Applying metabolic flux analysis to hydrogen fermentation using a metabolic network constructed for anaerobic mixed cultures.

In this study, a mixed-cultural metabolic network for anaerobic digestion that included the concept of a "universal bacterium" was constructed, and metabolic flux analysis (MFA) applying this network was conducted to evaluate the flow of electrons and materials during H2 fermentation under various conditions. The MFA results from two H2 fermenters feeding glucose with (GP) or without (GA) the addition of peptone suggest that hydraulic retention time (HRT) presents a significant impact on hydrogen production, and the reversed trends could be observed at HRTs below and above 4 h. From the MFA results of lactate/acetate-fed H2 fermenter, the highest flux of H2 production is associated with more significant acetate consumption and the following pathways toward the anaplerotic reactions cycle that produces NADH. The occurrence of acetogenesis in the H2 fermenters using various types of bioethanol-fermented residues (BEFRs) was also identified according to the MFA results. By analyzing the MFA results of all 49 sets of data from H2 fermenters via Pearson's correlation, it was revealed that the flux of H2 production positively correlates to the reduction of ferredoxin with pyruvate oxidation, acetate formation, and acetate emission when lactate was produced in the system. On the contrary, negative relationships were found between the flux of H2 production and these three fluxes. The extended application of MFA provides additional information, including the fluxes between intracellular metabolites, and the information has the potential to be used in decision-making systems during the future operation of anaerobic processes by connecting operational parameters.

Congener profiles of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in sediment, water, and fish at a soil contamination site in Taiwan.

The relationship of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in sediment, water, and fish was studied for 55 fish farms near a contaminated site in Tainan, Taiwan. Samples were collected from the farms and analyzed for seventeen 2,3,7,8-substituted PCDD/Fs congeners. High correlations were found between PCDD/Fs in water and sediment in regard to both concentration and toxicity (R(2) = 0.933 for concentration and R(2) = 0.832 for toxicity). The congener profiles of the 17 PCDD/Fs in water were similar to those in the sediment. However, the PCDD/Fs congener composition in the fish and fish belly samples were different from those in the sediment and water samples obtained from the same fish farm and were also different among the fish samples. It is thus suggested that the biotic PCDD/Fs distribution is more complex than the abiotic PCDD/Fs distribution. Among the seven factors analyzed, only the lipid percentage presented a relationship with the PCDD/Fs congener composition in the fish and fish bellies. A multiple linear regression of the concentration of each congener in the fish was conducted using the concentration of each congener in the site-matched sediment and the lipid content of the fish as independent variables. The results showed that only seven PCDD/Fs congeners with a lower degree of chlorination, which were 4-6 chlorine substitutes, in the fish presented a significant correlation with the lipid content in the fish and their concentration in sediment (r > 0.65, P < 0.005 for both independent variables). In addition, the octanol-water partition coefficients were not significantly related to this distribution behavior.

Molecular analysis of methanogens involved in methanogenic degradation of tetramethylammonium hydroxide in full-scale bioreactors.

This study investigated methanogenic communities involved in degradation of tetramethylammonium hydroxide (TMAH) in three full-scale bioreactors treating TMAH-containing wastewater. Based on the results of terminal-restriction fragment-length polymorphism (T-RFLP) and quantitative PCR analyses targeting the methyl-coenzyme M reductase alpha subunit (mcrA) genes retrieved from three bioreactors, Methanomethylovorans and Methanosarcina were the dominant methanogens involved in the methanogenic degradation of TMAH in the bioreactors. Furthermore, batch experiments were conducted to evaluate mcrA messenger RNA (mRNA) expression during methanogenic TMAH degradation, and the results indicated that a higher level of TMAH favored mcrA mRNA expression by Methansarcina, while Methanomethylovorans could only express considerable amount of mcrA mRNA at a lower level of TMAH. These results suggest that Methansarcina is responsible for methanogenic TMAH degradation at higher TMAH concentrations, while Methanomethylovorans may be important at a lower TMAH condition.

Biological treatment of N-methylpyrrolidone, cyclopentanone, and diethylene glycol monobutyl ether distilled residues and their effects on nitrogen removal in a full-scale wastewater treatment plant.

