Abstract/Summary

Greywater of both treated (TGW) and untreated (GW) types are significant alternatives to mains water (MW) for sustaining the growth and expansion of green infrastructure. The aims of this thesis were first to evaluate GW and TGW as alternatives to MW for the purpose of irrigation of green walls and green roofs. Second, to determine whether irrigation water that has percolated through a green walls soil matrix can be further recycled and reused. GW was treated by a membrane bioreactor (MBR) and produced a high quality TGW, which met British Standards GW reuse requirements. A number of significant water quality improvements were achieved including the complete removal of bacterial species. Notably, GW turbidity was reduced from S.B±4.7 NTU to 0.6±0.2 NTU. Reduction in sodium (Na) concentrations were negligible or below limits of detection with inflow GW having 19.74±S.33 mg/l and outflow TGW 19.67±4.93 mg/1. Sodium was a constituent of particular interest since it is a key constituent of bathroom products as well as causing detrimental effects on soil and plant health in significant concentrations. Green wall irrigation trials showed that when comparing soils irrigated with synthetic GW and MW that no elevation ofsodium concentrations in the filtrate and soil samples was observed. The nutrient content and microbiological quality of green wall filtrate were influenced to a greater extent by its interaction with the soil matrix than the irrigation water type (synthetic GW, MW and TGW). Literary research has shown that GW irrigation ofsoils significantly reduced the SWHC (soil water holding capacity). The green walls irrigation trial results showed that the SWHC decreased by 24%, 23% and 20% when irrigated with synthetic GW, MWand TGW respectively. This demonstrates that the MW irrigation caused a SWHC decrease and that the additional decrease due to GW irrigation was only 1 %. Lightly loaded GW irrigation would not only allow for the replacement of MW but also provide filtered water, which can be collected and utilised. This project highlights a sustainable irrigation alternative to further integrated green walls into the urban environment. Results show that there was minimal effect of GW irrigation on soil, filtrate and leaf tissue in comparison to MW and TGW irrigation.