CO2 capture, utilization, and storage (CCUS) is a promising technology wherein CO2 is captured and stored in solid form for further utilization instead of being released into the atmosphere in high concentrations. Under this framework, a new process called accelerated carbonation has been widely researched and developed. In this process, alkaline materials are reacted with high-purity CO2 in the presence of moisture to accelerate the reaction to a timescale of a few minutes or hours. The feedstock for accelerated carbonation includes natural silicate-minerals (e.g., wollastonite, serpentine, and olivine) and industrial residues (e.g., steelmaking slag, municipal solid waste incinerator (MSWI) ash, and air pollution control (APC) residues). This research article focuses on carbonation technologies that use industrial alkaline wastes, such as steelmaking slags and metalworking wastewater. The carbonation of alkaline solid waste has been shown to be an effective way to capture CO2 and to eliminate the contents of Ca(OH)2 in solid residues, thus improving the durability of concrete blended with the carbonated residues. However, the operating conditions must be further studied for both the economic viability of the technology and the optimal conditions for CO2 reaction.

Mitigation and adaptation are viable strategies for resolving climate change issues which may pose significant challenges to both ecosystems and human populations around the world. Aqueous carbonation is a promising process for mitigating CO2, due to the permanent storage of gaseous CO2 into carbonate precipitations (CaCO3 and/or MgCO3). In this study, aqueous carbonation of blended hydraulic slag cement (BHC) for CO2 sequestration was investigated and evaluated under various operating conditions, i.e., different reaction temperatures and CO2 concentrations, in a slurry reactor. The suspension BHC slurry was strongly alkaline (pH ~11.4) before carbonation, whereas the pH of the slurry dropped rapidly to nearly a weakly acidic solution (i.e., pH ~6.3) after introducing CO2 gas into the reactor. The results show that the maximum CO2 capture capacity was 181 g CO2 per kg BHC at a reaction time of 120 min, a CO2 concentration of 10%, and a gas flow rate of 2.5 L/min at 65°C. The reaction temperature slightly influenced the carbonation conversion of BHC, with an increasing temperature resulting in relatively higher conversion. In addition, the SEM and XRD results suggest that the BHC should be carbonated with CO2 to form CaCO3 in a slurry reactor. It was thus concluded that the CO2 could be successfully captured by the carbonation of BHC in this manner. Furthermore, the experimental data were utilized to determine the rate-limiting mechanism based on the shrinking-core model (SCM), which was validated by the observations of SEM images. The SCM results indicate that the overall carbonation reaction of BHC in a slurry reactor was controlled by the ash-layer diffusion mechanism.

Carbon capture, utilization, and storage (CCUS) is one of the most prominent emerging technologies for mitigating global climate change. In this study, a comparative evaluation for CO2 fixation by carbonation of steelmaking slag was performed by life cycle assessment (LCA) using Umberto 5.5.4 software, with the Swiss Eco-invent 2.2 database. Six scenarios of carbonation for basic oxygen furnace slag (BOFS), steel converted slag (SCS), and blended hydraulic slag cement (BHC) in different types of reactors and/or method were established. The environmental impacts for each scenario are quantified using the valuation system of ReCiPe, where global warming potential (GWP), ecosystem quality potential (EQP), and human health potential (HHP) were evaluated. In addition, sensitivity analysis was carried out to evaluate the relevant uncertainties of heating efficiency on the GHG emissions in direct carbonation processes. According to the results of LCA and sensitivity analysis, the direct carbonation of steelmaking slag in a slurry reactor was found to be the most attractive method, since the GWP was the lowest among the selected scenarios. Furthermore, the best available technology (BAT) for CO2 capture by carbonation processes of alkaline wastes was proposed according to the key performance indicators (KPIs) with respect to engineering considerations and environmental impacts. It was concluded that the accelerated carbonation of steelmaking slag should be performed by combining the slurry reactor with a rotating packed bed (RPB) to maximize carbonation conversion and minimize environmental impacts and additional CO2 emissions.

