Comparative genomics: Dominant coral-bacterium Endozoicomonas acroporae metabolizes dimethylsulfoniopropionate (DMSP).

Dominant coral-associated Endozoicomonas bacteria species are hypothesized to play a role in the coral sulfur cycle by metabolizing dimethylsulfoniopropionate (DMSP) into dimethylsulfide (DMS); however, no sequenced genome to date harbors genes for this process. In this study, we assembled high-quality (>95% complete) draft genomes of strains of the recently added species Endozoicomonas acroporae (Acr-14T, Acr-1, and Acr-5) isolated from the coral Acropora sp. and performed a comparative genomic analysis on the genus Endozoicomonas. We identified DMSP CoA-transferase/lyase-a dddD gene homolog in all sequenced genomes of E. acroporae strains-and functionally characterized bacteria capable of metabolizing DMSP into DMS via the DddD cleavage pathway using RT-qPCR and gas chromatography (GC). Furthermore, we demonstrated that E. acroporae strains can use DMSP as a carbon source and have genes arranged in an operon-like manner to link DMSP metabolism to the central carbon cycle. This study confirms the role of Endozoicomonas in the coral sulfur cycle.

Adsorptive conversion of nitrogen dioxide from etching vent gases over activated carbon.

Some metal etching operations emit limited flow rates of waste gases with reddish-brown NO2 fume, which may cause visual and acidic-odor complaints, as well as negative health effects. In this study, tests were performed by passing caustic-treated waste gases vented from Al-etching operations through columns packed either with virgin or regenerated granular activated carbon (GAC) to test their adsorptive conversion performance of NO2 in the gases. The gases contained 5-55 ppm NO2 and acetic and nitric acids of below 3 ppm. Exhausted carbon was regenerated by scrubbing it with caustic solution and water, and dried for further adsorption tests. Results indicate that with an (empty bed residence time (EBRT) of 0.15 sec for the gas through the GAC-packed space, around 60% of the influent NO2 of 54 ppm could be removed, and 47% of the removed NO2 was converted by and desorbed from the carbon as NO. GAC used in the present study could be regenerated at least twice to restore its capacity for NO2 adsorption. Within EBRTs of 0.076-0.18 sec, the adsorptive conversion capacity was linearly varied with EBRT. In practice, with an EBRT of 0.20 sec, a conversion capacity of 0.80 kg NO2 (kg GAC)-1 with an influent NO2 of 40 ppm can be used as a basis for system design. IMPLICATIONS: Some metal etching operations emit waste gases with reddish-brown (yellow when diluted) NO2 fume which may cause visual and acidic-odor complaints, as well as negative health effects. This study provides a simple process for the adsorptive conversion of NO2 in caustic-treated waste gases vented from metal-etching operations through a GAC column. With an EBRT of 0.20 sec, a conversion capacity of 0.80 kg NO2 (kg GAC)-1 with an influent NO2 of 40 ppm can be used as a basis for system design. Saturated GAC can be regenerated at least twice by simply scrubbing it with aqueous caustic solution.

Biotrickling filtration of airborne styrene: A comparison of filtration media.

