Effect of the specific surface area and operating mode on biological phenol removal using packed bed reactors

The efficiency of packed bed reactors on the biological degradation of phenol was studied in this work. In particular, the effect of the specific surface area of the support material and the operating mode on biodegradation efficiency were determined. Phenol removal was studied using two pilot-scale packed bed reactors loaded with different support materials, i.e., calcite gravel and plastic tubes. The draw-fill operating mode was tested for the two reactors, while in the case of the plastic tube packed-bed reactor the draw-fill operating mode with recirculation was also investigated. Indigenous bacteria from olive pulp were enriched and used as inoculum for the reactors. The enrichment of the bacterial community capable for phenol degradation was based on natural selection. The maximum removal rate achieved at the two reactors filled with gravel support material and plastic tubes under draw-fill operation was found to be 25.3 g phenol/d and 14.03 g phenol/d respectively, for a feed phenol concentration of 500 mg/l. Increase of feed phenol concentration to about 2750 mg/l demonstrated inhibitory effects on bacterial growth, while the corresponding removal rate was reduced. The operating mode of draw-fill with recirculation for the packed-bed reactor loaded with plastic tubes, resulted in a maximum removal rate of 29.9 g phenol/d for feed phenol concentration of about 500 mg/L, which even exceeded the maximum recorded removal rate of the gravel media reactor, under draw-fill operation.

Phenol is a toxic compound and it should be removed from wastewater before disposal to the environment. In this work, phenol removal in ap- propriate packed beds was examined and the main conclusions are: • The use of indigenous bacteria populations from olive pulp provided durability under the various operating conditions tested. • The specific surface area strongly affects the observed phenol biodegradation rate. • The time needed for complete phenol degradation in the pilot-scale packed bed reactor with gravel support media was found to be about the half of that recorded at the plastic tube media reactor, when operated without recirculation. Adding recirculation mode, the required time for complete phenol removal becomes even shorter than in the case of gravel support media. • Attached growth processes at high phenol con- Phenol removal rate (g/d) Operating cycle (hrs) Phenol feed concentration (mg/l) Fig. 5. Duration of operating cycles and phenol removal rates for various feed phenol concentrations (500, 1000, 1550, 2200 and 2750 mg/l) in the pilot-scale packed bed reactor with plastic tube support media, under draw-fill operation.