Manufacturing processes in semiconductor and photonics industries involve the use of a significant amount of organic solvents. Recycle and reuse of these solvents produce distillate residues and require treatment before being discharged. This study aimed to evaluate the performance of the biological treatment system in a full-scale wastewater treatment plant that treats wastewater containing distillate residues from the recycling of electronic chemicals. Batch experiments were conducted to investigate the optimal operational conditions for the full-scale wastewater treatment plant. To achieve good nitrogen removal efficiency with effluent ammonia and nitrate concentrations below 20 mg N/L and 50 mg N/L, respectively, it was suggested to control the ammonia concentration and pH of the influent below 500 mg N/L and 8.0, respectively. In addition, the biodegradability of N-methylpyrrolidone, diethylene glycol monobutyl ether, and cyclopentanone distillate residues from the electronic chemicals manufacturing process were evaluated under aerobic, anoxic, and anaerobic conditions. N-methylpyrrolidone and cyclopentanone distillate residues were suggested to be treated under anoxic condition. However, substrate inhibition occurred when using cyclopentanone distillate residue as a carbon source with chemical oxygen demand (COD) levels higher than 866 mg/L and nitrate levels higher than 415 mg N/L. Under aerobic condition, the COD from both N-methylpyrrolidone and cyclopentanone distillate residues could be easily degraded. Nevertheless, a negative effect on nitrification was observed, with a prolonged lag time for ammonia oxidation as the initial COD concentration increased. The specific ammonia oxidation rate and nitrate production rate decreased under high COD concentration contributed by N-methylpyrrolidone and cyclopentanone distillate residues. Furthermore, the biodegradability of diethylene glycol monobutyl ether distillate residue was found to be low under aerobic, anoxic, and anaerobic conditions. With respect to the abundance of nitrogen removal microorganisms in the wastewater treatment plant, results showed that Comammox may have an advantage over ammonia oxidizing bacteria under high pH conditions. In addition, Comammox may have higher resistance to environmental changes. Dominance of Comammox over ammonia oxidizing bacteria under high ammonia condition was first reported in this study.

Nitrifying bacterial community structures and their nitrification performance under sufficient and limited inorganic carbon conditions.

This study examined the hypothesis that different inorganic carbon (IC) conditions enrich different ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) populations by operating two laboratory-scale continuous-flow bioreactors fed with 15 and 100 mg IC/L, respectively. During this study, both bioreactors maintained satisfactory nitrification performance and stably oxidized 250 mg N/L of influent ammonium without nitrite accumulation. Based on results of cloning/sequencing and terminal restriction fragment length polymorphism targeting on the ammonia monooxygenase subunit A (amoA) gene, Nitrosomonas nitrosa lineage was identified as the dominant AOB population in the high-IC bioreactor, while Nitrosomonas europaea and Nitrosomonas nitrosa lineage AOB were dominant in the low-IC bioreactor. Results of real-time polymerase chain reactions for Nitrobacter and Nitrospira 16S rRNA genes indicated that Nitrospira was the predominant NOB population in the high-IC bioreactor, while Nitrobacter was the dominant NOB in the low-IC bioreactor. Furthermore, batch experiment results suggest that N. europaea and Nitrobacter populations are proliferated in the low-IC bioreactor due to their higher rates under low IC conditions despite the fact that these two populations have been identified as weak competitors, compared with N. nitrosa and Nitrospira, under low ammonium/nitrite environments. This study revealed that in addition to ammonium/nitrite concentrations, limited IC conditions may also be important in selecting dominant AOB/NOB communities of nitrifying bioreactors.

Biosorption and biotransformation behaviours of veterinary antibiotics under aerobic livestock wastewater treatment processes.