This study compares the performances of fern and plastic chips as packing media for the biofiltration of a styrene-laden waste gas stream emitted in a plant for the manufacture of plastic door plates. Fern chips (with a specific surface area of 1090 m2 m-3) and plastic chips (with a specific surface area of 610 m2 m-3) were packed into a pilot-scale biotrickling filter with a total medium volume of 50 L for the performance test. Field waste gas with styrene concentrations in the range of 161-2390 mg Am-3 at 28-30 °C) was introduced to the bed and a fixed empty-bed retention time (EBRT) of 21 sec, a volumetric gas flow rate of 8.57 m3 hr-1, and superficial gas velocity of 53.6 m hr-1 were maintained throughout the experimental period. Nutrients containing metal salts, nitrogen, phosphorus, and milk were supplemented to the filters for maintaining the microbial activities. Results reveal that the biotrickling filter developed in this study had the highest styrene monomer (SM) elimination capacities (170 g m-3 hr-1 for fern-chip packing and 300 g m-3 hr-1 for plastic-chip packing) among those cited in the literature. The plastic medium is a favorable substitute for endangered fern chips. The thermal-setting nature of plastic chips limits their recycle and reuse as raw materials, and the study provides an opportunity for the utilization of the materials. IMPLICATIONS: Biotreatment of contaminants in air streams offers an inexpensive and efficient alternative to conventional technologies. Biofiltration has a great potential for the degradation of gas-borne styrene and total hydrocarbon (THC) removal efficiency of around 80%. The objective of this research was to compare the performances of fern chips and a kind of plastic chips as packing media for biofiltration of the styrene-laden waste gas stream emitted from cutting operations of stripes of premixed unsaturated polyester (UP) and styrene paste before hot-pressing operations for making plastic door plates. From a practical point of view, the plastic medium can be a good substitute medium for fern chips, which has been declared as a protected plant. This study provides an experimentally verified model for the design and operation of such biotreatment systems.

Biofiltration of odorous fume emitted from recycled nylon melting operations.

This study aimed to develop a biofilter packed only with fern chips for the removal of odorous compounds from recycled nylon melting operations. The fern chip biofilters could avoid the shortcomings of traditional media, such as compaction, drying, and breakdown, which lead to the performance failure of the biofilters. A pilot-scale biofilter consisting of an acrylic column (14 cm2 x 120 cm height) packed with fern chips to a volume of around 19.6 L was used for the test. Experimental results indicate that oxygen- and nitrogen-containing hydrocarbons as well as paraffins were major volatile organic compounds (VOCs) emitted from thermal smelting of recycled nylon at 250 degrees C. With operation conditions of medium pH of 5.5-7.0, empty bed retention time (EBRT) of 6-12 sec, influent total hydrocarbon (THC) concentrations of 0.65-2.61 mg m(-3), and volumetric organic loading of 0.05-0.85 g m(-3) hr(-1), the fern-chip-packed biofilter with nutrients of milk, potassium dihydrogen phosphate, and glucose could achieve an overall THC removal efficiency of around 80%. Burnt odor emitted from the smelting of the recycled nylon could be eliminated by the biofilter.

Volatile organic compound emissions from wastewater treatment plants in Taiwan: legal regulations and costs of control.

This study assessed volatile organic compound (VOC) emission characteristics from wastewater treatment plants (WWTPs) in five Taiwanese industrial districts engaged in numerous manufacturing processes, including petrochemical, science-based industry (primarily semiconductors, photo-electronics, electronic products and biological technology), as well as multiple manufacturing processes (primarily pharmaceuticals and paint manufacturing). The most aqueous hydrocarbons dissolved in the wastewater of Taiwanese WWTPs were acetone, acrylonitrile, methylene chloride, and chloroform for the petrochemical districts; acetone, chloroform, and toluene for the science-based districts; and chlorinated and aromatic hydrocarbons for the multiple industrial districts. The aqueous pollutants in the united WWTPs were closely related to the characteristics of the manufacturing plants in the districts. To effectively prevent VOC emissions from the primary treatment section of petrochemical WWTPs, the updated regulations governing VOC emissions were issued by the Taiwanese Environmental Protection Administration in September 2005, legally mandating a seal cover system incorporating venting and air purification equipment. Cost analysis indicates that incinerators with regenerative heat recovery are optimal for treating high VOC concentrations, exceeding 10,000 ppm as CH(4), from the oil separation basins. However, the emission concentrations, ranging from 100 to 1,000 ppm as CH(4) from the other primary treatment facilities and bio-treatment stages, should be collected and then injected into the biological oxidation basins via existing or new blowers. The additional capital and operating costs required to treat the VOC emissions of 1,000 ppm as CH(4) from primary treatment facilities are less than USD 0.1 for per m(3) wastewater treatment capacity.

Treatment of propylene glycol monomethyl ether acetate in air streams by a biofilter packed with fern chips.

