Clean non-polluted water is a major basic requirement for all the living things. Nowadays, its availability becomes a major problem in the ecosystem. This problem is expected to increase in the future due to population growth and industrialization processes. The processes discharge of domestic, industrial and agricultural wastes contribute largely to the contamination of existing natural waters in the environment. Therefore, at the present moment, it is important that the pathogens and pollutants are completely removed from the waste water to cater for the needs of domestic use, industrial use, and irrigation purposes. This paper discusses two processes of oxidation and advanced oxidation that are applied in water and waste water treatment.
Oxidation and Advanced oxidation processes:
Oxidation is the chemical process by which a molecule, ion, or atom losses electrons or increases its oxidation state. On the other hand, advanced oxidation refers to a set of chemical treatment procedures that are designed to eliminate organic materials from waste water and water through reactions with hydroxyl radicals (Glaze, William, Kang, Joon-Wun, Chapin, Douglas H. 1987).In the past, less efficient methods such as physical treatment and convectional biological were applied but were less efficient in the treatment of water and waste water. The oxidation and advanced oxidation processes are cheap, more efficient, and eco-friendly in the overall process of degradation of any kind of toxic substances present in water and waste water. The Advanced oxidation processes (AOPs) have the ability of generating hydroxyl radical which is a strong oxidizing agent. This oxidant mineralizes and completely degrades the pollutants present in waters non-selectively into forms that are harmless.
In the advanced oxidation processes, the chemical contaminants present in water and waste water are oxidized by four reagents; hydrogen peroxide, air, ozone, and oxygen. In the real sense, the pre-programmed sequences, combinations, and dosages that are to come in place for the process to be effective in attacking the chemical contaminants that is harmful to the body system of humans. In some cases, these chemical procedures are also combined with specific catalysts, UV radiation, and Ultra sound reactors. These combinations are always aimed at producing hydroxyl ions which are ideal for the process of oxidation of contaminants available in water. The procedure of AOP plays a particular role in cleaning the non-degradable or biologically toxic materials such as the pesticides, volatile compounds, aromatic compounds, and petroleum constituents present in waste water. These contaminant materials are broken down by the oxidation process and converted to inorganic compounds that are stable and safe for the human system. The end products of this breakdown include non harmful salts, carbon dioxide, and water. Existence of these compounds in water and waste water is not a risky factor that could compromise the health of an individual; therefore, water can be safe for human consumption. This water could also be used for irrigation purposes due to lack of compounds that could increase the acidity of salt hence affect crops.
A case study on advanced oxidation processes established that the use of Ozonation in the natural waters brings about the complete mineralization of certain resistive pharmaceuticals (Huber and Canonica et al., 2003, pp. 1016--1024). Mineralization is the process by which an organic substance is oxidized into inorganic substances. The oxidation of most organic substances in the presence of hydroxyl ions or oxygen in the open air results to the formation of carbon dioxide and water, products which are inorganic in nature and non-harmful when present in water and waste waters. The study revealed that AOP’s and Ozonation methods were recorded as the most effective ways of removing pharmaceuticals present in drinking water (Huber and Canonica et al., 2003, pp. 1016—1024). The removal of pesticides from water has been currently effected by the use of granular activated carbon method (GAC). This method was less effective when compared to the AOP in Netherlands, which was able to remove pesticides that were present in waste water up to eighty percent atrazine degradation (Comninellis and Kapalka et al., 2008, pp. 769--776).
Other oxidation processes and applications:
Another form of advanced oxidation process is In situ chemical oxidation (ISCO) that uses a specific chemical oxidant to oxidize soil or water contaminants in ground water contamination. The main oxidants involved in this process are hydrogen peroxide, permanganate, iron, ozone, and per sulfate. This form of oxidation has its advantages over other methods involved in treatment of water such as moderate costs involved and rapid treatment of water. This method has limitations with health and safety issues, oxidants being consumed by other materials, rebound of contamination, and short oxidant lifetimes.
This method of oxidation ensures that the compounds formed after being broken down are environment friendly as well as the human system. Products formed from oxidation of organic compound to be inorganic in nature and can be separated and made useful in other related ways.
Another process involved in the treatment of waste water is the process of aerobic digestion. It refers to the process by which microorganisms present in water and waste water are broken down by organic matter in the presence of oxygen gas. This is currently the major type of waste water treatment that is employed in many areas to treat water and there is a possibility of it having the potential to be used for treatment of water for drinking purposes. Currently, the method uses a process in which an activated sludge containing the microorganism is cultivated under conditions that optimize the consumption of influent biodegradable organic matter. This sludge, therefore, breaks down most of the organic matter as a pretreatment for the overall process (Hamilton, Braun, Dare, Koopman & Svoronos, 2006).
Currently, the biggest issue that needs to be addressed in WWTP is the DO control. The levels of DO have a significant influence on the aerobic reactors on the activity and behavior of autotrophic and heterotrophic microorganisms that live in the activated sludge. A case study established that the use of aerobic digestion to degrade the sludge with a specific water temperature of 25-30 degrees Celsius was the most effective method to be applied Hartman and Smith et al., 1979, pp. 2353--2365).
Making the sludge well aerated is a major part in maintaining the process of the activated sludge because aerobic conditions are important and conducive for the growth of large variety of certain microbes such as heterotrophic bacteria that are responsible for the removal of biochemical oxygen demand from water and waste waters. It is a well nitrifying bacterium responsible for oxidation of ammonia ions to nitrate compounds (Hamilton et al., 2006). Due to the fast and strong effects of aeration on biomass development and growth, the DO concentration is the most widely studied control problem in the process of water and waste water treatment.
Aerobic digestion plays a major role in breakdown of sewage in wastewater treatment. The use of this process for other application process is not very common. Study findings indicate that aerobic digestion van is applied in bioremediation of an oil spill. The use of a variety of bacteria in large quantity over one was found to allow for more oil to be degraded (Oling and Milner et al., 2002, pp. 5537--5548).
In summary, oxidation and advanced oxidation processes have proven to be the most effective, cheap, and environment friendly in the process of waste water treatment. This is achieved by their ability to oxidize chemical contaminants present in waste water into inorganic compounds that have less destructive effects on crops and the human system.
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