Discussion on "Influence of Roofing Materials and Lead Flashing on Rainwater Tank Contamination by Metals" by MI Magyar, AR Ladson, C Daiper and VG Mitchell

Investigations by the writer established that the quality of rainwater collected from roofs at Figtree Place and nearby houses in Newcastle occasionally exceeded the values from Australian drinking water guidelines for ammonia, pH and lead (Coombes et al, 2000; Coombes, 2002). However, no exceedance...

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Bibliographic Details
Published in:Australian journal of water resources 2015-01, Vol.19 (1), p.86-90
Main Author: Coombes, P J
Format: Article
Language:English
Subjects:
Design and construction
Metal roofing
Pollution
Prevention
Storage
Storage tanks
Water
Water quality management
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Summary:Investigations by the writer established that the quality of rainwater collected from roofs at Figtree Place and nearby houses in Newcastle occasionally exceeded the values from Australian drinking water guidelines for ammonia, pH and lead (Coombes et al, 2000; Coombes, 2002). However, no exceedances of the guidelines were observed for chemical and metal parameters including Lead in the water column of the storages or at hot water taps. This discovery suggested that rainwater quality in storages improves because metal and chemical contaminants settle to the bottom of the tanks where they sorb to a biofi lm that is commonly known as sludge. Samples taken from the sludge revealed accumulation of lead (0.033 mg/L) and iron (0.93 mg/L). This led to the hypothesis that the water treatment processes of flocculation, settlement, sorption and bio-reaction operate in rainwater storages to improve quality of stored rainwater. Rainwater storages are bioreactors with biofilms at the water surface micro layer, on internal walls and at the bottom as sludge. An important insight was that rainwater should not be drawn from the bottom 100 mm of a rainwater tank to maximise the quality of water by avoiding disturbance of the sludge. Field observations and laboratory experiments revealed that a first flush device designed to capture the first 0.25 mm of roof runoff can remove 11% to 94% of dissolved solids and 62% to 97% of suspended solids from the first flush of runoff into a rainwater tank which would limit the infl ow of chemicals and metals to stored rainwater.
ISSN:1324-1583
2204-227X
DOI:10.1080/13241583.2015.11465459