This study aimed to develop a biofilter packed only with fern chips for the removal of airborne propylene glycol monomethyl ether acetate (PGMEA). Fern chips could avoid the shortcomings of traditional media, such as compaction, drying, and breakdown, which lead to the performance failure of the biofilters. In addition, the fern chip medium has the following merits: (1) simplicity in composition; (2) low pressure drop for gas flow (<20 mmH2O x m(-1)); (3) simple in humidification, nutrient addition, pH control, and metabolite removal; (4) economical (US$174-385 x m(-3)), and (5) low weight (wet basis around 290 kg x m(-3)). A two-stage downflow biofilter (2.18 m in height and 0.4 x 0.4 m in cross-sectional area) was constructed for the performance test. Both stages were packed with fern chips of 0.30 m in height and 0.40 x 0.40 m in cross-section. Results indicate that with operation conditions of media moisture content controlled in the range of 50-74%, media pH of 6.5-8.3, empty bed retention time (EBRT) of 0.27-0.4 min, influent PGMEA concentrations of 100-750 mg x m(-3), volumetric organic loading of <170 g x m(-3) x hr(-1), and nutrition rates of Urea-nitrogen 66 g x m(-3) x day(-3), potassium dihydrogen phosphate (KH2PO4)-phosphorus 13.3 g x m(-3) x day(-3), and milk powder 1.00 g x m(-3) x day(-1), the fern-chip-packed biofilter could achieve an overall PGMEA removal efficacy of around 94%. Instant milk powder or liquid milk was essential to the good and stable performance of the biofilter for PGMEA removal.

Regenerative thermal oxidation of airborne N, N-dimethylformamide and its associated nitrogen oxides formation characteristics.

In this study, a two-bed electrically heated regenerative thermal oxidizer (RTO) was used to test the thermal destruction and oxides of nitrogen (NOx) formation characteristics in burning airstreams that contain either N, N-dimethylformamide or dimethylformamide (DMF) mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m x 0.14 m x 1 m (L x W times] H) beds, both packed with gravel particles with an average diameter of approximately 0.0111 m and a height of up to 1 m with a void fraction of 0.42 in the packed section. The thermal recovery efficiency (TRE) and the gas pressure drop over the beds were also studied. Experimental results reveal that, with a valve shifting time (ts) of 1.5 min, a superficial gas velocity (Ug) of 0.39 m/sec (evaluated at an influent air temperature of around 30 degrees C) and preset maximum destruction temperatures (Ts) of 750-950 degrees C, no NOx was present in the effluent gas from the RTO when it was loaded with DMF-free air. When only DMF was present in the influent air, the average destruction efficiencies exceeded 96%, and increased with the influent DMF concentration from 300 to 750 mg/N x m3. The "NOx-N formation/DMF-N destruction" mass ratios were in the range 0.76-1.05, and decreased as the influent DMF concentration increased within the experimental range. When both DMF and MEK were present in the influent gas, the NO, formation ratio was almost the same and the DMF destruction efficiency increased with the influent MEK/DMF ratio from 150/300 to 4500/300 (mg/mg) and in the preset temperature range. The NOx formation ratios were in the range 0.75-0.96. The TRE decreased as Ug increased but was invariant with Ts. The Ergun equation was found to suffice in the estimation of the pressure drop when the gas flowed over the packing beds.

UV/ozone degradation of gaseous hexamethyldisilazane (HMDS).

