Stabilization-solidification-utilization of MSWI fly ash coupling CO2 mineralization using a high-gravity rotating packed bed.

Municipal solid waste incineration fly ash (MSWI-FA) has been regulated as a hazardous waste that needs to treat with stabilization, solidification and landfill due to its amount of heavy metals, chlorides, sulfates and dioxin. While the proper treated MSWI-FA can be utilized as pozzolanic material to reduce the usage of Portland cement. The present article aims to develop an integrated wet-extraction and carbonation process for MSWI-FA stabilization, solidification and utilization via the high-gravity technology. A benchtop experiment demonstrated the dechlorination and CO2 sequestration of MSWI-FA and the carbonated product was applied as a supplementary cementitious material (SCM) in the cement mortar. Physical, chemical and thermal characteristics of raw, wet-extracted, and carbonated MSWI-FA were addressed in terms of the mean diameter, micropore area, micropore volume, chemical compositions, mineralogy and morphology. The effects of the liquid-to-solid ratio and high gravity factor were evaluated. Overall, a chloride extraction ratio of 36.35% and a CO2 capture capacity of 258.5 g-CO2 kg-FA-1 were achieved in the batch experiment. The results of water-energy consumption of chloride removal and CO2 fixation provided a novel insight into the future process criterion. In addition, the carbonated FA was found as binder to partially substitute Portland cement due to its large content of calcium carbonate. The workability and mechanical strength of cement mortar with partial substitution of stabilized FA were evaluated to determine the potential FA utilization pathway. Finally, the continuous process tests determined the key operation indexes for future process scale-up.

Development and deployment of integrated air pollution control, CO2 capture and product utilization via a high-gravity process: comprehensive performance evaluation.

In this study, a proposed integrated high-gravity technology for air pollution control, CO2 capture, and alkaline waste utilization was comprehensively evaluated from engineering, environmental, and economic perspectives. After high-gravity technology and coal fly ash (CFA) leaching processes were integrated, flue gas air emissions removal (e.g., sulfate dioxide (SO2), nitrogen oxides (NOx), total suspended particulates (TSP)) and CO2 capture were studied. The CFA, which contains calcium oxide and thus, had high alkalinity, was used as an absorbent in removing air pollution residues. To elucidate the availability of technology for pilot-scale high-gravity processes, the engineering performance, environmental impact, and economic cost were simultaneously investigated. The results indicated that the maximal CO2, SO2, NOx, and TSP removal efficiencies of 96.3 ±â€¯2.1%, 99.4 ±â€¯0.3%, 95.9 ±â€¯2.1%, and 83.4 ±â€¯2.6% were respectively achieved. Moreover, a 112 kWh/t-CO2 energy consumption for a high-gravity process was evaluated, with capture capacities of 510 kg CO2 and 0.468 kg NOx per day. In addition, the fresh, water-treated, acid-treated, and carbonated CFA was utilized as supplementary cementitious materials in the blended cement mortar. The workability, durability, and compressive strength of 5% carbonated CFA blended into cement mortar showed superior performance, i.e., 53 MPa ±2.5 MPa at 56 days. Furthermore, a higher engineering performance with a lower environmental impact and lower economic cost could potentially be evaluated to determine the best available operating condition of the high-gravity process for air pollution reduction, CO2 capture, and waste utilization.

Performance evaluation of modified bioretention systems with alkaline solid wastes for enhanced nutrient removal from stormwater runoff.

Bioretention systems have been found to be potential candidates for the removal of various pollutants/nutrients from rainfall or stormwater runoff. Despite bioretention has been widely developed for the removal of nutrients from stormwater, effective removal of both phosphorus and nitrogen is still a challenge. Hence, in this study, bioretention systems modified by alkaline solid waste media have been reported for the effective removal of nutrients. Six different types of solid wastes were first assessed using leaching and adsorption tests, and then the bottom ash from a refuse incineration plant was selected as a modifier. The bottom ash was mixed with soil to form a special media as the filter layer in the bioretention systems. The nutrient removal efficiencies of the modified bioretention systems were evaluated and also compared with those of the unmodified control. For this purpose, the design of the modified filter media with a saturated zone was combined to enhance the simultaneous removal of nitrogen and phosphorus. The effect of different rainfall intensities and nutrient concentrations in stormwater runoff on the removal efficiency of nutrients was evaluated. The results indicated that the modified bioretention with bottom ash modified soil media and saturated zone could exhibit the excellent removal efficiency of nitrogen and phosphorus from stormwater runoff. The extent of removal of total nitrogen, total Kjeldahl nitrogen, and total phosphorus was found to be 58-70%, 66-82% and 82-97%, respectively. The performed correlation analysis showed that the bioretention cell using the special media could simultaneously enhance the removal of phosphorus and nitrogen. As a part of this study, the adsorption isotherms of phosphorus removal by the modified bioretention systems have also been determined. Finally, the implications and opportunities for deploying modified bioretention systems for optimizing water-energy nexus and stormwater management were illustrated. In overall, this study demonstrated that the modified bioretention systems could substantially enhance the removal efficiencies of nutrients from stormwater runoff.

CO2 Mineralization and Utilization using Steel Slag for Establishing a Waste-to-Resource Supply Chain.

