Electrochemical Disinfection of Simulated Ballast Water Using RuO2-TiO2/Ti Electrode.

The present work investigated the treatment of ballast water via electrochemical disinfection using a RuO2-TiO2/Ti electrode. Batch tests were conducted with simulated ballast water containing Escherichia coli as an indicator organism. The effect of varying NaCl concentrations (1%, 2%, and 3%; w/v) and current densities (0.3, 1.0, 2.0, and 3.0 mA/cm2) on the inactivation of E. coli was examined. Results showed higher disinfection efficiency of E. coli was obtained at higher NaCl concentration and current density. Complete inactivation of E. coli was attained within 2 and 1 min at 0.3 and 1 mA/cm2, respectively, under 3% NaCl concentration. Meanwhile, complete disinfection at 1 and 2% NaCl concentrations was observed in 6 and 2 min, respectively, using a current density of 0.3 mA/cm2. The 100% inactivation of E. coli was achieved with an energy consumption in the range of 2.8 to 2.9 Wh/m3 under the NaCl concentrations at 1 mA/cm2 and 1 min of electrolysis time. The complete disinfection attained within 1 min meets the D-2 standard (<250 CFU E. coli/100 mL) of ballast water under the International Maritime Organization. The values of energy consumption of the present work are lower than previous reports on the inactivation of E. coli from simulated ballast water.

Electrochemical effect on bioleaching of arsenic and manganese from tungsten mine wastes using Acidithiobacillus spp.

Mine wastes from tungsten mine which contain a high concentration of arsenic (As) may expose many environmental problems because As is very toxic. This study aimed to evaluate bioleaching efficiency of As and manganese (Mn) from tungsten mine wastes using the pure and mixed culture of Acidithiobacillus ferrooxidans and A. thiooxidans. The electrochemical effect of the electrode through externally applied voltage on bacterial growth and bioleaching efficiency was also clarified. The obtained results indicated that both the highest As extraction efficiency (96.7%) and the highest Mn extraction efficiency (100%) were obtained in the mixed culture. A. ferrooxidans played a more important role than A. thiooxidans in the extraction of As whereas A. thiooxidans was more significant than A. ferrooxidans in the extraction of Mn. Unexpectedly, the external voltage applied to the bioleaching did not enhance metal extraction rate but inhibited bacterial growth, resulting in a reverse effect on bioleaching efficiency. This could be due to the low electrical tolerance of bioleaching bacteria. However, this study asserted that As and Mn could be successfully removed from tungsten mine waste by the normal bioleaching using the mixed culture of A. ferrooxidans and A. thiooxidans.

Electrochemical removal and recovery of iron from groundwater using non-corrosive electrodes.

Iron contamination in groundwater has attracted much attention from environmentalists and government agencies because it can cause many problems in human life and in industrial and agricultural activities when groundwater is directly used without any treatment. This study aims to investigate the electrochemical oxidation of Fe(II) to Fe(III) and recovery of insoluble Fe(III) using non-corrosive graphite electrode which serves as a controllable, low-cost, low maintenance and virtually unlimited electron acceptor for Fe(II) oxidation. The lab-scale results indicated that Fe(II) removal up to 100% was obtained at an applied voltage higher than 2 V. The Fe(II) removal efficiency was linearly increased with the increase of potential supply in the range of 1-4 V in the salinity 0.5%. The Fe(II) removal rate could no longer be enhanced at the applied potential higher than 8 V in the condition without salinity. The results from SEM-EDS and XRD revealed that Fe was recovered as FeOOH by conventional filtration with a recovery efficiency of 82.7-92.1%. The electrochemical Fe(II) removal might be an alternative for the conventional method of the in situ Fe removal from groundwater. Besides, the recovered FeOOH can be used as a raw material for environmental remediation and pigment industry.

Biodegradation of diesel by mixed bacteria immobilized onto a hybrid support of peat moss and additives: a batch experiment.

We report microbial cell immobilization onto a hybrid support of peat moss for diesel biodegradation. Three strains isolated from a site contaminated with diesel oil were used in this study: Acinetobacter sp., Gordonia sp., and Rhodococcus sp. To increase not only diesel adsorption but also diesel biodegradation, additives such as zeolite, bentonite, chitosan, and alginate were tested. In this study, a peat moss, bentonite, and alginate (2/2.9/0.1 g, w/w/w) hybrid support (PBA) was the best support matrix, considering both diesel physical adsorption capacity and mixed microbial immobilization.

