated in the flowing
wastewater, returned to it in wanted amounts, and kept in suspension by agitating
the mixed liquor with air. This can also be done mechanically using trickling filters
and activated-sludge tanks, which produce trickling filter humus and excess acti-
vated sludge.
6. Excess nitrogen and phosphorous nutrients are usually removed by advanced de-
sign and management of the biological treatment processes mentioned in point 5.
7. Some pathogenic bacteria and other organisms are removed from wastewater along
with the solids in which they are embedded or to which they cling. Others die be-
cause the imposed environment is too unfavorable. Fuller and more direct destruc-
tion is accomplished by disinfection with ozonation or chlorination units.

10.7.2 Sludge Management and Disposal
The solids separated from wastewater in treatment works contain much water and organic
matter. Sludge settling from wastewater by plain sedimentation contains about 95% water;
activated sludge, 98% or more. If the daily flow of wastewater is millions of gallons, the