Emission characteristics of VOCs from three fixed-roof p-xylene liquid storage tanks.

This study evaluates emission characteristics of volatile organic compounds (VOCs) caused by standing loss (L S) and working loss (L W) of three vertical fixed-roof p-xylene (p-X) liquid tanks during 1-year storage and filling operation. The annual net throughput of the tanks reached 70,446 t, resulting in 9,425 kg of p-X vapor emission including 5,046 kg of L S (53.54 %) and 4,379 kg of L W (46.46 %). The estimated L W of AP-42 displayed better agreement with the measured values of a VOC detector than the estimated L S of AP-42. The L S was best correlated with the liquid height of the tanks, while the L W was best correlated with the net throughput of the tanks. As a result, decreasing vapor space volume of the tanks and avoiding high net throughput of the tanks in a high ambient temperature period were considered as effective means to lessen VOC emission from the fixed-roof organic liquid storage tank.

Adsorption, desorption, and thermodynamic studies of CO2 with high-amine-loaded multiwalled carbon nanotubes.

Commercially available multiwalled carbon nanotubes (CNTs) were functionalized with a high mass load of 3-aminopropyltriethoxysilane (APTS) to study their behaviors in the cyclic CO(2) adsorption as well as the associated thermodynamic properties. The breakthrough curve showed a fast kinetics of CO(2) adsorption resulting in percentage ratios of working capacity to equilibrium capacity greater than 80%. The adsorption capacity of CNT(APTS) was significantly influenced by the presence of water vapor and reached a maximum of 2.45 mmol/g at a water vapor of 2.2%. The adsorption capacities and the physicochemical properties of CNT(APTS) were preserved through 100 adsorption-desorption cycles displaying the stability of CNT(APTS) during a prolonged cyclic operation. The heat input required to regenerate spent CNT(APTS) was determined, and the result suggests that adsorption process with solid CNT(APTS) is possibly a promising CO(2) capture technology.

Adsorption of carbon dioxide from gas streams via mesoporous spherical-silica particles.

A relatively new mesoporous silica sorbent for environmental protection applications (i.e., mesoporous spherical-silica particles [MSPs]), was modified by N-[3-(trimethoxysilyl)propyl]ethylenediamine (EDA) solution and was tested for its potential in the separation of carbon dioxide (CO2) from flue gas. The CO2 adsorption capacity of MSP and MSP (EDA) increased with temperature from 20 to 60 degrees C but decreased with temperature from 60 to 100 degrees C. The mechanism of CO2 adsorption on both samples is mainly attributed to physical interaction regardless of temperature change. The MSP (EDA) have good adsorption performance as compared with EDA-modified zeolite or granular activated carbon conducted in this study and many types of silica sorbents reported in the literature. The cyclic CO2 adsorption showed that spent MSP (EDA) could be effectively regenerated at 120 degrees C for 25 min and CO2 adsorption capacity of MSP (EDA) was preserved during 16 cycles of adsorption and thermal regeneration. These results suggests that MSP (EDA) are efficient CO2 sorbents and can be stably used in the prolonged cyclic operation.

Capture of CO2 from flue gas via multiwalled carbon nanotubes.

Carbon nanotubes (CNTs) were modified by 3-aminopropyl-triethoxysilane (APTS) solution and were tested for its CO2 adsorption potential at multiple temperatures (20-100 degrees C). The physicochemical properties of CNTs were changed after the modification, which makes CNTs adsorb more CO2 gases. The adsorption capacities of CO2 via CNTs and CNTs(APTS) decreased with temperature indicating the exothermic nature of adsorption process and increased with water content in air at 0-7%. The mechanism of CO2 adsorption on CNTs and CNTs(APTS) appears mainly attributable to physical force regardless of temperature change, which makes regeneration of spent CNTs at a relatively low temperature become feasible. The CNTs(APTS) have good adsorption performance of CO2 at 20 degrees C as compared to many types of modified carbon or silica adsorbents documented in the literature. This suggests that the CNTs(APTS) are promising low-temperature adsorbents for CO2 capture from flue gas.

Adsorption kinetic, thermodynamic, and desorption studies of isopropyl alcohol vapor by oxidized single-walled carbon nanotubes.