To study the fate of veterinary antibiotics released from swine wastewater treatment plants (SWTP), 10 antibiotics were investigated in each unit of a local SWTP periodically. Over a 14-month period of field investigation into target antibiotics, it was confirmed that tetracycline, chlortetracycline, sulfathiazole, and lincomycin were used in this SWTP, with their presence observed in raw manure. Most of these antibiotics could be effectively treated by aerobic activated sludge, except for lincomycin, which was still detected in the effluent, with a maximum concentration of 1506 µg/L. In addition, the potential for removing antibiotics was evaluated using lab-scale aerobic sequencing batch reactors (SBRs) that were dosed with high concentrations of antibiotics. The SBR results, however, showed that both sulfonamides and macrolides, as well as lincomycin, can achieve 100% removal in lab-scale aerobic SBRs within 7 days. This reveals that the potential removal of those antibiotics in field aeration tanks can be facilitated by providing suitable conditions, such as adequate dissolved oxygen, pH, and retention time. Furthermore, the biosorption of target antibiotics was also confirmed in the abiotic sorption batch tests. Biotransformation and hydrolysis were identified as the dominant mechanism for removing negatively charged sulfonamides and positively charged antibiotics (macrolides and lincomycin) in SBRs. This is due to their relatively low sorption affinity (resulting in negligible to 20% removal) onto activated sludge in abiotic sorption tests. On the other hand, tetracyclines exhibited significant sorption behavior both onto activated sludge and onto soluble organic matters in swine wastewater supernatant, accounting for 70%-91% and 21%-94% of removal within 24 h, respectively. S-shape sorption isotherms with saturation were observed when high amounts of tetracyclines were spiked into sludge, with equilibrium concentrations ranging from 0.4 to 65 mg/L. Therefore, the sorption of tetracyclines onto activated sludge was governed by electrostatic interaction rather than hydrophobic partition. This resulted in a saturated sorption capacity (Qmax) of 17,263 mg/g, 1637 mg/g, and 641.7 mg/g for OTC, TC, and CTC, respectively.

Resource recovery from lignocellulosic wastes via biological technologies: Advancements and prospects.

Lignocellulosic wastes were recently considered as biomass resources, however, its conversion to valuable products is still immature although researchers have put lots of effort into this issue. This article reviews the key challenges of the biorefinery utilizing lignocellulosic materials and recent developments to conquer those obstacles. Available biological techniques and processes, from the pretreatments of cellulosic materials to the valorization processes, were emphasized. Biological pretreatments, including hydrolysis using microbial consortia, fungi, enzymes, engineered bacterial/fungal strains, and co-culture systems, could enhance the release of reducing sugar. Resources recovery, including biogases, ethanol, butanol, PHA, etc., from lignocellulosic materials were also discussed, while the influences of composition of lignocellulosic materials and pretreatment options, applications of co-culture system, and integrated treatments with other wastes, were described. In the review, co-culture system and metabolic engineering are emphasized as the promising biological technologies, while perspectives are provided for their future developments.

Recycled Steel Slag as a Porous Adsorbent to Filter Phosphorus-Rich Water with 8 Filtration Circles.

Steel slag is a secondary product from steelmaking process through alkaline oxygen furnace or electric arc furnace (EAF). The disposal of steel slag has become a thorny environmental protection issue, and it is mainly used as unbound aggregates, e.g., as a secondary component of asphalt concrete used for road paving. In this study, the characteristics of compacted porous steel slag disc (SSD) and its application in phosphorous (P)-rich water filtration are discussed. The SSD with an optimal porosity of 10 wt% and annealing temperature of 900 °C, denoted as SSD-P (10, 900) meets a compressive strength required by ASTM C159-06, which has the capability of much higher than 90% P removal (with the effluent standard < 4 mg P/L) within 3 h, even after eight filtration times. No harmful substances from SSD have been detected in the filtered water, which complies with the effluent standard ISO 14001. The reaction mechanism for P-rich water filtration is mediated by water, followed by two reaction steps-CaO in SSD hydrolyzed from the matrix of SSD to Ca2+ and reacting with PO43-. However, the microenvironment of water is influenced by the pH value of the P-rich water at different filtration times and the kind of P-rich water with different free positive ion that interferes the reactions of the release of Ca2+. This study demonstrates the application of circular economy in reducing steel slag deposits, filtering P-rich water, and collecting Ca3(PO4)2 precipitate into fertilizers.

Biological treatment of volatile organic compounds (VOCs)-containing wastewaters from wet scrubbers in semiconductor industry.

