**1. Introduction**

The earth's surface is covered by 70% of the water of which 97.5% are from seas and oceans which are salty for consumption, out of the remaining 2.5% water, 1.73% are in form of glaciers and ice-caps, left only with 0.77% available for freshwater supply. The amount of water available on the earth that can be renewable is only

0.0008% in the rivers and lakes for humans and agricultural use [1]. Fundamentally water is needed by all living creations of God, hence it must be provided in the rest state for their consumption, therefore clean water becomes a critical issue as the world population increases [2]. The populace activities are a factor that causes an increase in pollution from both organic and inorganic compounds sources that require serious attention to ensure clean water that the same growing world needs to consume.

Clean water becomes a critical issue as the world population increases. It has been estimated that by the year 2025, there would be an additional 2.5 billion people on the earth that will live in a region already lacking sufficient clean water [1]. Similarly, scholars have indicated that the recent problems in water treatment originate primarily from the increasing pollution of water by an organic compound that is difficult to decompose biologically because these substances resist the self-purification capabilities of the rivers as well as decomposition in conventional wastewater treatment plants [3, 4]. Further observations state that the conventional mechanical-biological purification is no longer sufficient and must be supplemented by an additional stage of processing [5].

Adsorption is the capacity of the adsorbate to form a bond with the adsorbent [6]. It is also defined as a physical and chemical process in which substances are accumulated at the interface between the faces which may be liquid-liquid, liquid-solid, or gas-liquid [7]. Adsorption differs from absorption in that it is the process by which the surface concentrates fluid molecules by chemical or physical force while absorption is the partial chemical bonds formed between adsorbed species or when the absorbate gets into the channels of the solids [8]. In other words, fluid molecules are taken up by a liquid or solid and distributed throughout the liquid or solid. Adsorbate is the substance that is removed from the wastewater or the amount of contaminant adhering to the surface of the adsorbent, while the adsorbent is the solid phase that accumulates the pollutant. This may be activated carbon or other biosorption materials [7]. For adsorption to take place, the adsorbate must have less free energy on the surface of the adsorbent in solution.

Organic contaminants are occasionally termed persistent organic pollutants (POP), their occurrences in the environment are frequent and possess the ability to move fast across the water and settle from where they are sources. Accumulated in the fat tissues of wildlife and human beings and are very toxic to their organics. Degradations of POP are very difficult since they are persistent and also termed semivolatile for example PAHs. Apart from POPs other toxic organic contaminants which can create subtle ecological effects are the Emerging Organic Contaminants (EOCs), the extent to which the environment can be adversely affected by EOCs is still under study. One of such is the (PhACs) which are products of synthetic chemicals, natural organic chemicals, or microorganisms not controlled. They possess the ability to penetrate the aquatic environment and alter the natural quality leading to adverse health issues in human and ecological disorders [9, 10].

The Petroleum and Pharmaceutical industries are seen among others as major contributors of organic contaminants because of continuous usage and pollutant from them are emerging and steady in the environment [10].

Produced water and crude oil spills are the major sources of pollutants generated by the petroleum industry. Produced water is the largest by-product of wastewater attributed to the petroleum industry and it is a mixture of salt, organic and inorganic compounds.

Among the organic constituent of crude oil is a group of hydrocarbons called PAHs [11]. These are large groups of organic contaminants, which are characterized

### *Adsorption Technique an Alternative Treatment for Polycyclic Aromatic Hydrocarbon (PAHs)… DOI: http://dx.doi.org/10.5772/intechopen.104789*

by the presence of at least two fused aromatic rings and are seen by the United States Environmental Agency (USEPA) as priority organic pollutants [12]. PAHs are highly lipophilic contaminants that are ubiquitously present in the environment [13] because of their low biodegradation and bioaccumulation in the adipose tissues of organisms and biomagnifications through the food chain, they are considered persistent organic pollutants POPs [14].

The pharmaceutical industries on the other hand have to do with the well-being of living organisms. Their products refer to a group of chemicals used for the diagnosis, treatment, or prevention of health conditions. Most of the chemicals or ingredients used in production can be active, inactive, additive, or preservative. When most of these ingredients are no longer used for the intended purpose and if the pharmaceutical product is designated for discarding, it is then classified as pharmaceutical waste. Active chemicals like paracetamol (acetaminophen), salbutamol, amoxicillin, ibuprofen, chloramphenicol, etc. can be referred to as pharmaceutically active compounds (PhACs), and preservatives such as parabens, e.g., ethyl, propyl, etc. are called excipient [15]. Pharmaceutical wastes are EOCs of concern and are mostly unregulated contaminants that need future regulation [16].

