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Characterising and modelling pollutant dynamics in urban stormwater constructed wetlands

Bosnina, Mohamed 2021. Characterising and modelling pollutant dynamics in urban stormwater constructed wetlands. PhD Thesis, Cardiff University.
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Constructed wetlands (CWs) are a worldwide growing natural treatment technology for their effective treatment of various polluted waters, especially urban stormwater, to meet the requirements of authority legislations and for environmentally friendly and cost effective application. Using a novel tidal flow vertical flow CW (VFCW) mainly overcomes the lack of flow distribution, oxygen supplementation, nitrate-nitrogen (NO3-N) reduction and land availability. Therefore, the aim was to understand and model of the various urban stormwater pollutants immobilisation in the long-term operation of novel pilot-scale VFCWs designed with different substrates configuration receiving different loading rates (catchment area sizes) and wet-dry operation conditions. Generally, the results showed that VFCWs configurations of substrate type, pollutants loading, and wet-dry operation conditions affect the stormwater pollutants retention performance variably based on the mass balance analysis. From the experimental data of the first four VFCWs used loamy sand, gravel, and BFS as main substrates, significant changes in the chemical structure of the medias were noticed indicating chemical adsorption and calcium precipitation play a vital role in retaining heavy metals and nutrients causing the significant differences (p ≤ 0.01) in the performance while total suspended solids (TSS) alongside with the metals in the particulate form were more likely removed via straining, settling, and interception mechanisms. Six loamy sand VFCWs were experimentally and statistically evaluated to account the effect of three cases of both wetland to watershed area ration (WWAR) and wet-dry operation condition. Changing WWAR values influence significantly on the removal performance of TSS, iron (Fe), and phosphorus (P) while no significant impact on the removal performance of both total nitrogen (TN) and zinc (Zn) was accounted. The operation condition impact negatively on the removal of TSS as the condition changes from wet to partially and extended dry while these conditions did not influence statistically the VFCWs performance towards Fe, Zn, TN, and P retentions, which could be elicited to increase the substrate porosity as a result of shrinkage during the dry period and in the same enhance the diffusion of the pollutant into substrate’s surface. All experimental data extracted from various operation conditions were gathered to build statistical predicting models using partial least square analysis (PLS). The resulted models were able with a high degree of accuracy to predict both the training and test data of Fe, Zn, TN, TP, and PO4-P at various operation conditions based on the pollutant loading rate and mass of substrate. III The internal N transformation dynamics were established theoretically and then with the experimentally measured data of stormwater VFCWs 1 and 2 were methodically modelled using STELLA software. The model produced a good agreement between the observed effluent data of organic-N, NH4-N, NO3-N, and TN and the predicted once for both model calibration and validation. The model revealed that N mostly removed via NH4-N adsorption (41%) while 19% and 9.55% of TN were removed via denitrification and plants uptake respectively. Altogether, results showed that CW configuration has a great impact, not on stormwater pollutants removal but also the performance prediction. However, further research at field scale would be beneficial to understand practically more the underline processes of N transformation dynamics and also to enhance P adsorption.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: stormwater constructed wetlands; Long-term stormwater pollutants immobilisation in Vertical Flow Constructed Wetlands; Pollutant removal behaviour under different wet-dry regimes in constructed wetlands; Pollutant removal behaviour under different wetland/watershed area ratios in CWs; Modelling of Vertical Flow Constructed Wetlands operation conditions; Modelling nitrogen dynamics in tidal flow constructed wetlands by STELLA software.
Date of First Compliant Deposit: 7 July 2021
Last Modified: 07 Jul 2021 14:41

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