Rainwater catchment system for disadvantaged community

Rainwater catchment system for disadvantaged community
Ulisses T. Bezerra1,a, Normando P. Barbosa2,b, Hector G. Morales3,c, Janean M. Shedd3,c,
Jennifer E. Hewitt3,c, Justin Fu3,c, Kelsey Evezich3,c, Matthew T. Tobin3,c, Uzoma B.
Ayogu3,c, Wanyi Ng3,c, Diego S. Amorim2,d, Guilherme O. Oliveira2,d, Helen K. R. F.
Pinto2,d, Jacqueline G. Silva2,d, Jessé P. Gomes Júnior2,d, Márcio S. Gonçalves2,d, Rafaela
L. Silva2,d, Roberto M. P. F. Mendonça2,d
1
Federal Institute of Paraiba-IFPB, Av. 1º de Maio, 720, Jaguaribe, João Pessoa-PB,
Brazil, 58015-435
2
Federal University of Paraiba-UFPB, Center of Technology – LABEME, Campus I, Cidade
Universitária, s/n, Castelo Branco, João Pessoa-PB, Brazil, 58051-900
3
DUKE University, Pratt School of Engineering, 100 Science Dr, Durham, NC 27705,
United States of America
a
[email protected], [email protected], [email protected],
d
[email protected]
Keywords: water sustainability, rainwater tank, toilet flushing, disadvantaged community.
Abstract. A partnership between Federal University of Paraiba - UFPB (Brazil) and DUKE
University (USA) chose an economically-impaired community in Northeastern Brazil for the
implementation of a rainwater catchment system. The goal was to collect rainwater for using it in
toilet flushing in order to achieve: (i) water consumption reduction; (ii) use of gravity force; (iii)
electric consumption reduction; (iv) utilization of an extra water source. This project, started in the
end of 2013, was developed during the first semester of 2014, and implemented from July to
August, 2014. For this purpose, engineering undergraduate students from DUKE University
traveled to Brazil and, joining the Brazilian academic group. They constructed two rainwater
catchment systems as well as the supply piping for three bathrooms. Each system was built in a
different location: one in a place belonging to a non-governmental organization and the other in a
local popular home. Low-cost construction materials were employed, always aiming to follow
safety and sanitary normative requirements. The tanks are located in an intermediate height between
the roofs and the toilet water inlet so that the water is conducted along the piping by gravity only.
Results have shown that: (i) water consumption decreased in both systems, (ii) rainwater is
currently used with efficiency, and (iii) electric consumption was also reduced. Henceforward, the
main idea is to propose to local governments the adoption of such rainwater catchment systems for
all the community (500 families) as to introduce a sustainable use of water from rainfalls.
Introduction
Despite the economic development that has occurred in emerging countries during the last
decades, a certain portion of society remains on the margins of social and economic progress. In
these countries, peripheries of big cities present many infrastructure problems. In addition, the lack
of adequate housing conditions, water, sanitation, etc., are part of a disturbing reality, where the
most affected are those who are more vulnerable: the children and the elderly [1]. In Brazil,
hundreds of low-income communities suffer from problems related to the insufficiency (or even
absence) of essential elements of urban infrastructure.
In terms of statistical data, according to the Brazilian Basic Sanitation Plan (PNSB) [2], less than
60% of the national population has access to collection and treatment sewage systems, which are
basic services to be provided for citizens.
Given this scenario, the Brazilian government has established development policies related to
university extension programs that support projects aiming to approach the society and academia.
This new paradigm in higher education has attracted specific actions towards the application of
theoretical knowledge to solve both recurring and urgent everyday problems faced by citizens.
In this context, the present community work project of the Federal University of Paraiba (UFPB)
aimed at dialogic interventions in the scope of the housing infrastructure, in a partnership with the
organization DUKE Engineers for International Development (DEID) [3], from DUKE University
(Durham, US), and the Non-Governmental Organization (NGO) Casa dos Sonhos [4] (Santa Rita,
Brazil).
The interventional actions were planned at UFPB’s Center of Technology, with tasks divided
into groups of students and professors from the respective universities. All the phases of the project
(description of constructive methods, sizing of pipes, definition of construction materials, etc.), as
well as further actions, were done during the initial project steps in the respective institutions. Later,
the execution activities were carried out with the presence of DUKE students in Brazil.
Thus, the goal of this project was to conceive and implement a rainwater catchment system that
allows the use of rainwater in toilet flushing in houses of the community, through a bilateral work
of two higher education institutions (UFPB and DUKE).
Materials and methods
The project was performed during eight months and was composed of three phases.