Carbon dioxide (CO2) emission reduction in industry should be a portfolio option; for example, the carbon capture and utilization by mineralization (CCUM) process is a feasible and proven technology where both CO2 capture and alkaline waste treatment occur simultaneously through an integrated approach. In this study, the challengeable barriers and significant breakthroughs of CCUM via ex-situ carbonation were reviewed from both theoretical and practical perspectives. Recent progress on the performance of various carbonation processes for different types of alkaline solid wastes was also evaluated based on CO2 capture capacity and carbonation efficiency. Moreover, several process intensification concepts such as reactor integration and co-utilization with wastewater or brine solution were reviewed and summarized. In addition, the utilization of carbonated products from CCUM as green materials including cement, aggregate and precipitate calcium carbonate were investigated. Furthermore, the current status of worldwide CCUM demonstration projects within the iron- and steelmaking industries was illustrated. The energy consumption and cost analyses of CCUM were also evaluated.

Basic oxygen furnace slag (BOFS) exhibits highly alkaline properties due to its high calcium content, which is beneficial to carbonation reaction. In this study, accelerated carbonation of BOFS was evaluated under different reaction times, temperatures, and liquid-to-solid (L/S) ratios in a slurry reactor. CO2 mass balance within the slurry reactor was carried out to validate the technical feasibility of fixing gaseous CO2 into solid precipitates. After that, a multiple model approach, i.e., theoretical kinetics and empirical surface model, for carbonation reaction was presented to determine the maximal carbonation conversion of BOFS in a slurry reactor. On one hand, the reaction kinetics of BOFS carbonation was evaluated by the shrinking core model (SCM). Calcite (CaCO3) was identified as a reaction product through the scanning electronic microscopy and X-ray diffraction analyses, which provided the rationale of applying the SCM in this study. The rate-limiting step of carbonation was found to be ash-diffusion controlled, and the effective diffusivity for carbonation of BOFS in a slurry reactor were determined accordingly. On the other hand, the carbonation conversion of BOFS was predicted by the response surface methodology (RSM) via a nonlinear mathematical programming. According to the experimental data, the highest carbonation conversion of BOFS achieved was 57% under an L/S ratio of 20 mL g(-1), a CO2 flow rate of 0.1 L min(-1), and a pressure of 1013 kPa at 50 degrees C for 120 min. Furthermore, the applications and limitations of SCM and RSM were examined and exemplified by the carbonation of steelmaking slags. (C) 2016 Elsevier Ltd. All rights reserved.

Accelerated carbonation of alkaline solid wastes is an attractive method for CO2 capture and utilization. However, the evaluation criteria of CaCO3 content in solid wastes and the way to interpret thermal analysis profiles were found to be quite different among the literature. In this investigation, an integrated thermal analyses for determining carbonation parameters in basic oxygen furnace slag (BOFS) were proposed based on thermogravimetric (TG), derivative thermogravimetric (DTG), and differential scanning calorimetry (DSC) analyses. A modified method of TG-DTG interpretation was proposed by considering the consecutive weight loss of sample with 200-900 degrees C because the decomposition of various hydrated compounds caused variances in estimates by using conventional methods of TG interpretation. Different quantities of reference CaCO3 standards, carbonated BOFS samples and synthetic CaCO3/BOFS mixtures were prepared for evaluating the data quality of the modified TG-DTG interpretation, in terms of precision and accuracy. The quantitative results of the modified TG-DTG method were also validated by DSC analysis. In addition, to confirm the TG-DTG results, the evolved gas analysis was performed by mass spectrometer and Fourier transform infrared spectroscopy for detection of the gaseous compounds released during heating. Furthermore, the decomposition kinetics and thermodynamics of CaCO3 in BOFS was evaluated using Arrhenius equation and Kissinger equation. The proposed integrated thermal analyses for determining CaCO3 content in alkaline wastes was precise and accurate, thereby enabling to effectively assess the CO2 capture capacity of alkaline wastes for mineral carbonation. 2015 (C) Elsevier B.V. All rights reserved.

To simultaneously solve the dilemma of energy demand, waste management, and greenhouse gas emission for communities globally, the waste-to-energy (WTE) supply chain as district energy system should be a viable method towards circular industrial economy. Several essential state-of-the-art WTE technologies including combustion, gasification and anaerobic digestion were evaluated. Portfolio options of technologies for different types of WTE supply chains were illustrated for achieving circular economy system. Since policy makers have to address the public concerns prior to promulgate and implement relating regulations, the strategies on implementation of WTE supply chain were proposed to overcome the challenging barriers from the aspects of technology, finance, institution and regulation. A total of eight key task-forces were also proposed for effectively executing the strategies. Furthermore, several successful lessons on WTE supply chains such as green fuel pellet for heating supply and co-digestion of organic wastes for bio-gas production around the world were reviewed and illustrated.