Single-walled carbon nanotubes (SWCNTs) were oxidized by sodium hypochlorite (NaOCl) solution and used as adsorbents to study adsorption kinetics, thermodynamics, and desorption of isopropyl alcohol (IPA) vapor in an airstream. The adsorption capacity of IPA decreased with temperature, indicating an exothermic nature of the adsorption process, and slightly decreased with relative humidity, showing a hydrophobic nature of the adsorbent surface. The adsorption mechanism appears mainly attributable to physical forces from 5 to 25 degrees C but appears primarily attributable to chemical forces from 25 to 35 degrees C. A comparative study on the cyclic IPA adsorption between SWCNTs(NaOCl) and granular activated carbon, GAC(NaOCl), was also conducted and the results revealed that the SWCNTs(NaOCl) show better repeated availability of IPA adsorption during 15 cycles of operation than the GAC(NaOCl). This suggests that the SWCNTs(NaOCl) are efficient IPA adsorbents and can be used in the prolonged cyclic adsorption/desorption operation.

A new approximate solution for chlorine concentration decay in pipes.

Biswas et al. (1993. A model for chlorine concentration decay in pipes. Water Res. 27(12), 1715-1724) presented an analytical solution of a two-dimensional (2-D) steady-state chlorine transport equation in a pipe under the turbulent condition and employed fractional error function and regression technique to develop an approximate solution. However, their approximate solution may not give a good result if the wall decay parameter is large. This paper provides a more accurate approximate solution of the 2-D steady-state chlorine transport equation under the turbulent condition. This new approximate solution has advantages of easy evaluation and good accuracy when compared with the approximate solution given by Biswas et al. (1993). In addition, this paper also develops a methodology that combines simulated annealing (SA) with this new approximate solution to determine the wall decay parameter. Two cases are chosen to demonstrate the application of the present approximate solution and methodology. The first case is to use this new approximate solution in simulating chlorine decay in pipes with the experiment-observed data given by Rossman (2006. The effect of advanced treatment on chlorine decay in metallic pipes. Water Res. 40(13), 2493-2502), while the second case presents the determination of the wall consumption at the end of the pipe network.

Comparisons of sorbent cost for the removal of Ni2+ from aqueous solution by carbon nanotubes and granular activated carbon.

The reversibility of Ni2+ sorption by NaOCl oxidized single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs) and granular activated carbon (GAC) was investigated to evaluate their repeated availability performance in water treatment. Under the same conditions, the SWCNTs and MWCNTs possess more Ni2+ sorption capacities and show better reversibility of Ni2+ sorption and less weight loss after being repeated sorption/desorption processes than the GAC, suggesting that they are effective Ni2+ sorbents and can be reused through many cycles of water treatment and regeneration. A statistical analysis on the replacement cost of these sorbents revealed that SWCNTs and MWCNTs can be possibly cost-effective Ni2+ sorbents in water treatment regardless of their high unit cost at the present time.

Comparisons of adsorbent cost for the removal of zinc (II) from aqueous solution by carbon nanotubes and activated carbon.

The reversibility of Zn2+ sorption onto single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and powdered activated carbon (PAC) was investigated to evaluate their repeated availability performance in water treatment. Under the same conditions, the Zn2+ sorption capacity of SWCNTs and MWCNTs was more than that of PAC and could be maintained after several cycles of water treatment and regeneration. A statistical analysis on the replacement cost of these adsorbents based on the best-fit regression of the measured equilibrium capacity of each water treatment cycle was also conducted. The results revealed that the SWCNTs and MWCNTs could be reused through a large number of water treatment cycles and thus appear cost-effective in spite of their high unit cost at the present time.

Adsorption thermodynamic and kinetic studies of trihalomethanes on multiwalled carbon nanotubes.

Multiwalled carbon nanotubes (MWCNTs) were purified by mixed HNO3/H2SO4 solution and were employed as adsorbents to study adsorption kinetics and thermodynamics of trihalomethanes (THMs) from chlorinated drinking water. The amount of THMs adsorbed onto CNTs decreased with a rise in temperature and high adsorption capacities were found at 5 and 15 degrees C. Under the same conditions, the purified CNTs possess two to three times more adsorption capacities of CHCl3, which accounts for a major portion of THMs in the chlorinated drinking water, than the commercially available PAC suggesting that CNTs are efficient adsorbents. The thermodynamic analysis revealed that the adsorption of THMs onto CNTs is exothermic and spontaneous.

Adsorption of trihalomethanes from water with carbon nanotubes.

Commercial carbon nanotubes (CNTs) were purified by acid solution and were employed as adsorbents to study adsorption of trihalomethanes (THMs) from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after acid treatment which made CNTs become more hydrophilic and suitable for adsorption of low molecular weight and relatively polar THM molecules. The adsorption of THMs onto CNTs fluctuates very little in the pH range 3-7, but decreases with pH value as pH exceeds 7. A comparative study between CNTs and powdered activated carbon (PAC) for adsorption of THMs from water was also conducted. The short time needed to reach equilibrium as well as the high adsorption capacity of CHCl3, which accounts for a significant portion of THMs in the chlorinated drinking water, suggests that CNTs possess highly potential applications for THMs removal from water.

