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
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Hisrorical change in capacity of MWTP in total p.e.
Municipal wastewater treatment plants (MWTP) in Greece Today there are about 300 Today there are about 300 MWTPMWTP in operation in operation They serve about 65% of the country’s permanent They serve about 65% of the country’s permanent
populationpopulation It is estimated that 1,800 small MWTP will be needed, It is estimated that 1,800 small MWTP will be needed,
with most competent natural treatment systems like WSP with most competent natural treatment systems like WSP and constructed wetlandsand constructed wetlands
The remaining 14% of the population is in small villages The remaining 14% of the population is in small villages and remote areas and thus on site sanitation technologies and remote areas and thus on site sanitation technologies should be used for them. should be used for them.
Municipal wastewater treatment plants (MWTP) in Greece
The majority of The majority of MWTPMWTP employ employ the activated the activated sludge processessludge processes
From the small plants, oneFrom the small plants, one out of three had been out of three had been incomplete or had failed, while from those in incomplete or had failed, while from those in operation, one out of four was operating below operation, one out of four was operating below the standards set (Tsagarakis the standards set (Tsagarakis et al.et al., 2000), 2000)
WSP IN GREECE
WSP are not so popular in Greece, despite the locally favourable WSP are not so popular in Greece, despite the locally favourable climatic conditions. climatic conditions.
The presented data are not readily available and originate from The presented data are not readily available and originate from on-site visits.on-site visits.
Only Only 13 13 WWaste aste SStabilization tabilization PPonds (WSP) have been constructed onds (WSP) have been constructed -only a few are in operation-only a few are in operation
In a cost analysis that compared different wastewater treatment In a cost analysis that compared different wastewater treatment systems, it was concluded that when land is cheap (this is the case systems, it was concluded that when land is cheap (this is the case for many rural areas), WSP is the cheapest among other for many rural areas), WSP is the cheapest among other conventional and natural systems (Tsagarakis conventional and natural systems (Tsagarakis et al.et al., 2003)., 2003).
Existing WSP systems in Greece
City Operation p.e.1 Status Ponds2 Comments Kokkinochoma 1 1995 1000 Operation FMMRF Kokkinochoma 2 1998 1000 Operation FMMRF Platanotopos 1000 Failed FMMRF Stopped the construction Antiphilipi 1000 FMM Designed/not constructed Kariani 1000 Failed FMM Stopped the construction Prinos 2000 FMMM Designed/not constructed Messoropi 800 Failed FMMRF Stopped the construction Maries 1000 Failed FM Stopped the construction Ano Poroia 1992 2000 Operation FMMRF Mavrolofos 500 Operation FM Messorachi 1991 500 Operation FMM Pentapoli 1989 3000 Failed FMM Failed due to damage of the inlet pipe Sitochori 1982 1000 Operation FMM The first system constructed Vamvakofito 1988 1000 Operation FMM Haropo 1994 2300 Operation FMM Simi 10000 2xAFMM Designed/not constructed
WSP at Sindos (Northern Greece)
A
F
F
F
M
M
M
M
M
M
R
Line 1
Line 2
Line 3
A: Anaerobic pondF: Faculatative pondM: Maturation PondR: Reservoir
Influent
Influent
WSP system at Sindos
WSP system at Sindos The only well designed and maintained pilot research project, adjacent to the MWTP of 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 Thessaloniki, at the area of Sindos. This is the only project where research results have been published on WSP in Greece been published on WSP in Greece
Raw sewage from the conventional wastewater treatment plant of Thessaloniki, after 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. 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 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.(Q = 90 m³/d) Line 2.
Line 1Line 1,, after the anaerobic pond consisted of a facultative pond and two maturation after the anaerobic pond consisted of a facultative pond and two maturation ponds. ponds.
Line 2 layout was similar to line A, but with a recirculation of 180 m³/d from the last 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. maturation pond to the facultative pond.
Line 3 received primary treated effluent (Q = 50 m³/d) from the nearby treatment plant 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 pondsand consisted again of a facultative pond and two maturation ponds (Figure 1) (Figure 1). Treated . Treated effluent from the three lines was stored into a reservoir and then used for irrigation of 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 edible and non-edible crops, after algae being reduced by an intermittent slow sand filter of 100 m² . filter of 100 m² .
