A modified constructed wetland system for greywater treatment

Green spaces in urban areas improve the local microclimate, promoting reduction of energy consumption and benefiting public health, besides other advantages. The use of greywater for developing such spaces should be considered and the use of natural treatment systems is an attractive option. For this purpose, a modified constructed wetland system, named "EvaTAC" was proposed. The system is a combination of an evapotranspiration and treatment tank (CEvaT) with an inbuilt anaerobic digestion chamber (AnC), followed by a horizontal subsurface flow-constructed wetland (HSSF-CW). The hypothesis was that the AnC would replace a pre-treatment unit, with a double function: (i) retaining solids and (ii) equalising the inflows, avoiding clogging and improving the stability of the system. To better understand the capacity of the AnC to equalise daily variations of flow and organic load, two 24-h and one 8-d monitoring profiles were performed. The results show that the two units complement each other. The 8-d profile shows that, within the CEvaT, the AnC presents the highest removal efficiency of the studied parameters. The HSSF-CW operates as an efficient polishing unit, resulting in an average effluent turbidity of 8 NTU. During 3 years of operation, neither sludge withdrawal nor maintenance of the pipes was required. The system was quite acceptable to the householders, not disturbing their routine, rendering a green site totally integrated into the garden, without the use of potable water for irrigation.