RAINWATER QUALITY ASSESSMENT IN A ONE-FAMILY BUILDING IN THE SOUTHEAST OF BRAZIL

Transcription

1 RAINWATER QUALITY ASSESSMENT IN A ONE-FAMILY BUILDING IN THE SOUTHEAST OF BRAZIL André Teixeira Hernandes São Carlos Federal University (UFSCar) R. Alberto Coselli, 611 Ribeirania Ribeirão Preto São Paulo Brazil athernandes@keynet.com.br Simar Vieira de Amorim São Carlos Federal University (UFSCar) Rodovia Washington Luis (SP 310), km 23.5 CEP São Carlos - São Paulo Brazil simar@power.ufscar.br ABSTRACT Human beings have been collecting rainwater from thousands of years, in a variety of ways, be naturally or artificially. Ensuring an uninterrupted, safe and suitable water supply is a mankind s goal that requires a great amount of effort besides being essential to its own subsistence. With populations gathering in cities, it was necessary to conceive large scale public water supply systems, becoming the main resource to deliver potable water to the buildings. On the other hand, the fast growth of urban centers and the changes in its population s lifestyle are putting water resources under almost unbearable stress. The coming back to the habit of using rainwater in small scale (individual or semi-collective) is seen as a positive solution which meets the new circumstances and needs. The big public systems are highly trustworthy whereas water quality (potability aspects) is considered, due to the developed technology supported by the whole society. Could we guarantee the same quality for the small systems? The first stage should be to identify the physicochemical and microbiological characteristics of rainwater in a collection system. Its characteristics are strongly affected by regional aspects, either by climate or by techniques and materials used. The rainwater collection system of a prototype residence in southeast of

2 Brazil was monitored qualitatively and quantitatively. The characteristics of the water were pointed out and its several uses were accommodated with the available regulatory requirements. This paper is meant to show the results of a monitoring research. In Brazil the usage of rainwater is neither described in the present code of laws nor common practice in residential buildings. The system above mentioned was conceived for the water to be used in toilet flushing and other maintenance activities that do not require potable water. With results in hand it will be possible to recommend specific indications to the use of rainwater in Brazilians buildings, at the environmental and current circumstances of the studied matter at issue. INTRODUCTION The most controversial aspect of rainwater harvesting system is the water quality. Because of this polemical issue, all discussion must necessarily be done according its purpose. Gould and Nissen- Petersen (1999) say no one alternative source of water is 100% secure full time. Still according them, the issue that must be analyzed is the acceptable level of risk based on socioeconomic models of a society in the face of your available water supply quality. As pointed by many authors (GOULD and NISSEN-PETERSEN, 1999; MIRBAGHERI, 1997), the rainwater contamination is strongly influenced by anthropogenic action. Urbanization associated with a high level of economic activities of modern societies in small areas like cities, produces high concentration of pollutants (as heavy metals and chemical substances as result of fossil fuel burning), which contact with free falling rainwater, can contaminate it. This fact affects rainwater quality for some uses. Even in rural areas, massive use of fertilizers, pesticides, herbicides or insecticide may become rainwater inappropriate for its use (MACOMBER, 2001). OBJECTIVES The goal of this paper is to assess the qualitative and qualitative aspects of a rainwater harvesting system in its particular circumstances. The rainwater use inside buildings has always been a controversial issue. In Brazil, due to the lack of attention given to the use of this technique, this paper intends to clear up the potential of this technique, specially its efficiency to mitigate urban flooding, as well the whole system. The level exposure of contamination hazard of system s users is fundamentally one of the most important questions to be answered. System METHODOLOGY The house is a single family, one-store house, 300 square meter roof catchment area, composed of three bedrooms, two full bathrooms, one half bathroom, two cars garage and a 200 square meter backyard. It was designed for a total number of six habitants. Water supplied by public system is dedicated for human consumption (ingestion, food preparation, personal care). Rainwater is used at the three bathrooms toilets, car washing and garden irrigation. So, the house reckons upon a double supply system which can deliver potable and work (less quality) water, generating a monthly economy of 20 to 30% on public system water consumption. In this system, there is 11,250 liters of available volume, where 10,000 l are stored at an underground reservoir (cistern) and 1,250 l are stored at a header tank. The transfer happens through an electric pressure pump system. The underground reservoir was built in reinforced concrete and waterproofed with the help of conventional material easily found at the local market. The header tank is, in fact, split in two tanks, one of which supplies water specifically to the toilets, with 250 l capacity. These tanks are

