Biological Treatment

The microorganisms capable of degrading phenol are highly specialized and require a controlled, stable environment. Under ideal conditions several weeks are required to develop the proper biological sludge. The efficiency of an acclimated biological system treating phenolic wastes depends strongly on temperature, pH, nutrients (nitrogen, phosphorus, minerals), oxygen concentration, phenol concentration, and other organics concentrations in the waste-water.

To degrade phenol, the microorganism population must be stable. Fluctuation in any of the preceding variables shifts the balance of this population, reducing system efficiency and possibly killing the biological organisms. Optimum phenol removal occurs at neutral pH (7.0), 70°F and constant phenol concentration.

Biological methods of phenol removal include activated sludge, trickling filters, oxidation ponds, and lagoons. Efficiency ranges from 65-90% removal, depending on the ability of the particular wastewater treatment system to control the process variables listed. Activated sludge, trickling filters, and oxidation ponds are all capable of high phenol removal if properly designed and operated; however, the trickling filter process is regarded as being more capable of withstanding slug loads without loss of performance. Lagoons for treating phenolic wastes are designed to avoid overflow, with evaporation and seepage used to balance the influent flow. This method is less desirable, due to the possibility of ground water pollution, odor, and overflows from rainfall.

Frequently, phenolic wastes are diluted with sanitary wastes and treated at the local municipal plant (Muller and Covertry 1968). Combined municipal-industrial treatment buffers the dilution and provides an ample supply of nutrients and microorganisms should the system be upset. Phenolic wastewaters should be neutralized prior to discharge to the municipal sewer system.

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