Purification of Rainwater Using a Photocatalysis Technique to be Applied to Communities in Ciudad del Carmen, Campeche, Mexico

*Carlos Montalvo, Claudia A. Aguilar, Rosa A. Martínez, Rosa M. Cerón, Alejandro Ruiz, Eric Houbron and Juan C. Robles*

### **Abstract**

Small communities far from the municipal seat do not have access to drinking water, so many children suffer from various gastrointestinal diseases, which cause these children to grow up with nutritional deficiencies. In the state of Campeche, there are 300 sunny days. This energy can be used to install water treatment systems to make it drinkable. Therefore, a treatment system with heterogeneous photocatalysis was proposed using a zinc oxide catalyst doped with silver nanoparticles. The reactor has a metal structure with a flat plate where clay plates support the catalyst. Samples were taken every 2 h to carry out the corresponding analyses and in a period of 8 h of reaction. For the characterization of rainwater adhered to Mexican regulations. The results showed that there was 6400 NMP/100 mL for fecal coliforms at the beginning, and after 4 h, this parameter goes to <2 NMP/100 mL. Initially, the same happened for fecal coliforms; 9200 NMP/100 mL was determined. After 4 h, this parameter drops to <2 NMP/100 mL. The same behavior was observed with chlorides, hardness, and total alkalinity, which showed a tendency to decrease significantly. This confirms that the system works properly to eliminate organic compounds and purify rainwater.

**Keywords:** rainwater, zinc oxide, photocatalysis, drinking water, falling film photocatalytic reactor (FFPR)

#### **1. Introduction**

Water is one of the essential natural resources and, together with air, land, and energy, constitutes the four essential resources on which development is based [1].

Water, as a natural resource, is manipulated by man, thus altering its cycle. Water is extracted from ecosystems for use. But a greater supply of water to the cities brings with it a greater discharge of wastewater, which damages the vegetation and the quality of the subsequent discharge. It is here where the importance of sustainable

development must be recorded, which is the one that makes it possible to make the use of resources compatible with the conservation of ecosystems.

The amount of water we have on Earth is neither increasing nor decreasing, but the human population has grown drastically, and therefore, our need for this resource has also grown. Also, while the amount of water is constant, the way it is distributed over time is not: it is irregular throughout the year. It varies differently depending on global climatic conditions. In the same way, the diverse ecosystems, such as humid forests, pine forests, scrublands, grasslands, or deserts, influence the way and the amount of water that enters the aquifer systems, its conservation in the soil, or its passage into the atmosphere, which causes the availability of this resource to be variable in each region of the planet [2].

Access to good quality water is directly linked to human health and development. At present, the use of water for human consumption is limited since various sources contaminate most of the available fresh water.

In many parts of the world with high or medium rainfall, the quantity and quality of water necessary for human consumption is unavailable. Rainwater is used as a source of supply.

The observation of this acute and critical problem induced to seek and promote some practical methods that provide the small communities of the Municipality of Carmen, Campeche, with water of a certain quality for their consumption; therefore, in this investigation, the design and construction of a falling film photocatalytic reactor, in which a ZnO-Ag photocatalyst is fixed utilizing clay plates, with the purpose of degrading organic components through the incidence of solar radiation, is proposed.

The methodology considers the design, dimensions, and materials for constructing the photocatalytic reactor: the processes for preparing the solutions to be treated, the process of adequacy and photo deposition of the catalyst, and the optimal operating parameters of the falling film system.

#### **2. Collection and storage**

Rainwater harvesting and storage have been practiced for over 4000 years. In the case of Mexico, the "aguadas" (artificial deposits) were used in pre-Colum-

bian times to irrigate crops in small areas.

In archeological zones of the Yucatan peninsula, from the year 300 A.D., collection systems known as "chultus" were used, whose function is to collect rainwater from the patios and conduct it through channels to deposits built with stone to be utilized later [3]. The average annual rainfall for the Mexican territory is 1500 cubic kilometers of water. If 3% of this amount were used, it would be possible to supply 13 million Mexicans who currently do not have drinking water; two supplemental irrigations would be given to 18 million hectares of rainfed land; 50 million animals would be supplied, and 100,000 hectares of greenhouses would be irrigated [4, 5].

The collection, treatment, and use of rainwater is an essential source of water supply for human, livestock, and agricultural use and consumption for rural communities or populations of less than 2500 inhabitants, which have difficulties with their collection due to their topography, isolation, dispersion of hamlets, or lack of supply sources, whether surface or subway [4].

*Purification of Rainwater Using a Photocatalysis Technique to be Applied to Communities… DOI: http://dx.doi.org/10.5772/intechopen.112579*

#### **2.1 Water use in Campeche**

In the state of Campeche, despite having several sources of fresh water and annual rainfall reaching an average of 1681.4 mm, there are no storage and treatment systems to use for human consumption, livestock, aquaculture, and vegetable irrigation, since there is no adequate technology to ensure that the water meets the specifications for these purposes [6].