In the first phase, UFPB engineering students realized some visits to the community for
recognition of its socioeconomic reality and diagnosis of its main infrastructure problems related to
the proposed project.
Secondly, the intervention actions to be developed in the community were formulated,
prioritizing cost reduction. Then, weekly meetings were set for project conception. The DUKE
team’s task was to design the rainwater tanks as well as to choose and estimate the materials needed
for their construction, whereas the UFPB team was responsible for the design of the necessary
piping for the rainwater catchment - and toilet flushing - system.
During the first two phases, a constant communication was established between UFPB, DUKE
students, the project coordinators (professors from both universities), the NGO and the community,
in order to assure that every action was compatible with the needs of the beneficiaries of the project.
In the third and last phase, the students (from UFPB and DUKE), UFPB professors, NGO
members, and other volunteers implemented the developed designs during over one month in the
community. UFPB gave support to the students by offering a van to transport the students from and
to the community on a daily basis. The project was brought to public attention through television
and online social networks.
Two places were chosen for the rainwater catchment systems, where the tanks would be built:
one tank at the NGO Therapy Center (with four roofs) and one tank at the house of a community
resident. The catchment system is composed of the gutters that collect the rainwater from the roofs,
a diverting system that will discard a first portion of the rainwater, piping that takes the water
into/from the tank, water tanks and other accessories.
The Brazilian Standard for the use of rainwater for non-potable purposes, NBR 15527 [5], states
that a certain volume of rainwater has to be discarded by flush diverters, due to the presence of tree
leaves, small debris and organic matter from the roofs; such volume depends on the roof area from
which the water is collected and prevents the system from having flow impairments or a bad water
quality. For this purpose, barrels were installed to the piping, before the connection with the tanks,
in order to catch and discard the first volumes of water. Once these barrels are filled up with the
dirtier water, they are automatically closed and the cleaner water continues to be driven to the tanks.
Finally, once the rainwater is stored, it is directed to toilet flushing and can be used in the
bathrooms of four houses.
Figure 1. NGO floor plan with the piping system detached. Gutters (magenta color) conduct
rainwater from roofs to pipes (yellow color). The inlet piping (also in yellow) connects the reservoir
(blue rectangle). Outlet piping is shown in green color, leading the stored water from the tank to
toilets (red circles).
Rainwater flow estimate
First the volume of water to be collected per hour of rain on the roof was estimated. According to
the Brazilian standard NBR 10844 [6], which regulates rainwater catchment systems in buildings,
the rainfall intensity (i.e. the thickness of a water layer over a 1m² area) to be considered depends
on the location of the construction site. A rainfall return period of five years and a duration of five
minutes were considered for choosing the adequate rainfall intensity.
Because no statistical data was found for the city of Santa Rita, the rainfall intensity was adopted
to be the same as that of Joao Pessoa, approximated to 140 mm/h in the standard table, which is the
capital of the state. This consideration can also be justified by the fact that Joao Pessoa is the
nearest big city and its metropolitan region comprises Santa Rita. Then, no significant differences
would be found between these urban centers, in terms of data related to rainfall features, as both are
subject to similar meteorological phenomena.
Sizing of gutters and piping system
The flow rate of water to be collected by gutters of a roofing, which is called design flow rate, is
a function of rainfall intensity (I, in mm/h) and the area of contribution (A, in m²).
(1)
Design flow rate equation
Q: design flow rate (l/min)
I: rainfall intensity (mm/h)
A: area of contribution (m²)
The gutters and piping until the tanks are designed as free conducts through Manning’s equation
and should have a uniform slope of at least 0.5% and up to 1.0%. Thereafter, the dimension
estimate of the vertical and horizontal pipes was found out through abacuses and tables presented in
the NBR 10844 standard.
(2)
Manning’s equation
Q: design flow rate (l/min)
S: cross-sectional area of flow (m²)
: hydraulic radius (m)
I: rainfall intensity (mm/h)
n: Manning’s coefficient
Rainwater tanks
Many construction materials were considered for use on the tanks. For each construction site,
different solutions were adopted, prioritizing the economic sustainability of the applied building
methods and taking into consideration spatial restrictions. At the NGO Therapy Center,
conventional masonry blocks (containing eight holes) were used to build the walls to support
prefabricated concrete slabs. At the house, pre-fabricated containers were utilized with a supporting
foundation built in conventional masonry bricks as well. Each tank contains a piping system that
not only has its inlet and outlet pipes, but also two others that allow for the tank’s overflow (on the
top) and complete drainage (on the bottom), if necessary.
