Step 3 – Initial coding

It is a known fact that the waste water from the industries must be treated before discharging it. Wastewater treatment involves using known technology to improve or upgrade the quality of wastewater.The principal objective of wastewater treatment is generally to allow industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment (Robinson, et al., 2001). Over the years, several methods have been used for this purpose of wastewater treatment. Each treatment methods offer varying cost-effectiveness, operational efficiency, availability of raw materials et.c. Wastewater treatment can be organized or categorized by the nature of the treatment process operation being used. The categories are biological, chemical and physical treatment methods.

2.1.4.1 Biological treatment method

Biological treatment involves the use of microorganisms, mostly bacteria, in the biochemical decomposition of wastewaters to stable end products. More microorganisms, or sludges, are formed and a portion of the waste is converted to carbon

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dioxide, water and other end products. Treatment to control odors, to retard biological activity, or destroy pathogenic organisms may also be needed.Biological methods of removing waste water pollutants include biodegradation methods such as microbial degradation, fungal decolourization, absorption by living or dead microbial biomass, reverse osmosis, bioremediation and liquid membrane permeation (Sofia, et al, 2005).

Generally, biological treatment methods can be divided into aerobic and anaerobic methods, based on availability of dissolved oxygen. Aerobic treatment methods include;

activated sludge treatment method, trickling filtration, oxidation ponds, lagoons and aerobic digestion while the anaerobic treatment methods are; anaerobic digestion, septic tanks and lagoons.

These methods are commonly applied to the treatment of industrial effluents because many micro organisms such as bacterial, yeasts, algae and fungi are able to accumulate and degrade different pollutants. Biological treatment is often the most economic alternative when compared to chemical and physical methods. However, their applications are often restricted because of technical constraints. It usually requires a long time to achieve great efficiency. Biological treatment requires a large land area and is constrained by sensitivity towards diurnal variation as well as the toxicity of chemicals which may be generated or released during the biological treatment process, and less flexibility in process design and operation (Sofia, et al., 2005). Further, biological treatment is incapable of obtaining satisfactory removal with current conventional biodegradation processes. Production of large sludge volume is an undesirable factor.

Moreover, although many organic molecules are degraded, many others are recalcitrant due to their complex chemical structure and synthetic organic origin (Robinson et al, 2001).

2.1.4.2 Chemical treatment method

This involves the treatment of industrial effluents using chemicals or chemical reactions so as to enhance the quality of the wastewater before discharge.The chemical methods

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employed in removing wastewater pollutants include electrochemical oxidation by an oxidizing agent, coagulation/flocculation, ozonation, precipitation (Afshin et al, 2012).

Others are neutralization, solvent extraction, electrochemical processes, chlorination, ion exchange etc (Ehssan and Yehia, 2011).

Probably the most commonly used chemical process is chlorination (Afshin, et al., 2012).

Chlorine, a strong oxidizing chemical, is used to kill bacteria and to slow down the rate of decomposition of the wastewater. The Bacterial kill is achieved when vital biological processes are affected by the chlorine. Another strong oxidizing agent that has also been used as an oxidizing disinfectant is ozone. Neutralization is a chemical process commonly used in many industrial wastewater treatment operations (Ehssan and Yehia, 2011). Neutralization consists of the addition of acid or base to adjust pH levels back to neutrality. Since lime is a base it is sometimes used in the neutralization of acid wastes.

Coagulation consists of the addition of a chemical that, through a chemical reaction, forms an insoluble end product that serves to remove substances from the wastewater.

Polyvalent metals are commonly used as coagulating chemicals in wastewater treatment and typical coagulants would include lime (that can also be used in neutralization), certain iron-containing compounds (such as ferric chloride or ferric sulfate) and alum aluminium sulfate) (Ehssan and Yehia, 2011). Processes such as ion exchange, which involves exchanging certain ions for others, are not used to any great extent in wastewater treatment (Afshin, et al., 2012).

These chemical techniques are often expensive, and although the pollutants are sufficiently removed, accumulation of concentrated sludge creates another problem— a disposal problem. There is also the possibility of a secondary pollution problem arising because of excessive chemicals used. Recently, other emerging techniques such as advanced oxidation processes which are based on the regeneration of powerful oxidizing agents such as hydroxyl radical have been applied with success for the pollutant degradation. Although these methods are more efficient for the treatment of waste water contaminated with pollutants, some of them are costly and commercially unattractive.

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The high electrical energy demand and the consumption of chemical are common problems.

2.1.4.3 Physical treatment method

Treatment of wastewater using physical treatment methods involves using physical phenomena to improve or treat the wastewater with no chemical or biological changes.Examples of physical techniques mostly used in the treatment of wastewater effluents include nanofiltration, electrodialysis, membrane filtration, sedimentation, screening, aeration, flotation and skimming, degasification, equalization and adsorption technique.

In the process of sedimentation, physical phenomena relating to the settling of solids by gravity are allowed to operate (Ehssan and Yehia, 2011). Usually, this consists of simply holding wastewater for a short period of time in a tank under quiescent conditions, allowing the heavier solids to settle, and removing the "clarified" effluent. Sedimentation for solids separation is a very common operation and is routinely employed at the beginning and end of wastewater treatment operations. While sedimentation is one of the most common physical treatment processes that is used to achieve wastewater treatment, another physical treatment process consists of aeration which is the process of physically adding air, usually to provide oxygen to the wastewater. Still,another physical phenomenon used in wastewater treatment is the filtration. Here wastewater is passed through a filter medium to separate solids. An example would be the use of sand filters to further remove entrained solids from treated wastewater. Recently, emphasis has been shifted to the use of adsorption technique for the removal of pollutants from wastewater, hence making adsorption technique the most widely used for the removal of pollutants from wastewater (Ehssan and Yehia, 2011). Equally, certain processes may actually be physical and chemical in nature. The use of activated carbon to "adsorb" or remove organics, for example, involves both chemical and physical processes.

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