Shih-Hsiung Chen

Chemical binding of heavy metals in anoxic river sediments.

Acid volatile sulfides (AVS) in sediments are available for binding with divalent cationic metals through the formation of insoluble metal-sulfide complexes, thereby controlling the metal bioavailability and subsequent toxicity to benthic biocommunities. However, when the molar concentrations of simultaneously extracted metals (SEM) were greater than AVS, the unexpectedly low or nondetectable levels of metal in pore water could also be found. Thus, except AVS, additional binding phases in sediments were supposed to provide the binding sites for SEM. The aims of this study are to realize the spatial distribution of AVS, SEM, and other binding phases of heavy metals in anoxic sediments of the Ell-Ren river and to elucidate what may be the main additional binding phases except AVS in the anoxic river sediments. By comparing the spatial distributions of SEM/ AVS ratio with various binding phases in extremely anoxic sediments (redox potential was between -115 and -208 mV), both organic matter and carbonates could be considered to be the main additional binding phases of SEM other than AVS. In addition, AVS appeared to have the priority to bind with SEM. By comparing the binding phases of heavy metals before and after AVS extraction, it could be found that Fe-oxides could also be considered to be the main additional binding phase associated with Zn in slightly anoxic sediments (redox potential was between -50 and -130mV), while organic matter with Cu being the next.

Correlation analyses on binding behavior of heavy metals with sediment matrices.

This article presents the amounts of heavy metals bound to the sediment matrices (carbonates, Fe-oxides, Mn-oxides, and organic matter), the correlations between any two heavy-metal binding fractions, and the correlations between sediment matrices and their heavy-metal binding fractions. Data consisted of 313 sets obtained from five main rivers (located in southern Taiwan) were analyzed by statistical methods. Among six heavy metals analyzed (Zn, Cu. Pb, Ni, Cr, and Co), the statistical results show that Zn is primarily bound to organic matter, and Cr is primarily bound to Fe-oxides. Principal component analysis (PCA) and correlation analysis (CA) result in significant correlations between carbonates bound Ni and carbonates bound Cr, Fe-oxides bound Ni and Fe-oxides bound Cr, and Mn-oxides bound Cu and Mn-oxides bound Cr. From linear regression results, the levels of the six heavy metals bound to either organic matter or Fe-oxides is moderately dependent on the contents of organic matter or Fe-oxides, especially true for Cr and Pb. According to slope values of linear regression, Cu and Cr have the highest specific binding amounts (SBA) to organic matter and Fe-oxides, respectively. A significant correlation between organic matter and organically bound heavy metals implied that organic matter contained in the sediments of the Potzu river and the Yenshui river can be adequately used as a normalizing agent. However, the six heavy metals bound to either carbonates or Mn-oxides do not correlate with carbonates or Mn-oxides. The obtained results also imply that competitions of various sediment phases in association with heavy metals occur, and organic matter and Fe-oxides are more accessible to heavy metals than other sediment phases.

CuO impregnated activated carbon for catalytic wet peroxide oxidation of phenol

This paper presents an original approach to the removal of phenol in synthetic wastewater by catalytic wet peroxide oxidation with copper binding activated carbon (CuAC) catalysts. The characteristics and oxidation performance of CuAC in the wet hydrogen peroxide catalytic oxidation of phenol were studied in a batch reactor at 80 degrees C. Complete conversion of the oxidant, hydrogen peroxide, was observed with CuAC catalyst in 20 min oxidation, and a highly efficient phenol removal and chemical oxygen demand (COD) abatement were achieved in the first 30 min. The good oxidation performance of CuAC catalyst was contributed to the activity enhancement of copper oxide, which was binding in the carbon matrix. It can be concluded that the efficiency of oxidation dominated by the residual H2O2 in this study. An over 90% COD removal was achieved by using the multiple-step addition in this catalytic oxidation.

Effect of CO2 treated polycarbonate membranes on gas transport and sorption properties

The effect of polycarbonate (PC) membranes treated with super critical carbon dioxide on gas sorption and transport properties was studied. It was found that the gas permeability of PC membranes hardly changed after the CO2 treatment. However, the gas sorption and diffusion properties showed a significant change. The transport properties were determined by measuring the sorption and permeation properties. The oxygen and nitrogen sorption measurements were carried out at 35C over the pressure range of 1‐25 atm. It was found that exposed CO2 treatment hardly changed the gas permeability but slightly increased the selectivity of oxygen to nitrogen. This study also showed that the increase in gas solubility was contributed by increasing Langmuir-type sorption of CO2 treated membranes rather than Henry-type sorption. The change in polymer packing of membrane was evidenced by glass transition temperature measurements. This study showed that the free volume of membranes increased with the increase of exposed CO2 density.

Multivariate correlations of geochemical binding phases of heavy metals in contaminated river sediment.

