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This study evaluated the use of natural coagulants (Moringa oleifera and chitosan) under different conditions with a mixed culture (C1 mixed culture). This culture was used for the biodegradation of hydrocarbons present in the effluent from fuel distribution terminals contaminated with diesel oil and gasoline. The biodegradation was evaluated by two central composite design (CCD) experiments: the first with varying concentrations of Moringa oleifera (MO), drying temperatures (TE) and seed drying times (TI); the second with varying concentrations of chitosan and the hydrochloric acid in which chitosan had been solubilized. The responses monitored in the CCD experiments included the sludge volume index (SVI), the turbidity removal (TR) and the specific rate of oxygen uptake (SOUR). Subsequently, the biodegradation was monitored in a sequencing batch reactor (SBR) under the optimal conditions obtained for each CCD experiment. The results indicated that the best coagulant was chitosan solubilized in 0.25 N HCl at a concentration of 50mg/L. Within five cycles with chitosan as a coagulant, the total organic carbon (TOC) removal increased from 77±1.0% to 82±0.5%, the volatile suspended solids (VSS) increased from 1.4±0.3 to 2.25±0.3 g/L and the total petroleum hydrocarbon (TPH) removal increased from 75±1.0% to 81±0.5%., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This study evaluated the use of coagulants (ferric chloride and aluminium sulphate) and an anionic polyelectrolyte (polyacrylamide) in the settling of a mixed culture (C(1)), which was used for the biodegradation of hydrocarbons present in effluent of fuel distribution terminals contaminated with diesel oil and gasoline. In preliminary investigations conducted in jar tests, the optimal concentrations of coagulant were obtained for further studies. After preliminary tests, biodegradation was evaluated in a central composite design (CCD) with varying concentrations of ferric chloride and polyelectrolyte. Ferric chloride and polyelectrolyte concentrations ranged from 77.9 to 422.12 mg/L and 0.0 to 3.2mg/L, respectively. The responses monitored in CCD experiments included the sludge volume index (SVI), turbidity, and specific rate of oxygen uptake (SOUR), where values of 100mL/g, 840 nephelometric turbidity unit (NTU) and 58 mg O(2)/gh, respectively, were obtained. Subsequently, biodegradation was monitored in a sequencing batch reactor (SBR). The results indicated that within five cycles, total petroleum hydrocarbon (TPH) removal increased from 75 ± 1.0% to 79 ± 0.5%, while the volatile suspended solids (VSS) increased from 1300 to 2500 mg/L., (Copyright © 2010. Published by Elsevier B.V. All rights reserved.)

We examined the effects of aeration interval and agitation speed in an effort to optimize the biodegradation of effluent contaminated with diesel oil and gasoline. The biodegradation process employed a C(1) mixed culture and intermittent aeration. Optimization was performed using central composite design (CCD). The independent variables were aeration interval (X(1)) and agitation speed (X(2)) and the dependent variable was the degree of removal of total petroleum hydrocarbons (TPH). The optimum aeration interval (33h) and agitation speed (110rpm) resulted in TPH removal of 75.9% after 3 days. Five hydrocarbons classes were identified using gas chromatography: paraffins, isoparaffins, olefins, naphthenics, and aromatics. The following reductions were observed: 91.8% for the paraffins, 83.3% for the isoparaffins, 80.9% for the olefins, 39.3% for the naphthenics, and 80.9% for the aromatics. In comparative studies performed under constant aeration (CA), without aeration (WA), and intermittent aeration (IA) conditions, intermittent aeration resulted in the highest TPH removals, with 90% reduction after 22 days. Under the IA condition, the degradation percentages were 99.6% for the paraffins, 94% for the isoparaffins, 95.4% for the olefins, 70.8 for the naphthenics, and 83.4% for the aromatics.

We studied the effects of fuel concentration (diesel and gasoline), nitrogen concentration and culture type on the biodegradation of synthetic effluent similar to what was found at inland fuel distribution terminals. An experimental design with two levels and three variables (2(3)) was used. The mixed cultures used in this study were obtained from lake with a history of petroleum contamination and were named culture C(1) (collected from surface sediment) and C(2) (collected from a depth of approximately 30cm). Of the parameters studied, the ones that had the greatest influence on the removal of total petroleum hydrocarbons (TPH) were a nitrogen concentration of 550mg/L and a fuel concentration of 4% (v/v) in the presence of culture C(1). The biodegradability study showed a TPH removal of 90+/-2% over a process period of 49 days. Analysis using gas chromatography identified 16 hydrocarbons. The aromatic compounds did not degrade as readily as the other hydrocarbons that were identified.