Potential for Potable Water Savings in Buildings by Using Stormwater Harvested from Porous Pavements
Lucas Antunes, Liseane Thives, Enedir Ghisi
There is a growing concern about the scarcity of water resources due to population growth and increased demand for potable water. Thus, the rational use of water has become necessary for the conservation of such resources. The objective of this study is to estimate the potential for potable water savings in buildings of different sectors-residential, public and commercial-in the city of Florianópolis, southern Brazil, by using stormwater harvested from porous pavements. Models were constructed
... o assess infiltration and rainwater quality; samples of stormwater from a local road were collected to evaluate its quality; and computer simulation was performed to assess the potential for potable water savings and rainwater tank sizing. Draining asphalt concrete slabs with two types of modifiers were used, i.e., tire rubber and SBS polymer-styrene-butadiene-styrene. The Netuno computer programme was used to simulate the potential for potable water savings considering the use of rainwater for non-potable uses such as flushing toilets and urinals, cleaning external areas, and garden watering. Average stormwater infiltration was 85.4%. It was observed that stormwater is not completely pure. From the models, the pH was 5.4 and the concentrations of ammonia, phosphorus, nitrite, and dissolved oxygen were 0.41, 0.14, 0.002, and 9.0 mg/L, respectively. The results for the stormwater runoff of a paved road were 0.23, 0.11, 0.12, 0.08, 1.41, 2.11, 0.02, and 9.0 mg/L for the parameters aluminium, ammonia, copper, chromium, iron, phosphorus, nitrite, and dissolved oxygen, respectively; and the pH was 6.7. In the city of Florianópolis, which has a surface area of paved roads of approximately 11,044,216 m², the potential for potable water savings ranged from 1.2% to 19.4% in the residential sector, 2.1% to 75.7% in the public sector and 6.5% to 70.0% in the commercial sector. In the state of Victoria, the use of rainwater is relatively common, especially in rural areas, where 13% of families use it in domestic activities. Despite having water availability around 33,000 m 3 per capita per year (a rate considered very high by the United Nations Environment Programme (UNEP)) , Brazil can also suffer from water shortages due to poor distribution of population in relation to water resources. The Southeast and Northeast regions have less than 5000 m 3 per capita per year (considered low by UNEP). Estimates show that by 2100 these regions will have water availability lower than 1000 m 3 per capita per year (catastrophically low). However, there is a great potential for potable water savings by using rainwater in Brazil  . Many studies available in the literature have been performed to estimate the potential for potable water savings by using rainwater in buildings [1, 11, 12 ] to quote just a few). In Brazil, Ghisi et al.  analysed the residential sector of 62 cities and obtained potential for potable water savings ranging from 34% to 92%. Marinoski  found potential for potable water savings that could be achieved through the implementation of a rainwater utilization system for non-potable uses in an educational institution in Florianópolis; the potential for potable water savings was 45.8%. However, most of the articles found in the literature, as in the cases mentioned above, deal with the use of rainwater harvested from roofs of buildings [15-18] amongst many others). Few articles address stormwater collected from public roads and/or the assessment of its quality, which can be an important resource against water scarcity [19-23] to quote just a few). The number of roads built in cities is growing rapidly due to the fast urbanization. The surfaces of these highways are, in most cases, of low permeability, which increases the area of impervious surfaces. Thus, water cycle and stormwater quality are affected. Runoff of urban roads is considered to be one of the main sources of environmental pollution. Quality of runoff depends on many factors such as the type of surface, air quality, and anthropogenic local actions such as vehicle traffic density. Without proper treatment, pollutants found in the runoff, such as organic pollutants, copper, lead, zinc, and other heavy metals, are of concern because of their harmful effects. However, studies about the quality of water collected from the runoff of roads and control of pollutants could provide safer and more reliable basis for the use of stormwater in the future. Certain practices are used in order to decrease the volume of runoff in urban roads. Examples include infiltration systems, storage systems, and alternative road structure (porous pavements, for example). However, some of these practices reduce runoff but are inefficient for the removal of pollutants  . Different types and specifications of pavements that can filter stormwater and also reduce freeway noise are already widely used in developed countries    . However, in some cases, the investment made in these types of pavements aims at increasing road safety by decreasing the number of accidents caused due to the excess of water on the roads. According to Scholz and Grabowiecki , the runoff management in urban areas has been seen in a more ecological way due to the appearance of sustainable drainage systems that collect, store, process, and redistribute or recycle water. Compared to the traditional drainage, the stormwater infiltration process and the system retention are sustainable and suitable for urban areas. In addition, these systems have benefits such as reducing runoff, groundwater recharge, as well as water savings by recycling and pollution prevention. Conventional flexible pavement is usually applied in public roads of most cities. In this type of pavement, the surface layer is, in general, impermeable. However, porous pavements could be used to collect stormwater from the pavement surface in order to minimize effects such as aquaplaning and hydroplaning. Thus, the permeable layer in porous pavements can be located on the pavement surface or underneath, depending on the layer chosen to collect the stormwater. Also, the pavement surface (asphalt concrete) can be produced using conventional asphalt or asphalt modified (SBS polymer-styrene-butadiene-styrene, asphalt rubber, SBR-styrene-butadiene-rubber, EVA-ethyl-vinyl-acetate, or other polymers).