In order to reduce CO2 emissions and waste generation from the steelmaking industry; a high-gravity carbonation process via rotating packed bed (RPB) was developed using cold-rolling mill wastewater (CRW) and basic oxygen furnace slag (BOFS). Since mass transfer among phases is believed to be a key to effective carbonation for CO2 fixation, in this study, a mass transfer model for the high-gravity carbonation process was developed based on two-film theory. The mass transfer characteristics including overall gas-phase mass transfer coefficient (K(G)a) and height of a transfer unit (HTU) were determined accordingly. The results indicated that the mass transfer resistance of carbonation using BOFS/CRW in an RPB was mainly lay on the liquid side. In addition, the effect of key operating variables such as rotating speed, slurry flow rate, gas flow rate, and liquid-to-solid (L/S) ratio on mass transfer characteristics was evaluated. The developed model was validated with the experimental data, where the experimental K(G)a values lay within +/- 20% of the values estimated. Based on the obtained results, empirical models of K(G)a and HTU values were established. Furthermore, response surface methodology (RSM) was applied to optimize the high-gravity carbonation process from the viewpoint of mass transfer characteristics. The obtained RSM results were in fairly good agreement with the results of the developed model based on the two-film theory. Based on the theoretical models and statistical analyses, the optimum gas-phase mass transfer rate for high-gravity carbonation process of steelmaking slags in an RPB was graphically determined. (C) 2015 Elsevier Ltd. All rights reserved.

The adsorption of three pharmaceuticals, namely, acetaminophen, diclofenac, and sulfamethoxazole onto granular activated carbon (GAC), was investigated. To study competitive adsorption, both dynamic and steady-state adsorption experiments were conducted by careful selection of pharmaceuticals with various affinities and molecular size. The effective diffusion coefficient of the adsorbate was increased with decease in particle size of GAC. The adsorption affinity represented as Langmuir was consistent with the ranking of the octanol-water partition coefficient, K(ow). The adsorption behavior in binary or tertiary systems could be described by competition adsorption. In the binary system adsorption replacement occurred, under which the adsorbate with the smaller K(ow) was replaced by the one with larger K(ow). Results also indicated that portion of the micropores could be occupied only by the small target compound, but not the larger adsorbates. In multiple-component systems the competition adsorption might significantly be affected by the macropores and less by the meso- or micropores.

Adsorption is one of the main mechanisms of compounds of emerging concerns (CECs) rejection by a membrane process. CECs could be adsorbed not only by membrane but also by suspended solid during membrane filtration. In this study, the adsorption of five CECs by natural organic matter (NOM) and NF270 was investigated by using 96-h bottle and batch tests at 25 degrees C, respectively. Humic acid (HA), which is the major ingredient of NOM, was added into Milli-Q water as NOM to simulate the natural water. HA added into the solution was found insolubility at pH 7 in this study. Adsorption of CECs by HA was strongly correlated with log K-ow of compound. Adsorption capacity was observed to be maximum with HA followed by NF. The study also found that the removal efficiency of CECs by NF could be affected by NOM present in the water. Micro-pollutants, such as CECs, could be adsorbed by HA and then be removed easily during the membrane filtration. Moderate existence of HA would be contributive for CECs removal, but too much HA would cause fouling phenomenon resulted in a worse removal efficiency.

Accelerated carbonation of alkaline wastes including municipal solid waste incinerator bottom ash (MSWI-BA) and the cold-rolling wastewater (CRW) was investigated for carbon dioxide (CO2) fixation under different operating conditions, i.e., reaction time, CO2 concentration, liquid-to-solid ratio, particle size, and CO2 flow rate. The MSWI-BA before and after carbonation process were analyzed by the thermogravimetry and differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The MSWI-BA exhibits a high carbonation conversion of 90.7%, corresponding to a CO2 fixation capacity of 102g perkg of ash. Meanwhile, the carbonation kinetics was evaluated by the shrinking core model. In addition, the effect of different operating parameters on carbonation conversion of MSWI-BA was statistically evaluated by response surface methodology (RSM) using experimental data to predict the maximum carbonation conversion. Furthermore, the amount of CO2 reduction and energy consumption for operating the proposed process in refuse incinerator were estimated. Capsule abstract: CO2 fixation process by alkaline wastes including bottom ash and cold-rolling wastewater was developed, which should be a viable method due to high conversion.