The municipality of Carmen is located southwest of the state of Campeche, bordered to the north by the Gulf of Mexico and the city of Champotón, to the south by the state of Tabasco, to the east by the towns of Escárcega and Candelaria, and to the west by the municipality of Palizada. It is located between parallels 17°52′ and 19°01′ north latitude and meridians 90°29′ and 92°28′ west longitude of Greenwich. It has a territorial extension of 9720.09 km2 , representing 17.09% of the state's surface [4].

The municipality is in the Grijalva-Usumacinta hydrological region, the most crucial hydrological system in the state; due to its rainfall, periods of drought, and the topography of the terrain, it maintains a regime of irregular flows throughout the year, with the highest flows during the rainy season in summer and autumn, which decreases in winter and spring.

Today's world depends without exception on chemicals, whether to increase food production, protect health, or facilitate daily life [7, 8].

#### **2.2 Water pollution**

Three-quarters of the planet's surface is covered by water; approximately, there are 1385, 000, 000 km3 of water, of which 97.3% is salt water, 2.08% is frozen at the poles, and only 0.62% is available for the development and sustainment of human life [9].

Water pollution is defined as the presence of foreign substances or organisms in a body of water in such quantities and with such characteristics that they prevent its use for specific purposes [4]. Such contamination can be of natural or anthropogenic origin, a direct consequence of the development of water resources [4].

Such pollution can be of natural or anthropogenic origin, directly from sewage or industrial runoff (point sources) or indirectly from air pollution or agricultural or urban runoff (non-point sources) [10].

There is a great variety of components in water, which their nature or size can classify. Their physical or biological nature can distinguish them by size; they are classified as suspended matter, colloidal matter, and dissolved matter.

Chemical pollutants include organic and inorganic components, each with specific characteristics in contaminated water. The presence of organic compounds decreases the amount of oxygen dissolved due to their biodegradation by aerobic microorganisms. On the other hand, the presence of inorganic compounds is related to toxicity, especially in the case of heavy metals. Some inorganic compounds, such as sulfites and nitrites, oxidize, generating a demand for dissolved oxygen [11, 12].

Physical pollutants include thermal pollution due to the discharge of slightly hot water used in heat exchangers, turbidity (caused by suspended solids), color, foaming, and radioactivity [11].

Biological contaminants include remains of plants, animals, and microorganisms. These contaminants are responsible for transmitting diseases, some of which are transmitted by biological pollutants, such as cholera, typhoid, paratyphoid, and so on.

#### **2.3 Water decontamination**

The use of water is limited by its quantity and quality. Water quality used to be qualified only by some physical parameters such as appearance, color, taste, and odor, and now, with the scientific and technological advances that have had an impact on the development of analytical techniques and processes capable of identifying a wide range of compounds, giving way to chemical and biological parameters, to such an extent that it is possible to make drinking water by purifying wastewater.

Physical parameters are the characteristics that the senses can perceive, such as suspended solids, turbidity, color, taste, odor, and temperature.

In water, there are biological species of different sizes and complexity for which there are biological parameters; the presence of specific organisms, bacteria, viruses, and protozoa, can be used as an indicator of a contaminant.

#### **2.4 Heterogeneous photocatalysis**

Heterogeneous photocatalysis is a discipline whose main objective is to decrease the energy activation of a photochemical reaction. Heterogeneous photocatalysis includes various reactions: moderate or total oxidation, dehydrogenation, metal deposition, water detoxification, removal of gaseous pollutants, and so on. It can be considered one of the new "advanced oxidation technologies" for water and air purification treatments [13].

Photocatalysis differs from conventional heterogeneous catalysis by activating the solid catalyst through photo absorption instead of thermal activation [13, 14].

This type of activation requires a semiconductor material as a catalyst, which must be provided with radiation energy higher than its forbidden band.

The overall process is like a conventional catalysis, which can be broken down into five independent steps:


Three components are fundamental for a heterogeneous photocatalytic reaction: a photon source (with appropriate wavelength), a catalytic surface (usually a semiconductor material), and an electron acceptor, which in many cases is oxygen.

Charge carriers are transferred to the photocatalytic surface, allowing REDOX reactions with the adsorbed reactants. On the catalytic surface, REDOX reactions are separated into oxidation and reduction processes, involving, on the one hand, conduction band electrons and electron acceptors, for example, oxygen molecules (<sup>−</sup> +• − ), and, on the other hand, valence band holes and adsorbed electron donors, such as organic molecules or generally specific pollutants (h <sup>+</sup> + • + ). Indirect oxidation reactions also occur by forming the highly oxidizing hydroxyl radical (HO•) generated by water oxidation by the voids [15–17].

