Monitoring Drainage Water Quality during Green Roof Irrigation Trials Using Synthetic Greywater.
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Date
2016-04
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Abstract
Aims: To evaluate the potential for substituting green roof mains water irrigation by irrigation using
lightly loaded synthetic greywater.
Study Design: The planted green roof system was designed to be operated and tested within a
glasshouse.
Place and Duration of Study: Schools of Engineering, and Plant Sciences, The University of
Reading, for 28 days commencing 28th of May 2012.
Methodology: A trial was conducted for comparing two planting schemes using Sedum and
Stachys Byzantina and a third unplanted control. The three sets of growing boxes were subdivided
between substrate depths of 10 cm and 20 cm. By further subdivision, half of each set were
watered using mains water, and half using a synthetic greywater. The soil composition and water
quality of the drainage (filtrate) water were monitored. Statistical analysis of the results was
conducted.
Results: Consistency was observed in influent pH and EC, in both mains and greywater samples.
Influent Na concentrations were higher in the greywater samples due to detergent content. The Na
mass balance calculations for all boxes showed that some Na mass was unaccounted for when
comparing aggregated concentrations in influent, plant tissue and soil with the aggregated Na
mass in filtrate, plant tissue and soil water. It was concluded that this was likely to be due to
retained/ponded irrigation water in the boxes, difficulties in attaining homogenous box flushing and
the underestimation of soil Na. The variation in substrate depth affected all results. The plants
themselves seemed to have little significant influence on the measured parameters, with the
exception of the accumulation of Na mass in plants irrigated with greywater. Conclusion: No improvement was observed in the quality of the greywater following filtration
through the soil matrix. For longer term watering using greywater, a choice of Na resistant species
should be considered, although the Sedum species used in this trial showed no recorded adverse
growth effects due to Na accumulation.
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Keywords
Rainwater harvesting (RWH), Sedum and Stachys green roofs, irrigation of green roofs with greywater, sodium accumulation in green roof species, BSI-standard greywater
Citation
Smith Matthew, Hyde Katherine. Monitoring Drainage Water Quality during Green Roof Irrigation Trials Using Synthetic Greywater. British Journal of Environment and Climate Change. 2016 Apr-June; 6(2): 138-148.