In Bioremediation Technologies for Polycyclic

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Compounds. Proceedings from the Fifth International Symposium on In Situ and. On-site Bioremediation. 5(8):309-314. COMPARISON OF BENCH-SCALE AND ...
In Bioremediation Technologies for Polycyclic Aromatic Hydrocarbon Compounds. Proceedings from the Fifth International Symposium on In Situ and On-site Bioremediation. 5(8):309-314. COMPARISON OF BENCH-SCALE AND FIELD TREATMENTS FOR SEDIMENT BIOREMEDIATION T.P. Murphy (Environment Canada, Burlington, Ontario, Canada) A. Lawson (Environment Canada, Burlington, Ontario, Canada) J. Babin (Golder Associates, Kowloon Tong, Hong Kong) M. Kumagai (Lake Biwa Research Institute, Shiga Prefecture, Japan). ABSTRACT: Sediment samples from several contaminated sites were evaluated for the potential for polycyclic aromatic hydrocarbon (PAH) biodegradation, sulphide oxidation, and phosphorus inactivation. Sediments with a high total petroleum hydrocarbon (TPH) content had rates of PAH biodegradation as high as 1.75% a day. Sites with low TPH concentration had low to negative rates of biodegradation. In two samples, the short term negative rates of biodegradation were related to production of two and three ringed PAHs, presumably from very large PAHs that could not be measured. Only one site appeared to have metal suppression of bio-oxidation/biodegradation. Nutrient inactivation could be achieved but conditions were then not ideal for bioremediation. Laboratory results from glovebox enclosures agreed well with results obtained in pilotscale treatments. In pilot-scale treatments in Hamilton Harbour for PAHs, Hong Kong Harbour for odour, and Lake Biwa for phosphorus, about half of the PAHs were biodegraded, 99% of sulphides were oxidized, and 80% of phosphorus precipitated, respectively. INTRODUCTION In spite of the common demonstration of PAH biodegradation, PAHs can be resistant to biotreatment. There are several reasons for PAHs not to biodegrade but sometimes they can be overcome. Some sediments are relatively easy to bioremediate and some sediments cannot be bioremediated. The difficulty for managers of in situ treatment is to optimize treatment without increasing project costs excessively. Benchscale and pilot-scale testing are essential to ensure that treatments are optimized and the expectations for full-scale treatment are realistic. Reasons for poor biodegradation include; -lack of oxidant -lack of nutrients including phosphate precipitation -bacterial community not adapted to contaminants -poor biodegradability caused by a lack of natural surfactants, bioemusifiers, or natural “solvents” -toxicity caused by other toxins such as metals or other organic chemicals -physical limitations such as poor mixing of added materials or cold temperature -ongoing discharges of contaminants Objective. In this paper we will review the relative biotreatability of PAHs in sediments in bench-scale treatments conducted over four years from several sites. Biotreatments

had first been optimized with sediments from two sites in southern Ontario that are rich in PAHs and TPHs. Pilot-scale results will be compared to bench-scale testing. Sulphide and phosphate data are used to evaluate the effectiveness of injection of oxidants in situ. Site Descriptions. Hamilton Harbour is an industrial harbour with Canada’s largest steel mills (Murphy et al. 1995). Marine Site B is an urban marine lagoon in southern Europe with rich organic sediments and serious odour problems. Lake Ontario Site A is in the outer harbour of Toronto; it is moderately contaminated, mostly with TPHs. Industrial Site B is an American aluminium manufacturer on a freshwater lake. Lake Ontario Site B is in the inner harbour of Toronto near a storm sewer discharge. Industrial Site C is a waste oil pond of an European car maker. Marine Site A is an aluminium manufacturer on an estuary in Canada. The Hong Kong Site is adjacent to the former airport; it is rich in sewage wastes. Lake Biwa in Shiga prefecture, Japan is eutrophic from municipal and rural waste discharges. Asian Site B is a brackish eutrophic Japanese lake. MATERIALS AND METHODS Bench-scale treatments. Amber bottles (1 L) were filled with approximately 600 ml sediment and 100 ml of water plus proprietary amendments. The bottles were purged with helium and the bottles were stored in a sealed glovebox under helium atmosphere and shaken by inversion twice per week. In all treatments, three microcosms were left as controls and calcium nitrate at a concentration of 1 g NO3-N/L was added to three microcosms. Additional nitrate was added to treated microcosms to bring concentrations back to original values after 10 and 17 days incubation. Pilot-scale treatments. Two injection procedures were used. The injections in Lake Biwa and Asian Site B used a device 1m by 1m square with 100 17-cm rods with holes to inject at a depth of 15 cm.. Pilot-scale sediment injections in Hamilton Harbour and Hong Kong were done with a 8 m wide boom (Babin et al. 1998). At least three sediment cores were collected from each treatment and control. The sediment was extruded then analyzed for AVS concentrations by ion selective electrodes using a diffusion method (Brouwer and Murphy, 1994). Diffusion chambers were added to each treatment and control in triplicate two weeks after the injection and were left to incubate in the sediment for two weeks. Pore water samples were immediately acidified to a pH of 2 with concentrated nitric acid then analysed for iron and manganese by atomic absorption spectroscopy. The total reactive phosphorus in the acidified pore water samples was measured by a an ascorbic acid method. Gas Chromatographic/Mass Spectrographic (GC/MS) Procedure. The sediment sample (10 g) was spiked with a known amount of a surrogate mixture of deuterated PAHs, then extracted in a Soxhlet apparatus with an acetone-hexane (59:41) solvent mixture. The organic extract was base-partitioned with 2% potassium bicarbonate solution to separate the acidic compounds from the PAHs and other neutral compounds. The aqueous medium was back-extracted with 50 ml of hexane. The organic fractions were combined, dried through sodium sulphate and concentrated to ca. 3-5 ml. The resulting solutions were analyzed for 16 selected PAHs by GC/MS under the following conditions: GC: Hewlett-Packard model 5890, Split splitless injection; 30 m fused silica capillary column, DB-5; Injection temperature 300oC Program: 30oC held for 1 min, 30oC to 285oC at 6oC/min, hold 16.5 min. MS; HewlettPackard series 5970 mass spectrometer; Source Temperature 200oC; Electron ionization