WSP at Sindos (Northern Greece)
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
The performance of the WSP at Sindos .Characteristics of the wastewater at different treatment stages, for air temperatures above
10°C
WSP system of Kokkinochoma
WSP system of Kokkinochoma
WSP system of Vamvakofito
Primary falcutativepondpond
Maturationpond
Maturationfilter
RockEphemeralriver
Pond layout for the WSP system of Kokkinochoma
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
Designed, final constructed, and the proposed dimensions of the WSP of Kokkinochoma WSP
WSP system of Kokkinochoma
Influent Effluent Constituent Unit Average STD Average STD
Removal rates (%)
BOD5 mg/L 420 80.2 21.4 27.82 95 COD mg/L 635 173.1 145.7 58.72 77 SS mg/L 239 79.3 45 60.99 91 N-NH3 mg/L 101 22.0 TN 36.0 8.80 68 TP mg/L 51 19.2 26.4 5.65 49 DO mg/L 3.98 0.6 5.1 3.14 Cl- mg/L 101.4 19.6 92 17.93 pH 8.05 0.3 7.8 0.18 EC μs/cm 1556 157.6 1279 110 Hardness mg CaCO3/L 346 71
Qualitative data for the WSP of Kokkinochoma
Primary aerated pondV=20,000 m³
Sludgestoragelagoon
Sendimentationarea
Sludge recirculation
Secondary aerated pondV=16,000
Maturation pondV=16,000
5 m
0.5 m
Air diffuser
Schematic cutInfluent
Floating element
Effluent
Layout of the aerated pond system (SEBATH, XANTHI, GREECE)
AERATED POND ( SEVATH-TOMATO FACTORY )
AERATED POND ( SEVATH-TOMATO FACTORY)
Year 1985 1986 1987 1988 1989 1990
Units In Out In Out In Out In Out 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
Layout of the aerated pond system (SEBATH)
PROBLEMS
Design problems Construction deficiencies Operation deficiencies Effluent management Health and safety
Design problems Population projection was not proper as the intensive urbanization Population projection was not proper as the intensive urbanization
of the last two decades had not been foreseen.In most plants of the last two decades had not been foreseen.In most plants (which serve rural communities), decreasing figures followed the (which serve rural communities), decreasing figures followed the increasing population of the 60s, 70s and 80s. Therefore, an over increasing population of the 60s, 70s and 80s. Therefore, an over design has taken placedesign has taken place
Inappropriate values were considered, for pollutants. For example Inappropriate values were considered, for pollutants. For example at Kokkinochoma an influent BOD5 concentration of 200 mg/L at Kokkinochoma an influent BOD5 concentration of 200 mg/L was considered, while the real value was in average more than was considered, while the real value was in average more than doubledouble
In many cases the final layout of the plant was different from the In many cases the final layout of the plant was different from the one initially designed (eg. different number and size of the ponds, one initially designed (eg. different number and size of the ponds, and layout of the system) . and layout of the system) .
Construction Deficiencies
Missing inlet and outlet structuresMissing inlet and outlet structures Inlet in the facultative ponds is very close to the Inlet in the facultative ponds is very close to the
embankments and above surface, resulting to embankments and above surface, resulting to locally sludge deposition and consequent odors. locally sludge deposition and consequent odors. This should be made below the water surface.This should be made below the water surface.
There is no discharge overflow at the last ponds, There is no discharge overflow at the last ponds, resulting in no possibility of water level balance. resulting in no possibility of water level balance.
Operation deficiencies
Effluent of the last pond is pumped for irrigation during Effluent of the last pond is pumped for irrigation during the summer. When water is over pumped and pond is the summer. When water is over pumped and pond is emptied, this makes a lot of plants to grow at the bottom emptied, this makes a lot of plants to grow at the bottom of the pondsof the ponds
These plants disturb normal flow in the pond and These plants disturb normal flow in the pond and encourage the breeding of mosquitoes and other insects.encourage the breeding of mosquitoes and other insects.