This study investigated biological treatment for two kinds of volatile organic compounds (VOCs)-containing wastewaters collected from wet scrubbers in a semiconductor industry. Batch test results indicated that one wastewater containing highly volatile organic compounds was not suitable for aerated treatment conditions while the other containing much lower volatile organic compounds was suitable for aerobic treatment. Accordingly, two moving bed bioreactors, by adding commercial biocarrier BioNET, were operated under aerobic and anoxic conditions for treating low volatility wastewater (LVW) and high volatility wastewater (HVW), respectively. During 280 days of operation, the aerobic LVW bioreactor attained the highest chemical oxygen demand (COD) removal rate of 98.9 mg-COD/L/h with 81% of COD removal efficiency at hydraulic retention time (HRT) of 1 day. The anoxic HVW bioreactor performed above 80% of COD removal efficiency with the highest COD removal rate of 16.5 mg-COD/L/h at HRT of 2 days after 380 days of operation. The specific COD removal rates at different initial substrate-to-biomass (S0/X0) ratios, using either suspended sludge or microorganisms attached onto BioNET from both bioreactors, followed the Monod-type kinetics, while the half-saturation coefficients were generally higher for the microorganisms onto BioNET due presumably to relatively poor mass transfer efficiency. Based on the results of microbial community analysis using the next generation sequencing technique, the dominant communities of suspended sludge and BioNET, including nitrifiers, denitrifiers, and degraders for polycyclic aromatic hydrocarbons, were similar in the corresponded bioreactors, but microbial community shifts were observed with increased organic loadings.

Recent advancement on biological technologies and strategies for resource recovery from swine wastewater.

Swine wastewater is categorized as one of the agricultural wastewater with high contents of organics and nutrients including nitrogen and phosphorus, which may lead to eutrophication in the environment. Insufficient technologies to remove those nutrients could lead to environmental problems after discharge. Several physical and chemical methods have been applied to treat the swine wastewater, but biological treatments are considered as the promising methods due to the cost effectiveness and performance efficiency along with the production of valuable products and bioenergies. This review summarizes the characteristics of swine wastewaters in the beginning, and briefly describes the current issues on the treatments of swine wastewaters. Several biological techniques, such as anaerobic digestion, A/O process, microbial fuel cells, and microalgae cultivations, and their future aspects will be addressed. Finally, the potentials to reutilize biomass produced during the treatment processes are also presented under the consideration of circular economy.

Aerobic degradation of high tetramethylammonium hydroxide (TMAH) and its impacts on nitrification and microbial community.

Tetramethylammonium hydroxide (TMAH) was often used as developer in the high-tech industries. Information regarding biological treatment of high TMAH-containing wastewater is limited. This study investigated aerobic degradation of high TMAH, its impacts on nitrification, and microbial community in a sequencing batch reactor (SBR). The initial TMAH concentrations of SBR gradually increased from 200 to 4666 mg L-1 (equivalent to 31 to 718 mg-N L-1) to enrich microbial community for aerobic TMAH degradation and nitrification. The results indicated that the aerobic specific TMAH degradation rates followed the Monod-type kinetics with a maximum specific TMAH degradation rate of 2.184 mg N hour-1 g volatile suspended solid (VSS)-1 and the half-saturation coefficient of 175.1 mg N L-1. After TMAH degradation and ammonia release, the lag time for the onset of nitrification highly correlated with initial TMAH fed for the SBR. According to the microbial community analysis using next generation sequencing (NGS), potential aerobic TMAH-degraders including Mycobacterium sp. and Hypomicrobium sp. were enriched in the aerobic SBR. The results of real-time quantitative polymerase chain reaction (qPCR) and reverse transcript (RT)-qPCR indicated that Hyphomicrobium sp. may be able to utilize both TMAH and its degradation intermediates such as trimethylamine (TMA), while Thiobacillus sp. can only utilize TMAH. The qPCR and RT-qPCR results suggested that TMAH may inhibit nitrification by inactive expression of amoA gene and the intermediates of TMAH degradation may compete ammonia monooxygenase (AMO) enzyme with ammonia for nitrification inhibition.

Effects of copper on biological treatment of NMF- and MDG-containing wastewater from TFT-LCD industry.

