What Is a Phenol?

Phenol (C ₆ H ₅ OH) ^[1] is a colorless needle-like crystal with a special odor, ^{[2] is} toxic and is important for the production of certain resins, fungicides, preservatives and drugs (such as aspirin). raw material. Can also be used for disinfection of surgical instruments and excreta, ^[3] skin sterilization, itching and otitis media. Melting point is 43 . It is slightly soluble in water at room temperature and easily soluble in organic solvents. When the temperature is higher than 65 , it can be miscible with water in any proportion. Phenol is corrosive and denatures local proteins after contact. The solution can be washed on the skin with alcohol. ^{[4] A} small part of phenol is oxidized by oxygen to quinone when exposed to air, which is pink. When the trivalent iron ion turns purple, this method is usually used to test phenol.

Phenol was a German chemist Runge F in 1834

The phenol molecule consists of a hydroxyl group directly attached to the benzene ring.

Relative vapor density (air = 1): 3.24

Can absorb moisture in the air and liquefy. It has a special odor and a very thin solution has a sweet taste. Extremely corrosive. Strong chemical reaction ability. Reacts with aldehydes and ketones

Phenol was first recovered from coal tar, and most of it is currently synthesized. By the mid-1960s, the cumene process was used to produce phenol,

The research on phenol degradation started earlier abroad.

So far, many phenol-degrading strains have been isolated and studied.

The microorganisms that have been isolated and identified include rhizobia, alga Ochromaonas, yeast (Yeast trichosporon), A. calcoaceticus, pseudomonas. Sp, and true nutrition Phenol-degrading bacteria such as Alcaligenes eutrophus and Denitrifying bacteria.

The most common phenol-degrading bacteria are Pseudomonas and Acinetobacter. Their maximum degradation concentration for phenol is generally below 1 200 mg / L. A bacterial strain that could grow with phenol, benzoic acid, p-cresol, benzene as the sole carbon source and energy source, and had the ability to simultaneously degrade monocyclic and bicyclic aromatic hydrocarbons was identified by Shen Xihui and other physiological and biochemical and 16SrRNA gene sequence analysis. Rhodococcus PNAN5 strain. The phenol degradation efficiency of the strain was maintained between 80% and 100% at a temperature of 20 to 40 ° C and a pH range of 7.0 to 9.0. The change in phenol concentration in the range of 2 to 10 mmol / L had no significant effect on the degradation efficiency. . This strain degrades aromatic hydrocarbons through the ring-opening pathway catalyzed by catechol 1,2-dioxygenase, which is different from the known Rhodococcus turbidus, which is catalyzed by catechol 2,3-dioxygenase. degradation.

The correlations between initial phenol concentration, TOC, and yeast biomass were explored. The results show that the degradation of phenol has a great correlation with the growth of yeast. The initial phenol concentration increases, inhibits the increase of yeast biomass, and the conversion rate decreases. During the degradation of phenol, the decrease in TOC is synchronized with that of phenol. TOC mainly comes from yeast metabolites.

For a culture solution with an initial phenol mass concentration of 559.0 mg / L, a yeast (biomass) of 328.2 mg / L can be obtained by degrading 90% of phenol, and the TOC of the culture solution can be degraded by approximately 87.3%. Nine strains of aerobic novolac were isolated, numbered -9, and identified by 16S rRNA gene sequence analysis, including Acinetobacter genus, Pseudomonas, and Bacillus spp., Which showed high efficiency except Phenol-reducing ability, strains I1 and I5 have a faster growth rate than other strains when the phenol concentration is 500 mg / L, and strains I2, I6, and I8 show strong aggregation ability, and with the pH value This ability weakened, and the I3 strain had lower phenol-reducing ability compared with other strains, but it could enhance the aggregation ability of I2 and I8 strains.

