**Abstract**

Environmental sustainability demands the advancement in water treatment and the use of lighting natural resources. Brazil has one of the most stable and intense solar irradiation in the world. It has to be used not only for energy generation purposes but also and mostly for water treatment, water quality polishment, and furthermore water disinfection. The chapter performs a comparison of different green technologies for water treatment as natural solar irradiation, simulated solar photolysis, solar photo-Fenton with and without hydrogen peroxide addition (solar/ Fe), solar photo-Fenton with and without peroxide (solar/Fe/H2O2), titanium oxide-mediated photocatalysis (UV/TiO2), photolysis under UV irradiation, and UV treatment with hydrogen peroxide (UV/H2O2). The chapter describes the solar photodecomposition calculations for pharmaceuticals and the emerging pollutants mostly found in polluted waters, including the decomposition route, kinetics, and process parameters. Many published works to point out the important properties to evaluate catalyzer and semiconductor materials after their use in photodecomposition processes. The essay includes the solar photodecomposition of dyes, carbamazepine, hormones, acetaminophen, antipyrine, bisphenol A, antibiotics, and the photodecomposition by-products. Finally, the chapter presents the synergistic effect between them with the probable mechanism and mineralization degree.

**Keywords:** pharmaceuticals, antibiotics, TiO2, semiconductor, solar, photodecomposition

## **1. Introduction**

The environmental performances are estimated using the life cycle assessment and the effective removal of 1 μg of 17α-ethynylestradiol (ES) for 1 liter of wastewater. The choice of ES was due to being a worldwide common micropollutant and endocrine-disrupting chemicals (EDCs) in a functional unit [1]. The natural solar photolysis exhibited an environmental footprint about 23 times greater than solar/Fe systems. The solar/Fe/H2O2 minimized the environmental footprint with the energy-intensive simulated solar irradiation that had a much higher, about five times, environmental footprint than the natural solar light. The UV photolysis also shows a low environmental impact. The TiO2 addition to UV and H2O2 to UV reduced the environmental impact of about 97% and 88%, not considering the footprint of the TiO2 production [2].

The total environmental footprint and the environmental sustainability of all the photodecomposition processes were directly proportional to water treatment efficiency and inversely proportional to treatment time (substantial energy input per time unit). The addition of TiO2, iron, and H2O2 improved the process efficiency and environmental sustainability considering only the electricity consumption; the introduction of renewable energy resources could reduce the environmental footprint of the oxidation processes by up to 87.5%.

A solar spectrum contains approximately 46% of infrared light, 4% of UV light, and 50% of visible light. Such natural radiation composition highlight the importance of the visible-light-responsive TiO2 development for natural and renewable solar photodecomposition applications. TiO2 displays photocatalytic role when irradiated by ultraviolet (UV) due to its large bandgap (3.0 eV for rutile and 3.2 eV for anatase). The development of visible light-responsive TiO2 includes chemical doping and photosensitization. The chemical doping is used to narrow the bandgap of TiO2; the doped ions in TiO2 act as recombination centers for photoexcited electrons and holes decreasing the photocatalytic activity.

The organic dye photosensitization on TiO2 represents the major limitation for applications due to the poor dye stability, which can undergo desorption, photolysis and oxidative degradation, and fastback electron transfer, which results in low quantum yield for the photocatalytic reaction. An alternative for organic dye use in the metallic nanoparticles (NPs) is used successfully as photosensitizers for TiO2 due to their stability and strong photoabsorption under visible light based on surface plasmon resonance [3]. It is a coherent oscillation of electrons on the metallic NP surfaces during the incident light irradiation.

The TiO2 photosensitizers were first described in 2005 using gold (Au) as nanoparticles with TiO2 (Au/TiO2) the resultant film oxidized the ethanol and methanol at the expense of oxygen reduction under visible light radiation. The use of Au/TiO2 for 2-propanol decomposition is induced by surface plasmon resonance photocatalytic process: (1) the Au NP adsorption of photons, (2) the Au NP electrons are injected into the conduction band of TiO2, and (3) the resultant electron-deficient Au NPs can oxidize 2-propanol to recover to the fundamental metallic Au NP state. The pharmaceutical waste in the environment cause adverse health effects in the reproductive, neurological, and immune systems of wildlife and humans. Commonly they are resultant of agricultural lands' runoff, septic tanks' leakage, and the discharge of sewage treatment plants' effluents [4]. They can cause significant severe environmental damage even in trace concentrations. Worldwide EDCs are continuously released, and the efficiency of conventional water treatment technologies against such contaminants is minimal.

