Anoxic Biodegradation of Naphthenic Acid Using Nitrite as an Electron Acceptor
Extraction of bitumen from oil sands by surface mining and alkaline hot water process has generated large amount of oil sand process water (OSPW) which are contaminated by naphthenic acids (NAs). Due to the toxic and harmful nature of NAs, OSPW have been stored on-site in extremely large tailing ponds. With the understanding that the OSPW must be treated before their release into the natural water bodies and the need for reuse of the water, there is an urgent need in finding ways to treat these OSPWs effectively and economically. Numerous works on different treatment methods including photocatalysis, ozonation, adsorption, phytoremediation, simulated wetlands and bioremediation have been conducted and bioremediation has been proved as one of the most feasible ways among these methods. Research works on biodegradation of NAs, both aerobically and anoxically, have been conducted intensively in our research group in the past several years. Using surrogate NAs, specially trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), aerobic (Paslawski et al., 2009a,b,c, Huang et al., 2012; D’Souza et al., 2013) and anoxic (Gunawan et al., 2014) biodegradations of NA have been studied in batch, CSTR, biofilm system and circulating packed-bed bioreactor. Effects of naphthenic acid concentration, temperature, and naphthenic acid loading rate on the biodegradation process have been investigated. The results of the anoxic biodegradation of trans-4MCHCA in the presence of nitrate as an electron acceptor revealed that its performance was similar or better than the aerobic biodegradation. The results of that study also indicated the production of nitrite during the denitrification of nitrate and its subsequent consumption as part of biodegradation process. Given the importance of denitritation (nitrite reduction) as an essential step in anoxic biodegradation in the presence of nitrate, and the potential inhibitory effect of nitrite, the current research was conducted with the aim of investigating the performance of the anoxic biodegradation of trans-4MCHCA in the presence of nitrite as an electron acceptor, using batch, CSTR and biofilm reactors. The results of batch studies showed that nitrite at concentration up to 690 mg L-1 did not have a marked inhibitory effect but concentrations above 920 mg L-1 imposed a strong inhibitory effect. The optimum temperature was found to be in the range 24 C to 30°C. Continuous anoxic biodegradation of trans-4MCHCA with nitrite in CSTR achieved the maximum trans-4MCHCA biodegradation rate of 14.4 mg L-1 h-1 at a trans-4MCHCA loading rate of 22.9 mg L-1 h-1, which was about seven fold lower than the maximum trans-4MCHCA biodegradation rate observed with nitrate as an electron acceptor (105.4 mg L-1 h-1; Gunawan 2013). Both the trans-4MCHCA and nitrite degradation rates decreased with further increase of trans-4MCHCA loading rate. Using the experimental data the biokinetic coefficients Y (biomass yield), Ke (endogenous rate constant), μm (maximum specific growth rate) and Ks (saturation constant) were determined as 0.3 mg cell mg substrate-1, ~0 h-1, 0.4 h-1 and 20.9 mg substrate L-1, respectively. Similar pattern was observed in the biofilm system whereby the maximum trans-4MCHCA biodegradation rate was 82.2 mg L-1 h-1 at a trans-4MCHCA loading rate of 171.8 mg L-1 h-1, was about five folder lower than the maximum trans-4MCHCA biodegradation rate observed when nitrate was used as an electron acceptor (435.8 mg L-1 h-1; Gunawan 2013). The findings of current study suggested that the anoxic NA biodegradation in the presence of nitrite occurred at rates which were lower than those observed in the presence of nitrate, as well as those obtained under aerobic conditions with oxygen as the electron acceptor.
DegreeMaster of Science (M.Sc.)
DepartmentChemical and Biological Engineering
CommitteeLin, Yen-Han; Meda, Venkatesh; Peng, Jian
Copyright DateOctober 2014