Like any EOCs, they do not need to persist in the environment to cause negative effects because they are continually being released into the environment mainly from manufacturing processes, disposal of unused products, and excreta [17]. At the 2005 Burger AEC programme on EDCs, it was reported that most EOCs can disrupt the endocrine system-a health condition called endocrine disruptors [18]. The WHO defines an endocrine-disrupting substance as an exogenous substance that alters the function of the endocrine system and consequently causes adverse health effects in an organism or its progeny or subpopulations [19].

Petroleum and pharmaceutical Industries have been seen as major generating sources of organic contaminants that create adverse effects on surface water which are the primary source of livelihood. For water to be available in its pure state, identifying and remediating processes of those contaminants is key, if clean water is a necessity [10].

Most research works had employed analytical techniques like gas and liquid chromatography, UV-spectrophotometers and gravimetric, etc. to identify organic contaminants, gas and liquid chromatography with mass spectrophotometer followed by a cleanup method such as solid-phase extraction (SPE) and solid-phase microextraction (SPME) [20] are seen as most effective techniques in determinations of organic pollutants in trace amount (or micro-pollutant).

Induced Gas Flotation (IGF) or the Induced Air Flotation cells are usually used as conventional treatment methods by petroleum industries to separate produced water from crude oil with Enviro-cell as the newest technology that uses the principle of gravity with differences in density between the oil and water [20].

The hydrocarbon content in either the produced water or water polluted with crude spills can be classified as free, dispersed, and dissolved oil [21, 22]. The conventional method is seen to be effective in the removal of dispersed oil and grease but cannot be used in the removal of the dissolved hydrocarbon which includes the PAHs. Different literature had reviewed that conventional wastewater treatment plants (WWTPs) are not the best in the removal of PAHs pollutants from wastewater, additional methods that had been researched and are still being researched is the adsorption mechanism. It had been suggested that carbon and membrane filtration with reverse osmosis are very effective in the removal of dissolved and emulsified oils [23, 24]. Many materials in their raw or waste form had been developed or modified

into adsorbent in adsorption of pollutants which could be agricultural materials, clay, zeolite, vibratory share enhanced process, etc.

The commonest adsorbent used by most industries for the removal and recovery of inorganic and organic substances from gaseous and liquid streams is activated carbon [25]. Because of its high internal surface area and porosity formed during the carbonization process, the adsorbent is said to have a high adsorption capacity. Similarly, the use of activating agents and heat during carbonization will influence the development of pore structure but its uses are limited to high cost hence the use of agricultural products or materials have been observed to be potential precursors in activated carbon production because of the abundant supply and low cost.

Most of the research conducted lately made use of agricultural product such as adsorbent in the removal of heavy metals from water and wastewater, such agricultural products are coconut shell and rice husk [26, 27], palm kernel shell, and oil palm fruit fiber [28], bamboo [3, 29], maize cob [6]. Other works had been done on the identification and remediation of organic contaminants in petroleum [30–31] and pharmaceutical wastes [32–33] but few works have been done on the use of adsorbents in remediating organic pollutants (PAHs and EOCs).

Since water is the prime necessity of life and very essential for the survival of all living organisms it is imperative to improve the quality of available water. The presence of pharmaceutical residues (PhACs) and PAHs as newly recognized contaminants in aquatic systems is one of the current environmental issues [34]. It should be noted that organic contaminants usually occur in multi-component in aquatic environments. Thus, it is expected that there will be interspecies interaction among these pollutants which will cause chemical reactions that can generate other metabolites compared to when the single contaminant is present [35].

Adsorption method of bioremediation had proven to be the chosen treatment option for PAHs and PhACs and other micro-pollutant in aqueous or any environmental media because it is easier to understand and has obvious advantages of convenience, easy operation, efficiency, effective, and very simple to design as compared to another kind of treatment. Apart from the identified attributes, it does not add harmful degradation metabolites or undesirable by-products [36].

Adsorption is better than any other wastewater treatment method due to its insensitivity to toxic substances and is economically based on types of materials employed as adsorbents [37]. But, the complete use of adsorption processes in purifying water is impeded by the insufficiencies of the commercial adsorbents like activated carbon and synthetic polymer resins, synthetic Nanomaterial. Hence, there is a need to develop a low-cost adsorbent for environmental research. So, the adsorbent of agricultural products is becoming the popular alternative for commercial and synthetic adsorbents due to the hydrophobic-oleophilic potential that is needed for bioremediation processes [38]. With this new trend in mind, this chapter will seek to explain courses of organic pollutants with a special interest in industrial wastewater and adsorption techniques as an alternative treatment.