#### *Purification of Rainwater Using a Photocatalysis Technique to be Applied to Communities… DOI: http://dx.doi.org/10.5772/intechopen.112579*

Each ion formed then reacts to form an intermediate and end product. Because of the reaction, photonic excitation of the catalyst appears as the initial step of the entire catalytic system. Hence, the photon efficiency must be considered a reactant, and the photon flows as a special fluid, the "electromagnetic" phase. The photon energy is adapted to the adsorption of the catalyst, not to that of the reactants. The activation of the process goes through the excitation of the solid but not through the reactants. As demonstrated below, the adsorbed phase has no photochemical process, only a proper heterogeneous catalysis regime [13].

Whenever different semiconducting materials have been tested under comparable conditions for the degradation of the same compounds, TiO2 has generally been shown to be the most active. This semiconductor is of particular interest as it can utilize natural (solar) UV because it has an appropriate energy separation between its valence and conduction bands, which can be overcome by the energy content of a solar photon (390 nm > γ > 300 nm) [18, 19].

Systems based on disinfection by heterogeneous photocatalysis using solar radiation have several advantages, such as [19–22]:

Non-consumption of high-value oxidizing agents and high production of TiO2. Since the ultraviolet radiation necessary for catalyst activation can be obtained from solar radiation, this system consumes minimal maintenance energy and no external energy consumption during operation.

The oxidants produced are high-powered and non-discriminating, with the advantage of eliminating most microorganisms and degrading or mineralizing most organic pollutants.

It can be applied in rural areas or areas of difficult access since other similar technologies, such as UV irradiation or ozone application, require an external energy source.

#### **2.5 Catalysts**

Zinc oxide (ZnO) is an economically accessible metal oxide, easily detectable. Low energy light can excite it, absorbing part of the solar radiation incident on the earth's surface. It has received interest in removing and destroying recalcitrant organic compounds within the photocatalysis technology [23, 24].

ZnO exhibits a broad spectrum of biocidal activity toward different bacteria, fungi, and viruses given to the production of reactive oxygen species and the release of Zinc ions (Zn2+); it is also demonstrated that the synthesis of this metal oxide by green chemistry routes has a higher bioactivity, which is possibly attributed to the greater surface area, higher absorption capacity, crystallinity, and transmission [24–26].

Ag (Silver) is the most studied agent, and therefore, more information is available regarding its mechanism of antimicrobial activity; it is active against Gram-negative (*Escherichia coli*) and Gram-positive (*Staphylococcus aureus*) bacteria [26].

#### **3. Methodology**

#### **3.1 Reagents**

The reagents used throughout the different processes for the development of the research work in the treatment of rainwater disinfection are:

Zinc oxide of the J. T. Baker brand, silver sulfate of the Fermon brand, pyridine of the Aldrich brand, silver nitrate of the J.T. Baker brand, sodium chloride of Baker, sodium chloride of the Zeus brand, potassium chromate of the Fermon brand, ammonium chloride of the Baker brand, and ammonium hydroxide of the Baker brand, among others, especially in the analysis of rainwater samples.

### **3.2 Equipment**

During the realization of this project, equipment located in the Catalysis Laboratory of the Faculty of Chemistry UNACAR was used, as described in the following **Table 1**.

#### **3.3 Falling film photocatalytic reactor (FFPR)**

The falling film photocatalytic reactor (FFPR) is designed with a metallic structure base that provides a surface area of 1.00 m2 ; with the impregnated catalyst, the contact area is increased to 852 m2 , with a height of 80 cm; the photoreactor presents an inclination that can be positioned at an angle of 15, 30, and 45°; the feeding works with a recirculation system by gravity and pressure action making use of a centrifugal electric pump with magnetic dragging that is supported by distributed hoses the water through channels that at the beginning circulate the water on the surface of the photoreactor and at the end lead the water to a tank where the experimental water is kept in a container, thus completing the connection of the recirculation system; the water flow is controlled with a ball valve as shown in **Figure 1**.

The materials used for the construction of this reactor are listed in **Table 2**. It is made up of a metallic structure, a ceramic bed where the doped catalyst is found, and a pumping system.

#### *3.3.1 Catalyst support*

Red clay plates support the catalyst on a porous surface due to their adsorption capacity, stability, and non-toxicity. To cover the area of 1.00 m2 , ten plates are selected, and the minimum necessary cuts are made to fit the reactor. They are leveled with sandpaper on one side to homogenize the surface and washed to eliminate loose dust. Finally, they are placed in the muffle for 1 hour at 550°C to eradicate moisture and organic matter.


