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Design optimization of artificial wetlands for the treatment of municipal wastewater using pilot plants

Mavrogiannis Dimitrios

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Summary

Constructed wetlands (CW) have been recognized as a sustainable, economical and efficient option for municipal wastewater management. In the context of this thesis, the optimization of the design parameters of CW for the treatment of municipal wastewater from the wastewater treatment of Chania was studied on a pilot scale. Three constructed wetlands of vertical sub-surface flow (VF CWs) were set up in the outdoor area of the greenhouse of the Faculty of Chemical and Environmental Engineering of the Technical University of Crete. In unit G (Gravel), gravel was used as a substrate, while in units P (Plastic) and C (Control), recycled HDPE plastic was used. Units G and P were planted with common reed Phragmites Australis, while C remained unvegetated.The systems became operational in July and the experiment lasted until December. The systems were watered with municipal wastewater, which came immediately after the primary sedimentation stage and for the first two months the feed was daily with a volume of 1.5 L. In September, the feeding was done every 3 days, leaving 2 days of rest for the systems, while the volume was increased to 5 L. From October to December, the watering mode remained the same, every 3 days, but the volume was increased to 8 L. The weekly experimental analyses carried out were on the inflow and outflow of the systems, for the characterization of pollutant removal efficiency.More specifically, the P unit showed the highest mean removals of BOD5, COD, TN, NH4-N (82.16 ± 13.90 %, 82.26 ± 7.39 %, 74.89 ± 16.44 %, 76. 37 ± 17. 49 %), while significant mean removals were also observed in TSS (83.19 ± 15. 30 %). Unit G had higher mean removals of TP, PO43--P and TSS (46.91 ± 14.43 %, 27.70 ± 19.85 %, 86.14 ± 16.13 %), and showed significant mean removals of BOD5, COD, TN and NH4-N (78.71 ± 13.36 %, 77.84 ± 15.09 %, 69.09 ± 18.45 %, 68.00 ± 20.09 %). Unit C, despite the absence of vegetation, showed the highest performance in mean TOC removal (62.61 ± 16.46 %), and showed significant COD and TSS removal (75.36 ± 10.82 %, 74.11 ± 19.12 %). Finally, the Electrical Conductivity of G, P and C were 1481 ± 487 μS/cm, 1553 ± 542 μS/cm, 2038 ± 1446 μS/cm, while the pH of all three units appeared slightly alkaline.

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