**1. Introduction**

There has recently been heightened concern among policymakers and scientists with regard to the effects of human and wildlife exposure to chemical compounds in the environment, particularly the aquatic environment. Phenolic compounds are among the chemicals of major concern in this regard as they tend to persist in the environment over a long period of time, accumulate and exert toxic effects on humans and animals [1]. Some phenolic compounds are

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

abundant in nature and are associated with the colours of flowers and fruits [2]. Others are synthesised and are used in varied aspects of mankind's everyday life.

The entrance of phenolic compounds into the aquatic environment results from natural, industrial, domestic and agricultural activities. Their presence may be due to the degrada‐ tion or decomposition of natural organic matter present in the water, through the disposal of industrial and domestic wastes into water bodies and through runoffs from agricultural lands [3]. These chemicals, upon entry into the water, have the tendency of undergoing transforma‐ tions into other moieties that can even be more harmful than the original compounds. This transformation is normally due to their interaction with physical, chemical and biological or microbial factors in the water [4].

Phenolic compounds have been enlisted by the United States Environmental Protection Agency (USEPA) and the European Union (EU) as pollutants of priority concern. This enlist‐ ment is due to the fact that these chemicals are noted to be toxic and have severe short‐ and long‐term effects on humans and animals [5]. The occurrence of phenolic compounds in the aquatic environment is therefore not only objectionable and undesirable but also poses a dan‐ ger as far as human health and wildlife are concerned. As a result, a number of wastewater treatment techniques have been developed and used for the removal of phenolic compounds from industrial, domestic and municipal wastewaters prior to their disposal into water bodies so as to minimise the devastating effects of these chemicals on human and aquatic lives. Some of these techniques include extraction, polymerisation, electro‐Fenton process, photocatalytic degradation and so on.

This chapter presents a general overview of selected topics in relation to phenolic compounds. It dwells on the sources and reactivity of phenolic compounds in water, their toxic effects on humans and methods of their removal from water. Specific emphasis is placed on the tech‐ niques of their removal from water with attention on both conventional and advanced meth‐ ods. Among these methods are adsorption, extraction, polymerisation, electro‐coagulation, photocatalytic degradation, biological methods, electro‐Fenton method, advanced oxidation processes, adsorption and ion exchange and membrane‐based separation techniques.
