Exchange pattern of gaseous elemental mercury in an active urban landfill facility

The environmental behavior of gaseous elemental mercury (Hg) in the ambient air was investigated from the center of a municipal landfill site (area approximately 0.6km(2)) located in Dae Gu, Korea in the winter of 2004. In order to provide insight on the Hg exchange processes in strong source areas, we continuously analyzed Hg concentration gradients developed across two heights between 1m and 5m over soil surfaces at hourly intervals. The results displayed Hg concentrations in the lower and upper levels in the range of 1.46-13.1ngm(-3) (3.33+/-1.29ngm(-3): N=139) and 1.20-13.7ngm(-3) (3.27+/-1.23ngm(-3): N=139), respectively. The results of our analysis, when divided separately into emission and dry deposition, showed that emission of Hg was fairly dominant in frequency (up to 58%) over dry deposition. By multiplying our Hg gradient data with the K-values predicted indirectly from the results of previous studies, the emission and deposition fluxes of Hg were estimated as 39.0+/-43.3ngm(-2)h(-1) (N=80) and -60.0+/-80.2ngm(-2)h(-1) (N=59), respectively. Although the magnitudes of exchange were moderately lower than previously investigated anthropogenic sources, the overall results of this study suggest that an active landfill site can act as an important source of Hg in an urban environment along with other man-made activities.     

Fatty acid fouling of forward osmosis membrane: Effects of pH, calcium, membrane orientation, initial permeate flux and foulant composition

Octanoic acid (OA) was selected to represent fatty acids in effluent organic matter (EOM). The effects of feed solution (FS) properties, membrane orientation and initial permeate flux on OA fouling in forward osmosis (FO) were investigated. The undissociated OA formed a cake layer quickly and caused the water flux to decline significantly in the initial 0.5 hr at unadjusted pH 3.56; while the fully dissociated OA behaved as an anionic surfactant and promoted the water permeation at an elevated pH of 9.00. Moreover, except at the initial stage, the sudden decline of water flux (meaning the occurrence of severe membrane fouling) occurred in two conditions: 1. 0.5 mmol/L Ca^2 +, active layer facing draw solution (AL-DS) and 1.5 mol/L NaCl (DS); 2. No Ca^2 +, active layer-facing FS (AL-FS) and 4 mol/L NaCl (DS). This demonstrated that cake layer compaction or pore blocking occurred only when enough foulants were absorbed into the membrane surface, and the water permeation was high enough to compact the deposit inside the porous substrate. Furthermore, bovine serum albumin (BSA) was selected as a co-foulant. The water flux of both co-foulants was between the fluxes obtained separately for the two foulants at pH 3.56, and larger than the two values at pH 9.00. This manifested that, at pH 3.56, BSA alleviated the effect of the cake layer caused by OA, and OA enhanced BSA fouling simultaneously; while at pH 9.00, the mutual effects of OA and BSA eased the membrane fouling.