Learning objective: to become familiar
with basic functions of various physical,
chemical and biological processes.
Ph
ysical ~
screening and filtration, sedimentation, flotation
Chemical ~ coagultation/flocculation, adsorption, precipitation, UV-radiation
Bio
log
ical
~
mic
robi
al d
ecom
posi
tion,
pre
datio
n, u
ptak
e in
pla
nts
4.6 Physical, biological and chemical treatment processes
What compounds can be removed from wastewater?
How can Nature assist or react?
Treatment results for small and large
water utilities
More than 2,000 persons
Less than 2,000 persons
J-O Drangert, Linköping University, Sweden
B: Physical processes
Possible combinations of physical processes
Jan-Olof Drangert, Linköping university, Sweden
screening forced micro- filtration
filtrationflotation and sedimentation
Screening of debris and other solid items
Solids trapped by a screen in a city wastewater treatment plant
Organics from kitchen pipe sorted out in a plastic screen
Jan-Olof Drangert, Linköping university, Sweden
Flotation and sedimentation processes
Inlet ofwastewater
Baffels
Outlet of treated water
Inspection hole
Floating grease, particles, organisms
Jan-Olof Drangert, Linköping university, Sweden
Sludge built up
Filtration – mainly by gravity
Saturated flow of wastewaterPartially unsaturated flowJan-Olof Drangert, Linköping university, Sweden
Forced micro-filtration
Manufactured porous material
Direction of filtered water flow
Appliedpressure
Jan-Olof Drangert, Linköping university, Sweden
C: Chemical processes
Adsorption of charged particles
G. Jacks, Royal Institute of Technology, Stockholm
OHH2PO4- + Fe OH
OH H2PO4- + Al OH
Adsorption of phosphateon ferric hydroxide
Adsorption of phosphate on aluminium hydroxide particles
The three important kinds of charged soil particles are:
1. Organic matter
RCOOH < > RCOO- + H+
(a negative pH-dependent charge)R is phenolic ring derived from lignite in residues of plants
2. Clay mineralsClay 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 <
> Fe(OH)2-
+ H+
(a pH-dependent positive charge)
R-COO
- Pb
2+
R-COO-
Organic ”overcoat” on a soil mineral
- -
K+ K
+ Mg
2+ -
- -
Cu 2+
OH
Fe(III) + HAsO4
-
OH
Adsorption of charged particles to soil medium
G Jacks, Royal Institute of Technology, Stockholm
Mineral grain
Adsorption of chemical compounds differ
Copper (Cu) and Zink (Zn) are positively charged, and adsorb easily on organic matter and clays when the pH > 7
Arsenic (As) is negatively charged and adsorbs easily on ferric hydroxides when pH < 7 G Jacks, Royal Institute of Technology, Stockholm
• 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
Precipitation and flocculation
+ -
-+
+-
- ++
Source: Ubomba-Jaswa et al. 2009
http://www.sodis.ch/Text2002/T-TheMethod.htm
UV-radiation by sunlight
Inactivation of micro-organisms by UVA-radiation and increased temperature
More diffuse stratification
Strong algal stratification
K Tonderski, Linköping University Sweden Courtesy of Duncan Mara, University of Leeds, UK
Vertical view of the pond
Shallow ponds with a dense population of algae
Ozonation and chlorination
D: Biological processes
Karin Tonderski, Linköping university, Sweden
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:
+ oxygenUnsaturated soil profile Aerobic
bacteria
Jan-Olof Drangert,
Linköping university, Sweden
Organic matter
Biological processes - without air
Many microorganisms can survive in environments with no oxygen and they use other compounds for their survival:
+ e.g. nitrate, sulphate or iron ions (Fe 3+ )
Organic matter in waste-water
CO2 + e.g. N2, S2-, Fe2+
Saturated soil profile with little or no oxygen
Anaerobic micro-organisms
Jan-Olof Drangert,
Linköping university, Sweden
Microorganisms attached to surfaces are more stable than those suspended in water
Grain particle
Jan-Olof Drangert, Linköping university, Sweden
O2 H2O (oxygenisation)
NO3- N2, N2O (denitrification)
MnO2 Mn2+
Fe(OH)3 Fe2+
SO42- H2S (sulphate-reduction)
CO2 CH4 (methanogenesis)
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
Gunnar Jacks, Royal Institute of Technology, Stockholm
“Redox-ladder”
Decrease in oxygen
Gunnar Jacks, Royal Institute of Technology, Stockholm
Changes in concentrations of electron acceptors when organic matter (TOC) decomposes
What happens in the root zone?
O 2, sugars, proteins,
etc
Jan-Olof Drangert, Linköping university, Sweden
Water, nutrients, heavy metals, gases (e.g. CO2)
Organic matter, O2, NO3
- , SO4
2-, CO2 etc
Predation on microorganisms stimulates decomposition
Courtesy of Frida Lögdberg, Linköping university
Soil organisms vary tremendously in size and numbers
Modified from Sylvia, D. et al. 2004. Principles and applications of soil microbiology
A teaspoon soil ~ one gram
Microbial group
Example Size (µm)
Numbers (per gram soil)
Biomass (g wet mass per m2 soil)
Bacteria Pseudomonas 0.5 – 1.5 108 - 109 30 – 300
Fungi Mucor 8 (hyphae diameter)
105 – 106 50 - 500
Protozoa Euglena 15 * 50 103 - 105 0.5 – 20
Nematodes Pratylenchus 1000 10 – 102 0.1 – 10
Earthworms Lumbricus 100 000 1 - 100
Organic matter is decomposed most efficiently in the top soil
Million organisms per gram soil
106
106
De
pth
in m
ete
rAnaerobic bacteria
Aerobic bacteria
0.5 m
Courtesy of G. Jacks, Royal Institute of Technology, Stockholm
Soil surface
0