E. E. Chang

Effects of bromide on the formation of THMs and HAAs

The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.

NOM characteristics and treatabilities of ozonation processes.

The objectives of this study were intended to evaluate the effects of the characteristics of natural organic matter on the treatabilities of ozonation, coagulation, filtration, and granular activated carbon processes. The ultra-violet absorbance (UV254) was used as a surrogate parameter to assess each process in reducing the disinfection by-product formation potential (DBPFP). The results indicate that the DBPFP varies with the sources of water samples and treatment processes, but is closely related to the measurement of UV254/DOC. Coagulation/sedimentation can eliminate large molecular weight organic fractions. Both pre- and post-ozonation processes can reduce some of DBP precursors than the conventional treatment process, and are more reliable for reducing the overall DBPFP.

Ex Situ CO2 capture by carbonation of steelmaking slag coupled with metalworking wastewater in a rotating packed bed

Both basic oxygen furnace (BOF) slag and cold-rolling wastewater (CRW) exhibiting highly alkaline characteristics require stabilization and neutralization prior to utilization and/or final disposal. Using CO2 from flue gases as the stabilizing and neutralizing agents could also diminish CO2 emissions. In this investigation, ex situ hot stove gas containing 30 vol% CO2 in the steelmaking process was captured by accelerated carbonation of BOF slag coupled with CRW in a rotating packed bed (RPB). The developed RPB process exhibits superior results, with significant CO2 removal efficiency (η) of 96-99% in flue gas achieved within a short reaction time of 1 min at 25 °C and 1 atm. Calcite (CaCO3) was identified as the main product according to XRD and SEM-XEDS observations. In addition, the elimination of lime and Ca(OH)2 in the BOF slag during carbonation is beneficial to its further use as construction material. Consequently, the developed RPB process could capture the CO2 from the flue gas, neutralize the CRW, and demonstrate the utilization potential for BOF slag. It was also concluded that carbonation of BOF slag coupled with CRW in an RPB is a viable method for CO2 capture due to its higher mass transfer rate and CO2 removal efficiency in a short reaction time.

Comparisons of metal leachability for various wastes by extraction and leaching methods.

The objective of this research was to evaluate three extraction tests, i.e., toxicity characteristic leaching procedures (TCLP), extraction procedure (EP), and American Society for Testing and Materials (ASTM) methods, for their ability to extract metals in chemical sludge and incineration bottom ash, in terms of the precision of analytical results. Typical chemical sludges, including the electroplating and dye-stuff sludges, the municipal solid waste incineration bottom ash, the leather debris, and the steel-mill bottom residue containing Cd, Cr, Cu, Pb, and Zn were prepared for the lysimetry test (dynamic testing) to compare with the extraction results. Results show that for bottom residue and dye-stuff sludge, the concentration of metal leached was almost the same between the lysimetry leaching and the TCLP tests. The metal concentration followed the order: TCLP approximately = EP > ASTM. TCLP and EP exhibited almost the same relative standard deviation (RSD) value. Therefore, the results of the TCLP tests for bottom residue and dye-stuff sludge, which have a low metal content and alkalinity, can be used to estimate the metal concentration leached by typical acid rain in Taiwan; whereas the ASTM extraction test may be a better indicator of the lysimetry test.

Modeling VOCs adsorption onto activated carbon

The activated carbon adsorption process is affected by the characteristics of adsorbent, adsorbate and environmental conditions. In this study, both adsorption and desorption processes are assumed to occur simultaneously and a numerical model was developed with a non-linear driving force in conjunction with the Langmuir model for predicting the overall adsorption process. The numerical model provides both adsorption and desorption rate constants and activation energies. The resultant equilibrium constants are of the same order of magnitude as reported by other studies. Results show that the model could well predict the adsorption isotherms and breakthrough curves under various conditions.

Characterization and application of Ti-containing mesoporous silica for dye removal with synergistic effect of coupled adsorption and photocatalytic oxidation.

Highly ordered mesoporous silica, Santa Barbara Amorphous-15 (SBA-15), and titanium-substituted mesoporous silica (TiSBA-15) materials were successfully synthesized, characterized, and evaluated. The textual and structural properties of the prepared materials with various titanium contents were characterized by inductively coupled plasma-mass spectrometer (ICP-MS), powder X-ray diffraction (XRD) patterns, nitrogen physisorption isotherms, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A limited content of titanium could be effectively substituted into the framework of SBA-15 without provoking structure change. The adsorptive performance was examined by methylene blue (MB) adsorbed on prepared materials. The isotherm models were analyzed to describe the adsorption behavior of prepared materials. The adsorption isotherms were well-fitted with Langmuir and Freundlich models in the simulation of the adsorption behavior of dyes. The SBA-15 and TiSBA-15 materials were found to be effective adsorbents for MB from aqueous solutions. The photodegradation of MB and total organic carbon (TOC) analysis on solid composites were used to evaluate the catalytical performance of Ti-containing mesoporous silica. The synergistic effect of adsorptive and photocatalytical ability of prepared TiSBA-15 was identified. The regeneration and cyclic performance were also proved. These results revealed that TiSBA-15 could be one effective alternative material for dye removal.

