The Effect Of Microbial Activity On Dewatering Of Oil Sands Tailings Sludge

Introduction The hot water process to extract bitumen from oil sands produces about 0.4 m3 of tailings sludge for each barrel of extracted bitumen. Densification of this sludge beyond 30% solids content Is extremely slow under gravity settling, leading to the accumulation of large quantities of liquid waste which poses problems in mining logistics and ultimate disposal. Many attempts to increase sludge dewatering or to provide methods for ultimate disposal have either failed or given only a partial solution. The most common reasons for the failure is the high cost of the treatment or technical difficulties due to the large quantity of the sludge. The possibility of treating oily sludges by microbiological activity was explored by several authors. Marks, Field and Wojtanowicz (1988) removed 70 - 79% of the oil from drilling mud with the help of bacteria cultures developed from microbes in domestic waste water or oil refinery biological treatment systems. Hocking (1977) incubated fertilized oil sands sludge from Great Canadian Oil Sands Ltd. They found that microbes, indigenous in the oil sands sludge, can utilize organic substances in the sludge under aerobic conditions and can enhance its dewatering. Wyndham and Costerton (1981) demonstrated that microbes isolated from Athabasca River sediments have the ability to degrade bitumen with the exception of its asphaltene fraction. Cullimore and Boerger (1985) studied the micro-flora of Syncrude Canada Ltd,'s tailings pond. They identified 33 genera and species of bacteria and fungi in the pond including genera which are known to have hydrocarbon degrading species. The above examples indicate that cultured and indigenous microbes in the oil sands sludge can degrade organic compounds in the sludge and gases and poly-saccharides excreted by the microbes may change sludge properties in a number of ways which may enhance sludge dewatering. This study intends to examine sludge behaviour when incubated under anaerobic conditions and enriched with mineral fertilizers and easily available carbon source. Methods Tailings pond sludge of 25% solids contentwas collected by M. MacKinnon in July, 1988 and stored in a cold room until April, 1989. The sludge was placed into 1000 ml graduated cylinders on April 25, 1989 and treated as follows: Control - no additives; Treatment # 1 - KCI = 750 ppm; Treatment # 2. N = 50 ppm, P = 150 ppm, K = 50 ppm; Treatment # 3 - N = 100 ppm, P = 300 ppm, K = 100 ppm; Treatment # 4 - N = 150 ppm, P = 450 ppm, K = 150 ppm; Treatment # 5 - N = 150 ppm, P = 450 ppm, K = 150 ppm, sucrose = 1000 ppm. Sources of mineral nutrients were urea, ammonium and potassium phosphates and potassium nitrate. KCI treatment was included to approximate the ionic concentration created by the addition of mineral nutrients in other treatments, facilitating the distinction between the effects of higher salt concentrations and the added nutrients. Sucrose was added as an easily available carbon source.