No abstract

The crystal structure of 1-(4-bromo-2,3,5,6-tetrafluorophenyl)-3benzylimidazolium bromide comprises columns of parallel bromotetrafluorophenyl rings with an interplanar distance of 6.936(6) Å separated by bromide anions. The - stacking between arenes and polyfluoroarenes is an increasingly important interaction in crystal engineering. 1,2 It is expected that other electron-rich species, in particular anions, would also interact with the electron-poor polyfluoroarenes and that this interaction may also be important. A number of crystal structures do indeed possess anions positioned a short distance from the face of a polyfluoroarene (represented as ArF•••X-), suggesting an attractive interaction, 3 in particular where a polyfluoroaryl group is a component of a cation. 4-8 These observations are supported by theroretical calculations that indicate that interactions between anions and hexafluorobenzene are attractive. 9-11 For example, the energies of the optimised C6F6•••Xinteraction where the anion lies on the normal from the centroid were calculated (using the MP2 method and the 6-31++G** basis set with corrections for basis set superposition and zero-point errors) to be-76.1,-52.7 and-48.5 kJmol-1 for fluoride, chloride and bromide respectively; the anions poisitioned at 2.570, 3.148 and 3.201 Å respectively from

A comparison of granular and biological activated carbon (GAC and BAC) media used for drinking water treatment was made to assess differences in surface elemental composition. Fresh GAC, recently commissioned GAC and end-of-service life BAC from a water treatment plant in New Zealand were analyzed using scanning electron microscopy, energy-dispersive spectroscopy, and inductively coupled plasma-mass spectrometry (ICP-MS). Imaging revealed dense microbial colonization of the BAC surface compared to GAC media, and a mineralized surface layer high in manganese and oxygen. ICP-MS analysis also confirmed high levels of Mn in the BAC media relative to GAC media. As many bacterial species known to colonize BAC filters are also known as Mn oxidizers, this suggests a biogenic origin of the Mn-oxide deposition on the BAC surface. Given the properties of Mn-oxides, they may be implicated in the mechanism by which bacteria capture and metabolize substrates in BAC filters.

The water quality in the Chicago Area Waterways (CAWs) has been improved in the past two decades as a result of intercepting combined sewer overflows (CSOs) by the deep tunnels that have been built under the Tunnel and Reservoir Plan (TARP) and better performance at the water reclamation plants discharging to the waterways. However, the storage capacity of the deep tunnels, of which most has been in use, is limited to under 6.9 million cubic meters (245 million cubic feet) and is insufficient for 803 square kilometers (310 square miles) of combined sewer areas, and CSO discharges via gravity CSO outfalls to the CAWs still frequently occur until the storage reservoirs are complete in about another decade. A recent Use Attainability Analysis (UAA) study for the CAWs by the Illinois Environmental Protection Agency (IEPA) required an evaluation of treating the gravity CSOs in the system and its impact on the water quality of the CAWs. An unsteady flow water quality model developed for the CAWs was used for the evaluation of eliminating gravity CSOs on the water quality of the CAWs. Two scenarios, with and without the gravity CSOs in the model, were simulated. The simulated hourly dissolved oxygen (DO) concentrations at thirty seven selected locations throughout the CAWs were analyzed and compared. The simulation results indicated that eliminating gravity CSOs increased stream DO concentrations in the entire system with different improvements at different locations. The simulated DO concentration increase was the most significant in the Upper North Shore Channel, where the stream flow was dominated by gravity CSOs during a storm. CSOs from a fairly large storm could have prolonged impact on stream DO concentrations, which could last for weeks. Even if all gravity CSOs were eliminated, which means the complete capture of the gravity CSOs to the system, the target DO value of 4 mg/L could not be satisfied 100 percent of the time at some locations in the CAWs under the summer conditions in 2001 and 2002.