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Revista mexicana de ciencias agrícolas
versão impressa ISSN 2007-0934
Rev. Mex. Cienc. Agríc vol.8 no.6 Texcoco Ago./Set. 2017
Investigation note
Rainwater for human consumption and domestic use in San Miguel Tulancingo, Oaxaca
1Posgrado de Hidrociencias y Edafología. Campus Montecillo-Colegio de Postgraduados. Carretera México Texcoco km 36.5, Texcoco, México. Tel. (595) 9520200. (opalacio@colpos.mx; anayam@colpos.mx; jtovar@colpos.mx).
The study was conducted in the municipality of San Miguel Tulancingo, Oaxaca where people use for their needs of water for human consumption and domestic use 30 L inhabitant-1 day-1. The goal was to design a system to capture rainwater to provide quality water, venough and in a continuous way to the inhabitants of the municipality. The design of the system consisted of: the location of the system at macro and micro level, the calculation of water demand, net rainfall, effective capture area, pipe diameters, sedimentation volume, storage and solar pump, to finally design the treatment train to purify the rainwater.
Keywords: water balance; rainwater collection; tank; water demand; water purification plant; net rainfall
El estudio se realizó en el municipio de San Miguel Tulancingo, Oaxaca donde los habitantes usan para sus necesidades de agua de consumo humano y uso doméstico 30 L habitante-1 día-1. El objetivo fue diseñar un sistema de captación del agua de lluvia para dotar con agua de calidad, en cantidad y de manera continua a los habitantes del municipio. El diseño del sistema consistió en: la localización del sistema a nivel macro y micro, calcular la demanda de agua, la precipitación pluvial neta, el área efectiva de captación, los diámetros de las tuberías, el volumen del sedimentador, los almacenamientos y la bomba solar, para finalmente diseñar el tren de tratamiento para potabilizar y purificar el agua de lluvia.
Palabras clave: balance hídrico; captación de lluvia; cisterna; demanda de agua; planta purificadora; precipitación pluvial neta
The Organization for Economic Co-operation and Development (OECD, 2012) predicts that by 2050 global water demand will increase by 55%. Agriculture will continue to be the world’s largest consumer of water, which in many countries often accounts for 70% or more of supplies from rivers, lakes and aquifers (FAO and WWC, 2015). By 2014, nearly 800 million people had no access to safe drinking water, and 6 to 8 million people died each year from disasters and water-related diseases (UN-Water 2013 quoted by Jiménez-Cisneros, 2014).
In México everyone has the right to access, provision and sanitation water for personal and domestic consumption as sufficient, safe, acceptable and affordable (SEGOB, 2012), the inhabitants of the municipality of San Miguel Tulancingo currently have 5 475 m3 year-1 of water to meet their consumption and domestic needs (CONAGUA, 2015), this equates to 30 L person-1 day-1, less than what is recommended by the World Health Organization (WHO), which recommends at least 50 L person-1 day -1 of water to ensure higiene and basic food (Howard, 2003).
Anaya (2006, 2014) mentions that the collection and purification of rainwater represents a viable, effective, efficient and sustainable alternative to provide water in quantity, quality and continuously to populations that do not have access to piped water.
The objective of this research is to develop a rainwater collection system (SCALL) project to supply water for human consumption and domestic use to the inhabitants of the municipality of San Miguel Tulancingo, which shows a high level of degradation in its soils, high water resource constraints and high marginalization; since six of the thirteen localities are classified with high degree and one with very high degree of marginalization (SEDESOL, 2010).
The SCALL was designed following the methodology proposed by the Centro Internacional de Investigación, Demostración, Capacitación y Servicio en Aprovechamiento del Agua de Lluvia (CIDECALLI) of the Colegio de Postgraduados (CP) (Anaya et al., 2013; Anaya and Chacón, 2015). The municipality of San Miguel Tulancingo, is located between the parallels 17° 42’ and 17° 48’ north latitude and the meridians 97° 24’ and 97° 29’ west longitude, at an average height of 2 200 masl (INEGI, 2010).
Rainwater collection system
The site selected to establish the SCALL is located in the central part of the municipality, is affected in 35% of its surface by water erosion (SEMARNAT and CP, 2002), with the lowest category of susceptibility to: instability of slopes, generation of flows, sinkings and landslides (CENAPRED, 2014).