Toilet flushing system
The piping needed to direct the water stored in the tanks towards the bathrooms was designed as
pressurized cold water conducts, according to the Brazilian standard NBR 5626/1998 [7], which
regulates water supply systems in buildings. The design aimed at using gravity force only to drive
the stored rainwater with satisfying pressure levels that would enable toilet flushing. This pressure
level at the connection point to the toilets should be 0.5 meters of water column.
Results and discussion
For a better understanding of the results achieved on the performance of the tanks, the rainwater
catchment systems are henceforward distinguished from each other: the System #1 corresponds to
the system implemented at the NGO Therapy Center and the System #2 refers to the one built at a
house of the community.
a) System #1 (NGO)
Gutters
At the construction site, some preexisting gutters already collected rainwater from part of the
roofs. These gutters were made of PVC (PolyVinyl Chloride) pipes with 150 mm of diameter, cut
longitudinally in half, or made of metallic plates in a rectangular transversal profile. All gutters
were cleaned for reuse and some had their direction of slope inverted, according to the project
requirements. Other gutters were installed in roofs where no collecting systems were found.
The slope required for the gutters was 0.5% [6] and it was reached by using a level tube (Figure
2).
Figure 2. Adjustments of gutters after establishing the project slope.
Tank’s foundation
It was discussed with the NGO members the most feasible spot for the construction of the tank.
Once it was defined, foundation ditches measuring 10 cm in depth and 40 cm wide were dug. A
lean concrete layer was cast in the ditches. Concrete specimens (Figure 3), obtained from the
technological control of other constructions, were used replacing stones. Then, foundation walls
were built (Figure 4). Over them, concrete channel blocks (30 cm x 19 cm x 15 cm) were placed.
Two parallel 10 mm steel bars were put into the channel blocks. After that, a concrete mixture (4
parts sand, 4 parts coarse aggregate, 1 part cement, by volume) was cast into the channel blocks,
covering the reinforcement bars.
Figure 3. Concrete specimens used as foundation elements.
The level of the bottom slab of the tank was fixed according to the design water pressure
required to the toilets, considering hydraulic losses in all pipe sections. The tank could not be built
on the ground level because the water would not reach toilet flushing with enough pressure without
the use of electricity. According to the NBR 5626/1998, the minimum necessary hydraulic pressure
for servicing toilets is 0.5 meters of water column.
One end of the level tube was placed at the highest inlet pipe among the project’s flushing
cisterns and the other end was placed at the level of the tanks foundation. Then, bricks were laid
until the latter level (foundation level). A line was used for marking levels and rows of bricks were
built until it reached 30 cm below the foundation level. For every row of bricks constructed,
horizontality was assured.
The last layer in the wall over the foundation consisted of another tie beam made of channel
blocks (similar to those previously used). The height of this layer was 15 cm. The additional 15 cm
corresponded to the distance between the lower inner surface and level of the outlet piping in order
to allow the sedimentation of debris in this non-utilized volume of water (Figures 4 and 5) and to
avoid having a dirty water go to the toilets.
Figure 4. Scheme of the NGO reservoir. Figure 5. Construction of the second tie beam.
Slab tank
A bottom precast slab was built over the foundation walls. Small prefabricated reinforced
concrete beams were arranged over the foundations’s last layer of channel blocks. In the transversal
direction. Ceramic bricks were placed between the concrete beams (Figure 6).
A steel mesh was placed over the blocks and tied to the beams. After setting up a wooden form,
concrete mixture was released on the structure.
Figure 6. Slab structure in the base of the tank.
Masonry
Firstly, reinforced concrete pillars were built. Next, more rows of bricks were added. At the level
of 40 cm, measured from the base of the tank, a third tie beam was constructed (with the same
procedure used for the previous ones) as to assure the stiffness of the masonry walls. The thickness
of this beam is 12.5 cm, being narrower than the first two tie beams. Four more row bricks were
added over this beam and a final tie beam was built near the top of the tank (Figure 7). Another slab
was built on top of the walls as the tank’s ceiling.
Figure 7. Position of the beams at the base and at the half height of the tank.
Inlet piping
Design indicated a 100 mm diameter for the inlet PVC pipes. A small mesh net was installed at
the entrance of the piping system to avoid obstructions caused by debris. The PVC tubes were fixed
onto the walls of the property by steel clamps. The clamps were screwed to the walls every 3 meters
keeping the design slope. All pipe connections were sealed with appropriate silicon sealant.