Effects of oxalic acid on the regrowth of heterotrophic bacteria in the distributed drinking water.

Three laboratory-scale water pipe systems were set up to study the effects of adding oxalic acid on the bacterial regrowth and biofilm formation in the distributed drinking water. The results of water pipe experiment displayed that around 38% carbon in the oxalic acid could be converted to bacterial biomass. The maximum HPCs in biofilm were equal to 3.5x10(4), 3.38x10(5) and 2.8x10(6) CFUcm(-2) while the maximum HPCs of free bacteria were equal to 1.2x10(3), 2.54x10(3) and 3.78x10(4) CFUml(-1) for the blank and with addition of 10 and 50 micrograms OA eq-Cl(-1), respectively. These results imply that the addition of oxalic acid to distributed water has positive effect on the assimilable organic carbon content of drinking water and bacterial regrowth in water pipe. This effect is enhanced with addition of high-level oxalic acid. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The bacterial regrowth potentials (BRPs) of the blank were equal to 4.25x10(3), 1.46x10(4), 4.9x10(4) and 7.54x10(4) CFUml(-1) for water samples collected from treatment plant effluent, commercial area, mixed area, and residential area, respectively. These results show that the biological stability of distributed drinking water is the highest in treatment plant effluent, the moderate in the commercial area and mixed area, and the lowest in the residential area.

Estimation of PAHs dry deposition and BaP toxic equivalency factors (TEFs) study at Urban, Industry Park and rural sampling sites in central Taiwan, Taichung.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in gas phase and particle bound were measured simultaneously at industrial (INDUSTRY), urban (URBAN), and rural areas (RURAL) in Taichung, Taiwan. And the PAH concentrations, size distributions, estimated PAHs dry deposition fluxes and health risk study of PAHs in the ambient air of central Taiwan were discussed in this study. Total PAH concentrations at INDUSTRY, URBAN, and RURAL sampling sites were found to be 1650 +/- 1240, 1220 +/- 520, and 831 +/- 427 ng/m3, respectively. The results indicated that PAH concentrations were higher at INDUSTRY and URBAN sampling sites than the RURAL sampling sites because of the more industrial processes, traffic exhausts and human activities. The estimation dry deposition and size distribution of PAHs were also studied. The results indicated that the estimated dry deposition fluxes of total PAHs were 58.5, 48.8, and 38.6 microg/m2/day at INDUSTRY, URBAN, and RURAL, respectively. The BaP equivalency results indicated that the health risk of gas phase PAHs were higher than the particle phase at three sampling sites of central Taiwan. However, compared with the BaP equivalency results to other studies conducted in factory, this study indicated the health risk of PAHs was acceptable in the ambient air of central Taiwan.

Biofiltration of 1,1,1-trichloroethane by a trickle-bed air biofilter.

The performance of a trickle-bed air biofilter (TBAB) in the removal of 1,1,1-trichloroethane (TCLE) was evaluated in concentrations varying from 0.025 to 0.049 g/m3 and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete TCLE removal could be achieved for influent carbon loading between 0.98 and 5.88 g/m3 h. The TBAB appeared efficient for controlling TCLE emission under low-carbon-loading conditions. Carbon recoveries higher than 95% were achieved, demonstrating the accuracy of results. The carbon mass rate of the liquid effluent was approximately two orders of magnitude less than that of the effluent CO2, indicating that dissolved TCLE and its derivatives in leachate were present in negligible amounts in the TBAB.

Treatment of waste gas from the breather vent of a vertical fixed roof p-xylene storage tank by a trickle-bed air biofilter.

This study applied a pilot-scale trickle-bed air biofilter (TBAB) system for treating waste gas emitted from the breather vent of a vertical fixed roof storage tank containing p-xylene (p-X) liquid. The volatile organic compound (VOC) concentration of the waste gas was related to ambient temperature as well as solar radiation, peaking at above 6300 ppmv of p-X and 25000 ppmv of total hydrocarbons during the hours of 8 AM to 3 PM. When the activated carbon adsorber was employed as a VOC buffer, the peak waste gas VOC concentration was significantly reduced resulting in a stably and efficiently performing TBAB system. The pressure drop appeared to be low, reflecting that the TBAB system could be employed in the prolonged operation with a low running penalty. These advantages suggest that the TBAB system is a cost-effective treatment technology for VOC emission from a fixed roof storage tank.

Adsorption kinetics, thermodynamics and desorption of natural dissolved organic matter by multiwalled carbon nanotubes.

