RESUMEN
Heavy metals accumulated in slurry of dual alkali flue gas desulfurization (FGD) present a significant catalysis to SO3(2-) oxidation, resulting in a waste of effective components for desulfurization. Na2S was adopted to precipitate heavy metal ions in FGD slurry, and the oxidation rate of SO3(2-) was obtained under different concentrations of heavy metal ions, to reveal the inhibition effect of Na2S on SO3(2-) oxidation catalyzed by heavy metal ions. Mn2+ showed a remarkable catalysis to SO3(-2) oxidation, as the initial oxidation rate of SO3(2-) was tripled to 0.65 mmol/(L x min) by adding 1.0 mmol/L Mn2+ into the slurry. SO3(2-) was catalytically oxidized rapidly with the reaction order 0.169 of Mn2+ within first 60 minutes, so it is of great importance to control the concentration of Mn2+ to inhibit SO3(2-) oxidation. At initial pH value of 6.50-8.50, Na2S removed heavy metal ions effectively from FGD slurry. Higher pH value favored the removal of heavy metal ions. The removal efficiencies of Mn2+, Zn2+, Ni2+ and Cd2+ were 91.0%, 88.1%, 85.5%, and above 99.9% respectively under the conditions of initial pH value 8.50 and Na2S dosage 240.0 mg/L. Mn2+ could be used as an indicator for the concentration of the heavy metal ions in the slurry. As the Mn2+ concentration decreased from 1.0 mmol/L to 5.0 x 10(-3) mmol/L by adding Na2S, the initial oxidation rate of SO3(2-) decreased by 64.6% to 0.23 mmol/(L x min). The desulfurization efficiencies increase 3.8%-5.1% by adding Na2S in a pilot scale setup. It comes to conclusion that heavy metal ions precipitation by adding Na2S with an indicator of Mn2+ to inhibit catalytic oxidation of SO3(2-) is feasible to reduce the consumption of desulfurizer in FGD slurry.
Asunto(s)
Contaminantes Atmosféricos/química , Contaminación del Aire/prevención & control , Metales Pesados/química , Sulfitos/química , Azufre/química , Álcalis/química , Catálisis , Concentración de Iones de Hidrógeno , Oxidación-Reducción , Administración de Residuos/métodosRESUMEN
The phosphorus pollution of the sediment from Dongxin River, an urban river in Hangzhou, was surveyed. Phosphorus release under various flow velocity (0.002-0.02 m x s(-1)), quality of overlying water (the total phosphorus concentration: 0.18, 0.072 and 0.007 mg x L(-1)), depth of overlying water (5, 10 cm) were carefully studied in a hydraulic simulation setup. The results indicate that phosphorus was feasible to release from the sediment with high ratio of water content (40.09%-68.57%) under alkali condition (pH 7.2-8.3). The phosphorus release was also influenced by high content of phosphorus (1.04-2.51 g x kg(-1)) in the sediment. Phosphorus release was mainly in the form of suspended solid under dynamic hydraulic condition, and depended definitely on flow velocity. The release rate reached 147.36 g x (m2 x h)(-1), which approached the maximum value, at flow velocity 0.008 m x s(-1) (i.e. 0.05 m x s(-1) in archetype). Phosphorus release, especially the initial release rate, was obviously affected by the quality of overlying water. Phosphorus tended to release under river water than tap water. However, the depth of overlying water had little influence on phosphorus release in shallow water. Therefore, it is possible to restrain or enhance phosphorus release by adjusting the hydraulic conditions and the quality of overlying water.
Asunto(s)
Agua Dulce/análisis , Sedimentos Geológicos/análisis , Fósforo/análisis , Contaminantes Químicos del Agua/análisis , China , Ciudades , Simulación por Computador , Modelos Teóricos , RíosRESUMEN
Methyldopa was selected to be degraded by Fenton's reagent in the experiment. The experimental results showed that it was feasible to the removal of Methyldopa and COD by Fenton's reagent. The mechanism of Methyldopa removal by Fenton's reagent was significantly different according to the Fe2+ :H2O2 ratio. With high ratio of Fe2+ :H2O2 (> or = 2), the Fenton reaction was coagulation enhanced by H2O2. With medium ratio of Fe2+ :H2O2 (= 1), the Fenton reaction could be characterized into two specific systems : oxidation and coagulation. With low ratio of Fe2+ :H2O2 (< or = 0.2), the Fenton reaction was oxidation, including H2O2 oxidation catalyzed by Fe2+ and degradation by a hydrated ferryl-complex Fe(aq)4+. With the analysis of the mechanism according to low ratio of Fe2+ :H2O2 (< or = 0.2), a kinetics model was adopted to describe the reaction, and the rate equation could provide the evidence for the main reaction pathway, which was fitted very well with the experiment data for the relative error below 10%. It was showed that the kinetic models could primary describe the process of the removal of Methyldopa and COD by Fenton's reagent.