Both steelmaking via an electric arc furnace and manufacturing of portland cement are energy-intensive and resource-exploiting processes, with great amounts of carbon dioxide (CO2) emission and alkaline solid waste generation. In fact, most CO2 capture and storage technologies are currently too expensive to be widely applied in industries. Moreover, proper stabilization prior to utilization of electric arc furnace slag are still challenging due to its high alkalinity, heavy metal leaching potentials and volume instability. Here we deploy an integrated approach to mineralizing flue gas CO2 using electric arc furnace slag while utilizing the reacted product as supplementary cementitious materials to establish a waste-to-resource supply chain toward a circular economy. We found that the flue gas CO2 was rapidly mineralized into calcite precipitates using electric arc furnace slag. The carbonated slag can be successfully utilized as green construction materials in blended cement mortar. By this modulus, the global CO2 reduction potential using iron and steel slags was estimated to be ~138 million tons per year.

Environmental Benefit Assessment for the Carbonation Process of Petroleum Coke Fly Ash in a Rotating Packed Bed.

A high-gravity carbonation process was deployed at a petrochemical plant using petroleum coke fly ash and blowdown wastewater to simultaneously mineralized CO2 and remove nitrogen oxides and particulate matters from the flue gas. With a high-gravity carbonation process, the CO2 removal efficiency was found to be 95.6%, corresponding to a capture capacity of 600 kg CO2 per day, at a gas flow rate of 1.47 m3/min under ambient temperature and pressure. Moreover, the removal efficiency of nitrogen oxides and particulate matters was 99.1% and 83.2%, respectively. After carbonation, the reacted fly ash was further utilized as supplementary cementitious materials in the blended cement mortar. The results indicated that cement with carbonated fly ash exhibited superior compressive strength (38.1 ± 2.5 MPa at 28 days in 5% substitution ratio) compared to the cement with fresh fly ash. Furthermore, the environmental benefits for the high-gravity carbonation process using fly ash were critically assessed. The energy consumption of the entire high-gravity carbonation ranged from 80 to 169 kWh/t-CO2 (0.29-0.61 GJ/t-CO2). Compared with the scenarios of business-as-usual and conventional carbon capture and storage plant, the economic benefit from the high-gravity carbonation process was approximately 90 and 74 USD per ton of CO2 fixation, respectively.

High-Gravity Carbonation Process for Enhancing CO2 Fixation and Utilization Exemplified by the Steelmaking Industry.

The high-gravity carbonation process for CO2 mineralization and product utilization as a green cement was evaluated using field operation data from the steelmaking industry. The effect of key operating factors, including rotation speed, liquid-to-solid ratio, gas flow rate, and slurry flow rate, on CO2 removal efficiency was studied. The results indicated that a maximal CO2 removal of 97.3% was achieved using basic oxygen furnace slag at a gas-to-slurry ratio of 40, with a capture capacity of 165 kg of CO2 per day. In addition, the product with different carbonation conversions (i.e., 0%, 17%, and 48%) was used as supplementary cementitious materials in blended cement at various substitution ratios (i.e., 0%, 10%, and 20%). The performance of the blended cement mortar, including physicochemical properties, morphology, mineralogy, compressive strength, and autoclave soundness, was evaluated. The results indicated that the mortar with a high carbonation conversion of slag exhibited a higher mechanical strength in the early stage than pure portland cement mortar, suggesting its suitability for use as a high early strength cement. It also possessed superior soundness compared to the mortar using fresh slag. Furthermore, the optimal operating conditions of the high-gravity carbonation were determined by response surface models for maximizing CO2 removal efficiency and minimizing energy consumption.

Building green supply chains in eco-industrial parks towards a green economy: Barriers and strategies.

As suggested by UNEP, the key to sustainable development is to create a "green economy" which should encapsulate all three sectors: the industry, the people, and the government. Therefore, there is an urgent need to develop and implement the green technologies into the existing facilities, especially in the developing countries. In this study, the role of green supply chains in eco-industrial parks (EIPs) towards a green economy was investigated. The strategies and effective evaluation procedures of the green economy were proposed by assessing the barriers from the perspective of institution, regulation, technology, and finance. In addition, three case studies from iron and steel-making, paper mill and pulping, and petrochemical industries were presented and illustrated for building the green supply chains. For example, in the case of Lin-Hai Industrial Park, a total of 15 efficient green supply chains using waste-to-resources technologies were established by 2012, resulting in an economic benefit of USD 100 million per year. It suggests that the green supply chains should be established to achieve both economic growth and environmental protection. With these successful experiences, building a green supply chain within industrial park should be extensively promoted to make traditional industries around the world being environmentally bearable, economic viable, and social equitable.

Seasonal source-receptor relationships in a petrochemical industrial district over northern Taiwan.

This study investigated the relationships between meteorological data, pollution sources, and receptors over northern Taiwan. During the intensive sampling period in summer 1992, the weather was controlled predominantly by a Pacific subtropical high and by Typhoon Mark. During the other intensive sampling period in winter 1993, while a cold frontal system approached Taiwan, the northeasterly winds prevailed most of the time. The local circulation such as land-sea breeze only developed under weak synoptic environment. Particle concentrations and element composition in winter were higher than in summer. This can be attributed to the high convection of air mass, which leads to the vertical dispersion of pollutants in summer. In addition to the subtropical high pressure, typhoons are frequently accompanied with high-wind speeds and unstable weather conditions that also dilute and eliminate the pollutants. In winter, the prevailing northeasterlies might carry pollutants from Midland China. Furthermore, the anticyclone system develops a stagnant condition that easily leads to pollutant accumulation. In this case, the wind direction affected the source contribution of the receptor and the PM10 displays a higher correlation with coarse and fine particulate than meteorological parameters in summer. In addition, the mixing height shows a high correlation with PM10 in winter.