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EXPERIMENTAL CONSTRUCTED WETLAND

THE CASE OF GALLIKOS RIVER, GREECE

 

Introduction

A prototype experimental treatment wetland was constructed in 1996, near Gallikos River in Thessaloniki, Greece (Figure 1). The project was sponsored by the General Secretariat for Research and Technology through the Operational Program for Research and Development of the EU. The wetland operates since April 1997 and is used for the secondary treatment of 100m3 municipal wastewaters per day.

The objectives of this project were:

The evaluation of a constructed wetland, planted with Typha latifolia L. and Phragmites australis L., to treat municipal wastewater.

To study the effect of temperature on the performance of the system.

To evaluate the ability of the wetland to reduce the concentration of microbial pollution indicator organisms.

 

Site location

The constructed wetland is situated on a site of 3.5 ha, on clay loam soil of high permeability and with 2% gradient. It consists of the following departments (Figure2, 3):

Surface flow constructed wetland  in Thessaloniki, Greece

Four Surface Flow (SF) beds in parallel, with dimensions of 40x13.8x1 m each. Two of them were filled to 60 cm depth with clay loam and the other two with sandy loam. The remaining depth of 40 cm was left to facilitate the water flow and the deposition of transferred material. At all four beds, the wetland macrophyte Typha latifolia L. was transplanted from the neighbouring region, at distances 0.8 m between lines and 0.6 m along the lines.

These beds were constructed to retain most of the soil particles, to prevent the reduction of the soil porosity by clogging at the Subsurface flow beds, and to reduce influent BOD.

A stabilization pond (SP) with dimensions of 26.2x20.8x2.1 m, which is characterized as aerobic-anaerobic, because it consists of three layers of different biological activity (surface aerobic, transitional aerobic-anaerobic, bottom anaerobic).

This pond was constructed to reduce the concentration of N through the denitrification process.

Two SubSurface Flow (SSF) beds in parallel, with dimensions of 32.4x19.2x1.0 each. These beds were filled with soil to 10 cm depth, then one bed with limestone gravel of 4-5 cm diameter (0.5 m depth) and the other one with limestone gravel of 2.5-3 cm diameter (0.5 m depth). Phragmites australis L. (common reed) was transplanted at both beds, at distances 0.7 m between the lines and 0.5m along the lines.

These beds were constructed at the end of the system in order to achieve reduction of P and final purification of water.

Sub-surface flow constructed wetland  in Thessaloniki, Greece

Side slopes of all the beds and the stabilization pond are 1:15. Phragmites and Typha, planted in the wetland, are commonly found species and are capable of adjusting to a wide range of environmental conditions.

Due to high soil permeability of the area, all wetland beds as well as SP, were sealed with an HDPE liner.

 

SITE LOCATION (Gallikos river, Greece) - CLICK TO ENLARGE

Figure 1. Map of the project area

 

Figure 2  (click to enlarge)

Figure 3  (click to enlarge)

Figure 2. Schematic representation of the constructed wetland

Figure 3. Aerial photo of the constructed wetland

 

The hydraulic retention time in each compartment was 3, 7 and 4 days for SF beds, SP and SSF beds respectively.

Water samples were taken every two weeks from the inflow and outflow of each wetland compartment for a period of 18 months. Water analysis included BOD5, COD, NH3-N, NO3-N, TSS, total Coliforms, and feacal Coliforms measurements.

Results

BOD5, COD, TSS, NH4-N, NO3-N

Mean inflow concentrations of measured parameters during the first 16 months of the wetland operation are shown in Figure 4. It has to be noted that the mean BOD inflow concentration was 145 mg/l and exceeded the value of 120 mg/l for which the wetland was designed to operate.

Figure 4  (click to enlarge)

Figure 4. Mean inflow concentrations

 

Mean outflow concentrations, are shown in Figure 5. Solid black horizontal lines in Figure 5, represent the adopted by legislation limits for the discharge of treated wastewater.

Figure 5  (click to enlarge)

Figure 5. Outflow concentrations

 

Table 1, presents in summary, the mean inflow and outflow concentrations, as well as percent reduction of measured parameters.

Table 1. Results of different parameters studied in the constructed wetland for municipal wastewater treatment

Parameters

Mean inflow conc.

Mean outflow conc.

