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Biodegradation of organic pollutants in pilot-scale constructed wetlands

Vamvakia Maria

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Summary

Artificial wetlands are an ecological engineering technology that has been widely applied in recent decades as it offers a multitude of benefits and contributes to wastewater treatment. This technology is based on the use of plants, which are able to remove pollutants or convert them into less harmful compounds through a series or physical, chemical and biological processes. The use of aerated wetlands can increase pollutant removal compared to non-aerated wetlands as there is an increase rate of oxygen transfer to the water that is being treated. Finally, electrolysis in artificial wetlands takes place in order to intensify the removal of nitrogen and phosphorus from wastewater.The main aim of this thesis is to examine the removal of different organic pollutants in three artificial constructed wetlands with different conditions each, and to determine the best one (with the fastest removal).The first wetland (W1) is the control wetland, the second CW (W2) is connected with an air compressor which is connected to a nanotube so that we have aeration in the form of nanobubbles and the last one (W3) consists of three iron plates- electrodes connected to a battery to have electrolysis in the system and have two cathodes with hydrogen production and an anode with oxygen production. The plant used in all three wetlands is called Juncus acutus.In the first stage of the experiment the pollutant added to the systems was phenol in two different concentration of 100 and 200 ppm. Then toluene was added in two different concentrations of 50 and 100 ppm. The next stage was the combination of the above pollutants in order to see the removal at a concentration of 100 ppm phenol and 100 ppm toluene. Finally in the last cycle the pollutants were again combined at the same concentration (100 ppm phenol and 100 ppm toluene) with the difference that wastewater was added to each tank. The parameters of pH, ORP, DO, EC, temperature were determined daily in the units as well as the concentration of each organic pollutant was estimated by HPLC; samples were collected from the outlet and the tank of each wetland. Furthermore, the following parameters were determined: total nitrogen TN, total phosphorus TP, COD , nitrate NO3-N. Lastly, at the end of each cycle the cells from a sample of each wetland were measured with the cytometer.The results for the removal reach 100% for the different pollutants and show that the best performance exhibited the wetland with artificial aeration (W2), where the removal took place in a shorter period of time compared to the other wetlands. Immediately after is the wetland with electrolysis (W2) where its performance is quite close to the control wetland (W1). Also, when wastewater was added, the performance of W3 was ameliorated. In the second wetland removal took place on average in 9 days for 100 ppm phenol and in 10 days for the same concentration of toluene, in wetland 3 in 9 days for phenol and in 8 days for toluene and in wetland 1 in 10 days for phenol and 13 days for toluene.Finally, a COD reduction of 96% was observed for W1, 98% for W2 and 97% for W3. TSS reduction of 65% for W1, 66% for W2 and 82% for W3. TP reduction of 92% for W1, 94% for W2 and 83% for W3. NO3-N reduction at a rate of 54% for W1, 89% for W2 and 78 for W3. TN reduction at a rate of 85% for W1, 87% for W2 and 90% for W3. Therefore, the systems had satisfactory removal in terms of TSS, COD, TP, TN.

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