Improvement of septic tank effluent and green coverage by shallow bed wetland roof system

•WR can be a potential technology for improving quality of septic tank effluent.•Cyperus Javanicus Houtt and Kyllinga Brevifolia Rottb were effective vegetation.•WR achieved removal rates of 27-33 kg COD ha−1 day−1 and 10-13 kg TN ha−1 day−1.•WR could create 63-92 m2 of green coverage per m2 of wetland area.

This study investigates the wastewater treatment performance of four local plant species in wetland roof systems (WRs). The tested species include Cyperus Javanicus Hot (WR1), Eleusine Indica (L.) Gaertn (WR2), StruchiumSparganophorum (L.) Kuntze (WR3) and Kyllinga Brevifolia Rottb (WR4). The plant growth rate, nutrient uptake, wastewater treatment performance and leaf coverage were investigated. The WRs were operated at hydraulic loading rates of 353-403 m3 ha−1 day−1. As a result, WR4 achieved the highest biomass growth of 73.7 g day−1 (fresh weight) or 12.0 g day−1 (dry weight). The nutrient accumulation of WR4, according to dry biomass, was 1.7% of total nitrogen (TN) and 0.05% of total phosphorus (TP). The highest COD and TN removal rates (33 ± 10 kg COD ha−1 day−1 and 14 ± 4 kg TN ha−1 day−1, respectively) were also recorded in WR4. There was statistically insignificant difference in TP removal rates (0.4-0.5 kg ha−1 day−1) among WRs. In terms of green leaf area coverage, WR1 and WR4 also introduced extremely high specific green leaf area as 98 and 99 m2 of green leaves per m2 of wetland area, respectively. Subsequently, WR1 and WR4 performed better than others in a range of benefits providing green area and treating septic tank effluent.

Graphical abstractDownload high-res image (245KB)Download full-size image