As a carcinogen, hexamethyldisilazane (HMDS) is extensively adopted in life science microscopy, materials science and nanotechnology. However, no appropriate technology has been devised for treating HMDS in gas streams. This investigation evaluated the feasibility and effectiveness of the UV (185+254nm) and UV (254nm)/O(3) processes for degradation of gaseous HMDS. Tests were performed in two batch reactors with initial HMDS concentrations of 32-41mgm(-3) under various initial ozone dosages (O(3) (mg)/HMDS (mg)=1-5), atmospheres (N(2), O(2), and air), temperatures (28, 46, 65 and 80 degrees C), relative humilities (20%, 50%, 65%, 99%) and volumetric UV power inputs (0.87, 1.74, 4.07 and 8.16Wl(-1)) to assess their effects on the HMDS degradation rate. Results indicate that for all conditions, the decomposition rates for the UV (185+254nm) irradiation exceeded those for the UV (254nm)/O(3) process. UV (185+254nm) decompositions of HMDS displayed an apparent first-order kinetics. A process with irradiation of UV (185+254nm) to HMDS in air saturated with water at temperatures of 46-80 degrees C favors the HMDS degradation. With the condition as above and a P/V of around 8Wl(-1), k was approximately 0.20s(-1) and a reaction time of just 12s was required to degrade over 90% of the initial HMDS. The main mechanisms for the HMDS in wet air streams irradiated with UV (185+254nm) were found to be caused by OH free-radical oxidation produced from photolysis of water or O((1)D) produced from photolysis of oxygen. The economic evaluation factors of UV (185+254nm) and UV (254nm)/O(3) processes at different UV power inputs were also estimated.

Partition of volatile organic compounds in activated sludge and wastewater.

The Henry's law constant is important in the gas-liquid mass transfer process. Apparent dimensionless Henry's law constant, or the gas-liquid partition coefficient (K'H), for both hydrophilic (methanol, isopropyl alcohol, and acetone) and hydrophobic (toluene and p-xylene) organic compounds in deionized (DI) water, a wastewater with a maximum total dissolved organic carbon (DOC) content of 700 mg/L, and DI water mixed with a maximum activated sludge suspended solid (SS) concentration of 40,000 mg/L were measured using the single equilibrium technique at 293 K. Experimental results demonstrate that the K'H of any of the test volatile organic compounds varied among three situations. First, the K'H of the hydrophilic compounds in mixed liquor with the maximum SS concentration was 9-21% higher than those in DI water. Second, those for toluene and p-xylene were 77% and 93% lower, respectively, in the mixed liquor with the maximum SS concentration. Third, the K'H values of all of the test compounds in the wastewater were only 10% lower than those in DI water. A model was developed to relate K'H with wastewater DOC and the SS concentration in the activated sludge using an organic carbon-water partition coefficient and activated sludge-water partition coefficient as model parameters. The model was verified and model parameters for test compounds estimated.

Degradation of gas-phase propylene glycol monomethyl ether acetate by ultraviolet/ozone process: A kinetic study.

A pilot-scale plug-flow reactor was built to investigate its performance in treating airborne propylene glycol monomethyl ether acetate (PGMEA) via ozonation, ultraviolet (UV) photolysis and UV/O3 technologies. Governing factors, such as the initial molar ratio of ozone (O3) to PG-MEA, UV volumetric electric power input, and moisture content in the influent airstream, were investigated. A 1-L batch reactor was used to investigate some photodegradation characteristics of PGMEA in advance. Experiments were conducted at a fixed influent PGMEA concentration of approximately 50 ppm and an ambient temperature of 26 degrees C. A gas space time of 85 sec in the plug-flow reactor was kept for either ozonation or photolysis reaction, whereas a gas space time of 170 sec was used for the UV/O3 degradation. Results show that an initial molar ratio of O3 to PGMEA of >2.91 and an UV volumetric electric input power of 0.294 W/L(-1) sufficed to obtain PGMEA decompositions of >90% by UV/O3. Kinetic analyses indicate that all types of PGMEA decomposition are pseudo-first order with respect to its concentration. Moisture content (relative humidity = 15-99%) and UV volumetric electric input power (0.147 and 0.294 W/L(-1)) were major factors that strongly affect the PGMEA degradation rate.

Decomposition of gas phase 1,3-butadiene by ultraviolet/ozone process.