Use of biosurfactant to remediate phenanthrene-contaminated soil by the combined solubilization-biodegradation process.

The applicability of the combined solubilization-biodegradation process was examined using soil-packed column. In the solubilization step, 50 pore volumes of 150 mg/l biosurfactants solution was injected and the percentage removal of phenanthrene (mg) was 17.3% and 9.5% from soil with pH 5 and 7, respectively. The highest solubility was detected at pH 5 and this result confirmed that adjusting the pH of the biosurfactants solution injected could enhance the solubility of phenanthrene. Following this, soil samples were completely transferred to batches and incubated for 10 weeks to monitor phenanthrene degradation. The phenanthrene concentration in the soil samples decreased significantly during the biodegradation step in all soil samples, except for the soil sample that was flushed with biosurfactants solution with pH 4. This indicated that the degradation of contaminants by specific species might not be affected by the residual biosurfactants following application of the solubilization process. Moreover, these results suggested that the biosurfactant-enhanced flushing process could be developed as a useful technology with no negative effects on subsurface environments and could be combined with the biodegradation process to increase the removal efficiency.

Effects of in-situ ozonation on indigenous microorganisms in diesel contaminated soil: survival and regrowth.

Soil column experiments were conducted to investigate the effects of chemical oxidation on the survival of indigenous microbes (i.e., heterotrophic microbes, phenanthrene-degrading microbes, and alkane-degrading microbes) for field soil contaminated with diesel fuel. Rapid decreases of total petroleum hydrocarbons (TPH) and aromatics of diesel fuel were observed within the first 60 min of ozone injection; after 60 min, TPH and aromatics decreased asymptotically with ozonation time. The three types of indigenous microbes treated were very sensitive to ozone in the soil column experiment, hence the microbial population decreased exponentially with ozonation time. The numbers of heterotrophic, alkane-degrading, and phenanthrene-degrading bacteria were reduced from 10(8) to 10(4), 10(7) to 10(3), and 10(6) CFU g soil(-1) to below detection limit after 900 min of ozonation, respectively. Except for the soil sample ozonated for 900 min, incubation of ozone-treated soil samples that were not limited by oxygen diffusion showed further removal of TPH. The soil samples that were ozonated for 180 min exhibited the lowest concentration of TPH and the highest regrowth rate of the heterotrophic and alkane-degrading populations after the 9 weeks of incubation.

Biofilm microbial community of a thermophilic trickling biofilter used for continuous biohydrogen production.

Molecular methods were employed to investigate the microbial community of a biofilm obtained from a thermophilic trickling biofilter reactor (TBR) that was operated long-term to produce H(2). Biomass concentration in the TBR gradually decreased as reactor bed height increased. Despite this difference in biomass concentration, samples from the bottom and middle of the TBR bed revealed similar microbial populations as determined by PCR-DGGE analysis of 16S rRNA genes. Nucleotide sequences of most DGGE bands were affiliated with the classes Clostridia and Bacilli in the phylum Firmicutes, and the most dominant bands showed a high sequence similarity to Thermoanaerobacterium thermosaccharolyticum.

Monitoring of petroleum hydrocarbon degradative potential of indigenous microorganisms in ozonated soil.

This study was performed to investigate the petroleum hydrocarbon (PH) degradative potential of indigenous microorganisms in ozonated soil to better develop combined pre-ozonation/bioremediation technology. Diesel-contaminated soils were ozonated for 0-900 min. PH and microbial concentrations in the soils decreased with increased ozonation time. The greatest reduction of total PH (TPH, 47.6%) and aromatics (11.3%) was observed in 900-min ozonated soil. The number of total viable heterotrophic bacteria decreased by three orders of magnitude in the soil. Ozonated soils were incubated for 9 weeks for bioremediation. The number of microorganisms in the soils increased during the incubation period, as monitored by culture- and nonculture-based methods. The soils showed additional PH-removal during incubation, supporting the presence of PH-degraders in the soils. The highest removal (25.4%) of TPH was observed during the incubation of 180-min ozonated soil during the incubation while a negligible removal was shown in 900-min ozonated soil. This negligible removal could be explained by the existence of relatively few or undetected PH-degraders in 900-min ozonated soil. After a 9-week incubation of the ozonated soils, 180-min ozonated soil showed the lowest TPH concentration, suggesting that appropriate ozonation and indigenous microorganisms survived ozonation could enhance remediation of PH-contaminated soil. Microbial community composition in 9-week incubated soils revealed a slight difference between 900-min ozonated and unozonated soils, as analyzed by whole cell hybridization. Taken together, this study provided insight into indigenous microbial potential to degrade PH in ozonated soils.

