WASTE STABILIZATION PONDS IN GREECE:
CASE STUDIES AND PERSPECTIVES
N. Kotsovinos
Democritus Univ. of Thrace, Dept. of Civil Engineering, Xanthi Greece
K.P. Tsagarakis
Univ. of Crete, Dept. of Economics, Greece &
National Agricultural Research Foundation, Institute of Iraklio
K. Tsakiris
Municipal Enterprise for Water Supply and Sewerage of Kavala, Greece
Presentation Outline

WASTEWATER TREATMENT IN GREECE

WSP IN GREECE

PROBLEMS AND SUGGESTED IMPROVEMENTS

CONCLUSIONS - RECOMMENDATIONS
Legend
Suspended growth
Attached growth
Natural systems
Location of the MWTP and system they employ
8000000
7000000
5000000
4000000
3000000
2000000
1000000
Year
Hisrorical change in capacity of MWTP in total p.e.
2005
2003
2001
1999
1997
1995
1993
1991
1989
1987
1985
0
1983
Total capacity p.e.
6000000
Municipal wastewater treatment plants (MWTP)
in Greece




Today there are about 300 MWTP in operation
They serve about 65% of the country’s permanent
population
It is estimated that 1,800 small MWTP will be needed,
with most competent natural treatment systems like WSP
and constructed wetlands
The remaining 14% of the population is in small villages
and remote areas and thus on site sanitation technologies
should be used for them.
Municipal wastewater treatment plants (MWTP)
in Greece
The majority of MWTP employ the activated
sludge processes
 From the small plants, one out of three had been
incomplete or had failed, while from those in
operation, one out of four was operating below
the standards set (Tsagarakis et al., 2000)

WSP IN GREECE




WSP are not so popular in Greece, despite the locally favourable
climatic conditions.
The presented data are not readily available and originate from onsite visits.
Only 13 Waste Stabilization Ponds (WSP) have been constructed
-only a few are in operation
In a cost analysis that compared different wastewater treatment
systems, it was concluded that when land is cheap (this is the case
for many rural areas), WSP is the cheapest among other
conventional and natural systems (Tsagarakis et al., 2003).
Existing WSP systems in Greece
City
Kokkinochoma 1
Kokkinochoma 2
Platanotopos
Antiphilipi
Kariani
Prinos
Messoropi
Maries
Ano Poroia
Mavrolofos
Messorachi
Pentapoli
Sitochori
Vamvakofito
Haropo
Simi
Operation
1995
1998
1992
1991
1989
1982
1988
1994
p.e.1
1000
1000
1000
1000
1000
2000
800
1000
2000
500
500
3000
1000
1000
2300
10000
Status
Operation
Operation
Failed
Failed
Failed
Failed
Operation
Operation
Operation
Failed
Operation
Operation
Operation
Ponds2
FMMRF
FMMRF
FMMRF
FMM
FMM
FMMM
FMMRF
FM
FMMRF
FM
FMM
FMM
FMM
FMM
FMM
2xAFMM
Comments
Stopped the construction
Designed/not constructed
Stopped the construction
Designed/not constructed
Stopped the construction
Stopped the construction
Failed due to damage of the inlet pipe
The first system constructed
Designed/not constructed
WSP at Sindos (Northern Greece)
A: Anaerobic pond
F: Faculatative pond
M: Maturation Pond
R: Reservoir
R
Influent
A
M
F
M
M
Line 1
F
M
M
Line 2
F
Influent
M
Line 3
WSP system at Sindos
WSP system at Sindos





