Phenol remediation by biofilm developed in sand soil media

Abstract

Laboratory scale sand columns were used in order to evaluate biodegradation of phenol, simulating the conditions which could be created in the non-saturated (vadose) zone by an accidental spill on the top of the soil, biologically remediated by a controlled recycled aqueous flow, enriched by the necessary nutrients. The parameters which have been studied as possible factors influencing the biodegradation process by fixed film biomass, included: (a) the effective size of the sand grain, coarse sand of 2.51 mm and medium sand of 0.81 mm operated in two different columns; (b) flow rate of the aqueous phase recycled through the columns, 0.090, 0.120 and 0.176 bed volumes/hr; (c) different initial loading of phenol applied on the top of the columns, 4, 5 and 6 grams. Daily monitoring of the experimental system included analyses of phenol, COD, turbidity, pH, ammonia, phosphate and suspended solids. Removal efficiencies of phenol were found to be high, close to 100%, within the first seven days following the exposure, indicating high rates of biodegradation. Measurements of volatile attached solids (VAS) connected to the sand, quantitatively indicating fixed film biomass, were higher at the top region and lower at the bottom, at a depth of about one metre: 44.5 and 28.1 mg VAS/gram of dry sand were obtained in the coarse sand column, 10.6 and 4.1 mg VAS/gram of dry sand in the medium sand column, respectively. The general yield coefficient was found to be 0.57 gram VAS/gram of phenol biodegraded. The results indicated that the medium sand size resulted in a slightly better performance, especially in cases of high flow rates, however, coarse sand showed quicker acclimation of microorganisms to biodegrade the phenol. Low rates of flow resulted in more effective biodegradation of phenol. High loading of phenol applied on the top of the columns inhibited, apparently, the microbial activity within the sand columns.