Design and development of two novel constructed wetlands: the duplex-constructed wetland and the constructed wetroof

Constructed wetlands (CWs) are man-made technologies, which mimic natural systems and their processes, to treat wastewater flowing through a filter media and plants. CWs are among the few natural treatment systems that can guarantee an efficient wastewater treatment and an appealing green space at the same time. Ergo, they are of worldwide importance since they can facilitate water reuse while freeing fresh water sources for potable use and, in the case of many urban areas, they can restore the lost green areas caused by extensive construction. However, CWs require large spaces for their construction which usually are not available in urban areas. This downside of CWs has been the motivation to develop wastewater treatment options with less space requirement. In this thesis, two options were designed and studied: the Duplex-CW and the constructed wetroof (CWR). The Duplex-CW is a hybrid CW composed of a vertical flow (VF) CW on top of a horizontal flow (HF) filter (HFF). The stacked arrangement is the key for reducing the CW footprint, since the two systems occupy the same space by having a vertical arrangement instead of the common horizontal arrangement. The CWR is a shallow HF CW placed on the roof of a building, thus it does not occupy any land. Along this document, several modifications and improvements have been tested in order to select the most appropriate Duplex-CW and CWR design for the treatment of domestic wastewater. In this study, the development of a compact CW (Chapter 3-6) demanded the evaluation of different design aspects such as arrangement modes (i.e. conventional and stacked for a single and hybrid system, respectively), configurations of the stacked arrangement (i.e. fill and drain -Fill&D-, stagnant batch and free drain), loading rates (i.e. hydraulic -HLR- and organic -OLR-), intensification (i.e. artificial aeration and recirculation), carbon source as electron donor for denitrification and post-treatment for phosphorus removal. Altogether, the stacked Fill&D Duplex-CW outperformed all other tested CWs due to the combination of the intermittent feeding, resting periods and a 1 d hydraulic retention time (HRT) in the VF CW with the saturated conditions and HRT of 3-4 d in the HFF. Artificial aeration, recirculation and the addition of a carbon source as an electron donor for denitrification were not necessary in the design with current operational conditions. The effluent quality achieved (41-69 mg L-1 for chemical oxygen demand (COD), 8-16 mg L-1 for total suspended solids (TSS), 6-24 mg L-1 for NH4+-N, 13-24 mg L-1 for total nitrogen (TN) and 2-5 mg L-1 for total phosphorus (TP)) met European discharge guidelines treating OLRs up to 37 g COD m-2 d-1 except for TP. Therefore, the recommended design requires an area of 2.6 m2 PE-1 (population equivalent) and a post-treatment filter for phosphorus removal. Efforts to develop the CWR (Chapter 7-8) included testing the mass, hydraulic and stability properties of different materials, the treatment capacity of each material and the effect of sun and rain on the treatment capacity and hydrology of the system. Overall, the CWR design consisted of a shallow (9 cm) filter bed (i.e. sand, light expanded clay aggregates -LECA- and polylactic acid beads) holding in together by means of the grass roots and stabilization plates. The intrinsic aeration guaranteed an efficient removal of organic matter (79-82% for COD) and nutrients (> 99% for NH4+-N). The phosphorus adsorption capacity of LECA explained the high TP removal (86-97%). For TN it was postulated that aerobic denitrifiers could have be present in the CWR. The CWR's hydrology was affected by the presence of sun and rain, but it did not deteriorate the effluent quality. In synthesis, this thesis demonstrates that the Fill&D Duplex-CW and the CWR are efficient domestic wastewater treatment technologies with a lower space requirement (< 2.6 m2 PE-1) than common European design (5 m2 PE-1). However, the Duplex-CW area requirement is still higher than many CW designs and therefore further improvements should be directed at increasing the loading rate and the VF CW HRT to decrease the area requirements. The CWR is the foremost option to save land areas since it requires 0 m2 of land PE-1