Phenolic contaminant elimination

Several authors have attempted to optimize the HRP C conditions to remove phenols from aqueous solutions. Among the main parameters evaluated to improve the elimination of contaminants are the reactor configuration, enzyme immobilization, and the use of additives to protect the enzyme from entrapment in the precipitating polymers (Hamid and Khalil-ur-Rehman 2009). 

When contaminated or held in storage at temperatures below 60°F (15.5°C), hindered phenols may tend to crystallize and fall from solution as relatively pure compounds. Often solvent dilution of hindered phenols can help to reduce the tendency of crystal dropout, but will not completely eliminate this problem. 

Finally, mention must be made of possible conjugation reactions in which a covalent bond is formed between a contaminant molecule and a second contami nant molecule or soil organic matter. Oxidative coupling reactions of phenolics and aromatic amines are catalyzed by extracellular enzymes, clays, and oxides (Wang et al., 1986 Liu et al., 1987 Fluang, 1990). The bioavailability of the synthetic organic within the product is reduced or possibly eliminated (Dec et al., 1990 Allard et al., 1994). 

Treatment of contaminated wastewater by pervaporation is superficially attractive, however, only a few commercial installations have been built. Phenol, which azeotropes with water at around 10wt%, is typically recovered by extraction in large plants, where measures to eliminate extractant loss can be economically applied. Pervaporation is an attractive and cost competitive alternative for small plants. Organophilic membranes in spiral wound modules are used in these applications. 

The risks of environmental contamination and to human health caused by volatile organic compounds have driven a lot of research designed to eliminate or remedy its deleterious effects. Several of these compounds, such as phenol and BTEX compounds (benzene, toluene, ethyl benzene and the isomers of xylene) are found in effluents from oil refineries, and they are important contaminants due to their high toxicity (Akhtar, 2007). 

To eliminate contaminating bacteria, the yeast slurry can be acid washed. Also, sometimes (but less frequently these days), the yeast slurry is sieved to remove contaminating trub (i.e. coagulated protein-phenol solid material). 

Recently, the cosolvent system of tertiary alcohols such as fert-butanol, ferf-amylalcohol, and acetonitrile has shown very promising results for F-fluorination in the presence of TBA" ((C4H9)4N ) salts, e.g., hydroxide or carbonate (Kim et al. 2006). Other functionalities with acidic protons (e.g., hydroxyls, phenols, thiols, or amides) or nucleophilic character (e.g., amines, carboxyls) have to be protected. Side products formed by elimination or the formation of the corresponding alcohols by hydrolysis of the high excess of precursor may coelute during HPLC purification and thus contaminate the product (pseudo carrier). 

Another important pathway leading to PAHs is the thermal elimination reaction of benzene derivatives (Figure 12.22). For example, the elimination of water from phenolic compounds (X = OH) yields, via 1,2-didehydrobenzene (often incorrectly called ben-zyn), another reactive intermediate benzobicyclo[2,2,2]triene and naphthalene as a final product. The contribution of endogenously generated compounds to the total dietary intake of PAHs is not too significant as the contamination of food is largely exogenous. 

Nagel, R., and K. Urich. 1981. Elimination and distribution of different substituted phenols by frog Rana temporaria) and crayfish (Astacus leptodactylus). Bulletin of Environmental Contamination and Toxicology 26 289-294. 

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