Skip to content
grön vägg
View original picture , opens in new tab/window

Green walls for greywater treatment – how effective are they?

Published: 6 March 2022

At Recolab, a test bed and research facility in Helsingborg that is run by Nordvästra Skånes Vatten och Avlopp (NSVA), a study on green walls for greywater treatment is carried out by Mashreki Sami, PhD candidate at Stormwater&Sewers, in collaboration with NSVA.

In Helsingborg, greywater ie wastewater from sinks, showers, baths, washing machines or dishwashers, is collected from five residential buildings, one office complex, two restaurants and two shops which in volume is 800 persons equivalent. A green wall treats a part of the collected greywater streams. In the green wall, five types of filter materials (pumice, biochar, hemp fiber,used coffee ground and compost) are investigated with three different hydraulic loading rates (HLR) (4.5, 9, 18 L/day) for irrigation. In addition, three plant species Juncus compressus, Myosotis scorpoiodes, and Carex nigra were selected based on their local availability in Scandinavia and persistence to polluted water like greywater. The green wall consists of 36 pots, a column of three pots being considered as one configuration with same filter material (see photo). Each pot of a configuration was planted with one species of plant.

green wall

Triplicate samples from each material type and hydraulic loading rates were analyzed for the organic matter (TSS, BOD, COD and TOC), nutrients (nitrogen and phosphorus), microorganisms (E.coli and enterococci) and surfactants. Plant growth and the survivability when irrigated with greywater were assessed visually during the whole experimental period and the greenness of the wall was evaluated.

The preliminary results from the analysis show significant reduction of BOD, COD, TOC and TSS. The hydraulic loading rates show low effect on the treatment of these organic matters. However, the treatment efficiency varies with hydraulic loading rates in the case of nutrients. Therefore, the results indicate the potential of a green wall and its filter materials in treating organic matter in greywater, with high reduction even under the influence of high hydraulic loading rates.

Mashreki Sami

Mashreki Sami, PhD Student

Phone: +46 (0)920 491829
Organisation: Urban Water Engineering, Architecture and Water, Department of Civil, Environmental and Natural Resources Engineering