Asunto(s)
Peróxido de Hidrógeno/química , Hierro/química , Eliminación de Residuos Sanitarios/métodos , Metildopa/química , Carbono/química , Estudios de Factibilidad , Cinética , Metildopa/aislamiento & purificación , Modelos Químicos , Compuestos Orgánicos/químicaRESUMEN
Heavy metals and suspended solid (SS) needed to be removed from the recirculation of dual-alkali flue gas desulfurization (FGD) system. The feasibility of coprecipitation of heavy metal and SS by water-soluble chitosan was studied in a lab scale experiment. The association between chitosan and metal ions was verified through DSC and FT-IR. The pH investigation revealed that at the pH ranged from 5 to 9, there were three stages for different actions: adsorption of chitosan for Mn(II), precipitation of manganese hydroxide and coprecipitation of manganese hydroxide and chitosan-Mn(II) complex. The ion selectivity experiments showed that the occurrence of Ca(II) in the solution had little influence on the adsorption of chitosan for Mn(II). The decrease rate of adsorption capacity was about 0.0023 mmol g(-1) per 1 mg L(-1) Ca(II). When adsorption and flocculation of chitosan occurred at the same time and at the sufficient addition of chitosan, chitosan not only made solids flocculate but also enhanced sorption capacity of chitosan. Application of chitosan for coprecipitation of Mn(II) and SS could remove Mn(II) efficiently and improve the settling characteristics of SS from dual-alkali FGD regenerating process.
Asunto(s)
Quelantes , Quitosano , Carbón Mineral , Incineración , Manganeso/aislamiento & purificación , Metales Pesados/aislamiento & purificación , Precipitación Química , Centrales EléctricasRESUMEN
A laboratory-scale well-mixed thermostatic reactor with continuously blasting air was used to investigate the oxidation inhibition of sulfite in dual alkali flue gas desulfurization (FGD) system. The effects of operating parameters such as pH value and catalyst concentration on the oxidation were studied. Sodium thiosulfate was used in the system, and was found that it significantly inhabited the sulfite oxidation. In the absence of catalyst, sodium thiosulfate at 12.67 mmol/L had an inhibition efficiency of approximately 98%. While in the presence of catalyst, sodium thiosulfate at 26.72 mmol/L had an inhibition efficiency less than 85.0%. The oxidation reaction order of sulfite in the sodium thiosulfate was determined to be -1.90 and -0.55 in the absence and presence of the catalyst, respectively. Apparent activation energy of oxidation inhibition was calculated to be 53.9 kJ/mol. Pilot tests showed that the consumption rate of thiosulfate agreed well with the laboratory-scale experimental results.
Asunto(s)
Contaminantes Atmosféricos/química , Contaminación del Aire/prevención & control , Sulfitos/química , Tiosulfatos/química , Álcalis , Catálisis , Concentración de Iones de Hidrógeno , Sulfato de Magnesio/química , Oxidación-Reducción , Azufre , Administración de Residuos/métodosRESUMEN
Sorption of carbon tetrachloride (CT) by zero-valent iron (ZVI) is the rate-limiting step in the degradation of CT, so the sorption capacity of ZVI is of great importance. This experiment was aimed at enhancing the sorption of CT by ZVI and the degradation rate of CT by modification of surfactants. This study showed that ZVI modified by cationic surfactants has favorable synergistic effect on the degradation of CT. The CT degradation rate of ZVI modified by cetyl pyridinium bromide (CPB) was higher than that of the unmodified ZVI by 130%, and the CT degradation rate of ZVI modified by cetyl trimethyl ammonium bromide (CTAB) was higher than that of the unmodified ZVI by 81%. This study also showed that the best degradation effect is obtained at the near critical micelle concentrations (CMC) and that high loaded cationic surfactant does not have good synergistic effect on the degradation due to its hydrophilicity and the block in surface reduction sites. Furthermore degradation of CT by ZVI modified by nonionic surfactant has not positive effect on the degradation as the ionic surfactant and the ZVI modified by anionic surfactant has hardly any obvious effects on the degradation.
