Available Technologies for Wastewater Treatment

*Ifeanyi Michael Smarte Anekwe, Jeremiah Adedeji, Stephen Okiemute Akpasi and Sammy Lewis Kiambi*

### **Abstract**

During the last three decades, environmental challenges related to the chemical and biological pollution of water have become significant as a subject of major concern for society, public agencies, and the industrial sector. Most home and industrial operations generate wastewater that contains harmful and undesirable pollutants. In this context, it is necessary to make continuous efforts to protect water supplies to ensure the availability of potable water. To eliminate insoluble particles and soluble pollutants from wastewaters, treatment technologies can be employed including physical, chemical, biological (bioremediation and anaerobic digestion), and membrane technologies. This chapter focuses on current and emerging technologies that demonstrate outstanding efficacy in removing contaminants from wastewater. The challenges of strengthening treatment procedures for effective wastewater treatment are identified, and future perspectives are presented.

**Keywords:** anaerobic digestion, bioremediation, coagulation, expanded granular sludge bed, ion exchange, membrane technology, microfiltration, nanofiltration

### **1. Introduction**

Wastewater is produced as a result of human and industrial activities. Different kinds of firms are emerging because of ever-changing needs and demands, and as a response, numerous new pollutants are deposited in wastewater, necessitating the development of advanced treatment techniques. To manage ever-changing wastewater discharges, advanced methods are essential, and there is always a connection between water and energy. Although it is impossible to completely eliminate wastewater formation because no business is 100% efficient, however, it is feasible to develop novel and improve existing wastewater treatment and reuse methods to satisfy water demand. Moreover, water reuse has an enormous prospective for replenishing water resource portfolios that are already overburdened.

Since wastewater treatment and reuse are linked to public health, they are extremely important. The existence of pathogenic organisms and polluted substances in wastewater presents the possibility of harmful health effects where contact, inhalation, or ingestion of substance or microbiological elements of health concern occurs. The impact of several

factors (such as pH, temperature, colour, and particle matter) and chemical components (cations, anions, and heavy metals) on human health have already been proven, and acceptable thresholds have been set. However, if industrial emission comprises a major portion of the wastewater, the influence of organic elements in treated water utilized for non-potable activities requires investigation [1]. Furthermore, while modern technologies can assist in reducing energy consumption and improving reliability, the difficulties in human understanding can be even more worrisome. Past and contemporary proof of disease carried by water (such as cholera, typhoid, malaria, dengue fever, and anaemia) has sparked public debate about the safety of reusing water [2]. On-line sensors, membranes, and enhanced oxidation mechanisms are examples of sophisticated technology that can aid to alleviate this impression. Nevertheless, a clearer knowledge of the processes of reuse and the qualities of reused water in comparison to freshwater resources will lead to a more favorable public opinion.

Wastewater treatment is an eco-friendly process because it protects the ecosystem by releasing less contamination; it employs sustainable resources; it offers the opportunity for unused products to be recycled, and it manages leftover wastes in a more biologically acceptable manner. The features and kinds of contaminants contained in the water, as well as the anticipated use of treated water, influence the choice of treatment technique. Activated sludge mechanisms and anaerobic digestion are century-old methods that continue to work well and have become the treatment of choice [3]. Emerging pollutants in wastewater and rising wastewater loads in water bodies necessitate immediate studies in this field to provide safe and clean water while also ensuring freshwater supplies. With this goal in mind, this chapter focuses on research into the present and emerging wastewater treatment and reuse technologies while highlighting their limitations and prospects [4].

## **2. Wastewater treatment technologies**

Physical, chemical, biological, and combined technologies are commonly used in wastewater treatment facilities. Primary, secondary, and tertiary treatment procedures make up a conventional wastewater treatment plant (WWTP). Primary processes consist of screening, filtration, centrifugation, sedimentation, coagulation, and flotation. Biological treatment, which can be oxic or anoxic, is the most common secondary procedure while oxidation, precipitation, reverse osmosis, electrolysis, and electrodialysis are examples of tertiary treatment. Advanced oxidation processes (AOPs), ion exchange, ultra and nanofiltration, adsorption/ biosorption, and advanced biological treatment combining algae, bacteria, and fungi are all emerging treatment methods that offer healthy and clean treated water [3].