Multiwalled carbon nanotubes (CNTs) were thermally treated and were employed as adsorbents to study their adsorption kinetics and thermodynamics of natural dissolved organic matter (NDOM) from aqueous solutions. The adsorption kinetics follows the first-order rate law while the adsorption thermodynamics indicates the exothermic and spontaneous nature. A comparative study on the adsorption/desorption properties of NDOM between CNTs and granular activated carbon (GAC) was also conducted and revealed that the CNTs possess more NDOM adsorption capacities and show less weight loss through 10 cycles of water treatment and reactivation than the GAC. This suggests that the CNTs are promising NDOM adsorbents for preventing the microbiological degradation of drinking water quality as well as the formation of disinfection by products in water treatment.

Effects of inorganic nutrients on the regrowth of heterotrophic bacteria in drinking water distribution systems.

Three laboratory-scale water pipe systems were set up to study the effects of adding three inorganic nutrients (ammonium, nitrate or phosphate) on biofilm formation in water pipes. The results showed that the effects of adding ammonium or nitrate on the biofilm formation were insignificant when levels below 0.1 mg N/l were added. Analogous results were observed when phosphate was added at levels below 0.005 mgP/l. However, as the addition of ammonium increased to 0.5 mgN/l, significant effects on biofilm formation were observed. Similar results were obtained phosphate was added at levels above 0.01 mgP/l. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The results indicated that the addition of ammonium, nitrate or phosphate to treatment plant effluent stimulates bacterial growth. In the distributed water of an urban area, the addition of nitrate or phosphate stimulated bacterial growth. The bacterial growth in the distributed water of a suburban area was not stimulated by adding any of these three inorganic nutrients.

Biofiltration of isopropyl alcohol by a trickle-bed air biofilter.

The performance of trickle-bed air biofilter (TBAB) for the removal of isopropyl alcohol (IPA) was evaluated in concentrations varying from 100 to 500 ppmv and at empty-bed residence time (EBRT) varying from 20 to 90 s. Nearly complete IPA removal could be achieved for influent carbon loading between 6 and 88 g/m3 x h. The TBAB appears efficient for controlling IPA emission under low-to-high carbon loading conditions. Carbon recoveries of 95-99% were achieved demonstrating the accuracy of results. Applicable operating conditions of TBAB for controlling IPA emission were suggested.

Effects of chlorine level on the growth of biofilm in water pipes.

Three analogous laboratory-scale water pipe systems were constructed to study the effects of three chlorine levels of finished water on the growth of biofilm. The experimental results indicated that the heterotrophic plate counts (HPCs) of biofilm for chlorine-free water were approximately 2 and 3 orders of magnitude higher than those for low-chlorine water (0.3-0.5mg Cl2/L) and high-chlorine water (1.2-1.5mg Cl2/L). The difference in HPC levels between low-chlorine water and high-chlorine water was below 1 order. Average biofilm formation rates are 325 ATP pg/cm2-day for chlorine-free water, 159 ATP pg/cm2-day for low-chlorine water and 118 ATP pg/cm2-day for high-chlorine water. The scanning electron microscope (SEM) observation showed that bacterial species separated from the biofilm were more complex than from the finished water. The Gram-negative bacteria were dominant in these species.

Toxic equivalency factors study of polycyclic aromatic hydrocarbons (PAHs) in Taichung City, Taiwan.

Airborne particles and polycyclic aromatic hydrocarbons (PAHs) in industrial, background and urban atmosphere environments were investigated using toxic equivalent factors (TEFs) in central Taiwan during the period of August-December 2002. Concentrations of airborne particles were 93.4, 81.3 and 102.4 microg/m3 for industrial, background and urban sites, respectively. Concentrations of 21 gaseous PAHs were 1530, 759 and 1030 ng/m3 for industrial, background and urban sites, respectively; for carcinogenic activity of gaseous PAHs, the benzo[a]pyrene (BaP) equivalent concentrations were 17.0, 7.29 and 12.6 ng/m3 for industrial, background and urban sites, respectively. Twenty-one particle-bound PAHs were only 10% of the 21 gaseous PAHs. Dibenzo(a,h)anthracene (DBA) serves as a surrogate to explain the carcinogenic activity of PAH mixtures in central Taiwan because its carcinogenicity is a high percentage of the total carcinogenic activity. During the sampling period, temperature inversion from a cold front from China occurred, leading to average daily temperatures of 16 degrees C. These cold fronts caused atmospheric particles and pollutants to accumulate in the troposphere, leading to extremely high concentrations of airborne particles and both gaseous and particle-bound PAHs in central Taiwan.