Material selection for a constructed wetroof receiving pre-treated high strength domestic wastewater

Abstract

A constructed wetroof (CWR) is defined in this study as the combination of a green roof and a constructed wetland: a shallow wastewater treatment system placed on the roof of a building. The foremost challenge of such CWRs, and the main aim of this investigation, is the selection of an appropriate matrix capable of assuring the required hydraulic retention time, the long-term stability and the roof load-bearing capacity. Six substrata were subjected to water dynamics and destructive tests in two testing-tables. Among all the materials tested, the substratum configuration composed of sand, light expanded clay aggregates, biodegradable polylactic acid beads together with stabilization plates and a turf mat is capable of retaining the water for approximately 3.8 days and of providing stability (stabilization plates) and an immediate protection (turf mat) to the system. Based on those results, a full-scale CWR was built, which did not show any physical deterioration after 1 year of operation. Preliminary wastewater treatment results on the full-scale CWR suggest that it can highly remove main wastewater pollutants (e.g. chemical oxygen demand, PO4(3-)-P and NH4(+)-N). The results of these tests and practical design considerations of the CWR are discussed in this paper.

Wetland Roofs as an Attractive Option for Decentralized Water Management and Air Conditioning Enhancement in Growing Cities—A Review

“…Protect the roof structure from excess moisture and root infringement Ethylene propylene diene monomer liner [10] Bituminous waterproofing membrane [9] Substratum Provides storage depth, hydrolysis, growing media for vegetation and biofilm, and appropriate hydraulic residence time Gravel, soil, sand, polylactic acid (PLA) beads [11] Water Retention Provides water storage, can act as growing media…”

“…Polyethersulfone water storage mat (Repotex D) [12] Physical substratum bed depth [11] Vegetation Increase the rate of evapotranspiration for flood control and temperature reductions Carex acutiformis Juncus inflexus Juncus effuses Lythrum salicaria [12] 3.1.…”

“…Wetland roof design follows an adapted multi-layered construction to that of an extensive green roof and is comprised of (from bottom to top): an impermeable root barrier liner protects the roof structure from excess moisture and root intrusion, substrata with water retention capability, and a top helophyte vegetative mat across the entire surface of the roof that must be regularly irrigated ( Figure 2) [11,12].…”

“…The substrata mix chosen should be of minimal weight so as not to exceed the load bearing capacity of the roof structure while providing the necessary hydraulic residence time in water treatment applications [11]. Realized wetland roof designs have previously implemented solid substrata combinations to provide both water retention and a reaction space for nutrient and contaminant removal from water [11].…”

Sustainability

“…Stormwater infiltration basins were also shown to remove nitrogen through various physiochemical and biological processes . A constructed wetland green roof was evaluated for the ability to treat wastewater, finding that the shallow system removed main wastewater pollutants including nutrients and constituents creating oxygen demand (Zapater-Pereyra et al, 2013).…”