### **2.1 Physical wastewater treatment technologies**

Physical methods, in which physical forces are utilized to remove contaminants, were among the first wastewater treatment technologies used. They are still used in most wastewater treatment process flow systems. These methods are typically employed when water is heavily polluted. The most often used physical wastewater treatment methods are:

*Available Technologies for Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.103661*

### *2.1.1 Screening, filtration, and centrifugal separation*

The first phase in a wastewater treatment operation is screening. The purpose of screening is to eliminate solid waste from wastewater, and it is applied to remove items such as faecal solids, fibre, cork, hair, fabric, kitchen trash, wood, paper, cork, and so on. As a result, different-sized screens are utilized, the size of which is dictated by the requirement, i.e. the size of the particles in the wastewater.

In the filtering process, water is filtered in via a substance having fine holes. This is usually done with a set-up having pore diameters ranging from 0.1 to 0.5 mm. It is used to remove suspended particles, greases, oils, germs, and other contaminants. Membranes and cartridges are examples of filters that can be employed. Filtration can remove particles smaller than 100 mg l–1, as well as oil smaller than 25 mg l–1, reducing it by up to 99%. For water purification, the filtering process is used. Filtration water is utilized in ion exchange, adsorption, and membrane separation processes. Furthermore, filtration devices create potable water [5, 6].

To remove suspended noncolloidal particles, centrifugal separation is performed (size up to 1 mm). Solids (sludges) are separated and released after the wastewater is put to centrifugal devices and rotated at different speeds. Suspended solids segregate to a degree proportional to their densities. Furthermore, the centrifugal machine's speed is also important for the removal of suspended materials. Oil and grease separation, as well as source reduction, are examples of applications.

### *2.1.2 Sedimentation and gravity separation*

This process removes suspended particles, grits, and silts by leaving water undisturbed/semi-disturbed in various types of tanks for varied time intervals. Under the pull of gravity, the suspended solids settle [5–8]. The size and density of the solids, as well as the velocity of the water if it is moving, determine the settling time. To speed up the sedimentation process, alums are occasionally utilized. Gravity separation alone can remove up to 60% of suspended particles. Sedimentation is normally carried out before the application of standard treatment methods. It's a cost-effective way to treat waste from the paper and refinery industries. Water is generated for membrane processes, ion exchange, industrial water supply, using this technology. Source reduction is another application of technology.

### *2.1.3 Coagulation*

Non-settleable solids are allowed to settle when suspended solids do not settle down through sedimentation or gravity. Coagulation is the term for this process [5, 7]. It is possible to employ alum, starch, ferrous minerals, aluminum salts, and activated silica. Coagulants made of non-ionic polymers, anionic polymers, and synthetic cationic polymers are also effective, but they are usually more expensive than natural coagulants. The most essential governing parameters in the coagulation process are temperature, pH, and contact time. Specific coagulants are added to biological treatment units to remove bacteria and other organics that may be floating in the water. It's the most significant part of a wastewater treatment unit, and it's used for a variety of purposes, including wastewater treatment, recycling, and pollution removal.

### *2.1.4 Flotation*

A conventional water treatment facility's flotation is a typical and necessary component. Flotation removes suspended particles, greases, oils, biological materials, and other contaminants by attaching them to air or gas [5, 9]. The solids bind to the gas or air and create agglomerates, which float to the water's surface and can be skimmed off easily. Alum, activated silica, and other substances enhance the flotation process. The flotation process is aided by compressed air flowing through the water. Electro-flotation (electro-flocculation) has been utilized for recycling and water treatment for a long time. This method may remove up to 75% of suspended particles while also eliminating up to 95% of grease and oil. It's a promising treatment method for paper and refinery sectors [5].

### *2.1.5 Membrane technologies of wastewater treatment*

Over the last two decades, as an emerging wastewater treatment approach, membrane technology has evolved into a substantial separation technique. The water world has been looking for new solutions as regulatory limits and esthetic criteria for consumer water quality have continued to progress. Membrane technology is an example of a novel technology. Membranes are employed as filters in separation processes in a variety of applications in this technology. Adsorption, sand filters, and ion exchangers are just a few of the technologies they can replace. Water filtration (covering desalination) and purification (such as groundwater and wastewater) are major applications of this technology, as are sectors such as biotechnology and food & beverage [10, 11]. **Table 1** illustrates the pore size different membranes technologies ranges.
