The document discusses the treatment of solids generated during wastewater treatment. Solids are produced during preliminary treatment like screening and grit removal, as well as primary and secondary treatment in the forms of scum and sludge. The solids treatment process includes thickening the sludge to reduce volume, stabilizing through processes like digestion to reduce pathogens, and dewatering to further reduce moisture content before final disposal or beneficial reuse.

1. Solids Treatment
Overview
WATR-082: ADVANCED WASTEWATER TREATMENT
SPRING 2019

2. Wastewater Treatment Train Solids Generation
Influent
Wastewater
Effluent
Wastewater
SOLIDS SOLIDS
Screening Grit Removal Primary Treatment Secondary Treatment
Preliminary Treatment

3. Solids from Preliminary Treatment
Screening Grit Removal
Solids
removed from
preliminary
treatment
include:
No nutrients
or organic
content
Are disposed
in a landfill
Rags
Tree
limbs
Grit
Plastics
Preliminary Treatment

4. Solids From Primary and Secondary Treatment
Needs
stabilization
Rich in
nutrients
and
substantial
organic
content
Contains
pathogens
Prevent
public
nuisance/
health
hazard
Will decay
causing
odors
Primary Treatment Secondary Treatment
Scum
Sludge Sludge
SOLIDS
Disposal
Beneficial
reuse

5. Solids From Primary and Secondary Treatment
Primary Treatment Secondary Treatment
Sludge Sludge
1-5%
solids
0.5%
solids
>95%
water
>99%
water
SLUDGE STABILIZATION PROCESS
Sludge
Thickening
Sludge
Thickening

6. Sludge Thickening
Primary Treatment Secondary Treatment
Sludge Sludge
Sludge
Thickening
Sludge
ThickeningGravity Thickener
Dissolved Air Floatation
Thickener (DAFT)
Removes
excess
water
Reduces
volume of
sludge to
be
stabilized
Reduces
treatment
costs
Optional
Suitable for
primary sludge
Suitable for
secondary
sludge
Thickening produces sludge
with <10% solids content

7. Digestion
Sludge Stabilization
Produces
solids that are
safe for final
use or
disposal
Final solids use or disposal options
Condition/Fertilize
Soil
Surface
disposal
Drying or
incineration
Land
application
Utilize the carbon
content
Regulated
under CFR Part
503 regs
Anaerobic
Aerobic
Alkaline
Stabilization
Composting
Long Term
Storage in
Lagoons
Thermal
Processes
Biosolids: Stabilized
sludge which meet
regulatory standards for
beneficial reuse
Most
Common
Sludge Stabilization Processes

8. Solids Dewatering
Digestion
produces
solids with
<5% solids
Not practical
to haul off-site
in this state
Sludge is
therefore
dewatered
Belt Filter Press Centrifuge
Most common methods
Makes
sludge
easier to
handle
Reduces
hauling
costs
Physical
process
Increases
solids
content to
15 – 30%

9. Solids Treatment Process Summary
Primary Treatment Secondary Treatment
Scum
Sludge
SLUDGE STABILIZATION PROCESS
Sludge
Thickening
Screening Grit Removal
Preliminary Treatment
Sludge
Thickening
Sludge
SOLIDS DEWATERING PROCESS
Disposal
or
Beneficial
Reuse
Landfill
Influent
Wastewater
Treated
Wastewater
Solids