**Table 1.** *Equipment used.*

*Purification of Rainwater Using a Photocatalysis Technique to be Applied to Communities… DOI: http://dx.doi.org/10.5772/intechopen.112579*

#### **Figure 1.** *Schematic diagram of the FFPR.*


#### **Table 2.**

*List of materials for the construction of the RFPD.*

#### *3.3.2 Catalyst synthesis*

To carry out the dry impregnation synthesis of the catalyst, a solution of distilled water and zinc oxide at non-fixed concentrations is prepared, preparing a total of 33 g of ZnO for 1600 mL of distilled water, after which it is applied on the surface face of each clay plate to cover the entire reactor and is left to stand for 90 minutes. After this step, to dry, adhere, and activate the catalyst, the plates are introduced into the muffle for 2 hours at 550°C.

#### *3.3.3 Catalyst doping*

Once the catalyst is supported on the plates, the catalyst is doped with silver nanoparticles, starting with the preparation of a solution of distilled water and avocado sulfate at a concentration of 400 ppm for 8 liters of distilled water, which is carried out with the photo deposition method on the impregnated catalyst, and the

recirculation of the silver sulfate solution is started. At the same time, it is irradiated with six ultraviolet light lamps of 365 nm and 15 watts of power for a time of 6 hours and is left to stand for 2 hours; the next step is activation by calcination, and for this, each plate is introduced to the muffle for 2 hours at 550°C. Ultimately, the plates are placed on the reactor, ready to test its functionality and disinfect the rainwater.

#### *3.3.4 Reactor start-up testing*

Four water absorption tests were performed before using the FFPR to treat rainwater. The results of this absorption are shown in **Table 3**.

It was shown that before incorporating the solution to be treated over the reactor, it was necessary to include at least 3 L of water and consider that the clay tiles absorb this amount.

To ensure reliability in the reaction system, initial tests are made with the degradation of the pyridine compound based on previous research results [27]. Initial concentrations of 50 parts per million (ppm) of the pyridine compounds were used as the model compound, which was treated for 8 h, taking samples of 50 mL every 2 hours, which were analyzed in a Cary-60 Uv–vis spectrophotometer. In this equipment, a sweep was performed from 200 to 600 nm.

#### **3.4 Rainwater samples**

Collecting, preserving, and storing samples for subsequent characterization and microbiological decontamination are necessary for the disinfection treatment of rainwater over the photocatalytic reactor.

The collection of 25 samples of 200 mL of rainwater was carried out during the rainy season in a period from June to September in Ciudad del Carmen, Campeche, at location 18.642522, −91.816223, with a collection system built to capture water directly from the source, in the open air; they were preserved and stored under refrigeration until they were handled for the corresponding characterization.

### **3.5 Characterization of rainwater**

The physical and chemical analyses are carried out by the Mexican Official Standard NOM-127-SSA1–1994, "Environmental Health, water for human use and consumption-permissible quality limits and treatments to which water must be subjected for its potabilization." In this case, 20 L of rainwater was treated in batches and treated in the reactor for 8 hours with exposure to sunlight; samples were taken every hour to see the progress of the disinfection or treatment given to this water.


**Table 3.** *Analysis of absorption tests.*

*Purification of Rainwater Using a Photocatalysis Technique to be Applied to Communities… DOI: http://dx.doi.org/10.5772/intechopen.112579*

In the Teaching, Research and Services, Management and Environmental Control Laboratory of the Faculty of Chemical Sciences of the Veracruzana University Orizaba campus, Veracruz., samples were analyzed, according to the official Mexican regulations.

**Table 4** shows the parameters analyzed and the regulations applied; each parameter is analyzed utilizing an official Mexican standard.

### **4. Results of the project**

The results obtained throughout this project of constructing a photocatalytic reaction system to treat rainwater and be used in small communities of Carmen, Campeche, are shown.

The construction of the photocatalytic reaction system in its different stages of development and the tests for using the reactor are shown. And in the same way, results regarding the collection, handling, and physical, chemical, and microbiological analyses of rainwater samples are presented.

#### **4.1 Construction of the falling film photocatalytic reactor**

For the construction of the falling film photocatalytic reactor, as the design was presented in the methodology, the materials listed in **Table 2** were used.

As shown in **Figure 2**, its metallic structure provided an occupation area of 1 m<sup>2</sup> to support the clay plates that, at the same time, kept the catalyst for its subsequent impregnation and doping process, working at an angle of 30° inclination (**Figure 2a**).


#### **Table 4.**

*Tests are carried out according to the corresponding regulations.*

#### **Figure 2.**

*Construction stages of the FFPR. (a) Metallic structure, (b) recirculation system, and (c) FFPR operating in previous degradation tests.*

We also proceeded to incorporate the recirculation system (**Figure 2b**), which was supported by the electric pump to supply the liquid through hoses that lead it to the distribution channel, descending through the surface of the reactor to be collected directly in the collection channel that leads the liquid to an outlet with a hose so that the liquid reaches the collection tank again.
