Wastewater treatment: Extensive (natural) and intensive (mechanical) processes

lyricalwillingMechanics

Feb 22, 2014 (3 years and 3 months ago)

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W
astewater
t
reatment: Extensive (natural) and intensive
(mechanical) processes


Prof.
Asher Brenner


Dept. of
Environmental Engineering, Faculty of Engineering Sciences,

Ben
-
Gurion University of the Negev, Be'er
-
Sheva, 84105 Israel

(
brenner@bgu.ac.il
)


Abstract


Growing problems of water scarcity and environmental pollution
are crucial challenges of the
warming, contaminating, and population
-
growing world. They require
develop
ment of

a
careful water resource management which is based on effective integration of natural water
sources, new water supplies, and
pollution prevention
. Wastewater reclamation can prevent
water pollution
, ecological damages,

and health hazards
,

on the one hand
, and contribute to
substitution of higher quality water supplies for various applications
,

on the other. While
pollution prevention and protection of human health are global necessities, the use of
reclaimed wastewater for the augmentation of natural wate
r supplies is a management issue
peculiar to arid and semi
-
arid countries due to the increasing water shortage.
Biological
treatment is the core and most important and sensitive component of wastewater treatment
processes. It is considered most economical
and environmentally
-
friendly technology for
pollution abatement since it is

based upon the degradati
on

activity of natural
microorganisms

that min
eralize
the parent contaminants.

The specific processes selected are dictated by the
characteristics of the ra
w sewage (especially the organic and nutrient content) and the
permitted destinations for the effluents (either reuse or disposal). There are two main classes
of biological processes, natural
-
extensive processes

and mechanical
-
in
tensive processes. The
natu
ral processes include phyto
-
remediation systems composed of plants (rooted or floating)
that can absorb pollutants, produce and transfer oxygen, and
thus stimulate growth of

bacteria
that can degrade organic matter and nutrients. The other type is based on

algae
-
remediation
sys
tems where microalgae and/or cyanobacteria absorb nutrients and produce
oxygen by
photosynthesis
,

which enhances growth of bacteria degrading organic matter and nutrients.
These algae
-
based processes are
commonly
termed oxidation pond
s or stabilization ponds.
Waste stabilization ponds for many years have been very common method of wastewater
treatment, especially in warm climate areas. These are simple systems th
e main advantage of
which
is the high efficient destruction of pathogens.
However, in developed countries due to
the
incomplete

purification efficiency,
the consumption of high land resources,
and the
stringent effluents standards

imposed today
,
these processes are gradually disappearing.

In
essence, the Activated Sludge system
is considered a reliable and an efficie
nt biological
treatment process
.
It is a
more complex system

that require
s

sophisticated engineering design
&

control

and

high energy
input

on
the
one hand
,

but
results in
better effluent quality
,

on the
other.

It is also considered a versatile process that can easily be
adapt
ed to meet nitrogen and
phosphorus limitations when effluents are destined for aquifer recharge, or disposal into
receiving water bodies. This process

can be applied as
a continuous flow sys
tem incorporating
a sequence of tanks or zones

each of them carrying out specific reactions. An alternative
design is the sequencing batch reactor (SBR)
whic
h
performs
all reactions in one tank with no
need of a separate secondary sedimentation and sludge
recycle. The Activated Sludge systems
are
also most suitable for further application of a tertiary treatment stage or can incorporate
internal membrane separation in place of sedimentat
ion (MBR)
.

The presentation will include
several case studies including

design principles and
mathematical modeling.