The only well designed and maintained pilot research project, adjacent to the
MWTP of Thessaloniki, at the area of Sindos. This is the only project where
research results have been published on WSP in Greece
Raw sewage from the conventional wastewater treatment plant of Thessaloniki,
after screening, was pumped into a covered deep anaerobic pond at a rate of Q =
120 m³/d. Approximately 1/4 of the discharge (Q = 30 m³/d) was feeding Line 1 and
the rest 3/4 (Q = 90 m³/d) Line 2.
Line 1, after the anaerobic pond consisted of a facultative pond and two maturation
ponds.
Line 2 layout was similar to line A, but with a recirculation of 180 m³/d from the
last maturation pond to the facultative pond.
Line 3 received primary treated effluent (Q = 50 m³/d) from the nearby treatment
plant and consisted again of a facultative pond and two maturation ponds (Figure
1). Treated effluent from the three lines was stored into a reservoir and then used for
irrigation of edible and non-edible crops, after algae being reduced by an
intermittent slow sand filter of 100 m² .
WSP at Sindos (Northern Greece)
The performance of the WSP at Sindos .Characteristics of the
wastewater at different treatment stages, for air temperatures above
10°C
Sampling location
BOD5
mg/L
COD
mg/L
SS
mg/L
TC
/100 ml
FC
/100 ml
Anaerobic pond influent (raw)
387
860
565
1.5x107
1.4x107
Anaerobic pond effluent
213
403
161
5x106
4x106
Line A effluent (filtered)
8
133
70
8x10²
4x10²
Line B effluent (filtered)
14
104
95
4.7x10³
3.4x10³
Line C inflow (primary treated)
134
290
119
Line C effluent (filtered)
11
118
93
1.2x10³
5x10²
WSP system of Kokkinochoma
WSP system of Kokkinochoma
WSP system of Vamvakofito
Ephemeral
river
Rock
Maturation
filter
pond
Maturation
pond
Primary falcutative
pond
Pond layout for the WSP system of Kokkinochoma
Designed, final constructed, and the proposed dimensions of the WSP
of Kokkinochoma WSP
Units
Design
Construction
Optimum
Population equivalent
-
900
900
900
Flow rate
m³/d
135
135
135
Influent BOD5
mg/L
200
200
400
Influent SS
mg/L
250
250
250
Influent FC
/100 ml
5x106
5x106
5x106
Temperature
°C
10
10
10
Ponds
-
FMMM
FMM
FMMM
Total volume
m³
3985
5000
6085
Effluent BOD5
30
30
30
30
Effluent FC
5000
5000
5000
5000
WSP system of Kokkinochoma
Qualitative data for the WSP of Kokkinochoma
Constituent
Unit
BOD5
COD
SS
N-NH3
TN
TP
DO
ClpH
EC
Hardness
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
mg/L
μs/cm
mg CaCO3/L
Influent
Average
420
635
239
101
51
3.98
101.4
8.05
1556
STD
80.2
173.1
79.3
22.0
19.2
0.6
19.6
0.3
157.6
Effluent
Average
21.4
145.7
45
STD
27.82
58.72
60.99
36.0
26.4
5.1
92
7.8
1279
346
8.80
5.65
3.14
17.93
0.18
110
71
Removal rates
(%)
95
77
91
68
49
Layout of the aerated pond system (SEBATH,
XANTHI, GREECE)
Sludge
Influent
recirculation
Sludge
storage
lagoon
Schematic cut
Floating element
Air
diffuser
5m
0.5 m
Primary
aerated pond
V=20,000 m³
Secondary aerated pond
V=16,000
Sendimentation
area
Maturation pond
V=16,000
Effluent
AERATED POND ( SEVATH-TOMATO FACTORY )
AERATED POND ( SEVATH-TOMATO FACTORY)
Layout of the aerated pond system
(SEBATH)
Year
1985
1986
Out
In
1987
Out
In
1988
Out
In
1989
Out
In
1990
Units
In
Out
In
Out
Qave
m³/d
3749
5915
9324
9756
6130
8349
Qmin
m³/d
605
1280
7675
3956
3600
6450
Qmax
m³/d
5942
8434
11548
11799
8170
11165
CODave
mg/L
940
98
525
38
357
36
73
47
502
41
338
36
CODmin
mg/L
104
60
136
17
104
22
143
19
116
27
196
22
CODmax
mg/L
1494
204
1289
64
564
56
478
90
867
90
504
62
BOD5ave
mg/L
716
40
269
10
145
10
134
15
295
19
191
8
BOD5min
mg/L
500
15
120
5
50
5
70
6
60
11
100
4
BOD5max
mg/L
1080
75
420
19
240
14
200
31
450
36
350
13
pHave
-
5.93
6.96
6.75
7.99
7.23
8.47
7.03
7.71
6.77
7.93
6.76
7.73
pHmin
-
5.25
6.78
5.60
7.33
6.85
7.87
6.70
7.20
5.90
7.20
6.50
7.40
pHmax
-
6.96
7.28
7.30
8.83
7.70
8.90
7.50
8.40
7.30
8.70
7.00
8.20
PROBLEMS