A pilot-scale plug-flow reactor was built to investigate its performance in treating airborne 1,3-butadiene (BD) via ozonation (O3) and ultraviolet (UV)/O3 technologies. Governing factors, such as the initial molar ratio of ozone to BD, UV volumetric electric input power, and moisture content in the influent airstream, were investigated. Experiments were conducted at an influent BD concentration of approximately 50 ppm, an ambient temperature of 26 degrees C, and a gas retention time of 85 sec. Results show that an initial molar ratio of ozone to BD of 3.5 and 2 sufficed to obtain BD decompositions of >90% for ozonation and UV/O3, respectively. The UV irradiance did not directly promote the decomposition of BD, rather, it played a role in promoting the production of secondary oxidants, such as hydroxyl radicals. Kinetic analyses indicate that both types of BD decomposition are peudo-first-order with respect to BD concentrations. Moisture content (relative humidity = 40-99%) and UV volumetric electric input power (0.147 and 0.294 W/L) are both factors that weakly affect the rate of BD decomposition. Economic evaluation factors, including both energy of ozone production and UV electric input power, were also estimated.

Bio-oxidation of airborne volatile organic compounds in an activated sludge aeration tank.

An activated sludge aeration tank (40 x 40 x 300 cm, width x length x height) with a set of 2-mm orifice air spargers was used to treat gas-borne volatile organic compounds (VOCs; toluene, p-xylene, and dichloromethane) in air streams. The effects of liquid depth (Z), aeration intensity (G/A), the overall mass-transfer rate of oxygen in clean water (KLaO2), the Henry's law constant of the tested VOC (H), and the influent gaseous VOC concentration (C0) on the efficiency of removal of VOCs were examined and compared with a literature-cited model. Results show that the measured VOC removal efficiencies and those predicted by the model were comparable at a G/A of 3.75-11.25 m3/m2 hr and C0 of approximately 1000-6000 mg/m3. Experimental data also indicated that the designed gas treatment reactor with KLaO2 = 5-15 hr(-l) could achieve > 85% removal of VOCs with H = 0.24-0.25 at an aerated liquid depth of 1 m and > 95% removal of dichloromethane with H = 0.13 at a 1-m liquid depth.

Determining the equilibrium partitioning coefficients of volatile organic compounds at an air-water interface.

The single equilibration technique (SET) was adopted to determine the partitioning coefficients (pc) at an air-water interface for volatile organic compounds (VOCs), including ethanol, iso-propanol (IPA), iso-butanol (IBA), methyl ethyl ketone (MEK) and toluene, all extensively used in industrial processes. Standard SET procedures were established. The liquid concentrations (CL) of tested VOCs ranged from 10 to 125 mg l(-1) for alcohols and MEK, and from 0.5 to 20 mg l(-1) for toluene. The temperatures (Tw) of aqueous VOC solutions were maintained at 27, 32, 38 and 42 degrees C to determine the gaseous concentrations at equilibrium (Cg*) and pc of VOCs, using the formula pc=(Cg*/CL). Results reveal that the pc values of all tested components increase slowly with Tw given a constant CL, and that the pc of alcohols and MEK fall as CL increases at a constant Tw. In contrast, the pc of toluene is not significantly impacted by a variation in CL at a constant Tw. However, the effect of CL concentration has seldom been discussed. The heats of liquid and gaseous phase transfer (DeltaHtr) of VOC, and the highly linear regression (with squared correlation coefficients, R2, from 0.901 to 0.999) between lnCg* and Tw(-1) are also evaluated. The experimental results and the VOC mass transfer characteristics are helpful for evaluating the emission of VOC from the water surface of wastewater treatment facilities.

VOC emission characteristics of petrochemical wastewater treatment facilities in southern Taiwan.

The wastewater treatment plants (WWTPs) of three representative petrochemical plants in southern Taiwan were sampled to investigate their VOC emission characteristics. Generally, emissions decline along the process flow, while the VOC concentration accumulates to as much as around 2400mg/m3 (as total hydrocarbons) at several closed vessel vents during the primary treatment. VOC emission rates (g/s) and fluxes (g/m2 hr) exhibit a similar trend of reducing concentrations in the WWTPs. From the field analysis data. VOC emission potential is best indicated by the concept of emission flux rather than concentration or emission rate. The Water 8 emission model version 4, developed by the U.S. EPA in 1995, was used to simulate the emission rate. The output results were compared to the calculated VOC liquid-gas mass equilibrium based essentially on the saturated gas concentration (Cg*) of the individual VOC components in wastewater. The comparisons clearly identified the proposed mass transfer approach using (Cg* as a reliable timesaving alternative to Water 8, which requires numerous input parameters and water analysis data.