Twenty-seven strains of phenol-degrading bacteria were isolated under low-oxygen conditions. Phenol, as a single carbon source and energy source, showed both ability to reduce phenol and reduce nitrate content. The results showed that aerobic degradation of 50 mol of phenol had both 140 ~ 200 mol nitrate reduction. Isolating aerobic phenol degrading bacteria from refining wastewater in northeastern Brazil, Candida tropicalis can survive in an environment with a phenol concentration of 500 mg / L or 1 000 mg / L, and uses phenol as the sole carbon source. With the increase of concentration, the longer the time required for degradation treatment, the strain released a large amount of polysaccharides in the middle stage of the treatment to weaken the toxic effect of high concentration of phenol. The results show that this strain has both strong phenol degradation ability and can be used as Surfactants provide a reference for treating oily wastewater. Candida tropicalis isolated from industrial phenol-containing wastewater can treat phenol at a concentration of 1 000 mg / L, and its growth kinetics is analyzed

The results showed that the best growth was achieved when the parameters were max = 0.174 / h, KS = 11.2 mg / L, and Ki = 298 mg / L. A new phenol-degrading bacterium EDP3 was successfully isolated from activated sludge. It can be grown in an aerobic environment containing phenol, sodium benzoate, paraben, phenylacetic acid, benzene, ethylbenzene, benzyl alcohol, etc. Degrades 1 000 mg / L of phenol at 25 ° C. Pseudomonas MTCC 4996 was isolated from soil contaminated with pulp wastewater. It can degrade phenol wastewater with a concentration of up to 1 300 mg / L within 156 hours. The pH range of complete degradation is 6.0 to 7.0, and the temperature range is 15 to 45. , the best degradation conditions are pH 7.0, temperature 37 , shaking speed 100 ~ 125 r / min, complete degradation takes 66 h, and static state requires 84 h. Low concentration of glucose and peptone can improve phenol treatment Effectively, the degradation rate of phenol is related to the added metal ions. Low concentrations of Fe, Cu, Pb, Zn, Mn, and Hg can increase the degradation rate. The maximum phenol-reducing concentration of Alcaligenes P5 isolated in an aerobic environment in the presence of oxygen and nitrate was 0.29 mmol / L, but only 0.16 mmol / L in the presence of oxygen. The isolated Acinetobacter aerobic calcium acetate can efficiently degrade high-concentration phenol, and it also has high aggregation ability with the participation of heat-sensitive adhesin protein.

After continuous culture in the SBR treatment system for 1 week, this degrading bacteria can be immobilized into 2 ~ 3 mm particles, has stable properties and can handle 200 ~ 2 000 mg / L of phenol. The corresponding phenol reduction rates in VSS are 993.6 and 519.3 mg / d. At the same time, a single strain can also survive at a phenol concentration of 1 500 mg / L. Confocal laser scanning microscopy tests show that Acinetobacter calcium acetate mainly survives. Below 200 ~ 250 m from the outer surface, and covered with extracellular polymer to resist the toxicity of phenol, the analysis and testing on the aggregation showed that it may be the role of secreted protein. ^[7]

Research Status of Phenol Degradation Genes

Phenol-degrading genes are usually clustered and located on large plasmids or chromosomes. In aerobic bacteria, the phenol hydroxylase gene is the key gene for phenol degradation. It encodes the first enzyme in the phenol degradation pathway and is responsible for converting phenol to catechol; ring-opening cleavage of catechol to tricarboxylic acid (TCA) products are responsible for ortho and meta enzymes. Further degradation of catechol has different pathways and enzyme systems: catechol 2,3-dioxygenase (C23O, meta-cleavage), or catechol 1,2-dioxygenase (CatA , Ortho cracking).

This type of dioxygenase (C23O, CatA) is encoded by dioxygenase genes such as C23O and CatA, respectively, and they have high homology among different degrading bacteria. Catechol 1,2-dioxygenase was extracted from Candida albicans TL3, which has high phenol resistance and high phenol-reducing performance. It is obtained from puriWed enzyme by ammonium sulfate precipitation, dextran G-75 gel Wltration and HiTrap Q agarose gel column chromatography. The optimal survival temperature and pH were 25 ° C and 8.0, respectively.

Analysis of the substrate showed that the puriWed enzyme is a catechol 1,2-dioxygenase. The peptide sequencing fragment of catechol 1,2-dioxygenase and the total amount of MALDI-TOF / TOF were determined as BLAST analysis provided amino acid sequence information. The results of BLAST analysis showed that catechol 1,2-dioxygenase has high homology with CaO19_12036 protein obtained from Candida.