Advanced oxidation processes (AOPs) are a promising technology for the removal of the persistent organic pollutants (POPs), such as pharmaceuticals and endocrine disrupters (EDCs) from polluted waters. The photocatalytic methods are likely the most promising, especially those involving visible light-responsive materials, i.e., heterogeneous solar photocatalysis.

The photocatalytic hydroxide radicals are potent oxidants and react fast and unselectively with surrounding chemical species via radical addition, hydrogen abstraction, or e- transfer mechanisms. Many oxidant species can also degrade the pharmaceuticals and endocrine disrupter compounds in some cases the intermediate compounds present higher decomposition effectiveness and ends up in complete mineralization with the production of CO2, H2O, and inorganic salts.

The mass transfer is the controlled slowest step of the photodecomposition reaction of adsorption/desorption. The reaction requires the reactant adsorption/ desorption on the catalyst surface and the presence of any barrier to reduce the reaction efficiency. Some experiments are performed keeping the reactor under dark conditions until the adsorption process reaches the equilibrium with the adsorbed mass at the semiconductor surface. After that, the reactor is irradiated and produces the radicals acting in the adsorbent surface and also in the solution. The radiation and the semiconductor generate e<sup>−</sup> and h+ pairs and radicals.

**69**

*Green Water Treatment for Pharmaceutical Pollution DOI: http://dx.doi.org/10.5772/intechopen.85116*

control for lower concentrations.

suspended particles control.

smaller rates for the first.

present [5].

medium behavior.

position efficiency.

reacts with the photogenerated electrons leading to O2

recombination of the generated e<sup>−</sup> and the h+

when the OH<sup>−</sup> ions are available to react with h<sup>+</sup>

(M − OH)surface + H<sup>+</sup> < = > (M − OH2

(M − OH)surface + OH<sup>−</sup>

intermediaries and by-product formation.

**2. Photodecomposition: kinetics and process parameters**

The heterogeneous photocatalysis shows a strong dependence on the operating temperature. The kinetics is usually dependent on the first step of the adsorption and the equilibrium modeled by Langmuir isotherms and Langmuir-Hinshelwood model. The first pseudo-order usually appears at the beginning of the reaction, just in the initial steps. As the reaction proceeds, the intermediate production could interfere with the radiation incidence. The observed decomposition rates as the pollutant start to decompose and begin the competition for the adsorption sites between the pollutants and the adsorbed species. The initial pollutant concentration starts to be the limiting reactant with mass transfer limitations with no kinetic

The increase of the catalyst mass promotes the photodegradation rate and the active catalyst sites. If the system is a slurry, the reaction rate reaches a maximum or optimal value and after that declines. The higher suspended particle concentration enhances the light scattering, the particle agglomeration, with light opacity enhancement, and after a certain point, the photodecomposition efficiency decreases. There is an equilibrium between the available surface site and the

The oxygen plays a vital role in the photodecomposition reactions; dissolved O2

kinetics of the air-saturated solutions and the pure oxygen solution often results in

The pH values influence the catalyst aggregations and its surface charges, with the valence band (VB) and conduction band (CB) position. At low pH values, the CB holes are more effective in comparison with VB. The change in the pH values allows the surface charge modification mostly when the amphoteric groups are

The adsorption equilibrium after decomposition depends on the pollutant pH

the more oxidizing species, the amount of ˙OH increases under alkaline conditions

oxidant (Eqs. (1) and (2)). This effect increases the ˙OH availability at higher pH values in spite of the negatively charged catalyst surface and also the pollutant repelling action at such pH values; the ˙OH radicals' attack can explain the pH

The presence of some anions like chloride, nitrate, and sulfate reduces the photocatalytic performance as a result of the competition for the adsorption sites to scavenge the ˙OH radicals. Natural organic matter and humic acids are scavengers of the reactive species and usually show negative photodegradation influence. Nevertheless, the presence of the carbonate and bicarbonate increases photodecom-

