Gil Ambats

Removal of selenium from contaminated agricultural drainage water by nanofiltration membranes

Abstract Seleniferous agricultural drainage wastewater has become a new major source of pollution in the world. In the USA, large areas of farmland in 17 western states, generate contaminated salinized drainage with Se concentrations much higher than 5 μg/I, the US Environmental Protection Agency water-quality criterion for the protection of aquatic life; Se values locally reach 4200 wg/1 in western San Joaquin Valley, California. Wetland habitats receiving this drainage have generally shown Se toxicosis in aquatic birds causing high rates of embryonic deformity and mortality, or have indicated potential ecological damage. Results of our laboratory flow experiments indicate that nanofiltration, the latest membrane separation technology, can selectively remove > 95% of Se and other multivalent anions from > 90% of highly contaminated water from the San Joaquin Valley, California. Such membranes yield greater water output and require lower pressures and less pretreatment, and therefore, are more cost effective than traditional reverse osmosis membranes. Nanofiltration membranes offer a potential breakthrough for the management of Se contaminated wastes not only from agricultural drainage, but from other sources also.

Distribution and significance of dicarboxylic acid anions in oil field waters

The origin, distribution, and interactions of low-molecular-weight organic acid anions have become an intensively studied field in geochemistry since their widespread occurrence in formation waters of sedimentary basins was first documented by Carothers and Kharaka ( 1978 ). High concentrations (up to 10,000 mg 1~ ) of monocarboxylic (mainly acetate, propionate, and butyrate) and dicarboxylic (mainly oxalate, malonate, and succinate ) acid anions have been reported from many sedimentary basins, with the highest values present in relatively young (Cenozoic age) petroleum reservoir rocks at subsurface temperatures of 80-120 ° C [ see Lundegard and Kharaka (1990) for a recent review with references ]. Geochemical interest in these organic anions stems mainly from their important role in mineral diagenesis in sedimentary basins (Kharaka et al., 1986; MacGowan and Surdam, 1990). In particular, these species act as sources or sinks of protons, as a source of CO2 and as pH and Eh buffering agents (Lundegard and Kharaka, 1990). They also form complexes with cations and metals such as Ca, A1, Fe, Pb, and Zn (Kharaka et al., 1985; Harrison and Thyne, 1992). Data on the concentrations of monocarboxylic acid anions in subsurface waters from many sedimentary basins worldwide are available and are generally accepted as representing the aqueous concentrations at depth. Data on the concentrations of dicarboxylic acid anions are much more limited, some reported values are controversial, and the total values reported range widely from 0 to 2640 mg 1-~ (Surdam et al., 1984; Kharaka et al., 1986; Barth, 1987; MacGowan and Surdam, 1988, 1990). Because of the wide range in the reported concentrations and because dicarboxylic acid anions generally form stronger complexes with A1, Fe, and other cations than do monocarboxylic acid anions, we resampled four oil wells in the San Joaquin basin, California, in order to better assess the role of these acid anions in water-rock interactions in sedimentary basins.

Generation of aliphatic acid anions and carbon dioxide by hydrous pyrolysis of crude oils

Abstract Two crude oils with relatively high (0.60 wt%) and low (0.18 wt%) oxygen contents were heated in the presence of water in gold-plated reactors at 300°C for 2348 h. The high-oxygen oil was also heated at 200°C for 5711 h. The compositions of aqueous organic acid anions of the oils and of the headspace gases were monitored inn order to investigate the distribution of organic acids that can be generated from liquid petroleum. The oil with higher oxygen content generated about five times as much organic anions as the other oil. The dominant organic anions produced were acetate, propionate and butyrate. Small amounts of formate, succinate, methyl succinate and oxalate were also produced. The dominant oxygen-containing product was CO2, as has been observed in similar studies on the hydrous pyrolysis of kerogen. These results indicate that a significant portion (10–30%) of organic acid anions reported i be generated by thermal alteration of oils in reservoir rocks. The bulk of organic acid anions present in formation waters, however, is most likely generated by thermal alteration of kerogen in source rocks. Kerogen is more abundant than oil in sedimentary basins and the relative yields of organic acid anions reported from the hydrous pyrolysis of kerogen are much higher than the yields obtained for the two oils.

Deep well injection of brine from Paradox Valley, Colorado: Potential major precipitation problems remediated by nanofiltration

Groundwater brine seepage into the Dolores River in Paradox Valley, Colorado, increases the dissolved solids load of the Colorado River annually by ∼2.0 × 108 kg. To abate this natural contamination, the Bureau of Reclamation plans to pump ∼3540 m3/d of brine from 12 shallow wells located along the Dolores River. The brine, with a salinity of 250,000 mg/L, will be piped to the deepest (4.9 km) disposal well in the world and injected mainly into the Mississippian Leadville Limestone. Geochemical modeling indicates, and water-rock experiments confirm, that a huge mass of anhydrite (∼1.0 × 104 kg/d) likely will precipitate from the injected brine at downhole conditions of 120°C and 500 bars. Anhydrite precipitation could increase by up to 3 times if the injected brine is allowed to mix with the highly incompatible formation water of the Leadville Limestone and if the Mg in this brine dolomitizes the calcite of the aquifer. Laboratory experiments demonstrate that nanofiltration membranes, which are selective to divalent anions, provide a new technology that remediates the precipitation problem by removing ∼98% of dissolved SO4 from the hypersaline brine. The fluid pressure used (50 bars) is much lower than would be required for traditional reverse osmosis membranes because nanofiltration membranes have a low rejection efficiency (5–10%) for monovalent anions. Our results indicate that the proportion of treatable brine increases from ∼60% to >85% with the addition of trace concentrations of a precipitation inhibitor and by blending the raw brine with the effluent stream.