The carbonation of alkaline wastes for CO2 capture was mainly controlled by the CO2 dissolution, i.e., mass-transfer controlled reaction, from the theoretical considerations. Several approaches to enhancing the CO2 dissolution rate were proposed and investigated in the literature. For instance, it was proven that the rate of carbonation reaction for alkaline waste was effectively increase mass transfer rate if a rotating packed bed (RPB), so-called "high-gravity" or "HIGEE" process, was utilized. In this study, the experimental data were utilized to develop the carbonation model in an RPB for carbonation of various types of alkaline wastes such as basic oxygen furnace slag (BOFS) and cold-rolling mill wastewater (CRW). The effect of different operating parameters including operation modulus and rotating speed on CO2 removal efficiency was evaluated. In addition, the overall volumetric gas-phase mass transfer coefficients (K(G)a) of BOFS/CRW carbonation in the RPB were calculated. Furthermore, according to the SEM observations, the alkaline wastes were found to be successfully carbonated with CO2 in an RPB, where calcite (CaCO3) was identified as the main product. It was thus concluded that accelerated carbonation of alkaline wastes using an RPB is an effective and efficient method for CO2 capture due to its higher mass transfer rate and carbonation conversion. (C) 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

The reaction kinetics of carbon dioxide (CO2) capture by the accelerated carbonation of basic oxygen furnace slag (BOFS) in a rotating packed bed (RPB) was evaluated using the surface coverage model. Experimental data were utilized to determine the reaction rate constants and maximum carbonation conversion of BOFS based on the surface coverage model. The results indicate that the carbonation of BOFS in an RPB can be well-expressed by the surface coverage model, with R-2 values from 0.98 to 0.99. In addition, the results of reaction kinetics could be validated by observation of SEM and XEDS before and after carbonation, which indicates that the reacted BOFS was surrounded by the CaCO3 product. On the other hand, the reaction kinetics of steelmaking slag in an RPB was compared with that in various types of reactors, i.e., autoclave and slurry reactors. The overall rate of carbonation in an RPB (i.e., 0.299 min(-1)) was greater than that in both a slurry reactor (i.e., 0.227 min(-1)) and an autoclave reactor (i.e., 0.033 min(-1)). Furthermore, the maximum carbonation conversion of BOFS was initially determined by the results of the surface coverage model and then confirmed statistically by the response surface methodology (RSM). It was thus concluded that accelerated carbonation of BOFS in the RPB is a viable method due to its faster reaction kinetics under relatively milder reaction conditions. Accelerated carbonation of BOFS in the RPB is a promising process for CO2 capture due to its relatively higher carbonation conversion of BOFS within a shorter reaction time. (C) 2013 Elsevier Ltd. All rights reserved.

Influence of water matrix on the removal of compounds of emerging concern (CECs) by nanofiltration (NF) has not been clearly delineated. In this study, rejection of eight CECs in different water matrices by NF is investigated. Two additives (humic acid and alginate) were added as natural organic matters (NOMs) to Milli-Q water to emulate raw river water and lake water. The results showed that an intermediate NOM concentration had better rejections of CECs than lower or higher concentrations in the levels of concentrations studied here. When a water matrix contained no NOM, CECs that carried negative charges gained better rejection than those that carried neutral or positive charge at pH of 7, which implies that the major mechanism of rejection is electrostatic repulsion. As the NOM concentrations in the water matrix got relatively higher, adsorption became a predominant mechanism for rejection; under these circumstances, CECs which had higher octanol-water distribution coefficient (k(ow)) could be adsorbed on NOMs and removed with them. The influence of NOM concentration on CEC rejection was considered and used to modify a quantitative structure-activity relationship (QSAR) model. The predicted values of the modified QSAR model were closer to the actual experimental data than those of the original model.

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), Ca-2(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.

