Effects of surfactant and temperature on biotransformation kinetics of anthracene and pyrene

The biotransformation and mineralization of a mixture of two polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, which are known contaminants of soil and groundwater, by an enrichment culture in the presence or absence of 100 mg l(-1) Tergitol NP-10, a non-ionic surfactant, and at temperatures of 10 degrees C and 25 degrees C were investigated. The overall biotransformation of 2 mg l(-1) total PAHs with free cell suspensions in batch culture was greater than 97.2% at both examined temperatures. At 25 degrees C, the overall mineralization of anthracene was 48.8% and that of pyrene was 66.1%. However, the decrease of temperature to 10 degrees C had a negative effect on the mineralization of PAHs and reduced it to 18.5% and 61.5% for anthracene and pyrene, respectively. Using a higher PAHs concentration of 20 mg l(-1) at 25 degrees C, the overall biotransformation of anthracene was 80.7% and that of pyrene was 100%, where only 17.3% anthracene and 7.6% pyrene were mineralized to carbon dioxide and water. The addition of surfactant at 25 degrees C increased the overall mineralization of anthracene and pyrene to 33.0% and 27.6%, respectively. However, the addition of surfactant at 10 degrees C had a negative impact on the overall biotransformation of anthracene and pyrene, reducing them to 20.6% and 14.0%, respectively. These results have significant implications in the bioremediation of PAHs-contaminated sites.     

Fluorescence-based monitoring of tracer and substrate distribution in an UASB reactor

In this work, rhodamine-related fluorescence was measured on-line at four reactor heights in order to study hydrodynamics within an upflow anaerobic sludge bed reactor. A linear dependence of the dispersion coefficient (D) on the upflow velocity was observed, while the influence of the organic loading rate (OLR) was insignificant. Furthermore, the Bodenstein number of the reactor loaded with granulated sludge was found to be position-dependent with the largest values measured at the bottom of the sludge bed. This trend was not observed in the reactor without sludge. Chemical oxygen demand (COD) and volatile fatty acid (VFA) concentrations were measured at the same reactor heights as in rhodamine tests using conventional off-line analytical methods and on-line multiwavelength fluorometry. Significant spatial COD and VFA gradients were observed at organic loading rates above 6g COD l(R)(-1)d(-1) and linear upflow velocities below 0.8m h(-1).     

Transport of gellan gum microbeads through sand: an experimental evaluation for encapsulated cell bioaugmentation

Transport of 10-40 microm gellan gum microbeads was studied in horizontal sand columns to evaluate the feasibility of using gel-encapsulated bacteria for bioaugmentation of contaminated aquifers. Three 5.2 x 110 cm columns were packed with sand (column A: 0.5-2 mm, column B: 0.25-2 mm, and column C: 0.125-2 mm). Microbeads in artificial groundwater were injected at 0.5 l h(-1) during intermittent 12-h periods. Breakthrough of microbeads increased with injection time, varying as a descending function of travel distance. After 72 h of injection, about 75% of injected microbeads were dispersed across a 5-110 cm distance from the inlet in column A, compared to 78% across a 5-50 cm in column B, and 76% across a 5-20 cm in column C. The wider dispersion of microbeads across the length of column A, compared to those observed in columns B and C, suggests a higher potential for the formation of a uniform bioactive zone of encapsulated cells across a sandy aquifer with such grain size distribution and hydrodynamic properties.     

Removal of pyrene and benzo(a)pyrene from contaminated water by sequential and simultaneous ozonation and biotreatment.

The removal of pyrene and benzo(a)pyrene from contaminated water by sequential and simultaneous ozonation-bioremediation techniques was investigated. During the sequential treatment, ozonation using 0.5 or 2.5 mg/L ozone was used as a pretreatment process, whereas, during the simultaneous treatment process, ozonation of hydrocarbon-contaminated water at a predetermined duration using 0.5 mg/L ozone was made in the presence of microbial biomass. Ozonation was not beneficial for the removal of pyrene. However, despite a decreased specific biodegradation rate, ozonation improved the overall elimination of benzo(a)pyrene during both treatment processes. The overall removal of benzo(a)pyrene increased from 23 to 91% after exposure of the water to 0.5 mg/L ozone for 30 minutes during the simultaneous treatment process and further to 100% following exposure to 2.5 mg/L ozone for 60 minutes during the sequential treatment mode, demonstrating the benefits of combined ozonation-biological treatment for the removal of polycyclic aromatic hydrocarbons.     