3 automatically fed by the cistern with the help of level sensors. The smaller reservoir was lowered in relation to the other, thus receiving water through gravity. To best understanding of how the system works, refer to the diagram in picture 01. Picture 01 Schematic diagram of the system Proceedings The methodology consists of assess qualitatively and quantitatively rainwater harvested at a urban site, including the total volume of potable and not-potable water consume and rainwater infiltrated into soil, and simultaneously, collect rainwater samples to analyze its quality in different points of the system. Some of the most important parameters were analyzed bi-weekly, and results compared with water standards for primary body contact uses, considering that the system it s not intended to provide potable water, but rainwater use for watering garden, washing cars and pavements, flushing toilet and soil infiltration. All results were compared with Brazilian recreational water use legislation (National Environmental Council-CONAMA). It s important to notice that Brazil doesn t have a specific policy for rainwater quality. So, for this research, were adopted either as reference similar others national recreational water use policy. They are: CONAMA # 274/2004 (for water bodies class 2 allows primary contact) Guidelines for Canadian Recreational Water Quality (GCRWQ-1992) Australian Water Quality Guidelines for Fresh and Marine Waters (AWQGFMW-1992) For this, rainwater samples are being collected bi-weekly at four points of the system: Free-falling rainwater; First flush device; Cistern; Usage points.

4 In all cases (excepted by free falling rainwater), the samples were analyzed for quantification of the following variables: Odor; Color; Turbidity; Total dissolved solids; Total coliforms; Thermotolerant coliforms and; E. Coli. Simultaneously, it was assessed both rainwater and potable water used by householders and capacity of retention and infiltration. All cold water plumbing system and reservoirs were monitored by water flow meters. RESULTS Water quality aspects: Table 01 - Falling rainwater quality Parameter Unit CONAMA AWQGFMW GCRWQ class #2 (1992) (1992) Maximum Average Minimum Odor Absent x Absent Absent in all of samples Color mg Pt/l 75 x x 10,00 5,42 2,50 ph 9,0-6,0 8,5-6,5 8,5-6,5 6,50 5,62 4,90 Turbidity N.T.U 100 x 50 7,29 5,02 2,84 TDS mg/l x 52,00 24,00 8,00 Table 02 - Water quality at the first flush device Parameter Unit CONAMA AWQGFMW GCRWQ class #2 (1992) (1992) Maximum Average Minimum Odor Absent x Absent Absent in all of samples Color mg Pt/l 75 x x >25,00 12,50 2,50 ph 9,0-6,0 8,5-6,5 8,5-6,5 6,90 6,70 6,40 Turbidity N.T.U 100 x ,00 132,39 1,70 TDS mg/l x 982,00 283,90 28,00 Thermo. Coliform CFU/100ml <1000 <150 x 77 x <1 E. Coli CFU/100ml <800 x <200 67,7% of the samples indicated presence Total Coliform CFU/100ml x x x Table 03 - Water quality at the Cistern Parameter Unit CONAMA AWQGFMW GCRWQ class #2 (1992) (1992) Maximum Average Minimum Odor Absent x Absent Absent in all of samples Color mg Pt/l 75 x x 10,00 3,13 2,50 ph 9,0-6,0 8,5-6,5 8,5-6,5 9,70 7,78 6,30 Turbidity N.T.U 100 x 50 5,30 2,46 0,95 TDS mg/l x 96,00 45,75 9,00 Thermo. Coliform CFU/100ml <1000 <150 x 77 x 1 E. Coli CFU/100ml <800 x < % of the samples indicated presence Total Coliform CFU/100ml x x x

5 Table 04 - Water quality at the usage points Parameter Unit CONAMA AWQGFMW GCRWQ class #2 (1992) (1992) Maximum Average Minimum Odor Absent x Absent Absent in all of samples Color mg Pt/l 75 x x 10,00 3,13 2,50 ph 9,0-6,0 8,5-6,5 8,5-6,5 9,30 7,28 6,30 Turbidity N.T.U 100 x 50 5,60 1,55 0,50 TDS mg/l x 88,00 35,55 11,00 Thermo. Coliform CFU/100ml <1000 <150 x 1 x 0 E. Coli CFU/100ml <800 x < % of the samples indicated presence Total Coliform CFU/100ml x x x 16 2,83 0 Results from samples taken from the storage tanks (Table 03 and 04) show that the average values for microbiological parameters (fecal coliforms, total coliforms) and physical chemical parameters not exceed the assumed guidelines. The bacterial contamination in the cistern (Table 03) appears to result from debris, soil and leaves that falls on the roof. First flush device play its role, removing dirties from roof water (table 02). Almost all results are below national recreational water standards. The water which is stored and purposed for all not-potable uses has enough quality. However, as it has contact with the user and in order to avoid contamination, it is suggested disinfection of the rainwater by means of chlorination. It was revealed important Brazil southeast rainwater s feature. The rain acidity was significant at all samples (table 01). The sources of this free acidity appear to be correlated to the different land-uses. The composition of rainwater appeared to be controlled mostly by three sources: soil dust, sugar cane burning and industrial emissions. Some factors appear to control the chemical composition of the rainfall in the Ribeirão Preto region. The fact that agricultural related factors, such as soil dust and sugar cane burning, have stringing influence on the atmospheric chemistry is probably caused by massive agricultural activity, since 85% of the basin is cropland, and sugar cane plantations alone cover almost of the region area. Sugar cane is burned every year from May to October, emitting annually to the atmosphere tons of organic matter. In addition, each 5 6 year plants are removed and replaced by new ones (Lara et al, 2001). This fact points to reduce the durability of the cistern, therefore it is made of concrete. A high alkalinity level was found in cistern water, because alkalis substances were removed from concrete surfaces of the cistern. By other hand, all plumbing systems don t show signals of acid corrosion, normally found in systems which are supplied with potable groundwater by local public facilities. Water quantity aspects: Picture 02 Rainfall average

