The physico-chemical and bacteriological quality of rainwater collected over different roofing materials in Ile-Ife, southwestern Nigeria

Abstract

Samples of bulk free-fall and roof-intercepted rainwater over five different roof types (iron-zinc corrugated sheets, concrete slate tiles, Adex/asbestos cement sheets, aluminium sheets, and thatch) were collected and analysed using standard methods with adequate quality-control and quality-assurance measures. The mean values of some of the investigated parameters for the roof-intercepted samples occurred within four continuous sets of ranges, viz: <0.11 mg l −1 (NH + 4 ), 0.11-1.00 mg l −1 (Na. The other parameters were: pH (6.68-7.45), conductivity (19.4-122.6 µS cm −1 ), colour (25.9-257.6 Pt-Co), and turbidity (6.4-24.7 NTU). The corresponding mean values for the free-fall samples were either within the low end of the same range or about one order of magnitude less than that of the roof-intercepted samples. The enrichment factors of the roof-intercepted samples were within the range of 1.03-4.92 with an overall mean of 2.9 ± 0.3 standard error. Most of the water-quality parameters, including bacterial counts and the number of isolated species were higher both at the beginning and end of the rainy season (when both dry and wet depositions were high) than during the mid-season period (when only wet deposition was high). They also showed an increase with the age of roof materials, especially the samples over Adex and concrete slate roofs. The rainwater sources were not potable without necessary treatment but suitable for a wide range of other applications.

Water quality and public health risks associated with roof rainwater harvesting systems for potable supply: Review and perspectives

“…Other metals that have been studied but reported to be of low or less severe concentrations include cadmium, chromium, nickel and selenium (Förster, 1999;Melidis et al, 2007;Mendez et al, 2011). Other studies observed that the concentrations of Mg, Na, K, nitrate, nitrites, chloride, sulphate and ammonium were not significantly different among free fall rainwater , asbestos and Fe-Zn and aluminium metal sheets (Adeniyi and Olabanji, 2005;Mendez et al, 2011). In other studies, high concentration of nitrates and sulphates in roof runoff were largely attributed to fossil fuel combustion rather than roof materials (Mouli et al, 2005;Evans et al, 2006;Melidis et al, 2007;Gikas and Tsihrintzis, 2012).…”

“…Several studies have demonstrated roof runoff contamination by physical, chemical and biological contaminants (Förster, 1998;Garnaud et al, 1999;Zhong et al, 2001) as well as microbiological contaminants (Corden and Millington, 2001;Jones and Harrison, 2004;Evans et al, 2006). Contamination mechanisms include air-borne and atmospheric deposition, direct leaching of metal constituents from metal sheets, colonisation by various plants and consequently direct weathering of roof material and the leaching of the accumulated particulate organic matter and flora on roof surfaces (Förster, 1999;Chang et al, 2004;Adeniyi and Olabanji., 2005). King and Bedient (1982) attributed leaching of chemical compounds from roofs to the acidic nature of ambient rainfall while Chang et al (2004) report that the rough surfaces and cracks associated with wood shingle roofs trap water, aerosols and debris which promote plant growth, particularly fungi resulting in increased organic matter retention on the roof.…”

“…In addition, concrete tiles and asbestos were found to be more prone to colonisation by various plants leading to softening of the roofing material. Although some studies did not establish clear correlations between contaminants and roof types (e.g., Chang et al, 2004;Mendez et al, 2010;Ahammed, 2011), Adeyini andOlabanji (2005) managed to separate their roof types into two clusters. One cluster consisting of asbestos and concrete tiles significantly correlated with Ca and bicarbonate ions, while the other cluster comprising of thatch, Al and Fe-Zn sheets were significantly correlated with K, Cl, sulphates and nitrate contaminants.…”

A Reliability Analysis of a Rainfall Harvesting System in Southern Italy

“…Runoff from rooftops is often considered unpolluted [10] or at least is of relatively good quality compared with runoff from surface catchments [11]. However, there is still disagreement about the quality of rooftop runoff, ranging from good or acceptable [12,13] to contaminated [14,15], depending on the roofing material, environmental conditions and atmospheric pollution. Subject to basic treatments such as filtration and/or chlorination, as necessary, collected rainwater can be utilized for different non-potable uses, including toilet flushing, washing machine use and garden irrigation (or any other use that does not require high-quality water).…”

Modern Urban Rainwater Harvesting Systems: Design, Case Studies, and Impacts

“…However, results from study roofs indicate that roofing materials can be long-term sources of pollutants. Clarke et al [27] and Adeniyi and Olabanji [28] found that contaminants from a range of roofing materials increased as the roof aged. In leaching studies, a range of roof materials including asphalt shingles, fake slate roofing shingles, and galvanized metal were all sources of lead, zinc, iron, and copper [27].…”