Effect of cycle time on biodegradation of azo dye in sequencing batch reactor

The effects of cycle time on the biodegradation of the azo dye remazol brilliant violet 5R (RBV-5R) were investigated in an anaerobic–aerobic sequencing batch reactor (SBR). System performance was determined by monitoring chemical oxygen demand (COD), color, anaerobic enzyme (azo reductase) and aerobic enzyme (catechol 2,3-dioxygenase), and aromatic amine concentration. SBR was operated in three different total cycle times (48 h, 24 h and 12 h), fed with a synthetic textile wastewater. In this study, the anaerobic period of SBR was found to allow the reductive decolorization of azo dye and the aerobic period was found to be effective on further COD removal after the anaerobic period. The percentage reductions in color by the anaerobic stage of the SBR were at 72%, 89% and 86% for the 24-h, 12-h and 6-h cycle times, respectively. Total COD removal efficiencies were over 75% for all operational conditions and about 70% of the COD removal was achieved in the first 3 h of anaerobic stages. During the decolorization of RBV-5R, two sulfonated aromatic amines (benzene-based and naphthalene-based) were formed and detected by HPLC. Aerobic phases of SBR with total cycle times of 48 h, 24 h and 12 h were able to remove benzene-based aromatic amines with removal efficiency of 64%, 92% and 89%, respectively. The results indicated that the best SBR performance in terms of color removal and aromatic amine degradation was achieved from total cycle time of 24 h.     

Ozonation of azo dye in a semi-batch reactor: a determination of the molecular and radical contributions

Azo dye ozonation was carried in a semi-batch reactor to evaluate both the molecular and radical contributions of ozone on the dye decay. From two mass balance equations, the simultaneous determination of mass transfer, self-decomposition and solubility parameters of ozone were determinated; thus establishing the steady state conditions in the experimental system. The results of kinetic studies showed that the decay of azo dye was a pseudo-first-order reaction with respect to dye concentration and the overall rate constant increased with an increase in the pH, however declined with an increase in the dye concentration. Furthermore, from the overall rate constants obtained at various pH values a mathematical analysis of dye decay was performed, which provides a practical new method to quantify the radical and molecular contributions in the ozonation of azo dyes.     

Investigation of how pressure influences the thermal decomposition behavior of azodicarbonamide

Azodicarbonamide (ADC) is a type of azo compound with outstanding application performance, it is always used as a blowing agent in the production of foamed plastics. Based on previous studies, it has been considered harmless in its practical application process. Nevertheless, our research has overturned this standpoint and denoted the special exothermic behavior of ADC under specific use processes, especially when it was placed in a high-pressure system. In this study, a simultaneous thermogravimetric analyzer (STA) was employed to preliminarily evaluate the thermal stability of ADC under atmospheric pressure. Followed with calorimetric experiments by high-pressure differential scanning calorimetry (HP DSC), the exothermic behaviors of ADC under different initial furnace pressures were investigated. The obtained results revealed that the thermal decomposition rate of ADC linearly increases along with increasing testing pressure, which shows a highly autocatalytic characteristic. The peak power of DSC curve breathtakingly reached 73 W/g when the initial testing pressure was set at 4 MPa, and the overall decomposition heat reached 1261 J/g with the scanning rate at 4 ^°C/min. Furthermore, the decomposition mechanism, thermal hazards, and explosion potential were comprehensively evaluated in this study for the first time.     

氧活性粒子脱除烟气中SO2的实验研究

为了解决目前气体电离放电脱硫方法存在的等离子源体积庞大、能耗高、以及需要依靠传统脱硫方法的协同作用等问题.拟用小流量高浓度氧活性粒子[O2+、O(1D)、O(3P)、O3]及引发剂HO2-分别注入烟道中,与烟气中H2O反应生成·OH;在无吸收剂、无催化剂及没有其他技术协同作用下,进行·OH氧化脱除大烟气量中的微量SO2并生成H2SO4的实验.结果表明:烟气温度为30℃,氧活性粒子与SO2摩尔比为3~4时,脱硫率达到94.6%,回收酸液中SO42-浓度达到9.3g/L.     