This study aimed to evaluate the effects of copper on N-methylformamide (NMF)- and methyl diglycol (MDG)-containing wastewater treatment using batch experiments and a lab-scale anoxic-oxic (A/O) sequencing batch reactor (SBR). Batch experimental results indicated that aerobic degradation of NMF followed Monod-type kinetics. Copper inhibition on nitrification also followed Monod-type inhibition kinetics with copper-to-biomass ratio instead of copper concentration. Specific degradation rates of NMF and MDG under both aerobic and anoxic conditions decreased in the matrix of full-scale wastewater, and high copper dosage would further reduce the degradation rates. In the long-term presence of 0.5 mg/L copper, the A/O SBR could maintain stable and complete degradations of NMF and MDG, 95% of COD removal, and more than 50% of total nitrogen (TN) removal. High concentrations of copper spikes, including 40 mg/L and 110 mg/L, slowed down degradation rates for both NMF and MDG, but did not affect COD and TN removal efficiencies in the full 24 h-cycle operation. The long-term A/O SBR operation revealed that daily dosage of 0.5 mg/L copper was not detrimental to NMF/MDG degradations due to regularly wasting sludge, but 110 mg/L of copper spike obviously reduced NMF/MDG degradation rate although it could be recovered later by regularly wasting sludge and maintaining SRT at 20 days.

Effect of soil organic matter on petroleum hydrocarbon degradation in diesel/fuel oil-contaminated soil.

The purpose of this study is to investigate the effect of soil organic matter (SOM) content levels on the biodegradation of total petroleum hydrocarbons (TPH). Batch experiments were conducted with soils with 2% or 10% organic matter that had been contaminated by diesel or fuel oil. In addition to the TPH (diesel or fuel oil) degradation efficiency, a comprehensive investigation was conducted on the TPH-degrading microbial community using molecular tools including oligonucleotide microarray technique and terminal restriction fragment length polymorphism analysis (T-RFLP). TPH was reduced from 10,000 mg/kg to 1849-4352 mg/kg dry weight soil. Higher biodegradation efficiencies and kinetic rate constants were observed in higher SOM contents. Hydrocarbon fractional analyses were conducted to explain the optimal operation with relatively low resin and aromatic fractions detected at the end of the remediation. The bacterial and fungal counts in the 10% SOM were approximately 10 CFU/g to 102 CFU/g above those in the 2% SOM, and the lowest fungal level was found when the least TPH degradability was measured. The internal transcribed spacer microarray identified the microorganisms that were introduced and proved their survival. The associated growth pattern confirmed that different kinds of contamination oils affected the microbial community diversity over time. Both the microarray and T-RFLP profiles indicated that Gordonia alkanivorans, G. desulfuricans, and Rhodococcus erythoropolis were the dominant bacteria, while Fusarium oxysporum and Aspergillus versicolor were the dominant fungi. The T-RFLP-derived nonmetric multidimensional scaling concluded that the dynamics of the microbial communities were impacted by the TPH degradation stages.

Altered carbon flow by polyphosphate-accumulating organisms during enhanced biological phosphorus removal.

The effect of carbon source availability during enhanced biological phosphorus removal (EBPR) was evaluated. To assess the EBPR activity of polyphosphate-accumulating organisms (PAOs), PAO-enriched sludge from a laboratory-scale sequencing batch reactor and activated sludge from a full-scale municipal wastewater treatment plant were used, and their EBRP performances were compared. Spiking with acetate (1000 mg/L chemical oxygen demand) during the aerobic phase disrupted the EBPR performance of both types of sludge; however, when the carbon source was removed, still in the aerobic phase, the EBPR performance of both types of sludge was restored. The PAO-enriched sludge showed 3 to 5 times greater glycogen restoration activity per biomass than the full-scale activated sludge. During high acetate loading in the anaerobic phase, PAOs are supposed to deplete internally stored polyphosphate, causing a "poly-phosphate limited condition". Under such a condition, unlike the full-scale activated sludge, the PAO-enriched sludge produced a higher fraction of poly-hydroxylvalerate. It was proposed that PAOs can use the glyoxylate pathway and the methymalonyl-CoA pathway through a full or partial tricarboxylic acid cycle under the anaerobic condition.

Effects of natural organic matters on bioavailability of petroleum hydrocarbons in soil-water environments.