In total, two inlet tubes were installed on the tank: one collects rainwater from a roof that
belongs to the NGO, whereas the other pipe catches rainwater from other three nearby houses of the
community. Each of the inlet tubes has its own flush diverter.
Because there is a difference between the levels at which each inlet pipe intersects the tank, i.e.
the pipe from the NGO roof is 30 cm higher than the other inlet pipe, a check valve was installed in
the lower tube. It prevents water reflux in the lower tube, when the water is near the maximum level
inside the tank. When this happens, the rainwater flow in the lower inlet pipe no longer contributes
to fill the tank and may be discarded through its flush diverter.
Outlet piping
There are two pipes for the outlet flow: one tube is connected to the NGO toilet and the other
conducts the water to three other toilets (community houses). The diameters of both pipes are 45
mm and 50 mm, respectively. The outlet pipes are placed at 15 cm and 23 cm, respectively, from
the level of the lower slab (Figure 8).
Figure 8. Outlet pipe with hydraulic valve.
All outlet pipes run below the ground level. For the NGO toilet, a small ditch was dug (10 cm
deep) from the tank to the toilet. A PVC pipe, with 45 mm of diameter, was then placed into the
ditch. At the toilet wall, a hydraulic component was applied to reduce the diameter from 45 to 20
mm)
Simultaneously, PVC pipes (diameter of 50 mm) were installed towards the other houses. A tee
connection was utilized to derive water from the House #2 to House #3. The end of the pipe that
feeds the House #2 is submitted to a reduction from 50 mm to 20 mm. In the House #3, the inlet
pipe is connected to the toilet tank. Another valve was installed in the preexisting piping system, as
to permit the use of either city water or tank water. A similar scheme was adopted for House #2.
b) System #2 (community house)
Tanks
Due to time constraints and aiming at the adoption of a rationally economic method, it was
decided to acquire three small containers with a 1 000 liters volume, each one, that were installed
side by side over a concrete slab. Each tube contains a central lid at the top. There is also a tap at the
base of each reservoir for complete drainage.
Foundation
The second catchment system was built at the backyard of a community house. The foundation
of the tanks was performed through a constructive process similar to the foundation executed at the
NGO tank (Figure 2). Ditches (35 cm wide, 20 cm deep) were dug for supporting the tank
foundation. The dimensions adopted for the foundation were 1 meter high, 1 meter wide and 3.3 m
long (Figure 9).
The ditches were filled out with concrete specimens and mortar until the ground level. The first
row of bricks (19 cm x 19 cm x 10 cm) was then placed. Differently from the foundation of the first
tank, channel blocks were not used at this stage. A layer of 1.5 cm of mortar was done.
Figure 9. Foundation of the tanks of System #2.
Slab
The precast slab structure was built over the masonry layers of bricks. Reinforced concrete
beams were placed in the horizontal plane. Thus, after putting ceramic blocks between concrete
beams, the concrete mixture was cast over this structure. The slab is 15 cm high (Figure 10).
Figure 10. Construction of the slab.
Gutters and piping
The house that started being supplied by the tanks already had a gutter that catches rainwater
from half of its roof. Instead of capturing water from the other half of the roof, the project members
decided to capture rainwater from a neighboring church’s roof, which was much larger, with proper
permissions. As a result, time and financial resources were saved.
The preexisting gutter had a diameter of 150 mm (PVC pipe longitudinally cut in half).
Screwed metallic clamps were used to attach the gutter to wood elements of the roofing frame.
The slope of the gutter was changed (to 0.5%) as to conduct the water towards the house backyard.
The same sealant procedure, as taken in System #1, was carried out for System #2
It was used an inlet pipe for the tanks, made of PVC, with 100 mm of diameter. A diameter
reduction (150 mm to 100 mm) device was also implemented between the gutters and such pipe. It
was also installed a little mesh to retain any debris from the roofs. Tee connections were also
utilized in these installations (Figure 11b). The flush diverters, for discharging of the first rainwater
volumes, have 100 liters of capacity with a drain outlet located at the base of this container.
A silicon-based sealant was applied at the connection between the inlet pipe and the entrance of
the tank.
(a)
(b)
Figure 11. Pipes that connect the three tanks (a) and the inlet piping (b).
The outlet piping catches rainwater from the three tanks and conducts it below the ground level
towards the house toilet. A closure valve was installed in this section (Figure 12).
Figure 12. Outlet piping (brownish pipe)
Difficulties encountered in the project
Project and execution
Prior to the teams’ arrival in Brazil, the previous plan considered the construction of cylindrical
tanks. It was thought that this geometric form would lead to utmost cost-effective relation, in terms
of the amount of necessary construction material to be used and the water volume to be stored.