Design problems

Construction deficiencies

Operation deficiencies

Effluent management

Health and safety
Design problems



Population projection was not proper as the intensive urbanization
of the last two decades had not been foreseen.In most plants
(which serve rural communities), decreasing figures followed the
increasing population of the 60s, 70s and 80s. Therefore, an over
design has taken place
Inappropriate values were considered, for pollutants. For example
at Kokkinochoma an influent BOD5 concentration of 200 mg/L
was considered, while the real value was in average more than
double
In many cases the final layout of the plant was different from the
one initially designed (eg. different number and size of the ponds,
and layout of the system) .
Construction Deficiencies
Missing inlet and outlet structures
 Inlet in the facultative ponds is very close to the
embankments and above surface, resulting to
locally sludge deposition and consequent odors.
This should be made below the water surface.
 There is no discharge overflow at the last ponds,
resulting in no possibility of water level balance.

Operation deficiencies



Effluent of the last pond is pumped for irrigation during
the summer. When water is over pumped and pond is
emptied, this makes a lot of plants to grow at the bottom
of the ponds
These plants disturb normal flow in the pond and
encourage the breeding of mosquitoes and other insects.
Due to low velocities in pipes (much lower than
designed) within the installation, settling solids have
minimized the active cross section of these pipes
Effluent management problems




The current practice is that the farmers pump water from
the last maturation pond for irrigation
This results to the complete evacuation of the last pond.
In the case of Kokkinochoma, they even used the effluent
from the first maturation pond to irrigate corn, as we
noticed that the water level was 30 cm below the outlet
In this system, it took up to the end of February to fill
again all ponds
Similar practices were reported to other WSP systems,
like Messorahi and Sitochori, were the effluent was used
to irrigate tobacco plants.
Health and safety





Some of the installations are fenced but entrance is not secured,
making access possible to everyone, including children
There are no notices to warn about the contents of the ponds
Major health risk comes from the unrestricted irrigation of corn
and tobacco crops, from farmers without any information on the
risks that come from the use of partially treated wastewaters.
It is estimated that only for the Kokkinochoma system over 7,500
m³ of partially treated wastewater are used each year for irrigation.
In Messorahi village farmers that use the effluent for irrigation
have reported skin bruises.
SUGGESTED IMPROVEMENTS
The construction of inlet structure using a
number of pipes , discharging wastewater at
different locations of the pond below the surface
of the water
 The construction of an outlet structure with the
possibility of water level control and an overflow
with a weir for the surface debris

SUGGESTED IMPROVEMENTS
1 .9 m
1 .5 m
Proposed inlet
structure and
depth to
avoid bottom
corrosion and
sludge build
1m
up
1 .7 0m
1 .6 0m
1 .2 0m
1 :3
0 .7 0m
Ö0 .4 0m
- 0 .1 0 m
Ö0 .3 0m
0 .2 0m
0 .0 m
Construction deficiencies
Outlet pipe and outlet
structure with water level
adjustments
Top water level
Sludge
Manually adjustable weir
Top water level
Surface debris
weir
Overflow with a weir for
surface debris
CONCLUSIONS - RECOMMENDATIONS




WSP systems may well give suitable effluent to comply with EU
and national standards. Such systems have not been used widely in
Greece, because those initially constructed, were either improperly
designed or neglected to operate without maintenance
There a few WSP systems in Greece which appear to provide a
reasonable effluent quality that can be discharged into the
environment without any damage.
Waste stabilization ponds (WSP) should always be considered as a
competitive alternative. When land is of low cost, they constitute
the most cost-effective technology.
WSP systems required low operation and maintenance effort
compared to other systems. This however should not be translated to
no need for their maintenance. An appropriate continuous
monitoring of qualitative and quantitative data should be undertaken
to properly evaluate the performance of these systems.