4.6 Physical, biological and chemical treatment processes

1
4.6 Physical, biological and chemical treatment
processes
Biological
microbial decomposition, predation, uptake in
plants
Physical
screening and filtration, sedimentation, flotation
Learning objective to become familiar with
basic functions of various physical, chemical and
biological processes.

Chemical coagultation/flocculation,
adsorption, precipitation, UV-radiation
What compounds can be removed from
wastewater? How can Nature assist or react?
2
Treatment results for small and large water
utilities
More than 2,000 persons
Less than 2,000 persons

J-O Drangert, Linköping University, Sweden
3
B Physical processes
flotation and sedimentation
screening
forced micro- filtration
filtration
Possible combinations of physical processes
Jan-Olof Drangert, Linköping university, Sweden
4
Screening of debris and other solid items
Organics from kitchen pipe sorted out in a
plastic screen
Solids trapped by a screen in a city wastewater
treatment plant
Jan-Olof Drangert, Linköping university, Sweden
5
Flotation and sedimentation processes
Inspection hole
Baffels
Inlet of wastewater
Outlet of treated water
Floating grease, particles, organisms
Sludge built up
Jan-Olof Drangert, Linköping university, Sweden
6
Filtration mainly by gravity

Saturated flow of wastewater
Partially unsaturated flow
Jan-Olof Drangert, Linköping university, Sweden
7
Forced micro-filtration
Manufactured porous material
Applied pressure
Direction of filtered water flow
Jan-Olof Drangert, Linköping university, Sweden
8
C Chemical processes
Adsorption of charged particles
Adsorption of phosphate on ferric hydroxide
OH H2PO4- Fe
OH
OH H2PO4-
Al OH
Adsorption of phosphate on aluminium hydroxide
particles
G. Jacks, Royal Institute of Technology, Stockholm
9
Adsorption of charged particles to soil medium

• The three important kinds of charged soil
  particles are
• Organic matter
• RCOOH lt gt RCOO- H
• (a negative pH-dependent charge)
• R is phenolic ring derived from
• lignite in residues of plants
• 2. Clay minerals
• Clay mineral consist of Al-Si-sheets
• with different cations (Na, K etc.)
• in between the sheets. There is a
• negative charge on sides and edges
• 
  3. Ferric
  hydroxides
  
  Fe(OH)3 lt gt Fe(OH)2- H
• 
  (a pH-dependent
  positive charge)

R-COO- Pb 2
R-COO-

Mineral grain
Organic overcoat on a soil mineral
Cu 2
- - K K
Mg 2 - - -
OH Fe(III) HAsO4-
OH
G Jacks, Royal Institute of Technology, Stockholm
10
Adsorption of chemical compounds differ
Copper (Cu) and Zink (Zn) are positively charged,
and adsorb easily on organic matter and clays
when the pH gt 7 Arsenic (As) is negatively
charged and adsorbs easily on ferric hydroxides
when pH lt 7
G Jacks, Royal Institute of Technology, Stockholm
11
Precipitation and flocculation

• Precipitation a chemical reaction between
  dissolved compounds to form solids
• Flocculation - an aggregation process (or
  processes) leading to the formation of larger
  particles from smaller particles

-
-

G. Jacks, Royal Institute of Technology, Stockholm
12
UV-radiation by sunlight
Inactivation of micro-organisms by UVA-radiation
and increased temperature
http//www.sodis.ch/Text2002/T-TheMethod.htm
Source Ubomba-Jaswa et al. 2009
13
Shallow ponds with a dense population of algae
More diffuse stratification
Vertical view of the pond
Strong algal stratification
Courtesy of Duncan Mara, University of Leeds, UK
K Tonderski, Linköping University Sweden
14
Ozonation and chlorination
15
D Biological processes
Karin Tonderski, Linköping university, Sweden
16
Biological processes - with air
Oxygen is vital for most living organisms,
including bacteria and viruses. When oxygen is
present, organic matter (measured as BOD) is
efficiently decomposed by organisms into CO2
water
Unsaturated soil profile
Organic matter
Aerobic bacteria
oxygen
Jan-Olof Drangert, Linköping university, Sweden
17
Biological processes - without air
Many microorganisms can survive in environments
with no oxygen and they use other compounds for
their survival
Organic matter in waste-water
e.g. nitrate, sulphate or iron ions (Fe 3 )
Anaerobic micro-organisms
Saturated soil profile with little or no oxygen
CO2 e.g. N2, S2-, Fe2
Jan-Olof Drangert, Linköping university, Sweden
18
Microorganisms attached to surfaces are more
stable than those suspended in water
wastewater flow
anaerobic biofilm
aerobic biofilm
Grain particle
Jan-Olof Drangert, Linköping university, Sweden
19
Redox-ladder
When microorganisms descend the redox-ladder they
first use O2 as an electron acceptor, then
nitrate NO3, and further down other compounds as
electron acceptors. The blue arrow indicates a
reaction with energy-rich organic substances
(electron donors) in

the wastewater
O2 H2O (oxygenisation)
NO3- N2, N2O
(denitrification) MnO2
Mn2 Fe(OH)3
Fe2 SO42-
H2S (sulphate-reduction)
CO2 CH4
(methanogenesis)
Decrease in oxygen
Gunnar Jacks, Royal Institute of Technology,
Stockholm
20
Changes in concentrations of electron acceptors
when organic matter (TOC) decomposes


Gunnar Jacks, Royal Institute of Technology,
Stockholm
21
What happens in the root zone?
Water, nutrients, heavy metals,
gases (e.g. CO2)
O2, sugars, proteins, etc
Organic matter, O2, NO3- , SO42-, CO2 etc
Jan-Olof Drangert, Linköping university, Sweden
22
Predation on microorganisms stimulates
decomposition
Courtesy of Frida Lögdberg, Linköping university
23
Soil organisms vary tremendously in size and
numbers
A teaspoon soil one gram
Modified from Sylvia, D. et al. 2004. Principles
and applications of soil microbiology
24
Organic matter is decomposed most efficiently in
the top soil
Million organisms per gram soil
Anaerobic bacteria
Aerobic bacteria
Soil surface
106
0
106
Depth in meter
0.5 m
Courtesy of G. Jacks, Royal Institute of
Technology, Stockholm