70 eV; Select ion monitoring (SIM) mode. The PAH results were done in triplicate in a certified laboratory. RESULTS AND DISCUSSION PAH Biodegradation. The bench-scale biodegradation of total PAHs was highly variable but significantly correlated to the TPH concentrations (r2=0.79, n=8). Two sample sites with low TPH appeared to produce PAHs. At least with Marine Site A, this may represent the production of 2- and 3-ringed PAHs from larger unmeasurable PAHs. In three month incubations in samples from Industrial Site B, also an aluminium production site, 2- and 3- ringed PAHs were increasing significantly but they biodegraded within six months. However, the bioproduction of metabolites from Industrial Site C is less likely; this site had 285 mg/L of Zn in the sediment porewater, had only 24% bioremediation of TPHs and unlike samples from all other treated sites, it remained toxic to MicrotoxTM. Changes in sediment matrix during the treatments may have enhanced PAH extractability by up to 10%. Another unusual observation is that in all 6 month biotreatments a similar proportion of the larger PAHS had also biodegraded (Murphy et al. 1995). These results are consistent with observations of Peters and Fan (1997) that there are only small intrinsic differences in PAH biodegradation; the rate limiting step is mainly physical differences in PAH solubility and bioavailability. Similarly Fogel and Findlay (1997) found oil to enhance biodegradation of benzo(a)pyrene. In our sites, the bioavailable PAHs appeared to be associated with TPHs.

The samples with the highest oil content (Hamilton Harbour) of 2% had much higher rates of PAH biodegradation (1.75%/d). These bench-scale biodegradation rates in Hamilton Harbour were similar but faster than observed in pilot-scale treatments in Hamilton Harbour (Murphy et al. 1995). It has been argued that in situ treatments would be slower due to inadequate mixing (Renholds 1998). This physical aspect could be important but in Hamilton Harbour, the biggest problem was the ongoing discharge of oil

sprayed onto coal piles to prevent dust problems (Curran et al. 1999). Ship resuspension of neighbouring untreated sediments were also a problem (Irvine et al. 1997). The other uncertainties with the Hamilton Harbour project were the end-points of treatment. The bioavailability of the residuals was not assessed but much of the refractory materials was likely coal dust. Although PAHS refractory to biotreatment may still be a serious problem, research has demonstrated that weathered PAHS are less of a risk to the environment (Knaebel et al. 1996, Paine et al. 1996, White and Alexander 1996). The site where Paine et al. (1996) found limited bioavailability of PAHs is the same as our Marine Site A where we found no biodegradation of PAHs. Ideally the endpoints should be based upon bioassays, and risk management using ongoing land management to optimize and prioritize remedial efforts. The steel mill study site in Hamilton, is improving its management of coal piles to reduce runoff; however, storm sewers will remain a concern (Irvine et al. 1998). Sulphide Oxidation. Pilot-scale treatments in Lake Biwa and Asian Site B, Japan oxidized 95-99% of AVS. Pilot-scale treatment of sediments in Hong Kong oxidized 99% of the AVS in the surface sediments (Figure 2, Babin et al. 1998). The bench-scale results for these treatments were similar to the pilot-scale results. Nitrate injections were not compromised by poor mixing. Bioremediation in the bench-scale was minimal (i.e. 15% of PAHs,