However, after inspections on the construction site, it became evident that rectangular tanks would
be more efficient in both spots (NGO property and house), due to the avoidance of structural
problems, higher speed of construction and optimized usage of the available area for construction.
For the next versions of the project, more planning will be dedicated to the optimum location of
tanks as a function of the height of the tubes coming from the gutters (System #1). Although an
innovative solution was performed for dealing with the difference of levels between inlet pipes, it
required more time of construction. The ideal solution would be establishing the same level for both
pipes. On the other hand, the tanks were built in the best possible locations, according to the
circumstances encountered.
The Project members would have preferred to build a tank for the house (System #2).
Nevertheless, because of time and space constraints, three premade containers (composed of a
polymeric material) were bought. These containers had smaller water capacity (1000 liters each)
and were of difficult maintenance
Communication and logistics
At the beginning of the project, there was some difficulty in communication among project
members, due to different language backgrounds (Portuguese and English). It interfered in
performing tasks at the site. Sometimes, services were made incorrectly and it needed more time for
correction. Over the days, communication between project members and people from the
community improved, becoming faster and more precise.
The Federal University of Paraiba provided logistic support for the transportation of project
members towards the construction site. However, this project also suffered from setbacks related to
transport of students and materials to the construction site, which has to be improved for future
related projects. Delays in the supply of materials, e.g. cement, bricks, pipes, etc., made it difficult
to meet some project deadlines.
Conclusions
The intervention actions developed at the community took place as projects in the engineering
field, having the engagement of several people from various undergraduate courses at UFPB,
DUKE and even other universities. This experience also involved the participants with activities
related to different academic areas of knowledge, which contributed to raising global and local
awareness and to the training of people.
Through the close contact with the community and the assistance of the NGO staff, students
could establish a diagnosis of the infrastructure as well as social and economic aspects of the
community and propose solutions to real problems based in social, environmental and economically
sustainable measures.
Therefore, the partnership with DUKE University and UFPB managed to develop a double
interaction: (i) integration of knowledge acquired by students and professors from both universities
and (ii) physical integration (through interpersonal relations) between the community and the
universities.
Finally, the project was reported by a local television station, social media and UFPB and DUKE
Websites as tools for broadcasting such extension experience.
Future trends
The partnership between both UFPB and DUKE universities intends to continue, as a mutual
work for development of future extension projects that may cover further areas of knowledge. Thus,
the goal is to give subsidies to achieve significant changes the infrastructure of this community and,
consequently, to bring better quality of life for the people and also opportunities for social
development for locals.
In terms of project plans, it has been planned to build other constructions with Mattone blocks
(soil-cement bricks), due to the ecological viability they present and also aiming at providing
adequate living conditions for citizens. Furthermore, it has also been planned to implement the
rainwater catchment system, for non-potable usage, in future construction works, for executing
models of sustainable construction. Other constructions, such as houses can also be donated to local
needy families.
Additionally, there is a possibility to construct a public library that will belong to the NGO,
covering a target audience and contributing to the improvement of the education system proposed
and offered by the NGO Casa dos Sonhos.
Acknowledgments
We are grateful to Helen Karla Ramalho de Farias Pinto, DUKE University and the group Duke
Engineers for International Development (DEID), Prof. Margareth Diniz, Rector of UFPB, that
collaborate with some financial support, Prof. Gilson Barbosa Athayde Júnior, from the Federal
University of Paraiba, Casa dos Sonhos NGO, UFPB engineering students as well as all volunteers
engaged in this project.
References
[1] BRUNDTLAND, Gro Harlem. Our common future: world commission on environment and
development. Second edition. Rio de Janeiro: Getúlio Vargas Foundation. 1991.
[2] Secretariat for Strategic Affairs (SAE). Published approval of the National Sanitation Plan
(PNSB)
in
the
Official
Gazette
on
Friday.
Source:
http://www.sae.gov.br/site/?p=19554#ixzz3CyCDgxCs.
[3] Duke Engineers for International Development. Available at http://sites.duke.edu/deid/.
[4] Social Statute of the Non-Governmental Organization ‘Casa dos Sonhos’. 2009. Available at:
http://www.casadosonhos.org/Estatuto%20social.php
[5] Brazilian National Standards Organization. NBR 15527: Rainwater – Catchment of roofs in
urban for non-potable purposes - Requirements. 2007.
[6] Brazilian National Standards Organization. NBR 10844: Building facilities for rainwater. 1989.
[7] Brazilian National Standards Organization. NBR 5626. Cold water building installation. 1998.