Η αξιοποίηση τεχνητών υγροβιότοπων στην επεξεργασία υδάτινων εκροών αυτοκινητοδρόμων.

Abstract

Στην παρούσα μεταπτυχιακή εργασία μελετάται η απόδοση τεσσάρων τεχνητών υγροβιότοπων για την επεξεργασία υδάτινων εκροών αυτοκινητόδρομων. Για τον σκοπό αυτό σχεδιάστηκαν και κατασκευάστηκαν, στα πλαίσια ερευνητικού προγράμματος, τέσσερεις πιλοτικού μεγέθους τεχνητοί υγροβιότοποι, που τροφοδοτούνται από μια δεξαμενή συλλογής ST χωρητικότητας περίπου 39 m3, που συλλέγει τις εκροές (Highway Run Off - HRO) ενός τμήματος συνολικής επιφάνειας 2.752,0 m2 της Εθνικής Οδού Ηρακλείου Αγίου Νικολάου στο ύψος της Χερσονήσου. Δύο από αυτούς είναι επιφανειακής ροής (Free Water Surface) και ονομάζονται (FWS 12), & (FWS 24), στους οποίους χρησιμοποιήθηκε εδαφικό υπόστρωμα. Οι άλλοι δύο είναι υποεπιφανειακής ροής (Sub Surface Flow) και ονομάζονται (SSF 12), & (SSF 24), στους οποίους χρησιμοποιήθηκαν χαλίκια διαφόρων διαστάσεων. Με βάση τα αποτελέσματα των μετρήσεων των βροχοπτώσεων και των αντίστοιχων εκροών, προσδιορίστηκαν στην συνέχεια οι βασικές παράμετροι σχεδιασμού για τους υγροβιότοπους.

Two Free Water Surface (FWS) and two Subsurface Flow (SSF) pilot size constructed wetlands together with a Storage Tank (ST) were used to treat highway runoff (HRO). The total amount of HRO treated from the four wetlands between September 2005 and August 2006 was 715 m3, collected from a highway section in the heart of the South-Central Mediterranean region, in the island of Crete, Greece, with total surface 2,752 m2. One FWS and one SSF were designed with a HRT of 12 hours named respectively FWS12 and SSF12, with each one able to treat in a controlled manner maximum 12.6 m3/day HRO. The other couple were designed with a HRT of 24 hours, named respectively FWS24 and SSF24, receiving maximum 6.3 m3/day HRO each. As a result the total HRO treating capacity of the system in 24hrs was approximately 38 m3, with the ST capacity approximately 39 m3. From the total HRO collected less than 20 % overflow through the ST into the near by stream without been treated by the wetlands. Influent and effluents were monitored for a number of physiochemical parameters including Cu, Ni, Pb and Zn. The influent had an average COD value of 103.6 mg/L, where for TSS, Total N (TN) and Total P (TP) the mean values were 208.9 mg/L, 5.62 mg/L and 4.90 mg/L, respectively. For the four metals the respective influent concentrations were 59.63 ± 72 μg/L, 146.6 ± 337 μg/L, 43.8 ± 91 μg/L and 259.1 ± 220 μg/L. The performance among the four beds was not significantly different based on ANOVA analysis (at p < 0.001) for almost all the above mentioned physiochemical parameters, suggesting that all systems performed similarly. However, based on mean effluent values, SSF24 performed better than the other wetlands, achieving in average 51.36 % removal of COD, 90.04 % removal of TSS, 58.93 % removal of TN, 72.00 % removal of NO3 and 66.63 % removal of TP. Regarding the four heavy metals the average effluent concentration of SSF24 was 18.26 ± 25 μg/L, 85.4 ± 159 μg/L, 33.9 ± 81 μg/L and 74.6 ± 56 μg/L for Cu, Ni, Pb and Zn respectively. One of the reasons for this slight advantage might be explained by the fact that SSF24 recorded the largest mean retention time of 18 hours, compared to the 16 hours of SSF12, 10 hours of FWS12 and 14 hours of FWS24.