Green walls for greywater treatment and recycling in dense urban areas: a case-study in Pune

This paper describes a pilot installation of a green wall treating greywater from an office building in Pune, Maharashtra State (NaWaTech project). The pilot installation is located at the main entrance of the state agency responsible for water supply and sanitation. The experimental analysis is in two phases. First phase analysed the results from green walls filled only with LECA ® (lightweight expanded clay aggregate). Since results from the first phase were not satisfactory, a second phase was developed. In the second phase, LECA plus sand and LECA plus coconut fibres were tested as porous media in order to increase residence times and consequently green wall treatment performance. The expected improvements in treatment efficiency have been confirmed by the wider range of observed removal rates between Phase I (chemical oxygen demand, COD, 16–20%) and Phase II (i.e. COD removal in the order of 14–86% and 7–80% for LECA-coconut and LECA-sand, respectively), denoting higher treatment potentialities for the new configurations. The obtained effluent quality was fulfilling the Indian law specifications for reuse in irrigation for all the analysed samples, while only the last samples collected during Phase II were showing an appropriate quality for reuse by flushing toilets.