Wastewater Treatment Glossary: Volatile Phenols

Volatile phenol: Phenolic compounds are classified as volatile or non-volatile phenols according to whether they can be distilled off together with water vapor. Phenols are protoplasmic poisons and highly toxic substances; ingestion of a certain amount by the human body produces acute poisoning symptoms, and long-term consumption of phenol-contaminated water can cause headaches, rashes, itching, anemia and various neurological symptoms. When the phenol content in water reaches 0.1-0.2 mg/L, fish develop an off-flavor; at levels above 5 mg/L, fish are poisoned and die. Wastewater with high phenol concentration should not be used for farmland irrigation, otherwise crops will wither or yield will decline. Phenols are commonly classified as volatile or non-volatile based on their boiling point, volatility, and whether they can be distilled off with water vapor. It is generally accepted that phenols with a boiling point below 230 C are volatile phenols, usually monophenols; those with a boiling point above 230 C are non-volatile phenols. Phenol, cresol, and xylenol are all volatile phenols, while diphenols and polyphenols are non-volatile. The main sources of phenol pollution are industrial wastewater from coal-gas washing, coking, synthetic ammonia, papermaking, wood preservation, and the chemical industry.

Numerous analytical methods exist for phenols, but the 4-aminoantipyrine photometric method is the one most widely adopted by various countries, and the phenol determination method promulgated by the International Organization for Standardization (ISO) is likewise this method.

For water samples with a volatile phenol concentration below 0.5 mg/L, the 4-aminoantipyrine extraction photometric method is used; for concentrations above 0.5 mg/L, the direct 4-aminoantipyrine photometric method is used.

High-concentration phenol-containing wastewater can be analyzed by the bromination volumetric method, which is suitable for wastewater at workshop discharge outlets or at untreated total-discharge sewer outlets.

If oxidants, reducing agents, oils, or certain metal ions are present in the water sample, they should be eliminated by pretreatment and pre-distillation.

1. Separate out the volatile phenols; 2. Eliminate interference from color, turbidity, metal ions, and the like.

For example, add ferrous sulfate to reduce free chlorine; add copper sulfate to precipitate sulfides, or drive them off as hydrogen sulfide under acidic conditions; remove oils by extraction with an organic solvent; and so on.

Sample preservation: Collect water samples using glassware. After collection, promptly check whether oxidants are present.

If necessary, add excess ferrous sulfate, immediately acidify with phosphoric acid to pH 4.0, and add an appropriate amount of copper sulfate (1 g/L) to inhibit the microbial bio-oxidation of phenols; the sample should also be refrigerated (5-10 C) and measured within 24 h of collection.