Thermophilic adaptation of a mesophilic anaerobic sludge for food waste treatment

As opposed to mesophilic, thermophilic anaerobic digestion of food waste can increase the biogas output of reactors. To facilitate the transition of anaerobic digesters, this paper investigated the impact of adapting mesophilic sludge to thermophilic conditions. A 5L bench scale reactor was seeded with mesophilic granular sludge obtained from an up-flow anaerobic sludge blanket digester. After 13 days of operation at 35 degrees C, the reactor temperature was instantaneously increased to 55 degrees C and operated at this temperature until day 21. The biomass was then fed food waste on days 21, 42 and 63, each time with an F/M (Food/Microorganism) ratio increasing from 0.12 to 4.43 gVS/gVSS. Sludge samples were collected on days 0, 21, 42 and 63 to conduct substrate activity tests, and reactor biogas production was monitored during the full experimental period. The sludge collected on day 21 demonstrated that the abrupt temperature change had no pasteurization effect, but rather lead to a biomass with a fermentative activity of 3.58 g Glucose/gVSS/d and a methanogenic activity of 0.47 and 0.26 g Substrate/gVSS/d, related respectively, to acetoclastic and hydrogenophilic microorganisms. At 55 degrees C, an ultimate gas production (Go) and a biodegradation potential (Bo) of 0.2-1.4 L(STP)/gVS(fed) and of 0.1-0.84 L(STP) CH(4)/gVS(fed) were obtained, respectively. For the treatment of food waste, a fully adapted inoculum was developed by eliminating the initial time-consuming acclimatization stage from mesophilic to thermophilic conditions. The feeding stage was initiated within 20 days, but to increase the population of thermophilic methanogenic microorganisms, a substrate supply program must be carefully observed.     

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in marine mussels from French coasts: levels, patterns and temporal trends from 1981 to 2005

The levels and temporal trends of toxic polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in archived marine mussels collected between 1981 and 2005 from selected sites along French coasts. The geographical distribution and levels of PCDD/Fs generally reflect regional inputs of these contaminants: the highest concentrations were determined in samples from the Seine river estuary (English Channel) and Toulon area (Mediterranean coast); the lowest levels were determined in Corsica (Mediterranean Sea). PCDD/F isomeric composition showed a fairly homogeneous distribution pattern throughout the various sampling sites. This pattern, dominated by 2,3,7,8-TCDF and OCDD, can be considered as typical for the study species. However, on a more local scale, some differences in isomeric composition in mussels were identified in relation to local source characteristics. The time trend study showed a pronounced decrease in PCDD/F concentrations over the 24-year period at most sites, except Toulon on the Mediterranean Sea, where the decrease was not significant. This overall decrease probably reflects the general drop in PCDD/F emissions in Europe since 1980. However, high concentrations were determined in mussels collected in recent years (1999, 2001 and 2005) from the mouth of the Seine river. These concentrations are related to particular hydrological conditions, and intensive sediment dredging due to a new port construction at the mouth of the estuary. The results presented in this paper provide reference data on the contamination of shellfish by persistent organic pollutants in the marine environment.     

Polybrominated diphenyl ethers (PBDEs) in mussels from selected French coastal sites: 1981-2003

The present study focused on the retrospective analysis of PBDEs in archived blue mussel (Mytilus edulis or Mytilus galloprovincialis) samples collected over the past 22 years (1981-2003) from coastal areas of France. We have found that PBDE levels in mussels from the English Channel increased markedly from 1981 to 1991-1995, doubling approximately every 5-6 years followed by a levelling off and a possible beginning of a decrease. The rate of the decline of hexa- and hepta-BDE congeners was more rapid than the decline of tetra- and penta-BDEs in these mussel samples. The difference in the course of time of lower and higher brominated PBDE concentrations suggests that the congener profile in the mussel samples changes over time. The increase in PBDE concentrations in the mussel samples contrasts with a concomitant constant decrease of chlorobiphenyls (CBs) in the same set of samples. However, pulse inputs of both groups of organohalogen compounds were determined for the mussel samples collected at the mouth of the Seine estuary and were probably related to riverine inundations and a flushing out of the deposited sediments from the internal estuary into the bay of the River Seine, as well as considerable dredging activities taking place during same years. In France, the highest PBDE concentrations were determined in the mussels from the English Channel, more precisely in the bay of the Seine, and the regional differences in PBDE levels were mainly connected to the difference in anthropogenic urban and industrial environmental pressures. Published data comparing PBDE levels in mussels have shown significant differences in concentrations between North/South America and Europe. This observation further confirms that the PBDE levels in the North American environment are higher than in Europe. However, the data used for this comparison of mussel contamination by PBDEs is still relatively sparse.     

A microcosm test for potential mineralization of chlorinated compounds under coupled aerobic/anaerobic conditions

In this study, the feasibility of using a mineralization test under coupled aerobic/anaerobic conditions was demonstrated. The coupling of anaerobic methanogenic and aerobic methanotrophic conditions in a microcosm required the presence of both a carbon source for anaerobic metabolism and oxygen for aerobic metabolism. These requirements were fulfilled by using a slow hydrolyzing organic matter along with intermittent addition of oxygen to the bottle headspace. Perchloroethylene (PCE) mineralization tests confirmed the effectiveness of the proposed methodology as well as PCE mineralization under coupled conditions.