New and effective multi-element alpha-hematite systems for reduction of trichloroethylene.

The reactivity of different alpha-hematite (alpha-Fe203) systems for dechlorination of trichloroethylene (TCE) in the presence of Fe(II) and CaO was investigated. Initially different experiments were conducted to investigate the reactivity of pure and doped alpha-Fe203. It was found that the presence of elements such as Si, Cu, and Mn in alpha-Fe203 had a significant effect on TCE reduction potential of alpha-Fe203; however, the reduction potential was less than that of alpha-Fe203 (Bayferrox- 110 M, used in a previous study). Further studies were carried out and alpha-Fe203 was synthesized in a manner similar to that of Bayferrox-110 M. This synthetic alpha-Fe203 showed improved reactivity and was found to follow pseudo-first-order kinetics when used in TCE reduction experiments. The preliminary end products analysis showed that TCE degradation was probably via beta-elimination pathway. Detailed investigations ofa-Fe203 systems were carried out using X-ray diffraction, X-ray fluorescence, and scanning electron microscopy with energy-dispersive spectrometry. The results demonstrated that the TCE reduction capacity of alpha-Fe203 was strongly dependent on the other elements present in iron powder used to synthesize alpha-Fe203. It was suspected that these multi-elements in alpha-Fe203 helped to improve its conduction property. Current findings suggest that alpha-Fe203 not in the pure but combined with other elements could be thought as a potential system for TCE reduction.

Dechlorination of liquid wastes containing chlorinated hydrocarbons by a binder mixture of cement and slag with Fe(II).

Iron-based degradative solidification/stabilization (DS/S-Fe(II)) is a modification of conventional solidification/stabilization (S/S) that incorporates degradative processes for organic contaminant destruction with immobilization. This study investigated the effectiveness of a binder mixture of Portland cement and slag in a DS/S-Fe(II) system to treat trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC), trichloromethane (CF), and dichloromethane (MC), which are major chlorinated hydrocarbons contained in waste oils and waste organic solvents. For TCE, 1,1-DCE, and VC, degradation experiments were conducted using three different binder combinations with Fe(II) (cement/Fe(II), slag/Fe(II), and cement/slag/Fe(II)). When cement and slag were mixed at a 1:1 ratio (% wt), the TCE and 1,1-DCE dechlorination rate was enhanced compared to that when cement or slag was used alone with Fe(II). Also, batch experiments were conducted in the solid phase consisting of cement, slag, sand, and Fe(II) to treat liquid wastes that contain chlorinated compounds at high concentrations. TCE was completely removed after 5 days in the cement/slag/sand/Fe(II) system, in which the initial TCE concentration was 11.8mM, with Fe(II) concentration of 565 mM. While the CF concentration was decreased by 95% after 5 days when the initial CF and Fe(II) concentration was 0.25 mM and 200 mM, respectively. However, MC was not degraded with the cement/slag/Fe(II) system.

Anaerobic treatment of palm oil mill effluent using combined high-rate anaerobic reactors.

Combined system of high-rate anaerobic reactors for treating palm oil mill effluent (POME) was developed and investigated in this study. The system composed of one common primary hybrid reactor which was shared by two different secondary filter reactors. An overall COD removal efficiency of 93.5% was achieved in both systems. The secondary reactors contributed not only in enhancing the COD removal efficiency, but also ensured the performance stability of the entire system. Biomass remained intact in the secondary reactor in contrast to the primary reactor in which occasional washout of biomass was observed. The pH of POME was adjusted at the beginning of the operation, as the process continued POME did not require the external pH adjustment as the pH was maintained in desired range. The biogas was produced up to 110 l/d with the yield of 0.171-0.269 l [CH4]/g [COD removed] and 59.5-78.2% content of methane.

Properties of synthetic monosulfate as a novel material for arsenic removal.

Monosulfate was examined as a novel material for As(V) removal since its layered double hydroxide structure was expected to possess a high capacity for anion exchange. Phase-pure monosulfate was synthesized by hydration at 80-90°C for 36 h using a stoichiometric mixture of tricalcium aluminate (calcined at 1300°C) and gypsum. The analyses of PXRD, WDXRF, and FE-SEM confirmed the successful synthesis of highly pure monosulfate with a negligible impurity of ettringite. Batch experiments were carried out to investigate the kinetics of As(V) removal by monosulfate. A close relationship between As(V) uptake and sulfate release was observed. The intercalation of arsenate in the interlayer of monosulfate was confirmed by PXRD and FT-IR analyses. From a series of equilibrium batch experiments, it is seen that initial sorption of As(V) on monosulfate follows Langmuir isotherm, whereas further injection of As(V) caused transformation of monosulfate to ettringite, which was confirmed by FE-SEM micrographs. However, after the transformation, the solid phases in the equilibrium experiments were found to significantly lose their ability to take up As(V) in exchange for sulfate. A possible explanation for this result was hypothesized and discussed in the context of the literature.