6 Picture 03 Potable water x Rainwater comparison monthly consume Table 05 Water consume Volumes (m 3 ) Rainwater harvested 446,10 Rainwater infiltrated 339,61 Rainwater overflow discharged 32,64 Rainwater consumption 73,84 Potable water consumption 188,27 Total water consumption 262,11 Table 06 Efficiency indicators Indicator % Rainwater consumption / Total water consumption 28,17 Potable water consumption/ Total water consumption 71,83 Total water consumption/ Rainwater harvested 58,75 Rainwater infiltrated/ Rainwater harvested 76,13 Rainwater consumption / Rainwater harvested 16,55 Rainwater overflow discharged/ Rainwater harvested 7,32 Rainwater consumption/ Potable water consumption 39,22 Table 07 Detention / infiltration system efficiency Pond infiltration / detention capacity = 1,90 m 3 Water detention of overflow (%) # Events % , , , , , ,1

7 , , , ,00 Total events ,00 Infiltrated rainwater total amount 339,61 m 3 Discharged rainwater total amount 32,64 m 3 Ribeirão Preto had during all period of evaluation (June / 2004 to May / 2005) an annual rainfall average of 1.844,40 millimeters, distributed as show in picture 02. It is important to emphasize that rainy season was atypical, besides annual average is a historical average. Quantity aspects results shows a very important contribution to reduce potable water consumption (table 06), besides a significant reduce of overflow discharges and a very high amount of water is infiltrated into soil. A large volume of rainwater was collected (446,10 m 3 ), as show in table 05. Picture shows rainwater and potable water monthly usage trend. This system can strongly contribute to minimize flooding in urban areas (table 07), retaining in site almost all (91,23%) of free falling rainwater. CONCLUSIONS Sampling analysis at Ribeirão Preto revealed that roof water collected comply with all water recreational guidelines (Brazil, Australia and Canada) for fecal, thermotolerant and total coliforms, ph, total dissolved solids, turbidity and aesthetical aspects. Although the chemical and metals parameters was not assessed because rainwater collected is not intended to drink, rainwater shows a very good quality for general purpose uses, as it occurs at this building. For Ribeirão Preto conditions, this system may be a helpful way to minimize the effects of urbanization, contributing with aquifer Guarani recharge. ACKNOWLEDGEMENTS The authors gratefully acknowledge the assistance provided by Mr. Carlos Farjani Neto and staff from Ribeirão Preto Water and Sewage Department and Mr. Renato Zorzenon and staff from University of Ribeirão Preto. REFERENCES Australia. Australian water quality guidelines for fresh and marine waters. Australian and New Zealand Environment Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra. vol 1, Canada. Minister of National Health and Welfare. Guidelines for Canadian recreational water quality. Ottawa, 1992 Gould, J.; Nissen-Petersen, E. Rainwater catchment systems for domestic supply: design, construction and implementation. London: ITDG Publishing 1999 Lara, L. B. L. S. Chemical composition of rainwater and anthropogenic influences in the Piracicaba River Basin, Southeast Brazil. Pergamon, Atmospheric Environment, 2001.

8 Macomber, S. H. P. Guidelines on rainwater catchment systems for Hawaii. Hawaii: College of Tropical Agriculture and Human Resources; University of Hawaii at Manoa, Mirbagueri, S. A. Sources of pollution for rainwater in catchment systems, and environmental quality problems. In: INTERNATIONAL RAINWATER CATCHMENT SYSTEMS CONFERENCE, 8., 1997, Iran. Proceedings... Iran: 1997.