Removal of Oxygen Demand and Acute Toxicity during Batch Biological Treatment of a Petroleum Refinery Effluent

Abstract

This study was undertaken in order to investigate the removal of oxygen demand and acute toxicity from a petroleum refinery effluent. The results of this study provide a better understanding of the biodegradation process occurring at the Chevron refinery wastewater treatment plant (WWTP) in Burnaby, BC. The WWTP consists of a deep shaft bioreactor followed by a dissolved air flotation clarifier and effluent polishing biofilters. The treatment plant is able to degrade approximately 75% of the COD and 95% of the BOD present in the wastewater. During the study period, the toxicity of the wastewater before and after treatment was 1.9±0.12 (%v/v) and 25.4±5.9 (%v/v), respectively (as measured by the 5 minute Microtox™ assay in EC50 units).The experimental program utilized two batch bioreactors operated at 35°C to characterize the removal of organic compounds (as measured by BOD and COD), and to deterrnine the capacity of the biomass for acute toxicity removal. A six-litre batch bioreactor was operated for 52.5 hours (Run 1), and a 15 L batch bioreactor was operated for 120 hours (Run 2). In order to assess the abiotic rate of volatilization, a stripping test was also performed using the six-litre batch reactor.In both runs, the BOD and COD reduction occurred over the first 24 hours of treatment. The BOD removal was 92-96%, and the COD removal was 73-75%. These values are similar to the removal levels reported at the Chevron refinery WWTP. Stripping accounted for 3% of the COD removal over 52.5 hours. Since stripping was insignificant, the compounds contributing to BOD and COD were most likely removed via biodegradation.Both runs showed similar patterns of toxicity removal. Rather than being continuously removed, as in the case of BOD and COD, toxicity appeared to be removed in discrete stages. The first stage of toxicity removal corresponded to the degradation of BOD and COD, and the second stage occurred after BOD and COD had been removed. The raw wastewater in Runs 1 and 2 had a 5-minute EC50 of 4.6+0.5% and 4.9±0.4%, respectively. In Run 1, the toxicity was reduced to a 5-rninute EC50 of 7.9±0.7% in 10 hours, and further removal did not occur until after 28 hours. In Run 2, a 5-minute EC50 of 16±3.2% was achieved over the first 10 hours, and the toxicity remained at this level until 48 hours. A second significant toxicity removal step between 48 and 72 hours resulted in a final 5-minute EC50 of 27.8±1.6%.ii Process ChemicalsCaustic soda, sulphuric and phosphoric acid,

Inhibition and biotransformation potential of naphthenic acids under different electron accepting conditions

“…NAs are corrosive and acutely toxic to both aquatic and terrestrial species, including bacteria, yeast, earthworms, fish, mammals, and both aquatic and terrestrial plants (Armstrong et al, 2008;Clemente et al, 2003;Frank et al, 2009Frank et al, , 2008Holowenko et al, 2002;Nero et al, 2006;Peters et al, 2007;Rogers et al, 2002;Sarathy et al, 2002;Scott et al, 2008;Thomas et al, 2009). NAs can be degraded under aerobic conditions; however, many NAs are persistent and remain in the wastewater systems even after biotreatment (Clemente and Fedorak, 2005;Del Rio et al, 2006;Quagraine et al, 2005a;Scott et al, 2005;Misiti, 2012;Misiti et al, 2012).…”

Effect of Alkyl Side Chain Location and Cyclicity on the Aerobic Biotransformation of Naphthenic Acids

“…Recently, use of advanced mass spectrometry techniques has shown that oil sands process-affected water (OSPW) and oil field and refinery wastewaters contain low levels of NAs with a broad spectrum of molecular structures. − The range of NA structures has recently been expanded to include other polar and N- and S-containing heteroatomic species and aromatic species found in the oil sands acid extractable fraction. ,− NAs in the wastewater is an ecological concern, as NAs are among the most toxic components of both OSPW and refinery process wastewater. The degree of toxicity depends on the concentration of NAs as well as their type and molecular structure. ,− …”

Fate and effect of naphthenic acids on oil refinery activated sludge wastewater treatment systems

“…NAs are corrosive and among the most toxic components of oil sands process waters, acutely toxic to both aquatic and terrestrial species, including bacteria, yeast, earthworms, fish, mammals, and both aquatic and terrestrial plants (Armstrong et al, 2008;Clemente et al, 2003;Frank et al, 2009Frank et al, , 2008Holowenko et al, 2002;Nero et al, 2006;Peters et al, 2007;Rogers et al, 2002;Sarathy et al, 2002;Scott et al, 2008;Thomas et al, 2009). Model NAs, commercial NA mixtures and NAs in oil sands process water samples have been found to degrade aerobically using inocula obtained from oil sands process waters and NA-affected natural systems; however, commercial NAs were found to be more readily degraded than the NAs in oil sands process waters (Clemente and Fedorak, 2005;Del Rio et al, 2006;Scott et al, 2005).…”