Due to low velocities in pipes (much lower than Due to low velocities in pipes (much lower than designed) within the installation, settling solids have designed) within the installation, settling solids have minimized the active cross section of these pipes minimized the active cross section of these pipes
Effluent management problems The current practice is that the farmers pump water from The current practice is that the farmers pump water from
the last maturation pond for irrigationthe last maturation pond for irrigation This results to the complete evacuation of the last pond. This results to the complete evacuation of the last pond.
In the case of Kokkinochoma, they even used the effluent In the case of Kokkinochoma, they even used the effluent from the first maturation pond to irrigate corn, as we from the first maturation pond to irrigate corn, as we noticed that the water level was 30 cm below the outletnoticed that the water level was 30 cm below the outlet
In this system, it took up to the end of February to fill In this system, it took up to the end of February to fill again all pondsagain all ponds
Similar practices were reported to other WSP systems, Similar practices were reported to other WSP systems, like Messorahi and Sitochori, were the effluent was used like Messorahi and Sitochori, were the effluent was used to irrigate tobacco plants.to irrigate tobacco plants.
Health and safety Some of the installations are fenced but entrance is not secured, Some of the installations are fenced but entrance is not secured,
making access possible to everyone, including childrenmaking access possible to everyone, including children There are no notices to warn about the contents of the pondsThere are no notices to warn about the contents of the ponds Major health risk comes from the unrestricted irrigation of corn Major health risk comes from the unrestricted irrigation of corn
and tobacco crops, from farmers without any information on the and tobacco crops, from farmers without any information on the risks that come from the use of partially treated wastewaters.risks that come from the use of partially treated wastewaters.
It is estimated that only for the Kokkinochoma system over 7,500 It is estimated that only for the Kokkinochoma system over 7,500 m³ of partially treated wastewater are used each year for irrigation.m³ of partially treated wastewater are used each year for irrigation.
In Messorahi village farmers that use the effluent for irrigation In Messorahi village farmers that use the effluent for irrigation have reported skin bruises.have reported skin bruises.
SUGGESTED IMPROVEMENTS
The construction of inlet structure using a The construction of inlet structure using a number of pipes , discharging wastewater at number of pipes , discharging wastewater at different locations of the pond below the surface different locations of the pond below the surface of the water of the water
The construction of an outlet structure with the The construction of an outlet structure with the possibility of water level control and an overflow possibility of water level control and an overflow with a weir for the surface debris with a weir for the surface debris
SUGGESTED IMPROVEMENTS
Proposed inlet Proposed inlet structure and structure and depth to depth to avoid bottom avoid bottom corrosion and corrosion and sludge build sludge build upup 1 .20m
1 .60m1.70m
1:3
0 .0m0.20m
- 0 .10m
0.70m
Ö0.40m Ö0 .30m
1m
1.5m1.9m
Sludge
Top water level
Manually adjustable weir
Surface debris
Top water level
weir
Construction deficiencies
Outlet pipe and outlet structure with water level adjustments
Overflow with a weir for surface debris
CONCLUSIONS - RECOMMENDATIONS WSP systems may well give suitable effluent to comply with EU WSP systems may well give suitable effluent to comply with EU
and national standards. Such systems have not been used widely in and national standards. Such systems have not been used widely in Greece, because those initially constructed, were either improperly Greece, because those initially constructed, were either improperly designed or neglected to operate without maintenancedesigned or neglected to operate without maintenance
There a few WSP systems in Greece which appear to provide a There a few WSP systems in Greece which appear to provide a reasonable effluent quality that can be discharged into the reasonable effluent quality that can be discharged into the environment without any damage. environment without any damage.
Waste stabilization ponds (WSP) should always be considered as a Waste stabilization ponds (WSP) should always be considered as a competitive alternative. When land is of low cost, they constitute competitive alternative. When land is of low cost, they constitute the most cost-effective technology.the most cost-effective technology.
WSP systems required low operation and maintenance effort WSP systems required low operation and maintenance effort compared to other systems. This however should not be translated compared to other systems. This however should not be translated to no need for their maintenance. An appropriate continuous to no need for their maintenance. An appropriate continuous monitoring of qualitative and quantitative data should be monitoring of qualitative and quantitative data should be undertaken to properly evaluate the performance of these systems.undertaken to properly evaluate the performance of these systems.