The bioremediation efficiency of petroleum hydrocarbons in natural soil-water systems is regulated by active microbial populations and other system parameters. Relevant factors include the transfer rate of petroleum contaminants from a medium into microorganisms, the partitioning behavior of contaminants from water into the soil organic matter (SOM), and the influence of the dissolved organic matter (DOM) on the contaminant level in water. The objectives of this study was aimed to determine the correlation among bioavailability of petroleum hydrocarbons, SOM content, and DOM level in soil-water systems. Heptadecane, pristane, and decylcyclohexane were selected as model hydrocarbon contaminants. The bioavailability of target contaminants in soil was examined using soils of different SOM contents (2% and 20%) in slurry bioreactors. In addition, the contaminant bioavailability as affected by various DOM levels (0-100 mgC/L) was also examined. The results showed that the SOM content affected the degrading rate of hydrocarbons significantly, where the rate constant was 4 times higher in 2% SOM microcosm than in the 20% SOM bioreactor for heptadecane degradation. Similarly, the pristane degrading efficiency after 240 h operation was 95% for the 2% SOM microcosm and only 38% for the 20% SOM microcosm. The hydrocarbon degradation rates in water phase were found to be enhanced by the added DOM level. A positive correlation existed between the contaminant bioavailability and the contaminant level in water as impacted by the SOM content in soil and the DOM level in water.

Application of molecular biological tools for monitoring efficiency of trichloroethylene remediation.

Trichloroethylene (TCE) is one of the most ubiquitous halogenated organic compounds of concerns of carcinogens in groundwater in Taiwan. Bioremediation has been recognized as a cost-effective approach in reducing TCE concentration. Five pilot-scale wells were constructed to monitor TCE concentrations in contaminated groundwater. With injection of EOS®, TCE was effectively degraded to 42%-93% by the end of 175 days. The biostimulation with EOS® was useful in establishing a micro-site anaerobic but with limited contribution. Dilution of the aquifer movement also caused the TCE reduction among injection and monitoring wells. The degradability was affected by the location and the proximity from the injection well. TCE concentrations found to be negatively correlated with the associated Dehalococcoides spp. and functional genes levels. Dhc concentration of 108 copies L-1 caused the initial 40% of TCE degradation. The well with the optimal degradation owned tceA of 109 cells L-1. T-RFLP results indicate the wells with the superior TCE degradability also performed the highest Shannon index number (means the highest diversity), which occurred on the same day that Dhc levels started to enlarge. Desulfovibrio desulfuricans and Desulfuromonas chloroethenica were predominant species identified in the T-RFLP fingerprint profile. In brief, a variety of different factors including well locations, geochemical indicators, and microbial contribution were useful to explain the site-specific optimal TCE remediation approach. The consistence among TCE degradation, Dhc growing pattern, functional gene levels, and the dynamics of the microbial community structure present the novelty of this study.

Biological treatment of DMSO-containing wastewater from semiconductor industry under aerobic and methanogenic conditions.

This study evaluated biological treatment of dimethyl sulfoxide (DMSO)-containing wastewater from semiconductor industry under aerobic and anaerobic conditions. DMSO concentration as higher as 1.5 g/L did not inhibit DMSO degradation efficiency in aerobic membrane bioreactor (MBR), while specific DMSO degradation rate at different initial DMSO-to-biomass (S0/X0) ratios from batch tests seemed to follow the Haldane-type kinetics. According to the microbial community analysis, Proteobacteria decreased from 88.2% to 26% as influent DMSO concentration increased, while Bacteroidetes, Parcubacteria, Saccharibacteria increased. Within the Bacteroidetes class, Flavobacterium and Laribacter genus significantly increased from less than 0.05%-26.8% and 13.4%, respectively, which might both be related to the DMS degradation. Hyphomicrobium and Thiobacillus, known as aerobic DMSO and DMS degraders, instead, decreased at higher DMSO conditions. Under methanogenic conditions, batch results implied DMSO concentrations higher than 3 g/L could be inhibitory, while DMSO and COD removal achieved 100% and 93%, respectively, using a pilot-scale anaerobic fluidized bed membrane bioreactor (AFMBR) with influent DMSO below 1.5 g/L. Results of terminal restriction fragment length polymorphism (TRFLP) analysis targeting on mcrA functional gene revealed that Methanomethylovorans sp. was dominant in AFMBR after 54 days of operation, indicating its importance on degrading DMS and mathanethiol (MT).

Application of biosurfactants, rhamnolipid, and surfactin, for enhanced biodegradation of diesel-contaminated water and soil.