The temperature has a limited effect in the photodecomposition efficiency until 80 Cº; after that there is the tendency to reduce the photocatalytic efficiency as a result of lower oxygen solubility in water. Different temperatures can also promote

speciation and the reactive species. Considering the low pH values, the h+

<sup>−</sup> radicals and preventing the

can be

pairs. The comparison between the

, and the ˙OH become the primary

)surface (1)

+

<sup>&</sup>lt; <sup>=</sup> <sup>&</sup>gt; (M <sup>−</sup> O−) surface <sup>+</sup> H2O (2)

*Green Chemistry Applications*

footprint of the oxidation processes by up to 87.5%.

electrons and holes decreasing the photocatalytic activity.

NP surfaces during the incident light irradiation.

materials, i.e., heterogeneous solar photocatalysis.

per time unit). The addition of TiO2, iron, and H2O2 improved the process efficiency and environmental sustainability considering only the electricity consumption; the introduction of renewable energy resources could reduce the environmental

A solar spectrum contains approximately 46% of infrared light, 4% of UV light, and 50% of visible light. Such natural radiation composition highlight the importance of the visible-light-responsive TiO2 development for natural and renewable solar photodecomposition applications. TiO2 displays photocatalytic role when irradiated by ultraviolet (UV) due to its large bandgap (3.0 eV for rutile and 3.2 eV for anatase). The development of visible light-responsive TiO2 includes chemical doping and photosensitization. The chemical doping is used to narrow the bandgap of TiO2; the doped ions in TiO2 act as recombination centers for photoexcited

The organic dye photosensitization on TiO2 represents the major limitation for applications due to the poor dye stability, which can undergo desorption, photolysis and oxidative degradation, and fastback electron transfer, which results in low quantum yield for the photocatalytic reaction. An alternative for organic dye use in the metallic nanoparticles (NPs) is used successfully as photosensitizers for TiO2 due to their stability and strong photoabsorption under visible light based on surface plasmon resonance [3]. It is a coherent oscillation of electrons on the metallic

The TiO2 photosensitizers were first described in 2005 using gold (Au) as nanoparticles with TiO2 (Au/TiO2) the resultant film oxidized the ethanol and methanol at the expense of oxygen reduction under visible light radiation. The use of Au/TiO2 for 2-propanol decomposition is induced by surface plasmon resonance photocatalytic process: (1) the Au NP adsorption of photons, (2) the Au NP electrons are injected into the conduction band of TiO2, and (3) the resultant electron-deficient Au NPs can oxidize 2-propanol to recover to the fundamental metallic Au NP state. The pharmaceutical waste in the environment cause adverse health effects in the reproductive, neurological, and immune systems of wildlife and humans. Commonly they are resultant of agricultural lands' runoff, septic tanks' leakage, and the discharge of sewage treatment plants' effluents [4]. They can cause significant severe environmental damage even in trace concentrations. Worldwide EDCs are continuously released, and the efficiency of conventional water treatment technologies against such contaminants is minimal. Advanced oxidation processes (AOPs) are a promising technology for the removal of the persistent organic pollutants (POPs), such as pharmaceuticals and endocrine disrupters (EDCs) from polluted waters. The photocatalytic methods are likely the most promising, especially those involving visible light-responsive

The photocatalytic hydroxide radicals are potent oxidants and react fast and unselectively with surrounding chemical species via radical addition, hydrogen abstraction, or e- transfer mechanisms. Many oxidant species can also degrade the pharmaceuticals and endocrine disrupter compounds in some cases the intermediate compounds present higher decomposition effectiveness and ends up in complete

The mass transfer is the controlled slowest step of the photodecomposition reaction of adsorption/desorption. The reaction requires the reactant adsorption/ desorption on the catalyst surface and the presence of any barrier to reduce the reaction efficiency. Some experiments are performed keeping the reactor under dark conditions until the adsorption process reaches the equilibrium with the adsorbed mass at the semiconductor surface. After that, the reactor is irradiated and produces the radicals acting in the adsorbent surface and also in the solution.

pairs and radicals.

mineralization with the production of CO2, H2O, and inorganic salts.

The radiation and the semiconductor generate e<sup>−</sup> and h+

**68**
