CO2/Brine Surface Dissolution and Injection: CO2 Storage Enhancement

Carbon capture and storage (CCS) is capable of reducing atmospheric emissions of greenhouse gases from coal or gas-fired power plants. The upward buoyancy of dense-phase carbon dioxide (CO2) in deep reservoirs means that sites need to be chosen with a methodology that carefully evaluates details of performance during and after the injection process. Standard methods of site evaluation for saline aquifers overwhelmingly focus on the aspects of geological containment and monitorability. Also important to storage-site performance is the engineering design of transport and injection. Transport to storage in offshore saline aquifers is normally expected to be by pipeline. There are several proposed methods of CO2 injection: for example, as a dense phase, in the liquid or supercritical phase, as water-alternating-gas cycles, or as carbonated brine. These result in different migration pathways in the aquifer during the short term (1 to 50 years) and different storage distributions in the long term (1,000 to 10,000 years). To develop a methodology suitable for making informed decisions for aquifers offshore of the UK, several of these different methods are being evaluated. A chemical-engineering and reservoir-engineering approach will be used to define some of the important surface-transport and subsurface interactions. Important surface features may include the energy balance, location, sizing, materials specification, and costing of surface equipment for mixing and transporting CO2.

Nutrient removal as a function of benzene supply within vertical-flow constructed wetlands

The role of benzene, macrophytes and temperature in terms of nutrient removal within constructed wetlands is unknown. Therefore, a research study over approximately 30 months was conducted to assess the potential of vertical-flow constructed wetlands to treat nutrients and to examine the effect of benzene concentration, presence of Phragmites australis (Cav.) Trin. ex Steud (common reed), and temperature control on nutrient removal. Experimental wetlands removed between 72% and 90% of benzene at an influent concentration of 1000 mg L(-1). A statistical analysis indicated that benzene is linked to increased effluent chemical oxygen demand and biochemical oxygen demand concentrations. However, there was no significant relationship between benzene treatment and both nitrogen and phosphorus removal. Phragmites australis played a negligible role in organic matter (chemical oxygen demand, biochemical oxygen demand, nitrogen and phosphorus) removal. Control of temperature favoured biochemical oxygen demand removal. However, no significant difference in chemical oxygen demand, and nitrogen and phosphorus removal was detected. Only the combination of the benzene and temperature variables had a significant impact on biochemical oxygen demand removal. The effluent biochemical oxygen demand concentrations in temperature-controlled benzene treatment wetlands were much lower than those located in the natural environment. However, any other combination between benzene, P. australis and the environmental control variables had no significant effect on biochemical oxygen demand, chemical oxygen demand, or nitrogen and phosphorus removal.

Processes impacting on benzene removal in vertical-flow constructed wetlands

The overall aim of this research project was to reduce low molecular weight hydrocarbons such as benzene in produced wastewaters. Over 30 months of research was conducted to test the treatment performance in terms of benzene removal in vertical-flow constructed wetlands. Based on an influent concentration of 1 g L(-1) benzene, the results show mean benzene removal efficiencies between 88.71% and 89.77%, and 72.66% and 80.46% for indoor and outdoor constructed wetlands, respectively. A statistical analysis indicated that the five days at 20 degrees C N-allylthiourea biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), nitrate-nitrogen (NO(3)-N), dissolved oxygen (DO) and electric conductivity (EC) values of the effluent were positively correlated with the effluent benzene concentrations following the order COD>DO>EC>NO(3)-N>BOD(5), and negatively correlated according to the order pH>redox potential (redox)>temperature (T)>turbidity. No strong relationships between benzene and the variables ortho-phosphate-phosphorus (PO(4)(3-)) and ammonia-nitrogen (NH(4)-N) were recorded.