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Optimization of pilot scale constructed wetlands with gravel and biochar for leachate treatment from Chania landfill

Asimakoulas Ioannis

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Year 2022
Type of Item Diploma Work
Bibliographic Citation Ioannis Asimakoulas, "Optimization of pilot scale constructed wetlands with gravel and biochar for leachate treatment from Chania landfill", Diploma Work, School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece, 2022
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In the context of the present thesis, the optimization of construction and operation parameters of constructed wetlands have been experimentally studied for the treatment of leachate from the landfill of Chania. The experiment concerns two horizontal subsurface flow constructed wetlands, which were placed in the outdoor area of the greenhouse of the School of Chemical and Environmental Engineering at the Technical University of Crete. Gravel was used as filling material to both units, while in one unit a layer of biochar was also placed. The units were labelled G (Gravel) and GB (Gravel & Βiochar) and were planted with the common reed Phragmites Australis.The inflow for the beds was leachate, which was collected after the flocculation stage at the leachate treatment plant of the Chania landfill. Moreover, methanol was added to both units at certain time period. The operating volume of each bed was 188.3 L and the average flow rate of volume for the units was 3.3L/day. The follow-up analyses concerned the inflow, outflow and the plant biomass of the units. More specifically, the inflow and outflows was analyzed for the determination of the following parameters: BOD5, COD, NO3--N, NO2--N, NH4+-N, PO43--P, Electrical Conductivity, pH, metals and metalloids. The analysis of the plant biomass aimed at the determination of TN (total Nitrogen), TP (total Phosphorus), metals and metalloids.The results of the mean yields for the G and GB units are as follows. For COD the efficiency in unit G was 43,3 ± 13,3% and in unit GB is 52,7 ± 15%. For NO3--N the yield of unit G was equal to 78,2 ± 16,2%, while for unit GB the yield reached 93,4 ± 5,8%. For NO2--N the yield was 94,9 ± 5,4% of the G unit and 99,0 ± 2,1% of the GB unit. Regarding NH4+-N, the unit G reached 82,3 ± 9,8% and the unit GB 87,6 ± 6,2%. Respectively, the yield for TSS was for unit G at 72,2 ± 14,8% and 66,3 ± 21,6% for GB. Moreover, the Electrical Conductivity seems to be higher than the inflow taking the values10,72 ± 6,2 and 11,59 ± 7,1 for units G and GB , while the pH is slightly alkaline. Also, BOD5 and PO43--P were almost undetectable in the outflows of the G and GB units. Finally, the results for metals and metalloids showed that there are some elements that are detected at higher concentrations, such as B, Mg, K, Ca, Cu, Fe and Zn, but they do not exceed the standard legal secondary wastewater effluent limits. Regarding plant biomass, it is found that plants basically tend to retain amounts of phosphorus and nitrogen more in their leaves and stems, while minerals retained in roots. The main conclusion is that the addition of biochar and methanol increases the pollutants’ removal efficiency.

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