Asunto(s)
Tetracloruro de Carbono/química , Hierro/química , Tensoactivos/química , Concentración de Iones de Hidrógeno , Contaminación del Agua/prevención & controlRESUMEN
Terylene artificial silk printing and dyeing wastewater (TPD wastewater), containing averaged 710 mg/L terephthalic acid(TA) as the main carbon source and the character pollutant, was subjected to expanded granular sludge bed (EGSB) process. The stability of the EGSB process was firstly conducted by laboratory experiment. TA ionization was the predominated factor influencing the acid-base balance of the system. High concentration of TA in wastewater resulted in sufficient buffering capacity to neutralize the volatile fatty acids (VFA) generated from substrate degradation and provided strong base for anaerobic system to resist the pH decrease below 6.5. VFA and UFA caused almost no inhibition on the anaerobic process and biogas production except that pH was below 6.35 and VFA was at its maximum value. Along with the granulating of the activated sludge, the efficiency of organic removal and production rate of biogas increased gradually and became more stable. After start-up, the efficiency of COD removal increased to 57%-64%, pH stabilized in a range of 7.99-8.04, and production rate of biogas was relatively high and stable. Sludge granulating, suitable influent of pH and loading were responsible for the EGSB stability. The variation of VFA concentration only resulted in neglectable rebound of pH, and the inhibition from VFA could be ignored in EGSB. The EGSB reactor was stable for TPD wastewater treatment.
Asunto(s)
Bacterias Anaerobias/metabolismo , Reactores Biológicos , Ácidos Ftálicos/metabolismo , Tereftalatos Polietilenos/metabolismo , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Cromatografía Líquida de Alta Presión , Concentración de Iones de Hidrógeno , Impresión , Seda , Eliminación de Residuos Líquidos/instrumentaciónRESUMEN
Aerobically activated sludge processing was carried out to treat terylene artificial silk printing and dyeing wastewater (TPD wastewater) in a lab-scale experiment, focusing on the kinetics of the COD removal. The kinetics parameters determined from experiment were applied to evaluate the biological treatability of wastewater. Experiments showed that COD removal could be divided into two stages, in which the ratio BOD/COD (B/C) was the key factor for stage division. At the rapid-removal stage with B/C>0.1, COD removal could be described by a zero order reaction. At the moderate-removal stage with B/C<0.1, COD removal could be described by a first order reaction. Then Monod equation was introduced to indicate COD removal. The reaction rate constant (K) and half saturation constant (K(S)) were 0.0208-0.0642 L/(gMLSS).h and 0.44-0.59 (gCOD)/L respectively at 20 degrees C-35 degrees C. Activation energy (E(a)) was 6.05 x 10(4) J/mol. By comparison of kinetic parameters, the biological treatability of TPD wastewater was superior to that of traditional textile wastewater. But COD removal from TPD-wastewater was much more difficult than that from domestic and industrial wastewater, such as papermaking, beer, phenol wastewater, etc. The expected effluent quality strongly related to un-biodegradable COD and kinetics rather than total COD. The results provide useful basis for further scaling up and efficient operation of TPD wastewater treatment.
Asunto(s)
Tereftalatos Polietilenos/aislamiento & purificación , Aguas del Alcantarillado/química , Eliminación de Residuos Líquidos/métodos , Aerobiosis , China , Colorantes , Cinética , TextilesRESUMEN
As the characteristic pollutant, terephthalic acid (TA) was in charge of 40%-78% of the total COD of terylene artificial silk printing and dyeing wastewater (TPW-water). The studies on biodegradability of TA were conducted in a serial of activated sludge reactors with TPW-water. TA appeared to be readily biodegradable with removal efficiency over 96.5% under aerobic conditions, hardly biodegradable with removal efficiency below 10% under anoxic conditions and slowly biodegradable with a turnover between 31.4% and 56.0% under anaerobic conditions. TA also accounted for the majority of BOD in TPW-water. The process combined by anoxic, anaerobic and aerobic activated sludge reactor was suitable for TA degradation and TPW-water treatment, Further, the aerobic process was essentially much more effective than the anaerobic or anoxic one to degrade TA in TPW-water.