Distributions of geochemical binding phases of seven heavy metals (Cr, Cu, Co, Zn, Ni, Pb, and Cd) in sediment cores taken from six heavily polluted sites of the Ell-Ren River in Southern Taiwan were studied. Sequential extraction procedures (SEP) were used to determine the variations of heavy metal binding phases (exchangeable, bound to carbonates, bound to manganese-oxides, bound to iron-oxides, and bound to organic matter) in different sediment depths. Multivariate analyses were used to explore the correlations among these geochemical binding phases of heavy metals. Results showed that the total amounts of various binding phases of heavy metals significantly varied with sediment depth, but their binding behaviors in various phases did not significantly change with depth. The organic matter content in the sediments increased with increasing Fe-oxide content. In addition, the binding affinities of carbonates with Zn, Pb, and Ni were higher than the affinities of carbonates with the other heavy metals. The binding affinity of Fe-oxides with Cr was higher than the affinities of Fe-oxides with the other heavy metals. Both correlation matrixes and principal component analyses demonstrated that distributions of Cu, Zn, Ni, and Cd had significant correlations with each other in both different depth horizons and various geochemical binding phases. The results indicate that these heavy metals might be discharged from the same pollution sources in the past, and also showed stable geochemical binding behaviors with the high silt sediment. However, Co had a poor correlation with the other six heavy metals in various binding phases, except with organic matter. Binding behaviors of Pb in the phases of bound to carbonates and exchangeable were different from the other six heavy metals. Cu was inversly correlated with the other six heavy metals in its binding behavior with reducible phases (Fe-/Mn-oxides).

Removing aqueous ammonia by membrane contactor process

ABSTRACT High-tech industries have been rapidly developing for the last two decades in Taiwan, which also result in high concentrations of various nitrogenous compounds in the wastewater, such as eutrophication. Polyvinylidene fluoride (PVDF) membranes with asymmetric structures and good hydrophobicity have been prepared by a phase-inversion method and applied for removal of ammonia from water by membrane contactor. Aqueous solution containing sulfuric acid was used as stripping solution to accelerate the removal of ammonia. It was found that the investigation of membrane contactor revealed that the flux of PTFE and PVDF (12 wt%) was 193.1 and 97.4 g , respectively. Therefore, membrane contact system has great potential for future applications in wastewater treatment with high strength of ammonium.

The Effect of Metal Ions on Humic Acid Removal and Permeation Properties in an Ultrafiltration System

Abstract With a view to improving the removal of humic acid from aqueous solution, the effect of metal ion addition on the separation of humic acid from water in an utrafiltration (UF) system was investigated. The valence of the metal ion and the molar ratio of humic acid to metal ion strongly affected the permeation flux during ultrafiltration. It was found that the ionic strength, dissociation constant and operating pressure were not major factors affecting the separation performance of the ultrafiltration process. As well as indicating that a suitable ratio of humic acid to metal ion and valence of metal ion were the key factors in improving separation efficiency. The results also showed that separation of humic acid depended on the level of formation of humic acid–metal ion complexes, and on the degree of fouling on the membrane surface.

Catalytic wet peroxide oxidation of p-nitrophenol by Fe (III) supported on resin.

Fe(III) supported on resin (Fe(III)-resin) as an effective catalyst for peroxide oxidation was prepared and applied for the degradation of p-nitrophenol (PNP). Catalytic wet peroxide oxidation (CWPO) experiments with hydrogen peroxide as oxidant were performed in a batch rector with p-nitrophenol as the model pollutant. Under given conditions (PNP concentration 500 mg/L, H(2)O(2) 0.1 M, 80°C, resin dosage 0.6% g/mL), p-nitrophenol was almost completely removed, corresponding to an 84% of COD removal. It was found that the reaction temperature, oxidant concentration. and initial pH of solution significantly affected both p-nitrophenol conversion and COD removal by oxidation. It can be inferred from the experiments that Fe(III) supported on resin was an effective catalyst in the mineralization of p-nitrophenol. In an acidic environment of oxidation, the leaching test showed that there was only a slight leaching effect on the activity of catalytic oxidation. It was also confirmed by the aging test of catalysts in the oxidation.

Microbial Degradation of Phenol in a Modified Three-Stage Airlift Packing-Bed Reactor

Phenol degradation was carried out by using a modified three-stage airlift packing-bed bioreactor. A laboratory-scale airlift packing-bed reactor, with hydrodynamic flexible packing material in the three-stage bioreactor, was constructed and operated for phenol removal from synthetic wastewater. The airlift packing-bed reactor successfully degraded phenol and lowered the chemical oxygen demand (COD) of wastewater. High COD removal was observed, and much lower sludge effluent was obtained in this investigation. This airlift bioreactor showed a superior hydrodynamics performance and broad operating conditions for phenolic material removal. Different operating modes were discussed to obtain the optimal condition for phenol degradation (i.e., hydraulic retention time [HRT] and gas flowrate of airlift). The HRT and feed phenol concentration of wastewater dominated the removal efficiency of phenol and COD. In this bioreactor, surface loading up to 2.84 g phenol/ m2 x d, almost 100% phenol removal, and over 90% COD removal was achieved. The lower operating cost combined with higher phenol-removal efficiency and a low sludge effluent concentration can be achieved by using this reactor for phenol wastewater treatment.

The removal of colloid and dissolved phosphorus by coagulation and membrane microfiltration

Abstract Micro‐filtration has its limitation to remove the dissolved matter and colloids which are smaller than the membrane pore size. Experiments were conducted to develop a preliminary methodology to optimize the operating conditions of membrane hybrid system (coagulation ‐ membrane micro‐filtration) in comparing with the removal of colloidal particles and dissolved phosphorus which are presented in water in particle and dissolved forms, respectively. The results showed that the coagulant dosage could be minimized and high removal efficiency obtained in treating water with colloid particles only. However, for dissolved phosphorus, its removal efficiency is dependent on water alkalinity as well as coagulant dosage and the associated sludge production could not be minimized. To determine the minimum coagulant dosage for the removal of colloidal particles, a few tests of membrane hybrid system were needed. But, to remove dissolved phosphorus, jar test was the only process required to determine the coagulant dosage for meeting effluent standards.