Decomposition of trichloroethylene and 2,4-dichlorophenol by ozonation in several organic solvents

The effects of chemical characteristics of organic solvents on the decomposition rate constants of undissociative trichloroethylene (TCE) and dissociative 2,4-dichlorophenol (2,4-DCP) by ozonation were studied. The TCE and 2,4-DCP decomposition by ozonation in organic solvents followed to the first-order reaction kinetics with respect to TCE or 2,4-DCP concentration. The orders of the rate constants among organic solvents for undissociative TCE and dissociative 2,4-DCP were different indicating that the ozonation rates for undissociative and dissociative compounds were dependent on the chemical property of organic solvent. The decomposition of undissociative TCE by ozonation was a simple electrophilic reaction, which was dependent on acceptor number (AN) of the solvent. On the other hand, the decomposition of dissociative 2,4-DCP was dependent on by the dissociation of the compounds and would be dependent on donor number (DN) of the solvent. Finally, TCE in acetic acid was transformed to chlorinated intermediates and chloride ion and then these intermediates were continuously oxidized to chlorine gas.     

An efficient venturi scrubber system to remove submicron particles in exhaust gas

An efficient venturi scrubber system making use of heterogeneous nucleation and condensational growth of particles was designed and tested to remove fine particles from the exhaust of a local scrubber where residual SiH4 gas was abated and lots of fine SiO2 particles were generated. In front of the venturi scrubber, normal-temperature fine-water mist mixes with high-temperature exhaust gas to cool it to the saturation temperature, allowing submicron particles to grow into micron sizes. The grown particles are then scrubbed efficiently in the venturi scrubber. Test results show that the present venturi scrubber system is effective for removing submicron particles. For SiO2 particles greater than 0.1microm, the removal efficiency is greater than 80-90%, depending on particle concentration. The corresponding pressure drop is relatively low. For example, the pressure drop of the venturi scrubber is approximately 15.4 +/- 2.4 cm H2O when the liquid-to-gas ratio is 1.50 L/m3. A theoretical calculation has been conducted to simulate particle growth process and the removal efficiency of the venturi scrubber. The theoretical results agree with the experimental data reasonably well when SiO2 particle diameter is greater than 0.1 microm.     

Pyrolysis kinetics and residue characteristics of petrochemical industrial sludge

This study investigated the pyrolysis characteristics of sludge from wastewater treatment plants in the petrochemical industry and focused on the pyrolysis kinetics, elemental composition of residue, and volatile organic compounds (VOCs) of exhaust gas. As pyrolysis temperature increased to 773 K, the increasing rate of crude oil production tended to a stable condition. The result indicated that the optimal temperature of crude oil and water mixed production was 773 K. When pyrolysis temperature increased from 673 to 973 K, carbon, oxygen, nitrogen, and hydrogen concentrations of residue decreased and the sulfur concentration of residue increased. The concentrations of benzene, toluene,ethylbenzene, and styrene increased by the increasing pyrolysis temperature. We found that the reaction order of sludge pyrolysis was 2.5 and the activation energy of the reaction was 11.06 kJ/mol. We believe that our pyrolysis system is transitional between devolatilization and combustion.     

Microbial kinetic analysis of three different types of EBNR process

The disadvantages of developed biological nutrient removal (BNR) processes (additional energy for liquid circulation and addition of external carbon substrate for denitrification in anoxic zones) were improved by reconfiguring the process into (1) an anaerobic zone followed by multiple stages of aerobic-anoxic zones (TNCU3 process) or (2) anaerobic, oxic, anoxic, oxic zones in sequence (TNCU2 process). These two pilot plants were operated at a recycling sludge ratio of 0.5 without internal recycle of nitrified supernatant. The sludge retention time was maintained at 10 d. The main objective of this study is to analyze the kinetics of different microorganisms in these two processes and A2O process by using the Activated Sludge Model No. 2d. The effective removal efficiency of carbon, total phosphorus and total nitrogen at 87-98%, 92-100% and 63-80%, respectively, were achieved in the testing runs. According to model simulations, the microbial kinetics in the TNCU3 and TNCU2 processes would be affected by different operations. When the step feeding strategy was adopted, the HRT was longer due to the less influent flowrate in the front stages and the microbes would grow in quantities by about 6% in the aerobic reactors. In the followed anoxic reactors, the microbes would decrease in quantities by about 12% due to the dilution effect. The dilution effects in TNCU3 and TNCU2 processes did not take place in A2O process because the recycling mixed liquid from the aerobic reactor to the anoxic reactor still contained particulate components. The XH, XPAO, and XAUT concentrations in the effluent of the last tank were lower when the step-feeding mode was adopted. The TNCU3 and TNCU2 processes could be operated efficiently without nitrified liquid circulation and addition of external carbon substrate for denitrification.     