This study investigated potential application of two biosurfactants, surfactin (SF) and rhamnolipid (RL), for enhanced biodegradation of diesel-contaminated water and soil with a series of bench-scale experiments. The rhamnolipid used in this study, a commonly isolated glycolipid biosurfactant, was produced by Pseudomonas aeruginosa J4, while the surfactin, a lipoprotein type biosurfactant, was produced by Bacillus subtilis ATCC 21332. Both biosurfactants were able to reduce surface tension to less than 30 dynes/cm from 72 dynes/cm with critical micelle concentration (CMC) values of 45 and 50 mg/L for surfactin and rhamnolipid, respectively. In addition, the results of diesel dissolution experiments also demonstrated their ability in increasing diesel solubility with increased biosurfactant addition. In diesel/water batch experiments, an addition of 40 mg/L of surfactin significantly enhanced biomass growth (2500 mg VSS/L) as well as increased diesel biodegradation percentage (94%), compared to batch experiments with no surfactin addition (1000 mg VSS/L and 40% biodegradation percentage). Addition of surfactin more than 40 mg/L, however, decreased both biomass growth and diesel biodegradation efficiency, with a worse diesel biodegradation percentage (0%) at 400 mg/L of SF addition. Similar trends were also observed for both specific rate constants of biomass growth and diesel degradation, as surfactin addition increased from 0 to 400 mg/L. Addition of rhamnolipid to diesel/water systems from 0 to 80 mg/L substantially increased biomass growth and diesel biodegradation percentage from 1000 to 2500 mg VSS/L and 40 to 100%, respectively. Rhamnolipid addition at a concentration of 160 mg/L provided similar results to those of an 80 mg/L addition. Finally, potential application of surfactin and rhamnolipid in stimulating indigenous microorganisms for enhanced bioremediation of diesel-contaminated soil was also examined. The results confirmed their enhancing capability on both efficiency and rate of diesel biodegradation in diesel/soil systems.

Methanogenic degradation of tetramethylammonium hydroxide by Methanomethylovorans and Methanosarcina.

This study evaluated the methanogens responsible for methanogenic degradation of tetramethylammonium hydroxide (TMAH) in a continuous flow bioreactor. The enriched methanogens attained an estimated maximum specific TMAH degradation rate and half-saturation constant of 39.5 mg TMAH/gVSS/h and 820 mg/L, following the Monod-type kinetic expression for methanogenic TMAH degradation. Presence of sulfide more than 20 mg/L significantly extended lag period and slowed down specific TMAH degradation rates. The results of terminal restriction fragment length polymorphism (T-RFLP), cloning/sequencing, and quantitative real-time PCR analyses targeting on the methyl coenzyme M reductase alpha subunit (mcrA) genes retrieved from the bioreactor and batch experiments indicated that Methanomethylovorans species were the dominant methanogens responsible for methanogenic degradation of TMAH. The isolated TMAH-degrading methanogen from the bioreactor, however, was identified closely related to Methanosarcina mazei. It is likely that a very low TMAH environment in the bioreactor favored the growth of Methanomethylovorans hollandica, while the much higher TMAH in the isolation growth medium proliferated Methanosarcina mazei.

Biological acetate production from carbon dioxide by Acetobacterium woodii and Clostridium ljungdahlii: The effect of cell immobilization.

This study investigated the acetate production from gas mixture of hydrogen (H2) and carbon dioxide (CO2) in the ratio of 7:3 using two acetogens: Acetobacterium woodii and Clostridium ljungdahlii. Batch result shows A. woodii performed two-phase degradation with the presence of glucose that lactate was produced from glucose and was reutilized for the production of butyrate and few acetate, while only acetate was detected when providing gas mixture. C. ljungdahlii produced butyrate and ethanol along with acetate when glucose was introduced, while only ethanol and acetate were found by feeding gas mixture. The acetate-to-ethanol (A/E) ratio can be enhanced by cell immobilization, while GAC immobilization produced only acetate and the production rate reached 0.072 mmol/d under fed-batch operation. Acetate production rate increased from 18 to 28 mmol/L/d with GAC immobilization when gas flowrate increased from 100 to 300 mL/min in anaerobic fluidized membrane bioreactor (AFMBR), and a highest A/E ratio of 30 implies the possible application of acetate recovery from H2 and CO2.