The chemical and biological characteristics of coke-oven wastewater by ozonation

A bench-scale bubble column reactor was used to investigate the biological and chemical characteristics of coke-oven wastewater after ozonation treatment through the examination of selected parameters. Color and thiocyanate could be removed almost entirely; however, organic matter and cyanide could not, due to the inadequate oxidation ability of ozone to remove ozonated byproducts under given experimental conditions. The removal of cyanide and total organic carbon were pH-dependent and were found to be efficient under neutral to alkaline conditions. The removal rate for thiocyanate was about five times that of cyanide. The ozone consumption ratio approached to about 1 at the early stage of ozonation (time <20 min), indicating that easily degraded matter was present, and mostly ozone was used to oxidize the pollutants. As ozonation progressed, the consumption ratio decreased to 0.2, and TOC removal (eta(TOC)) increased to 30%, indicating that easily degraded pollutants were degraded almost entirely. The effect of ozonation on the subsequent biological treatment unit (i.e., activated sludge process) was determined by observing the ratio of 5-day biological oxygen demand to chemical oxygen demand (BOD(5)/COD) and the specific oxygen utilization rate (SOUR). The results indicated that the contribution of ozonation to inhibition reduction was very significant but limited to the enhancement of biodegradation. The operation for ozonation of coke-oven wastewater was feasible under neutral condition and short ozone contact time in order to achieve better performance and cost savings.

Systematic approach to determination of maximum achievable capture capacity via leaching and carbonation processes for alkaline steelmaking wastes in a rotating packed bed

Accelerated carbonation of basic oxygen furnace slag (BOFS) coupled with cold-rolling wastewater (CRW) was performed in a rotating packed bed (RPB) as a promising process for both CO2 fixation and wastewater treatment. The maximum achievable capture capacity (MACC) via leaching and carbonation processes for BOFS in an RPB was systematically determined throughout this study. The leaching behavior of various metal ions from the BOFS into the CRW was investigated by a kinetic model. In addition, quantitative X-ray diffraction (QXRD) using the Rietveld method was carried out to determine the process chemistry of carbonation of BOFS with CRW in an RPB. According to the QXRD results, the major mineral phases reacting with CO2 in BOFS were Ca(OH)2, Ca2(HSiO4)(OH), CaSiO3, and Ca2Fe1.04Al0.986O5. Meanwhile, the carbonation product was identified as calcite according to the observations of SEM, XEDS, and mappings. Furthermore, the MACC of the lab-scale RPB process was determined by balancing the carbonation conversion and energy consumption. In that case, the overall energy consumption, including grinding, pumping, stirring, and rotating processes, was estimated to be 707 kWh/t-CO2. It was thus concluded that CO2 capture by accelerated carbonation of BOFS could be effectively and efficiently performed by coutilizing with CRW in an RPB.

Identifying the rejection mechanism for nanofiltration membranes fouled by humic acid and calcium ions exemplified by acetaminophen, sulfamethoxazole, and triclosan

This research investigated the fouling effect of humic acid and humic acid/calcium ions on the rejection of three target compounds, i.e., acetaminophen, sulfamethoxazole, and triclosan, by two nanofiltration (NF) membranes. A modified Hermia fouling model was used to describe the fouling process. The effects of solute and membrane characteristics on the rejection and flux decline at various pH levels and with various foulants were also investigated. Results show that fouling mechanisms include complete blocking and gel layer formation. The presence of humic acid and humic acid/calcium ions may positively influence the rejection of hydrophilic compounds and neutral compounds rejected only by size exclusion. The experimental rejections of solute by the NF270 membrane correlate well with the theoretical rejection model in which only size exclusion was considered. For NF membranes with pore sizes larger than the solutes (e.g., the NTR7450 membrane), the rejection could be determined from the model combining both size exclusion and electrostatic exclusion.

Effects of polydiallyldimethyl ammonium chloride coagulant on formation of chlorinated by products in drinking water

The objectives of this research work was to evaluate the reduction of THM precursors by cationic p-DADMAC and determine the correlations between the chlorine demand and trihalomethane formation in the presence of electrolyte solutions and ambient light. The chlorine demand was found to be significantly reduced provided that the H2SO4 electrolyte was fed to the sample solutions. The amount of CHCl3 formation was also decreased when the Na2SO4 electrolyte was introduced in spite of the levels of light intensity. The p-DADMAC can not only effectively remove the turbidity but also reduce the formation of CHCl3. The optimum dosage of p-DADMAC for reducing the turbidity, TOC and CHCl3 in the humic acid and source water samples was determined and depended upon the nature of organics.