Adsorption of paraquat on the physically activated bleaching earth waste from soybean oil processing plant

A series of regeneration experiments with physical activation were carried out on bleaching earth waste from the soybean refining process in a rotary reactor. The influence of activation parameters on the spent clay by varying the holding time of 1 to approximately 4 hours and temperature of 700 to approximately 900 degrees C was determined. The variations of pore properties as well as the change of chemical characteristics in the resulting solids were also studied. Results showed that the resulting samples were type IV with hysteresis loops corresponding to type H3 from nitrogen adsorption-desorption isotherms, indicating slit-shaped mesoporous characteristics. However, the regenerated clays had smaller surface areas (70 to approximately 117 m2/g) than that (245 m2/g) of fresh bleaching earth. Under the physical activation conditions investigated, the holding time of 1 hour and temperature of 700 degrees C were found to be optimal conditions for producing mesoporous clay with physical activation. The adsorption of paraquat on regenerated sample was also evaluated. The isotherm showed that the regenerated sample still had a high affinity for this herbicide. Thus, the regeneration of this agro-industrial waste is one option for utilizing the clay resource, and it may be used for water treatment applications to remove organic contaminants.     

Use of two different acidic aerosol samplers to measure acidic aerosols in Hsinchu, Taiwan

Acidic aerosol concentrations measured by an annular denuder system (ADS) and a honeycomb denuder system (HDS) in Hsinchu, Taiwan, were compared. Aerosols were also sampled by a MOUDI (micro-orifice uniform deposit impactor) and analyzed by an ion chromatograph to determine the size distributions of different species. Using the measured aerosol size distribution, theoretical analysis showed that positive HNO3 artifact due to volatilization of NH4NO3 is generally negligible for both samplers. Comparing two different denuder samplers, the average concentration of HNO3 measured by the ADS was found to be lower than that measured by the HDS, while the difference between the two samplers for the average concentration of other species was found to be within +/- 15%. A possible cause of the difference in HNO3 concentrations is due to a greater loss of HNO3 in the cyclone used by the ADS than in the impactor used by the HDS. The study also showed incomplete absorption of the evaporated HCl and HNO3 from the particles on the Teflon filter by the first nylon filter in the filter pack of the ADS. Collection efficiency and capacity of HCl and HNO3 by the nylon filters need further investigation.     

Effects of experimental parameters on NF(3) decomposition fraction in an oxygen-based RF plasma environment

Clean procedure is one of the major emitters of perfluorinated compounds (PFCs) in semiconductor manufacturing. Nitrogen trifluoride (NF(3)) is increasingly the process gas of choice for eliminating PFC emissions. However, its toxic to human and similar global warming potential compared to most other PFCs made NF(3) warranted much more investigation. This study demonstrated a radio-frequency plasma system for decomposing NF(3). The effects of experimental parameters: input power, O(2)/NF(3) ratio, operational pressure and NF(3) feeding concentration on NF(3) decomposition fraction (eta(NF3)) and energy efficiency E(NF3) were examined in detail. The analytical results demonstrated that the NF(3) was almost completely decomposed (>99%) at input power=30W, [NF(3)](in)=1.0% and eta(NF3) increased with input power. However, adding O(2) to the system inhibited NF(3) decomposition and decreased E(NF3). Moreover, eta(NF3) and E(NF3), decreased with gradually increasing operational pressure. Notably, increasing the NF(3) feeding concentration increased molecule density, reducing eta(NF3), but increasing E(NF3). Furthermore, the products detected in the NF(3)/O(2)/Ar plasma system were NO(2), NO, N(2)O, SiF(4), N(2) and F(2). Potential reaction pathways in the oxygen-based NF(3) plasma environment were built-up and elucidated.     

