WASTE STABILIZATION PONDS IN GREECE: CASE STUDIES AND PERSPECTIVES

1. 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

2. Presentation Outline • WASTEWATER TREATMENT IN GREECE • WSP IN GREECE • PROBLEMS AND SUGGESTED IMPROVEMENTS • CONCLUSIONS - RECOMMENDATIONS

3. Location of the MWTP and system they employ

4. Hisrorical change in capacity of MWTP in total p.e.

5. 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.

6. 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)

7. 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 on-site 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).

8. Existing WSP systems in Greece

9. WSP at Sindos (Northern Greece) WSP system at Sindos

10. 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 .

11. WSP at Sindos (Northern Greece)

12. The performance of the WSP at Sindos .Characteristics of the wastewater at different treatment stages, for air temperatures above 10°C

13. WSP system of Kokkinochoma

14. WSP system of Kokkinochoma

15. WSP system of Vamvakofito

16. Pond layout for the WSP system of Kokkinochoma

17. Designed, final constructed, and the proposed dimensions of the WSP of Kokkinochoma WSP

18. WSP system of Kokkinochoma

19. Qualitative data for the WSP of Kokkinochoma

20. Layout of the aerated pond system(SEBATH, XANTHI, GREECE)

21. AERATED POND ( SEVATH-TOMATO FACTORY )

22. AERATED POND ( SEVATH-TOMATO FACTORY)

23. Layout of the aerated pond system (SEBATH)

24. PROBLEMS • Design problems • Construction deficiencies • Operation deficiencies • Effluent management • Health and safety

25. 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) .

26. 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.

27. 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

28. 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.

29. 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.

30. 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

31. SUGGESTED IMPROVEMENTS Proposed inlet structure and depth to avoid bottom corrosion and sludge build up

32. Construction deficiencies Outlet pipe and outlet structure with water level adjustments Overflow with a weir for surface debris

33. 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.