The main urgent problem of humanity is related to clean water availability. Shortage of drinking water in most parts of the world has been a growing concern in recent times. This chapter will consider emerging contaminants present in the aquatic environment. The commonly present concentrations are in the range from mg/L to ng/L in wastewater, surface water, ground water, and drinking water. The challenges in wastewater and drinking water purification are dependent on the origin of the water. Solar photocatalysis is a new promising technology for the water purification. With solar, photocatalysis is possible to reduce organic contaminants present in water by using the sunlight. This chapter addresses the fundamental reaction mechanism, different type of photocatalytic nanomaterials based on TiO2, and recent developments in the reactor design for solar photocatalytic water purification from lab scale-up to large-scale application.
TopIntroduction
Today, the contamination of water resources has occurred globally due to the rapid pace of industrialization and tremendous increase in the population. Therefore, water is one of the main urgent problems of humanity together with energy and food. The lack of potable water in most parts of the world has been a growing concern in recent times. The World Health Organisation (WHO) estimates that 844 million people currently lack any form of drinking water purification, with around 159 million people relying on water from surface sources. The situation has been getting worse in underdeveloped and developing countries due to population growth and intensification of land and water use for industry and agriculture needs. Wastewater becomes a serious hazard to ecological and human health due to increasing sewage discharge generated from industrial manufacture and agriculture irrigation.
Some of the important classes of aquatic pollutants are heavy metal ions and dyes, and once these enter into the water, water is no longer safe for drinking purpose and sometimes it is very difficult to completely treat the contaminated water (Forgacs, Cserháti, & Oros, 2004; Rai, Bhattacharyya, Singh, Bansal, Vats, & Banerjee, 2005; Bratovcic, Odobasic, Sestan, & Nurkic, 2015).
Heavy metals such as lead, cadmium, mercury, and nickel are toxic and carcinogenic, even in low concentrations, as they are not biodegradable and can accumulate in organisms.
Pesticides can be defined as a natural or synthetic substances intended for use as a plant growth regulator, defoliant, desiccant, and agent for thinning fruit or preventing the premature fall of fruit.
Comparing with the municipal wastewaters, industrial wastewaters generally contain a high concentration of toxic or non-biodegradable pollutants, such as grease, oils, heavy metals, phenols and ammonia. Then, the water quality of industrial wastewaters varies from one to the other industries. For example, wastewater from the iron and steel industry has a large amount of ammonia, cyanide, benzene, naphthalene, phenol and cresol, resulting in the coke production in the reduction reaction in the blast furnace. The research carried by (Bratovcic, Odobasic, & Sestan, 2017) showed that the main contaminants present in industrial wastewaters in Bosnia and Herzegovina were oil and grease, heavy metals, inorganic substances, suspended solids, solid matter, nitrogen and phosphorus. The similar contamination shows textile waters in Bangladesh with the presence of aliphatic oils and grease, heavy metals and dye molecules (Hossain, Sarker, & Khan, 2018).
In contrast, relatively low concentrations of endocrine disruptors such as alkyl phenols have been found to be present in water sources in Europe (Valcárcel, Valdehíta, Becerra, López de Alda, Gil, Gorga, Petrovic, Barceló, & Navas, 2018).
The increasing world population with growing industrial demands has led to a situation where protection of the environment has become a major issue and a crucial factor for several industrial processes, which will have to meet the requirements of the sustainable development (Da Silva & Jardim, 2006). Aquatic pollutants are often very dangerous for living beings, and also affect the ecosystem. Therefore, the removal of these pollutants from contaminated water is an urgent need in order to prevent the negative effects on the human health and to the environment (Santhosh, Velmurugan, Jacob, Jeong, Grace, & Bhatnagar, 2016).
Bratovcic (2019)
reported that in recent years, photocatalytic degradation by metal oxide nanoparticles such as TiO2 has been successfully applied for the different kind of contaminants degradation present in surface water and wastewater. The same author in other paper discuss the issue of photocatalytic degradation of aromatic compounds, antibiotics, pesticides and herbicides as well as dyes as common organic molecules present in wastewaters and the mechanism of their degradation by TiO2 (Bratovcic, 2019). This is especially important for pharmaceuticals present in water which lead to undesirable interferences in the environment. Because of widespread and elevated consumption of pharmaceutical products in human-health care and veterinary practice they are very often found in waters and are classified as emerging water contaminants.