A multi-functional nature-based solution (NBS) for greywater treatment and reuse at the same plot

Water stress is destined to worsen due to rapid urbanization, high population growth as well as huge water demand and climate change in the upcoming days. To make the cities more water resilient, greywater treatment and reuse can be a sustainable solution to prevent discharge of greywater into the environment and reduce the import of freshwater into the cities. The aim of this study was to investigate the feasibility of implementing a multi-functional nature-based solution (NBS) for decentralized greywater treatment and reuse at the same plot. Therefore, an aerated vertical-flow constructed wetland (AVFCW) with a design capacity of 8 PE (population equivalent) was combined with an innovative cover layer on top, so that the wetland surface can be used wisely (saving space) for irrigation with the treated effluent as well as protect the constructed wetland from high water loss due to evapotranspiration (EVT). In the first investigation phase, the results showed that applying such a cover layer on the wetland surface did not have any influence on the treatment performance of the AVFCW operating at the BDZ-Research and Demonstration Centre for Decentralized Wastewater Treatment in Leipzig, Germany. The results from the second investigation phase showed a highly efficient treatment performance of the AVFCW system (BOD5 > 90%, COD>93%, TSS > 93%, TN > 60% and log-removal for E.coli of 0.81 ± 0.45) when feeding with synthetic greywater at the site. In the effluent from the AVFCW, the mean concentrations of BOD5, TSS and E.coli were found to be as 9 ± 5 mg/L, 4 ± 2 mg/L and 7.0 ± 5.4 MPN/100 mL, respectively, and the achieved results were in compliance with the EU recommended limits for the most restrictive Class A standard treated water quality (BOD5 < 10 mg/L; TSS < 10 mg/L; E.coli < 10 MPN/100 mL) for agricultural irrigation. Soil characteristics data at the depth of 10, 15 and 20 cm within the cover layer showed no remarkable effect of irrigation with treated effluent on the soil properties. Overall, this study demonstrated that the integrated and multi-functional NBS can be implemented as a more practical and attractive technology for greywater treatment and reuse (via sub-surface irrigation) at the same plot and can improve the aesthetic in urban settlements (e.g. backyard garden of the urban households, public park, roadside and touristic areas) as well as in warm climatic conditions of arid/semi-arid regions worldwide.