Packed Bed Slime Reactor: A New Technology For Petroleum Wastewater Purification

Abstract

Abstract The use of a high-density concentration of bacteria immobilized in a packed column (the packed bed slime reactor) is described for the biodegradation of organic petroleum wastewater effluents. The column has been characterized in terms of liquid holdup, mass transfer to a flowing countercurrent air phase and liquid dispersion. Equations are presented representing an accurate mechanistic modelof the biodegradation behaviour of the column for phenol, cresol and actual refinery wastewater. The column established a 200 micron thick slime layer of bacteria. Biodegradation of the phenolic pollutants was 100% efficient at a rate of 1.6*10−3 kg/m3 -s, significantly faster than any previously reported rates. Negligible air-stripping losses occurred during 100% biodegradation runs and the column responded swiftly to step changes in inlet concentrations reaching new steady stales within three hours after a disturbance. Introduction Petroleum operations involve the handling of a great deal of water along with crude oil and/or petroleum products. Frequently this water phase undergoes intimate contact with the oil phase whether it be due to co-production directly from the reservoir or due to condensates from steam stripping columns within an oil refinery. Depending on the current value of crude oil, it may be economical to pump recovery wells with many times more water than oil while most oil refineries require a vast quantity of fresh water to process that same crude oil into useful products. A typical oil refinery will consume 18 barrels of water for every barrel of crude oil it brings across its borders. Although much of this water may either be unspoiled or used as a secondary recovery fluid at production sites, frequently petroleum operations generate considerable quantities of polluted waters which must be safely discharged. The primary ingredients of discharge water and typical effluent concentration guidelines are Listed in Table 1 from Beychok(1). Of particular concern for petroleum operations are the organic phenols which contribute a major portion of the dissolved hydrocarbons in the wastewater. This is because the aromatic ring proves to be simultaneously a very stable and toxic molecule making phenols recalcitrant to natural degradation and poisonous to most forms of life. This paper will focus on a novel design for secondary treatment of petroleum wastewaters. The packed bed slime reactor (PBSR) will be shown to be much more efficient than the aerated lagoon for biodegradation of phenols. The enhanced efficiency combined with the traditional but simple design with result in less money for construction and operation. The phenol biodegradation characteristics of an actual refinery wastewater effluent will be shown to be identical to that of artificial mixtures used in research studies. Theoretical Modelling of the PBSR The major feature of the PBSR design is the establishment of a stable, thick slime layer. The slime represents a high-density population of bacteria which must be chosen to give swift and complete biodegradation of the organic phenolics(2). Simultaneously, there is downward flow of the polluted wastewater through the column and upward flow of air to provide "just enough" oxygen to promote growth of the aerobic bacteria culture.