Toxic effect of biosurfactant addition on the biodegradation of phenanthrene.

The effect of the biosurfactant rhamnolipid on phenanthrene biodegradation and cell growth of phenanthrene degraders was investigated. To compare the effect of rhamnolipid addition, two bacterial strains, 3Y and 4-3, which were isolated from a diesel-contaminated site in Korea, were selected. Without the biosurfactant, large amounts of phenanthrene were degraded with both strains at neutral pH, with higher rates of phenanthrene degradation when the cell growth was higher. Upon the addition of 240 mg/L rhamnolipid, the phenanthrene degradation and optical density were reduced, with this inhibitory effect similar for both 3Y and 4-3. To explain this inhibition, the cell growths of both strains were monitored with various concentrations of rhamnolipid, which showed significant toxic effects toward strain 3Y, but was nontoxic toward 4-3. Combining the inhibitory and toxicity results with regard to the biodegradation, different mechanisms can be suggested for each strain. In the biodegradation experiments, the toxicity of rhamnolipid itself mainly was responsible for the inhibitory effect in the case of 3Y, whereas the toxicity of solubilized phenanthrene or the increased toxicity of rhamnolipid in the presence of solubilized phenanthrene could have resulted in the inhibitory effect in the case of 4-3. This study demonstrated that the effectiveness of biosurfactant-enhanced biodegradation can be significantly different depending on the strain, and the toxicity of the biosurfactant should be considered as an important factor.

Comparative analysis of vertical heterogeneity of microbial community in sulfur-packed reactor used for autotrophic nitrate removal.

To better understand microbial community in sulfur-based nitrate removal process, comparative molecular analyses were performed with the biofilm formed on sulfur particles that were obtained from different bed-heights of a laboratory-scale reactor employed for the process. Microbial community in the reactor showed vertical heterogeneity in terms of total cell count and nitrate removal activity. DAPI (4',6-diamidino-2-phenylindole) staining revealed that total cell count (per g sulfur particle) gradually decreased as bed height increased until reaching approximately middle of the reactor bed, showing a nearly plateau afterward. This result partly supported ion chromatography result that most nitrate removal activity was found in the lower part of the reactor bed. Phylogenetic composition of bacterial community in the biofilm was almost similar regardless of bed height as determined by whole cell hybridization using group-specific probes. Cells affiliated with the beta- and gamma-Proteobacteria were the most abundant proteobacterial groups throughout the bed, although their fractions were fluctuating along the bed height. Total number of the two major groups decreased as bed height increased, showing similar trend to total cell count and nitrate removal activity. Denaturating gradient gel electrophoresis revealed similar profiles of nitrous oxide reductase gene (nosZ) fragments from denitrifying populations at the different bed-heights, suggesting similar diversity of the nosZ fragments regardless of bed height.

Monitoring the impact of dissolved oxygen and nitrite on anoxic biofilm in continuous denitrification process.

An anoxic biofilm involved in continuous denitrification process was monitored to investigate the effect of different concentrations of influent dissolved oxygen (DO) or nitrite on the biofilm. Microelectrode measurements evidenced nitrate removal activity of biofilm. When different concentrations of DO were applied to the reactor, generally decreased concentrations of DO were observed as bed depth increased from the bottom of the reactor. Greatest decrease of the DO was observed in the lower 20% of the bed depth. Nitrate removal efficiency was inversely proportional to influent DO concentrations (8.3-11.9 DO mg L(-1)) or nitrite loading rates (0-5.5 N-NO2- kg m(-3) day(-1)) employed in this study. Nitrite loading rates to achieve more than 90% of nitrate removal efficiency were 1.46 N-NO2- kg m(-3) day(-1) or less at pH 7.5 and 0.34 N-NO2- kg m(-3) day(-1) or less at pH 6.8. Nitrate removal efficiency was 63% or more within the lower 20% of the bed depth at the nitrite loading rates that allowed more than 90% of nitrate removal efficiency of the reactor. The results of this study provide first quantitative data that nitrate removal performance of an anoxic biofilm is inhibited by DO or nitrite, reported to be a limiting factor in the suspended biological denitrification process.