Quantitative evaluation of phenol hydroxylase diversity in bioreactors using functional gene analysis. First, the bacteria in laboratory-scale activated sludge were quantitatively analyzed for genetic diversity of phenol degradation. The first cis fluidized bed was fed with phenol-added synthetic sewage, and the DNA genome was extracted from the activated sludge. Conservative amplification of the subunit phenol hydroxylase (LmPH) gene and generation of a clone library. After phylogenetic analysis and 9-month real-time PCR analysis, the total number of LmPH gene copies remained basically stable, but in the revised phenol sludge, phenol degradation changed significantly while LmPH gene diversity also increased. Environmental protection and circular economy were increasing. This indicates that the efficiency of phenol degradation in activated sludge depends on the activity of some of the excess species combined.

In 2001, Testosterone clusters Porphyromonas R5 was isolated, and the phenol hydroxylase gene (Phc) of the R5 degradation pathway was further studied. It was found that it has a different transcriptional regulation mechanism from other phenol hydroxylase genes. Three regulatory proteins are involved in transcription, one of which is actively involved in regulating other phenol hydroxylase enzymes commonly found in the NtrC family, the other inhibits the disordered expression of Phc, and one amplifies and expresses Phc.

This meticulous mechanism makes the degrading bacteria R5 show a relatively high phenol oxygenation activity, and also indicates that the expression pattern of degrading enzymes will also be diverse and may affect the degradation behavior. Phenol and cresol-degrading Pseudomonas were isolated from phenol-contaminated water. Sequence analysis of phenol hydroxylase (LmPH) and catechol 2,3-dioxygenase, and the infection of pheBA by the plasmid The structure of the encoded catechol 1,2-dioxygenase and one-component phenol hydroxylase was compared between the strains indicating species and the systematic grouping of strains of genetic factors. CatA gene sequences were obtained from genetic factors B. LmPHs and C23Os are similar in P. Xuorescens strains, but genetic heterogeneity is obvious in P. mendocina strains. P. Xuorescens strains obtained from genetic factors C and F contain the pheBA genetic operon, which is obtained from genetic factor B. The P. putida strain degrades phenol through the ortho pathway. Most of these strains also detect this operon. The results of genetic diversity of metabolic genes combined indicate that there is almost no intermediate route for the degradation of phenolic compounds.

The suicide plasmid obtained from the Tn5 transposon of E. coli S17-1 was used as a vector to fuse with the plasmid pAG408 of an antibiotic-resistant donor bacterium. With the help of the plasmid pRK600 containing the mob gene of strain HB101, green fluorescence The protein gene gfp is transformed into the recipient Pseudomonas through bacterial mating. Pseudomonas is isolated from phenol-contaminated industrial wastewater and can degrade phenol. Engineering bacteria emit bright green light under ultraviolet light, which indicates that fusing the green fluorescent protein gene gfp to Pseudomonas will not affect their degradation performance.

Acinetobacter calcium acetate PHEA-2 was isolated from oil refinery wastewater and enriched and cultured in an environment of phenol and benzoic acid. Studies have shown that the phenol hydroxylase of Acinetobacter calcium acetate PHEA-2 and NCIB8250 belong to a complex The enzyme. Based on the complete nucleotide sequence, DNA sequence analysis showed that the phenol hydroxylase coding gene (mph) and its downstream coding gene in Acinetobacter calcium acetate PHEA-2 were different from those in Acinetobacter calcium acetate NCIB8250. The mph-ben-cat gene region may be present in Acinetobacter calcium acetate PHEA-2. ^[7]

in conclusion

Isolate and obtain highly efficient phenolic degrading bacteria from the polluted environment, study its degradation characteristics, and then apply it to wastewater treatment systems containing difficult degradation pollutants such as phenol. The application of these degrading bacteria in biodegradation reactors for treating wastewater, polluted places in water supply equipment systems, and waste dumping places has broad application prospects. ^[7]