Tank-connected food waste disposer systems – Current status and potential improvements

An unconventional system for separate collection of food waste was investigated through evaluation of three full-scale systems in the city of Malmö, Sweden. Ground food waste is led to a separate settling tank where food waste sludge is collected regularly with a tank-vehicle. These tank-connected systems can be seen as a promising method for separate collection of food waste from both households and restaurants. Ground food waste collected from these systems is rich in fat and has a high methane potential when compared to food waste collected in conventional bag systems. The content of heavy metals is low. The concentrations of N-tot and P-tot in sludge collected from sedimentation tanks were on average 46.2 and 3.9 g/kg TS, equalling an estimated 0.48 and 0.05 kg N-tot and P-tot respectively per year and household connected to the food waste disposer system. Detergents in low concentrations can result in increased degradation rates and biogas production, while higher concentrations can result in temporary inhibition of methane production. Concentrations of COD and fat in effluent from full-scale tanks reached an average of 1068 mg/l and 149 mg/l respectively over the five month long evaluation period. Hydrolysis of the ground material is initiated between sludge collection occasions (30 days). Older food waste sludge increases the degradation rate and the risks of fugitive emissions of methane from tanks between collection occasions. Increased particle size decreases hydrolysis rate and could thus decrease losses of carbon and nutrients in the sewerage system, but further studies in full-scale systems are needed to confirm this.     

A study of the extraction of vanadium and nickel in oil-fired fly ash

Annual production of oil-fired fly ash in Taiwan is approximately 43 000 tons, of this approximately 13 000 tons is electrostatically precipitated, the rest is cyclonically collected. Structurewise, both consist of porous unburned carbon, vanadium and nickel oxide, and water-soluble sulfate. Electrostatically precipitated fly ash contains large amounts of ammonium sulfate. If these ashes are not properly disposed of, they become environmental problems, such as dusting, leakage of acid liquids, and pollution with heavy metals. This paper discusses the experimental extraction of vanadium and nickel from oil-fired fly ash. The results indicated that leaching of oil-fired fly ash in 0.5 N of sulfuric acid led to an extraction of 65% vanadium, 60% nickel, and 42% iron, along with an increase in the concentration of sulfuric acid. When leached in 2 N sodium hydroxide solution, the extraction of vanadium was 80%, and the extraction of nickel was negligible. If leached in an ammonia water, the extraction of nickel increased, along with an increase in the concentration of ammonia in water. When leached with 4 N ammonia water, the extraction of nickel was 60%, the extraction of vanadium was less than that obtainable from leaching in sulfuric acid solution or in sodium hydroxide solution. If electrostatically precipitated fly ash was leached in a solution of 0.25 N ammonia water and 2 N ammonium sulfate, it would yield an extraction of 60% nickel and 8% vanadium—leading to a selective extraction of nickel. This study has established an extraction flowsheet in which fly ash was first leached in an ammoniacal solution containing ammonium sulfate to recover nickel. The leached residues were then leached in an alkaline solution to recover vanadium.     

Adsorption of acid dye onto activated carbons prepared from agricultural waste bagasse by ZnCl2 activation

A series of activated carbons were prepared from agricultural waste sugarcane bagasse by chemical activation with zinc chloride (ZnCl2) as an activating agent at 500 degrees C and 0.5 h soaking time. The Langmuir surface area and total pore volume were used to estimate the average pore diameter of the carbon products. The values of the surface area and pore volume increased linearly with increase in the impregnation ratio (IR) up to 100 wt%. The adsorption capacities of the derived adsorbents for Acid Orange 10 were measured at 20 degrees C and 40 degrees C to gain further insights into the acidic surface oxides of the adsorbent from the results of Fourier transform infrared (FTIR) spectroscopy analysis and pH measurement. Adsorption isotherms of the acid dye on adsorbents prepared were determined and correlated with common isotherm equations. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. The physical properties of these adsorbents were consistent with the parameters obtained from the isotherm equations.