Occurrence and methods for the removal of nonylphenolic compounds in drinking water have been gaining increased attention due to their widespread presence in natural water and the potential health risks from the consumptions of drinking water. The purpose of this study was to assess the occurrence of nonylphenol (NP), octylphenol (OP), and bisphenol-A (BPA) in water sources and treated water in Taiwan, to evaluate the treatment efficiencies of these compounds in both the conventional (coagulation, sedimentation, filtration and chlorination) and advanced treatment processes. The treatment efficiencies of these chemicals were assessed based on their concentrations in water sources, and the results were verified with laboratory simulated treatment processes. A survey of NP, OP, and BPA in 11 Taiwanese water sources showed that all of them could be identified in most of the sampled sources, and that higher concentrations of NP were found when the raw water was contaminated by domestic wastewater. However, higher treatment efficiency could be observed when the NP concentration in water source is high. Laboratory simulation studies of conventional treatment processes showed that chlorination played an important role in the degradation of NP in raw water. Treatment efficiencies of 60%–90% were achieved for NP removal when sufficient chlorine dosages were applied to satisfy chlorine demands. However, results also showed that conventional coagulation and rapid filtration processes were less effective in the reduction of phenolic compounds in water.

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.

Accelerated carbonation of BOF slag in an RPB is a viable method for CO2 capture due to its high mass transfer rate. However, the process chemistry of carbonation of BOF slag is not well-determined due to their complex compositions. In this investigation, the quantitative X-ray diffraction was utilized to determine the mechanism of carbonation reaction in an RPB. Rietveld refinement, which aims to minimize the difference between the experimental and refined XRD patterns by a least-square procedure, is performed to quantify the crystallized mineral. In addition, changes of physico-chemical properties of BOF slags before and after carbonation were evaluated.

The Nankan River, located in northern Taiwan, is one of the most contaminated rivers in Taiwan. The pollution of this river causes odor problems and affects use of the water resources. In this study, a systematic river basin water quality management strategy was developed to simulate water quality, evaluate wastewater management alternatives, and cost-effectiveness strategy plans for the Nankan River restoration and its water quality improvement. The main tasks consist of river water sampling and analysis, water quality modeling, total maximum daily load (TMDL) calculation, river pollution index (RPI) evaluation, and cost-effectiveness analysis (CEA). The QUAL2K model, developed by US Environmental Protection Agency, was adopted as the river water quality modeling framework in this study. The modeling effort was supported including four water quality data-sets of the river. Results of the water quality modeling show that the calculated TMDL for biochemical oxygen demand (BOD) and ammonia loading were 1,334 and 889kg/day, respectively. Approximately, 1,334kg/day of BOD and 889kg/day of ammonia needed to be reduced to improve the RPI from serious pollution level to moderate pollution level. Results also reveal that the odor problem caused by dimethyl sulfide and dimethyl trisulfide could be removed after the water quality improvement. Results from the CEA show that an annual cost of US$ 8million is required to reach the acceptable RPI level (moderate pollution). The developed strategies can be used as decision-making tools for water pollution control and river basin water quality management for the Nankan River and other similar rivers.

In this study, direct and indirect carbonation of basic oxygen furnace slag (BOFS) coupled with cold-rolling wastewater (CRW) was carried out via a rotating packed bed (RPB). The solid products were qualitatively characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and quantitatively analyzed with thermogravimetric analysis (TGA). The leachate was analyzed with inductively coupled plasma-optical emission spectroscopy (ICP-OES). The results indicate that the maximum achievable carbonation conversion (MACC) of BOFS was 90.7%, corresponding to a capture capacity of 0.277 g CO2/g of BOFS, by direct carbonation with CRW under a rotation speed of 750 rpm at 30 degrees C for 20 min. In addition, CO2 mass balance among the gas, liquid, and solid phases within an RPB was well-developed, with an error less than 10%, to confirm the actual CO2 capture capacity of BOFS with precision and accuracy. Furthermore, a reaction kinetic model based on mass balance was established to determine the reaction rate constant for various liquid agents (CRW and pure water). It was concluded that co-utilization of alkaline wastes including BOFS and CRW via the RPB is a novel approach for both enhancing CO2 capture capacity and reducing the environmental impacts of alkaline wastes. (C) 2013 Elsevier B.V. All rights reserved.