The SCALL was designed for a population of 500 inhabitants, with a daily water supply of 3.4 L for human consumption and 20 L for domestic use, requiring 4 270.5 m3 (638.75 m3 for human consumption and 3 631.75 m3 for domestic use) to complete the 50 L person-1 day-1.
For the calculation of net rainfall (PN), a catch coefficient of 0.9 and a runoff coefficient of 0.9 were considered, since the catchment area will be covered with PVC geomembrane (Anaya, 2011; FAO, 2013). A concrete cistern is four to five times more expensive than a geomembrane sheath (Hernández, 2005). The historical monthly rainfall in the municipality is 544.7 mm (SMN, 2012) and the PN is 412 mm.
With a demand of 4 270.5 m3 year-1 and 0.412 m of annual rainfall, the effective catchment area (Aec) to obtain 23.4 L of water for each inhabitant day-1, considering a 13% slope, is 10 452 m2. For the land reliefs conditions in the area, Aec was divided into two sections, section A of 6 388 m2 and section B of 4 065 m2 (Figure 1).
To conduct the water collected in section A, a pipe of 0.219 m in diameter (8”) and of 0.168 m (6”) was calculated for section B. In order to obtain the dimensions of the settlers, the methodology of the Pan American Center for Sanitary Engineering and Environmental Sciences (PAHO and CEPIS, 2005), the settler of section A must be 1.3 m wide, 7.57 m long and 1.5 m high in the interior and the settler of section B must have 1.1 m wide, 5.8 m long and 1.1 m high in the interior.
To determine the minimum storage volume a water balance was performed (Table 1), obtaining that it was necessary a container with capacity to store 1 891 m3 of water.
It is proposed to store the rainwater in six cisterns, four for the rainwater captured in section A and two for section B. The United States Department of Agriculture (USDA) formula was used to determine the dimensions of the cisterns. The advantage of this formula is that there volumes can be approximated where there are irregular landforms (Tuttle et al., 1982). Table 2 shows the dimensions of each tank.
Plano a= área de la excavación en la superficie del terreno (m2); plano b= área de la excavación en el punto medio (m2); plano c= área de la excavación en el fondo del estanque (m2).
Table 2 Volume of cisterns for SCALL in San Miguel Tulancingo, Oaxaca
Taking advantage of the natural slope of the land, the cisterns were designed in a staggered way to promote the decantation process, the water will fill the cistern A-1, the A-2, until reaching the A-4, later it will be pumped to the treatment plant. The tanks require a solar pumping equipment, the pump’s potential to extract the water from the cisterns of section A is 0.332 HP and for section B is 0.276 HP.
Finally, to determine the tertiary treatment stream and to purify the rainwater to be fit for human consumption, the rainwater runoff analysis was carried out in July. Most of the water quality parameters were below the allowable limits established in NOM-127-SSA1-1994 except for flavor, color, turbidity and the presence of aluminum (Al), iron (Fe) and mercury (Hg) (Table 3).
Table 3 Properties of rainwater in San Miguel Tulancingo, Oaxaca, that exceed the limits allowed by NOM-127-SSA1-94.
The first treatment, by the position of the stepped cisterns, will be the decanting of the fine particles, later the water deposited in the lower level cistern will be pumped to a chlorine doser and finally sent to a 5 000 L capacity tank, then it will be connected to the drinking water distribution network of the municipality and to the rainwater purification plant.
The purification treatment will consist of a tertiary train system, which has: sieve filter, activated carbon filter, polish filters, ozone, and ultraviolet rays. Activated carbon adsorbs gases and metal ions of mercury (Colpas et al., 2016.); as well as small amounts of iron and manganese (McFarland and Dozier, 2015). UV rays damage DNA molecules of microorganisms such as algae, parasites, fungi, bacteria and viruses (Escobedo et al., 2006).
Purified water will be packed in 19 L jugs, 92 jugs will be needed to cover 1 750 L day-1 demanded by the 500 inhabitants population. The continuity of the project will be ensured by organizing community participation workshops and training of selected personnel to operate and maintain SCALL.
Conclusions
Rainwater as an alternative source, will have a quality suitable for consumption, as long as the basic hygiene standards are followed from its collection, storage, treatment and disposal. The SCALL ensures that the inhabitants of the municipality of San Miguel Tulancingo have water in quantity, quality and of continuous way to satisfy their human consumption and domestic use needs.
Literatura citada
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Received: July 2017; Accepted: August 2017
Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons
