Two-stage Sequential Electrochemical Treatment of Nitrate Brine Wastes

Nitrates in concentrated brines can be electrochemically reduced in the cathodic chamber of a split-cell electrochemical reactor with formation of ammonium (and small amounts of nitrite). Fortunately, ammonium may be electrochemically oxidized to nitrogen gas in the anodic reaction chamber if a coupled sequential process is used. The presence of chloride in the brine waste is an important consideration in oxidative electrochemical processes, however, because it cycles through oxidized and reduced states at the electrode surfaces and in the bulk solution. Electrochemical oxidation converts chloride ions to “active chlorine” species with additional oxidizing capability (chlorine, hypochlorous acid and hypochlorite – essentially bleach), as well as to chlorates, depending on the reaction conditions. The production of these active species improves treatment performance in the ammonium oxidation phase since oxidation is no longer limited to the electrode surface. However, the process must be engineered to minimize loss of process efficiency due to parasitic side reactions (chloramines and chlorate). In this study, two-stage batch electrolysis was conducted using a three-electrode (copper anode, platinum-coated titanium cathode, silver/silver chloride reference) electrochemical cell, with the anodic and cathodic chambers separated by a Nafion 117 membrane. Treatment of nitrate and ammonium was tested with and without the presence of chloride in the waste. No significant difference was observed in cathodic nitrate reduction with chloride present or absent. However, the presence of chloride in the solution favored overall soluble nitrogen elimination upon oxidation. Increasing applied current increased production of undesirable byproducts (especially chlorate).     

Microbial nitrogen transformation potential in surface run-off leachate from a tropical landfill

Ammonium is one of the major toxic compounds and a critical long-term pollutant in landfill leachate. Leachate from the Jatibarang landfill in Semarang, Indonesia, contains ammonium in concentrations ranging from 376 to 929 mg N L⁻¹. The objective of this study was to determine seasonal variation in the potential for organic nitrogen ammonification, aerobic nitrification, anaerobic nitrate reduction and anaerobic ammonium oxidation (anammox) at this landfilling site. Seasonal samples from leachate collection treatment ponds were used as an inoculum to feed synthetic media to determine potential rates of nitrogen transformations. Aerobic ammonium oxidation potential (<0.06 mg N L⁻¹ h⁻¹) was more than a hundred times lower than the anaerobic nitrogen transformation processes and organic nitrogen ammonification, which were of the same order of magnitude. Anaerobic nitrate oxidation did not proceed beyond nitrite; isolates grown with nitrate as electron acceptor did not degrade nitrite further. Effects of season were only observed for aerobic nitrification and anammox, and were relatively minor: rates were up to three times higher in the dry season. To completely remove the excess ammonium from the leachate, we propose a two-stage treatment system to be implemented. Aeration in the first leachate pond would strongly contribute to aerobic ammonium oxidation to nitrate by providing the currently missing oxygen in the anaerobic leachate and allowing for the growth of ammonium oxidisers. In the second pond the remaining ammonium and produced nitrate can be converted by a combination of nitrate reduction to nitrite and anammox. Such optimization of microbial nitrogen transformations can contribute to alleviating the ammonium discharge to surface water draining the landfill.     

Electrodeposition of rare-earth elements from neodymium magnets using molten salt electrolysis

Rare-earth element is an important target for recycling in Japan. In our previous work, we demonstrated the selective leaching of rare-earth elements from waste neodymium magnets using chloride molten salt electrolysis. In this study, we investigated the electrodeposition of rare-earth elements using liquid metal as a cathode. The reduction potential obtained using a liquid-zinc electrode was higher than that obtained using a solid molybdenum electrode. A zinc–rare-earth alloy was formed as the electrodeposit. The total rare-earth element content of the electrodeposit was more than 99.8 mass% without zinc and other composition of electrolysis. The activity of rare-earth elements decreased upon alloy formation, suggesting that the oxidation rate of electrodeposited alloy will be decreased.     

膜电解法退镀废ABS电镀件及回收铜和镍

采用膜电解法对废丙烯腈-丁二烯-苯乙烯（ABS）电镀件进行退镀处理。以退镀废液作为阴极液和阳极液，在阳极室退镀ABS电镀件，在阴极室电解退镀废液，进行铜镍分离，回收铜粉和NiCl₂。实验结果表明：在阴极电流密度为500 A/m²、初始铜离子质量浓度为24.00 g/L的条件下电解160 min，阴极铜回收率可达97.65%，电流效率达86.60%，得到的铜粉纯度为97%~99%，处理1 L退镀废液可回收铜粉20.0 g，2 mol/L盐酸0.87 L，NiCl₂晶体43.8 g;在阳极电流密度为500 A/m²、液固比为6的条件下电解60 min， ABS电镀件的退镀率为77.22%。     

硫酸盐对微生物燃料电池脱氮的影响

构建了双室型微生物燃料电池(MFC),探讨了硫酸盐对MFC阴极脱氮效果和产电性能的影响。实验结果表明:缺氧阴极室中,硝酸盐氮、硫酸盐的还原存在一定的竞争关系,且硫酸盐对电子的竞争能力比硝酸盐氮强;当S与N的质量比(记为S/N)为2∶1时,72 h后的硫酸根去除率达96.41%,而硝酸盐氮去除率仅为36.86%;在S/N为2∶1的条件下,当电压达307.6 m V时,功率密度达最大值15.77 W/m2,电池内阻为100Ω,与未加入硫酸盐时相比产电性能明显提高。     

In situ hypochlorous acid generation for the treatment of syntan wastewater

A new treatment process was employed to treat wastewater generated from a factory manufacturing syntan (synthetic tannin). In this treatment process, in-situ production of hypochlorous acid was achieved by the use of an aqueous sodium chloride solution for chlorine production. As the graphite anode and stainless steel cathode zones were kept unseparated, the hypochlorous acid was produced by electrolysis. The hypochlorous acid was utilized for the oxidation of organic matter present in the wastewater. The results showed that for an initial COD concentration of 10,000 mg/l, a turbidity of 277 NTU, a tannin concentration of 4000 mg/l, a temperature of 27±1°C, a current density of 42.5 mA/cm², a sodium chloride content of 3% and an electrolysis period of 210 min showed an effluent COD concentration of 230 mg/l, a turbidity of 9 NTU, a tannin concentration below the detection limit and a temperature of 37±2°C.     

Comparison of PM2.5 and PM10 in A Suburban Area in Korea During April, 2003

Airborne particulate matter (PM) concentrations were measured in Iksan, a suburban area in South Korea during April, 2003. PM_2.5 (particles with an aerodynamic diameter less than 2.5 μm) and PM₁₀ (particles with an aerodynamic diameter less than 10 μm) samples were collected, and the chemical characteristics of particles were examined for diurnal patterns, yellow dust/rainfall influences, and scavenging effects. Average concentrations of PM_2.5 and PM₁₀ mass measured were 37.3 ± 16.2 μg m⁻³ and 60.8 ± 29.5 μg m⁻³, respectively. The sum of ionic chemical species concentrations for PM_2.5 and PM₁₀ was 16.9 ± 7.3 and 23.1 ± 10.1 μg/m³, respectively. A significant reduction in PM mass concentrations during rainfall days was observed for coarse mode (PM_{2.5 − 10}) particles, but less reduction was found for fine (PM_2.5) mass concentration. SO₄ ²⁻, NH₄ ⁺, and K⁺ predominated in fine particulate mode, NO₃ ⁻ and Cl⁻ predominated in fine particle mode and coarse particle mode, but Na⁺, Mg²⁺, and Ca²⁺ mostly existed in coarse mode. The high concentration of ammonium due to local emissions and long-range transport neutralized sulfate and nitrate to ammonium sulfate and ammonium nitrate, which were major forms of airborne PM in Iksan. Average mass concentrations of PM₁₀ in daytime and at night were 57.6 and 70.0 μg m⁻³, and those of PM_2.5 were 35.4 and 42.5 μg m⁻³, respectively. NO₃ ⁻ and Cl⁻ in both PM_2.5 and PM₁₀ were about double at night than in the daytime, while the rest of the chemical species were equal or a little higher at night than in the daytime. The results suggest the formation of ammonium nitrate and chloride when high ammonia concentration and low air temperature are allowed. Backward air trajectory analyses showed that air masses arriving at the site during yellow dust period were transported from arid Chinese regions, which resulted in high concentrations of airborne PM mass concentrations. In the meantime, air mass trajectories during a rainfall period were mostly from the Pacific Ocean or the East China Sea, along with a relatively low PM concentration.     

TEMPO-Mediated Oxidation of Hemp Bast Holocellulose to Prepare Cellulose Nanofibrils Dispersed in Water

Hemp bast holocellulose fiber (Cannabis sativa L. Subsp. Sativa) was oxidized by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation at various NaClO addition levels in water at pH 10. When carboxylate contents of the oxidized products were 1.5–1.7 mmol/g, TEMPO-oxidized cellulose nanofibrils almost completely dispersed at the individual nanofibril were obtained by mechanical disintegration of the TEMPO-oxidized hemp bast holocelluloses in water, where the nanofibrillation yields were 98–100 %. The sugar composition analysis revealed that most of hemicelluloses originally present in the hemp bast holocellulose were degraded and removed from the solid oxidized products, providing almost pure TEMPO-oxidized celluloses. X-ray diffraction patterns of all TEMPO-oxidized hemp bast holocelluloses had the same cellulose I crystal structure and similar crystallinity indices and crystal widths, indicating that carboxylate groups formed by the oxidation were selectively present on the crystalline cellulose microfibril surfaces in the holocellulose. However, the weight recovery ratios and viscosity-average degrees of polymerization of the TEMPO-oxidized hemp bast holocelluloses decreased to 69–59 % and 470–380, respectively, when their carboxylate contents increased to 1.5–1.7 mmol/g by the TEMPO-mediated oxidation. Atomic force microscopy height images showed that the nanofibril widths were 2.7–2.9 nm, and the average nanofibril lengths decreased from 590 to 400 nm as the NaClO addition level was increased from 7.5 to 12.5 mmol/g in the TEMPO-mediated oxidation.     

Thermogravimetric and XRD study of the effects of chloride salts on the thermal decomposition of mercury compounds

In this paper, the effects of chloride salt (MgCl₂, CaCl₂ or NaCl) addition on the thermal decomposition of five inorganic mercury compounds (HgCl₂, HgS, Hg(NO₃)₂·H₂O, HgO, and HgSO₄) were investigated by thermogravimetric analysis. Mercury-contaminated soil samples collected from Inner Mongolia were used to verify the results. The desorption temperatures of the mercury compounds increased in the following order: HgCl = HgCl₂ < HgS < Hg(NO₃)₂·H₂O < HgO < HgSO₄. Among the chloride salts, MgCl₂ had the greatest effect on thermal desorption of the mercury compounds, with the greatest reduction in the initial temperature of thermal desorption. After MgCl₂ treatment, the mercury removal rates for the soil were 65.67–81.35 % (sample A), 70.74–84.91 % (sample B), and 69.08 % (sample C). The increase in the mercury removal rate for sample C with addition of MgCl₂ was particularly large (34.96–69.08 %). X-Ray diffraction analysis of white crystals from the thermal desorption with MgCl₂ indicated that MgCl₂ promoted conversion of the mercury compounds in the soil to mercury(II) chloride and dimercury dichloride. This transformation is beneficial for applying thermal desorption to remedy mercury-contaminated soils and treat of mercury containing waste.     

Improvement of Synthesis and Dielectric Properties of Polyurethane/Mt-QASs<Superscript>+</Superscript> (Novel Synthesis)

Polyurethane-based nanocomposites were prepared and their dielectric properties were characterized. Polyurethane (PU) composites were prepared with different organoclay content (1, 3, 5, and 10 wt% for all cases). The composites included quaternary ammonium salts such as 1-methyl-di-octyl-1 phenyl ammonium iodide (QAS-1), 1-methyl-di-nonyl-1 phenyl ammonium iodide (QAS-2), and 1-methyl-di-dodecyl-1 phenyl ammonium iodide (QAS-3) which were newly synthesized for modification of Na⁺-montmorillonite. Addition of aluminum silicate enhanced the dielectric properties at a constant concentration. Dielectric constants of nanocomposites compounded with 3 %- and 5 %-organoclay were close in value. The characterization of PU/organoclay composites was carried out using Fourier transform infrared and X-ray diffraction.     

Chitin and Chitosan Extracted from Shrimp Waste Using Fish Proteases Aided Process: Efficiency of Chitosan in the Treatment of Unhairing Effluents

Extraction and depolymerisation of chitin and chitosan from shrimp waste material was carried out using fish proteases aided process. A high deproteinization level (80 %) was recorded with an Enzyme/Substrate ratio of 10 U/mg. The demineralization of shrimp waste was completely achieved within 6 h at room temperature in HCl 1.25 M, and the residual content of calcium in chitin was below 0.01 %. The degree of N-acetylation, calculated from the ¹³C CP/MAS-NMR spectrum, was 85 %. The chitin obtained was converted to chitosan by N-deacetylation. X-ray diffraction patterns also indicated two characteristics crystalline peaks approximately at 10° and 20° (2θ). Chitosan was then evaluated in the treatment of unhairing effluents from the tanning industry. A result showed that chitosan as a coagulant has good performance in alkaline pH and at concentration of 0.5 g/L. Within these conditions, chitosan could decrease turbidity value, total suspended solids (89 % at 1.5 g/L), biological oxygen demand (33.3 % at 1.5 g/L) and chemical oxygen demand (58.7 % at 1.5 g/L).     

Investigations on enhanced in situ bioxidation of methane from landfill gas (LFG) in a lab-scale model

The performance of an exogenous bacterium, Methylobacterium extorquens, in inducing bioxidation of methane from landfill gas (LFG) was assessed in a laboratory scale bioreactor. The study show that enhanced oxidation of methane is attained when the bacteria are introduced into the landfill soil. The maximum percentage reduction of methane fraction from LFG when the bioreactor was inoculated with the methanotrophic bacteria was 94.24 % in aerobic treatment process and 99.97 % in anaerobic process. In the experiments with only the indigenous microorganisms present in the landfill soil, the maximum percentage reduction of methane for the same flow rate of LFG was 59.67 % in aerobic treatment and 45 % in anaerobic treatment. The methane oxidation efficiency of this exogenous methanotrophic bacterium can be considered to be the optimum in anaerobic condition and at a flow rate of 0.6 L/m²/min when the removal percentage is 99.95 %. The results substantiate the use of exogenous microorganisms as potential remediation agents of methane in LFG.     

Investigating the performance of aerobic,semi-aerobic,and anaerobic bioreactor landfills for MSW management in developing countries

Three different laboratory bioreactors, each duplicated, with dimensions 0.5 × 0.5 × 1 m were set up and monitored for 160 days. Municipal Solid Wastes with an organic content of ~80 % and a density of 550 kg/m³ were placed in bioreactors. Fresh leachate collected from waste collection vehicles was used with a recirculation rate of 28 L/day. Aerobic bioreactors were aerated at a rate of 0.15–0.24 L/min/kg of waste. Almost the same level of treatment was observed in terms of chemical oxygen demand reduction of leachate, which was in the range of 91–93 %. However, for anaerobic bioreactor, it took almost twice the time, 160 vs. 76 days, to reach the same level of treatment and stabilization. The behavior of semi-aerobic bioreactor was somewhere between the aerobic and anaerobic ones. Total biogas production for anaerobic bioreactors was 90 L/kg of waste, which contained 57–63 % methane. Methane concentration measured in semi-aerobic bioreactor was below 5 %. The main advantage of aerobic bioreactor was the fast rate of the process, while for semi-aerobic bioreactor, it was the elimination of the need for energy to maintain aerobic conditions, and for anaerobic bioreactor it was the production of biogas and potential energy recovery.     

Recycling nickel from spent catalyst of Phu My fertilizer plant as a precursor for exhaust gas treatment catalysts preparation

In this study, a very promising way of treating and recycling spent nickel catalysts of fertilizer plants in Vietnam was proposed. Firstly, nickel was recovered from spent catalyst using HNO₃—leaching process. Results show that nickel recovery of over 90% with a purity of over 90% can be achieved with HNO₃ 2.1–2.5 M at 100?°C in 75 min. The residue after leaching is not considered as a hazardous waste according to the Vietnamese regulations. Then, the leachate solution was used as a precursor to prepare a model catalyst for exhaust gas (CO, HC, NO_x) treatment. In comparison with the catalyst prepared from the commercial nickel nitrate solution, the catalyst synthesized from recovered nickel exhibits similar properties and activities. The influence of Ni loading of Ni/alumina catalyst as well as the modification of active phase by some metals addition (Mn, Ba, Ce) was also investigated. It is feasible to modify active phase by transition metals such as Mn, Ba, and Ce for complete oxidation of CO and HC at 270?°C and a reduction of NO_x below 350?°C at high volumetric flow condition (GHSV?=?110.000 h^?1).     

Destruction of PAHS from soil by using pressurized hot water extraction coupled with supercritical water oxidation

Chemical processes utilizing water both as extraction solvent and reaction medium are promising "Green Chemistry" alternatives to conventional techniques. Equipment for on-line coupled hot water extraction and supercritical water oxidation was constructed to extract polyaromatic hydrocarbons and toluene from sea sand followed by oxidation using hydrogen peroxide. The effectiveness of the technique is based on the physico-chemical properties of heated and pressurized water. Extraction efficiency increased with temperature and time; the best results were obtained at 300 degrees C with 40 min extraction time. In the oxidation stage, conversion of the PAHs increased with reaction time and oxidant concentration and the best conversion (97.0-99.9%, depending on the compound) was obtained at 425 degrees C with 43 s reaction time. Benzaldehyde and benzoic acid were the most abundant reaction intermediates in the oxidation process. In addition, phenol, p-cresol, and benzyl alcohol were found as intermediates. The intermediates originated mainly from toluene, which was present in much greater concentration than PAHs in the reaction medium.     

Organic and nitrogen removal from landfill leachate in aerobic granular sludge sequencing batch reactors

Granule sequencing batch reactors (GSBR) were established for landfill leachate treatment, and the COD removal was analyzed kinetically using a modified model. Results showed that COD removal rate decreased as influent ammonium concentration increasing. Characteristics of nitrogen removal at different influent ammonium levels were also studied. When the ammonium concentration in the landfill leachate was 366 mg L⁻¹, the dominant nitrogen removal process in the GSBR was simultaneous nitrification and denitrification (SND). Under the ammonium concentration of 788 mg L⁻¹, nitrite accumulation occurred and the accumulated nitrite was reduced to nitrogen gas by the shortcut denitrification process. When the influent ammonium increased to a higher level of 1105 mg L⁻¹, accumulation of nitrite and nitrate lasted in the whole cycle, and the removal efficiencies of total nitrogen and ammonium decreased to only 35.0% and 39.3%, respectively. Results also showed that DO was a useful process controlling parameter for the organics and nitrogen removal at low ammonium input.     

Treatment of Stormwater using Fibre Filter Media

In this study, a high-rate fibre filter was used as a pre-treatment to stormwater in conjunction with in-line flocculation. The effect of operating the fibre filter with different packing densities (105, 115 and 125 kg/m³) and filtration velocities (20, 40, 60 m/h) with and without in-line flocculation was investigated. In-line flocculation was provided using 5, 10 and 15 mg/L of ferric chloride (FeCl₃·6H₂O). The filter performance was studied in terms of pressure drop (ΔP), solids removal efficiency, heavy metals (total) removal efficiency and total organic carbon (TOC) removal efficiency. It is found that the use of in-line flocculation at a dose of 15 mg/L improved the performance of fibre filter as measured by turbidity removal (95%), total suspended solids reduction (98%), colour removal efficiency (99%), TOC removal (reduced by 30–40 %) and total coliform removal (93%). The modified fouling index reduced from 750–950 to 12 s/L² proving that fibre filter can be an excellent pre-treatment to membrane filtration that may be consider as post-treatment. The removal efficiency of heavy metal was variable as their concentration in raw water was small. Even though the concentration of some of these metals such as iron, aluminium, copper and zinc were reduced, others like nickel, chromium and cadmium showed lower removal rates.     

Coagulation of Sericin Protein in Silk Degumming Wastewater Using Quaternized Chitosan

The evaluation of 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC), a biodegradable cationic polymer, for the coagulation of sericin in silk degumming waste solution was carried out using jar-test coagulation experiments. The coagulation efficiency was assessed by the factors of residual turbidity, sericin removal and COD_Cr. The results indicated that the efficiency were dependent on the operational parameters of pH, coagulant dosage and settling time. The optimal pH value was found to be around 8, while a 1 g/L HACC dosage was sufficient in providing more than 98 % turbidity removal and 76 % sericin removal. The results were comparable to those got by the use of conventional coagulants. The coagulation of sericin by HACC may be involved in a dual mechanism including charge neutralization and bridging mechanism. Moreover, the sludge cake from the coagulation, mainly containing sericin protein and modified chitosan, might be used as finishing agent for polyester fabric or food additive for animals after fundamental purified.     

Optimization of the food waste water incineration with respect to CO and NO<Subscript>x</Subscript> emission characteristics

The incineration of food waste water in conjunction with the domestic waste is getting attention as a food waste water treatment method, due to its low treatment cost and high efficiency. Many studies verified that the ammonia in the food waste water served as a reducing agent to suppress the generation of NO_x when the food waste water was injected and incinerated. However, they have not revealed the correlation between the change in the concentration of the CO and NO_x by the influence of the solid matters contained in the food waste water on the incineration of the wastes. The purpose of this study is to determine the optimum amount of the food waste water injected through four nozzles in the primary and secondary incineration chambers and to assess the correlation between the concentration of CO and NO_x in accordance with the food waste water injection in each chamber of the incinerator. For the study, four food waste water injection nozzles were installed; two (A and B) at the top of the primary incineration chamber and the other two (C and D) in the secondary incineration chamber. The correlation between the change in the concentration of CO and NO_x was studied adjusting the amount of the food waste water injected through the nozzles. From the result, Case II showed the concentration of CO and NO_x as 1.8–10 and 14–26 ppm, respectively, while Case I showed that of CO and NO_x as 15–30 and 9–18 ppm, respectively. Those levels are well below the Korean emission criteria, 50 ppm for CO and 80 ppm for NO_x. Based on the results, it is evident there is a certain trade-off between emission of CO and NO_x, and Case II which has relatively low concentration of CO is easier and cheaper to control.     

Photochemical Degradation of Aqueous Polyvinyl Alcohol in a Continuous UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> Process: Experimental and Statistical Analysis

Polyvinyl alcohol (PVA), being a dominant contributor of total organic carbon (TOC) in textile wastewater, is not easily degradable by conventional methods of wastewater treatment. This study investigates the degradation of aqueous PVA in a continuous UV/H₂O₂ photoreactor since the feeding strategy of hydrogen peroxide proves to have considerable effects on the process performance. Response surface methodology involving the Box–Behnken method is adopted for the experimental design to study the effects of operating parameters on the process performance. Experimental analysis shows that the TOC removal varies from 16.11 to 42.70 % along with a reduction of the PVA molecular weights from 56.7 to 95.3 %. The TOC removal is significantly lower than the molecular weight reduction due to the generation of the intermediate products during oxidation. Operating the UV/H₂O₂ process in a continuous mode facilitates the degradation of highly concentrated polymeric solutions using a relatively small hydrogen peroxide concentration in the feed with a small residence time ranges from 6.13 to 18.4 min.