*6.3.1. The liquid‐liquid extraction method*

these conditions, oxygen molecules (O<sup>2</sup>

428 Phenolic Compounds - Natural Sources, Importance and Applications

which in turn react with O2

tages of ozonation include [55]:

to developing resistance against ozone.

attained when the gas‐liquid contractor was adopted to HaN<sup>3</sup>

rised as liquid‐liquid extraction and solid phase extraction.

cal waste.

water.

alkaline medium [57].

**6.3. Extraction method**

from water.

) split to form highly reactive oxygen radicals (O•),

regime. The gas/liquid contrac‐

to form ozone. Ozone has a very high oxidising potential (‐2.74

V) which is much higher than that of hypochlorite ion (‐1.49 V) and chlorine (‐1.36 V) [54] which are all employed as oxidants for pollutant removal from water. This high oxidation potential forms the basis of the use of ozone as an oxidant for removal of organic pollutants

Ozonation process begins with the formation of ozone through corona discharge simulation of lightning, or the use of UV‐type ozone generator for simulation of ultraviolet radiation from the sun, by passing clean and dry air through high voltage ozone generators. The waste‐ water is then allowed to flow along a venture throat, which generates a vacuum and pulls the ozone into the wastewater, or the ozone is simply bubbled up through the wastewater. The ozone then oxidises and decomposes the pollutants leading to their elimination from the water. UV ozonation is mostly used for small‐volume wastewater treatment while the corona discharge method is employed in large‐scale wastewater treatment processes. Some advan‐

**(1)** The process is completely natural with no inclusion of chemicals and produces no chemi‐

**(2)** High microorganism elimination efficiency with the microorganisms having no potential

**(4)** Ability to remove organic, inorganic, microorganism and improve taste and odour of the

Based on the above advantages, several research works have been performed on the use of ozo‐ nation technique for phenolic compounds removal from wastewater. Treatment of olive mill wastewaters containing garlic, p‐hydroxybenzoic and p‐coumaric acids based on ozonation was studied by Chedeville et al. [56]. They identified that the highest ozonation process was

tor used permitted a comprehensive removal of the phenolic compounds within a short time. A maximum of 80% of the pollutants was eliminated with up to 95% ozone mass transfer. Ozonation was also used to treat ethylene glycol containing wastewaters with emphasis on the impacts of pollutant dose, process time, and pH on the decontamination efficacy. After 180 min, ethylene glycol removal efficiencies were 93.31, 89.96 and 85.01% at 10, 20 and 50 mg/l pollutant concentrations, respectively. Removal efficiency was observed to be highest in

Among the techniques used for removal of phenolics from water is extraction using polar organic solvents. The extraction method of phenolics removal from wastewater can be catego‐

**(3)** The process is self‐sustaining as the main source of ozone is oxygen from the air.

This technique separates compounds on the basis of their solubilities in two immiscible liq‐ uids. The compounds are normally separated from one liquid phase to another. The immis‐ cible liquids usually consist of water and an organic solvent.

The liquid‐liquid extraction method was used by Rao et al. [58] to remove phenol from sebacic wastewater. The experiment was performed using batch, and serial approaches through the application of different solvents such as Aliquat‐336, 1‐hexanol, 1‐octanol, 1‐heptanol and cas‐ tor oil. The extinction experiment which involved shaking and allowing for phase separation resulted in 75–96% extraction of phenol with the different solvents, where the solvent and the wastewater were mixed in a ratio of 5:250. The extraction efficiency was observed to vary according to the ratio of the solvent used. The best solvent for phenol extraction was Aliquat 336. Liu et al. [59] also used cumene to extract phenol from water. Cumene showed excellent extraction performance on phenol in acidic solution. The distribution coefficient was observed to be directly proportional to the temperature but decreased with increasing pH value.