% reduction

BOD5 mg/L

145

25

82

TSS mg/L

120

55

54

NH3-N mg/L

60

38

33

NO3-N mg/L

1-2

1

50

COD mg/L

260-490

135

66

 

Climatic factors such as temperature, found to affect the ability of the wetland to reduce both organic load (measured as BOD) and NH3-N. More specifically, BOD percent reduction was ranged between 50% at low temperatures (4 OC), and 95 % at temperatures between 22 and 24 OC (green line in Figure 6). The correlation between BOD percent reduction (y) and temperature (x), is described by the following polynomial equation:

y = -0,01 x3 +0,3627 x2 -1,0676 x + 50,562 (R2=0.705, p=0.05)

Figure 6  (click to enlarge)

Figure 6. Percent of BOD removal as a means of temperature (blue line refers to the percent reduction in surface flow beds, red line to both surface flow beds and stabilization pond, and green line to the whole wetland system, e.g. surface flow beds, stabilization pond, and subsurface flow beds).

 

NH3-N percent reduction was ranged between 30% (temperatures between 4 and 10 OC), and 85% (temp between 22-24 oC). The green line in Figure 7 presents N-NH3 percent reduction in the wetland vs. temperature. The equation describing the corellatioin between N-NH3 percent reduction (y) and temperature (x) is the following:

y = - 0,0209 x3 +0,9266 x2 - 8,2579 x + 38,825 (R2=0.938, p=0.05)

 

Figure 7  (click to enlarge)

Figure 7. N-NH3 percent reduction in the constructed wetland vs. temperature

 

Total and Feacal coliforms

Mean inflow Total coliforms concentrations, as well as outflow concentration at each compartment (Surface flow beds, stabilization pond, Subsurface flow beds), are presented in Figure 8.

Figure 8  (click to enlarge)

Figure 8. Total coliforms concentrations in each wetland compartment

 

Total coliforms percent reduction ranged between 88 and 99% (Figure 9), with highest values measured during spring (97,05 %), summer (99,11 %), and autumn (96,83 %), and being statistically different from lowest values that were observed during winter (88,66%). Similar were the results for the percent reduction of Feacal coliforms (Figure 10).

 

Figure 9  (click to enlarge)
Figure 9. Seasonal percent reduction of total coliforms in the constructed wetland

 

Figure 10  (click to enlarge)
Figure 10. The seasonally reduction percent of feacal coliforms

 

Solar radiation found to play a very important role in the reduction of coliforms. The correlation between Total coliforms percent reduction (y) and solar radiation (x) is described by the following equation:

y = 43,345 + 6,4297 * ln x (R2=0.89, p=0.05)

 

Figure 11  (click to enlarge)

Figure 11. The average monthly solar radiation vs. the percent of reduction o total coliforms in the wetland

 

Suggested literature

Broadbent, P., K.F. Baker, and Y. Waterworth. 1971. Bacteria andactinomycetes antagonistic to fungal root pathogens in Australian soils. Aust. J. Biol. Sci. 24:925-944.

Ford T.E. (ed.) 1993. Aquatic Microbiology: An ecological approach. Blackwell Scientific Publications, Boston.

Hammer D.A. (ed.). 1989. Constructed Wetlands for Wastewater Treatment, Municipal, Industrial, and Agricultural. Lewis Publishers Inc., Chelsea, Michigan.

Kadlec, R.H. and R.L. Knight. 1996. Treatment wetlands. Lewis Publishers, CRC Press, Boca Raton, Florida.

Karathanasis, A. 1995. Constructed wetlands. An Alternative for Wastewater Treatment. Department of Agronomy, University of Kentucky.

Reddy K. and W. Smith. (eds.) 1987. Aquatic Plants for Water Treatment and Resource Recovery. Magnolia Publishing Inc., Orlando, Florida.

Reed, S. C., R. Crites and E. Middle brooks. 1995. Natural systems for waste management and treatment. McGraw-Hill, Inc. United States of America.

Seidel, K. 1976. Macrophytes and water purification. Pages 109-120 in J. Tourbier and R.W. Pierson, editors. Biological Control of Water Pollution. University of Pennsylvania Press, Philadelphia, PA

Zalidis G., Sotiria Katsavouni, V. Takavakoglou, and A. Gerakis. 1998. Reduction of nutrients and organics using constructed wetlands. pp.373-382. In: Proccedings of the 7th Hellinic Soil Science Society Conference. May 27-30 1998, Agrinio, Greece (in Greek, English abstract).

Zdragas A., G. C. Zalidis, V. Takavakoglou, K. Eskridge, Sotiria Katsavouni, A. Panoras and E.T. Anastasiadis. 2002. The effect of Environmental conditions on the ability of a constructed wetland to disinfect municipal wastewaters. Environmental Management 29:510-515.

 

 

 

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