Performance Characteristics of a Regenerative Catalytic Oxidizer for Treating VOC-Contaminated Airstreams.

A pilot apparatus of a regenerative catalytic oxidizer (RCO) equipped with two electrical heaters and two 20-cm i.d. × 200-cm height regenerative beds was used to treat methyl ethyl ketone (MEK) and toluene, respectively, in an airstream. The regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m2/m3, and specific heat capacity 840 J/kg °C) as a solid regenerative material and K-type thermal couples for measuring solid and gas temperatures, respectively. The catalyst bed temperature was kept around 400 °C and the gas superficial velocity was operated at 0.234 m/sec. This investigation measured and analyzed distributions of solid and gas temperatures with operating time and variations of volatile organic compound (VOC) concentrations in the regenerative beds. The overall VOC removal efficiency exceeded 98% for MEK and 95% for toluene. Degradation of VOCs will exist for MEK on the surface of solid material (gravel) in the temperature range of 330-400 °C, but toluene does not exhibit this phenomenon.

Treatment of Toluene in an Air Stream by a Biotrickling Filter Packed with Slags.

This study utilized a biotrickling filter with blast-furnace slag packings (sizes = 20-40 mm; specific surface area = 120 m2/m3) to treat toluene in an air stream. Also studied were the effects of volumetric loading (L), nutrient addition, and superficial gas velocity (Ug) or gas retention time on toluene elimination capacity. Experimental results indicate that, for a test period of 121 days, with no excess biomass removal, toluene removal efficiencies of over 90% were obtained with Ug < 80 m/hr and L < 30 g/m3.hr. For a test period of 49 days, with Ug < 80 m/hr and L increased from 1.2 to 81 g/m3.hr, the absence of nutrient supplementation did not limit the toluene elimination capacity. Nutrients stored in the biofilm could adequately support the microbial activity for the toluene elimination. According to data regression, a simplified mass-transfer model is proposed, which correlates the contaminant concentration with the packing height or gas empty bed retention time. As verified, the model proposed herein can be applied to cases involving low influent contaminant concentrations or loadings to the extent that none or only a trace amount of the contaminant can be found in the recirculation liquid. Although small media with larger specific surface areas can achieve a better mass transfer, the problems of frequent backwashing and relatively greater gas resistance in using this type of media probably outweigh the advantages, particularly for full-scale systems that would not be watched as closely as laboratory test systems.

Treatment of 1,3-Butadiene in an Air Stream by a Biotrickling Filter and a Biofilter.

This paper presents results obtained from a performance study on the biotreatment of 1,3-butadiene in an air stream using a reactor that consisted of a two-stage, in-series biotrickling filter connected with a three-stage, in-series biofilter. Slags and pig manure-based media were used as packing materials for the biotrickling filter and the biofilter, respectively. Experimental results indicated that, for the biotrickling filter portion, the butadiene elimination capacities were below 5 g/m3/hr for loadings of less than 25 g/m3/hr, and the butadiene removal efficiency was only around 17%. For the biofilter portion, the elimination capacities ranged from 10 to 107 g/m3/hr for loadings of less than 148 g/m3/hr. The average butadiene removal efficiency was 75-84% for superficial gas velocities of 53-142 m/hr and a loading range of 10-120 g/m3/hr. The elimination capacity approached a maximum of 108 g/m3/hr for a loading of 150 g/m3/hr. The elimination rates of butadiene in both the biotrickling filter and biofilter were mass-transfer controlled for influent butadiene concentrations below about 600 ppm for superficial gas velocities of 29-142 m/hr. The elimination capacity was significantly higher in the biofilter than in the biotrickling filter. This discrepancy may be attributed to the higher mass-transfer coefficient and gas-solid interfacial area offered for transferring the gaseous butadiene in the biofilter.