Pressurized CO2/zero valent iron system for nitrate removal

A fluidized zero valent iron (ZVI) reactor pressurized by CO(2) gas for controlling pH was employed for nitrate reduction. The proposed CO(2) pressurized system potentially has advantages of using less CO(2) gas and reaching equilibrium pH faster than CO(2)-bubbled system. However, due to weak acid nature of carbonic acid, system pH gradually increased with increasing oxidation of ZVI and reduction of nitrate. As pH increased with progress of reaction, nitrate removal rate decreased continuously. The results indicate that nitrate removal efficiency increases with increasing initial ZVI dosage but reaches plateau at ZVI doses of higher than 8.25gl(-1), and initial nitrate concentration up to 100mg l(-1) as N has minimal impact on the removal efficiency. Unlike the fluidized system with pH control by strong acid reported in our pervious study, near 100% of nitrogen recovery was observed in the current process, indicating that nitrate reduction by ZVI with different pH controlled mechanisms will have different reaction routes.     

The crude oil market and the gold market: Evidence for cointegration,causality and price discovery

Given that the gold market and the crude oil market are the main representatives of the large commodity markets, it is of crucial practical significance to analyze their cointegration relationship and causality, and investigate their respective contribution, from the perspective of price discovery, to the common price trend so as to interpret the dynamics of the whole large commodity market and forecast the fluctuation of crude oil and gold prices.     

How China’s current energy pricing mechanisms will impact its marginal carbon abatement costs?

Economic and social costs and benefits are critical factors affecting greenhouse gas abatement activities. Recognizing that energy prices are one of the most important factors influencing abatement costs, this study improved the basic China Energy and Environmental Policy Analysis (CEEPA) model by introducing a current energy pricing mechanism for China. The improved model was applied to generate marginal abatement cost (MAC) curves for China including the current energy pricing mechanism and to analyze MACs for the whole country and main abatement sectors in China under different energy pricing mechanisms. The results show that China MACs are sensitive to pricing mechanisms for electricity and refined oil. Ignoring the current regulation of these prices will lead to MAC underestimation, and price liberalization of these two energy sources could lead to a decrease in China MACs. Under a 50 % emission reduction target, if the electricity price regulation is ignored, the China MAC is underestimated by almost 16 %. Energy pricing reforms will lead to variations in sectoral abatement costs and overall abatement potential, and these impacts are projected to be large in the electricity sector. Under a 50 % reduction target, if the electricity price regulation is liberalized, MAC for the electricity sector nearly will decrease 50 %.     

Fate of polycyclic aromatic hydrocarbons during vitrification of incinerator ash in a coke bed furnace

Fate of polycyclic aromatic hydrocarbons (PAHs) during the vitrification of fly ash and bottom ash from the municipal waste incinerator in a coke bed furnace was investigated. In this system, both coke and lime were added to enhance the melting reaction. The major PAH sources in this system were ash and coke, which respectively contributed 97% and 3% of PAHs in the input-mass. During vitrification process, low molecular PAHs (LM-PAH, 2-3-ring), median molecular PAHs (MM-PAH, 4-ring) and high molecular PAHs (HM-PAH, 5-7-ring) mass respectively accounted for >99%, >99% and 84% of the output-mass emitted as the stack flue gas; while those discharged from the slag were <1%, <1% and 16%, respectively. The O/I (output-mass/input-mass) ratio of LM-, MM- and HM-PAHs were 0.063, 0.002 and <0.001, respectively. The high distribution in flue gas and O/I ratio of LM-PAHs is reasonable since they are more easily evaporated, hence difficult to be removed by air pollution control devices. On the contrary, the HM-PAHs, having lower vapor pressure, primarily stays mainly in slag. Based on the 21 total PAH content in feeding ash and slag, the reduction efficiency of the coke bed furnace was >99.9%. To minimize the risk of secondary pollution, the efficiency of coke bed furnace should be improved to reduce the PAH emission into ambient air.     

Fluidized zero valent iron bed reactor for nitrate removal

A fluidized zero valent iron (ZVI) reactor is examined for nitrate reduction. Using the system, the pH of solution can be maintained at optimal conditions for rapid nitrate reduction. For hydraulic retention times of 15 min, the nitrate reduction efficiency increases with increasing ZVI dosage. At ZVI loadings of 33 gl-1, results indicate that the nitrate removal efficiency increases from less than 13% for systems without pH control to more than 92% for systems operated at pH of 4.0. By maintaining pH at 4.0, we are able to decrease the hydraulic retention time to 3 min and still achieve more than 87% nitrate reduction. The recovery of total nitrogen added as nitrate, ammonium, and nitrite was less than 50% for the system operated at pH4.0, and was close to 100% for a system without pH control. The possibility of nitrate and ammonium adsorption onto iron corrosion products was ruled out by studying the behavior of their adsorption onto freshly hydrous ferric oxide at variable pH. Results indicate the probable formation of nitrogen gas species during reaction in pH4.0.     

Performance of a constructed wetland treating intensive shrimp aquaculture wastewater under high hydraulic loading rate

A water treatment unit, mainly consisting of free water surface (FWS) and subsurface flow (SF) constructed wetland cells, was integrated into a commercial-scale recirculating aquaculture system for intensive shrimp culture. This study investigated performance of the treatment wetlands for controlling water quality. The results showed that the FWS-SF cells effectively removed total suspended solids (55-66%), 5-day biochemical oxygen demand (37-54%), total ammonia (64-66%) and nitrite (83-94%) from the recirculating water under high hydraulic loading rates (1.57-1.95 m/day). This led to a water quality that was suitable for shrimp culture and effluent that always satisfied the discharge standards. The area ratios of wetlands to culture tank being demonstrated (0.43) and calculated (0.096) in this study were both significantly lower than the reported values. Accordingly, a constructed wetland was technically and economically feasible for managing water quality of an intensive aquaculture system.     

Flexible options to provide energy for capturing carbon dioxide in coal-fired power plants under the Clean Development Mechanism

Mitigation and Adaptation Strategies for Global Change - Operators of coal-fired power plants with carbon dioxide capture and storage (CCS) can provide energy for carbon dioxide (CO2) capture by...