4.6 Physical, biological and chemical treatment

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22 Φεβ 2014 (πριν από 3 χρόνια και 1 μήνα)

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Physical

~


screening and filtration, sedimentation, flotation


C
hemical

~


coagultation/flocculation,

adsorption, precipitation, UV
-
radiation


Biological

~


microbial decomposition
,

predation, uptake in plants

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

filtration

flotation 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 of

wastewater

Baffels


Outlet of
treated water

Inspection
hole

Floating grease,
particles, organisms

Jan
-
Olof Drangert, Linköping university, Sweden












Filtration


mainly by gravity

Saturated flow of wastewater

Partially unsaturated flow

Jan
-
Olof Drangert, Linköping university, Sweden

Forced micro
-
filtration


Manufactured
porous material

Direction of filtered water flow


Applied

pressure

Jan
-
Olof Drangert, Linköping university, Sweden

C: Chemical processes


Adsorption of charged particles

G. Jacks, Royal Institute of Technology, Stockholm


OH

H
2
PO
4
-

+ Fe


OH


OH


H
2
PO
4
-

+ Al


OH

Adsorption
of phosphate

on 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 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

< > 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) + HAsO
4
-


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 CO
2

+ water:

+ oxygen

Unsaturated
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

CO
2

+ e.g.
N
2
, S
2
-
, Fe
2+

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


O
2

H
2
O
(oxygenisation)


NO
3
-

N
2
, N
2
O (denitrification)


MnO
2

Mn
2+


Fe(OH)
3

Fe
2+


SO
4
2
-

H
2
S (sulphate
-
reduction)


CO
2

CH
4

(methanogenesis)

When microorganisms descend the redox
-
ladder they first use
O
2

as an electron acceptor, then nitrate
NO
3
,

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




Gunnar Jacks, Royal Institu
te 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. CO
2
)


Organic
matter, O
2
,
NO
3
-

, SO
4
2
-
,
CO
2

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 m
2
soil)

Bacteria

P
seudomonas

0.5

1.
5

10
8

-
10
9

30

300

Fungi

Mucor

8 (hyphae
diameter)


10
5


10
6

50
-
500

P
rotozoa

Euglena

15 * 50

10
3

-
10
5

0.5


20

N
ematodes

Pratylenchus

1000

10

1
0
2

0.1

10

Earthworms

Lumbricus

100 000


1
-
100


Organic matter is decomposed most
efficiently in the top soil


Million organisms per gram soil

10
6

10
6

Depth in meter

Anaerobic bacteria

Aerobic bacteria

0.5 m

Courtesy of G. Jacks, Royal Institute of Technology, Stockholm

Soil
surface

0