Enhanced anaerobic fermentation with azo dye as electron acceptor： Simultaneous acceleration of organics decomposition and azo decolorization

Accumulation of hydrogen during anaerobic processes usually results in low decomposition of volatile organic acids（VFAs）. On the other hand, hydrogen is a good electron donor for dye reduction, which would help the acetogenic conversion in keeping low hydrogen concentration. The main objective of the study was to accelerate VFA composition through using azo dye as electron acceptor. The results indicated that the azo dye serving as an electron acceptor could avoid H2 accumulation and accelerate anaerobic digestion of VFAs. After adding the azo dye, propionate decreased from 2400.0 to 689.5 mg/L and acetate production increased from 180.0 to 519.5 mg/L. It meant that the conversion of propionate into acetate was enhanced. Fluorescence in situ hybridization analysis showed that the abundance of propionate-utilizing acetogens with the presence of azo dye was greater than that in a reference without azo dye. The experiments via using glucose as the substrate further demonstrated that the VFA decomposition and the chemical oxygen demand（COD） removal increased by 319.7 mg/L and 23.3% respectively after adding the azo dye. Therefore, adding moderate azo dye might be a way to recover anaerobic system from deterioration due to the accumulation of H2 or VFAs.     

Applications of thermal hazard analyses on process safety assessments

In 2011, a large petrochemical complex in Taiwan incurred several fire and explosion accidents, which had considerable negative impact for the industry on both environmental and safety issues. Reactive substances are widely used in many chemical industrial fields as an initiator, hardeners, or cross-linking agents of radical polymerization process with unsaturated monomer. However, the unpredictable factors during the process having risk to runaway reaction, thermal explosion, fire, and exposure to harmful toxic chemicals release due to the huge heat and gas products by thermal decomposition could not be removed from the process. This study used differential technology of thermal analysis to characterize the inherent hazard behaviors of azo compounds and organic peroxides in the process, to seek the elimination of the source of the harmful effects and achieve the best process safety practices with zero disaster and sound business continuity plan.     

Electrochemical decolorization of dye wastewater by surface-activated boron-doped nanocrystalline diamond electrode

Complex organics contained in dye wastewater are difficult to degrade and often require electrochemical advanced oxidation processes (EAOPs) to treat it. Surface activation of the electrode used in such treatment is an important factor determining the success of the process. The performance of boron-doped nanocrystalline diamond (BD-NCD) film electrode for decolorization of Acid Yellow (AY-36) azo dye with respect to the surface activation by electrochemical polarization was studied. Anodic polarization found to be more suitable as electrode pretreatment compared to cathodic one. After anodic polarization, the originally H-terminated surface of BD-NCD was changed into O-terminated, making it more hydrophilic. Due to the oxidation of surface functional groups and some portion of sp² carbon in the BD-NCD film during anodic polarization, the electrode was successfully being activated showing lower background current, wider potential window and considerably less surface activity compared to the non-polarized one. Consequently, electrooxidation (EO) capability of the anodically-polarized BD-NCD to degrade AY-36 dye was significantly enhanced, capable of nearly total decolorization and chemical oxygen demand (COD) removal even after several times of re-using. The BD-NCD film electrode favored acidic condition for the dye degradation; and the presence of chloride ion in the solution was found to be more advantageous than sulfate active species.     

Application of 'waste' wood-shaving bottom ash for adsorption of azo reactive dye

The utilization of wood-shaving bottom ash (WBA) for the removal of Red Reactive 141 (RR141), an azo reactive dye, was investigated. WBA/H(2)O and WBA/H(2)SO(4) were made by treating WBA with water and 0.1M H(2)SO(4), respectively, to increase adsorption capacity. Adsorption of RR141 from reactive dye solution (RDS) and reactive dye wastewater (RDW) by WBA/H(2)O and WBA/H(2)SO(4) involved the BET surface area and pore size diameter. Properties of adsorbents, effect of contact time, initial pH of solution, dissolved metals and elution studies indicated that the decolorisation mechanism involved both chemical adsorption and precipitation with calcium ions. In addition, the WBA/H(2)SO(4) surface might contain sulphate-cation complexes that were specific to enhancing dye adsorption from RDW. The adsorption isotherm had a best fit by the Freundlich model. Freundlich parameters showed that WBA/H(2)O used more heterogeneous surface than WBA/H(2)SO(4) and activated carbon for RDW adsorption. A thermodynamic study indicated that RDW adsorption was an endothermic process. The maximum dye adsorption capacities of WBA/H(2)O, WBA/H(2)SO(4) and activated carbon obtained from a Langmuir model at 30 degrees C were 24.3, 29.9, and 41.5mgl(-1), respectively. In addition, WBA/H(2)O and WBA/H(2)SO(4) could reduce colour and high chemical oxygen demand (COD) of real textile wastewater. According to the difficulty in the elution study, it was an environmentally safe disposal of this waste. Therefore, WBA, a waste from combustion of wood shavings, was suitable to be used as an effective adsorbent for azo reactive dye removal.