A biotechnological process is described to remove hydrogen sulfide (H(2)S) from high-pressure natural gas and sour gases produced in the petrochemical industry. The process operates at halo-alkaline conditions and combines an aerobic sulfide-oxidizing reactor with an anaerobic sulfate (SO(4) (2-)) and thiosulfate (S(2)O(3) (2-)) reducing reactor. The feasibility of biological H(2)S oxidation at pH around 10 and total sodium concentration of 2 mol L(-1) was studied in gas-lift bioreactors, using halo-alkaliphilic sulfur-oxidizing bacteria (HA-SOB). Reactor operation at different oxygen to sulfide (O(2):H(2)S) supply ratios resulted in a stable low redox potential that was directly related with the polysulfide (S(x) (2-)) and total sulfide concentration in the bioreactor. Selectivity for SO(4) (2-) formation decreased with increasing S(x) (2-) and total sulfide concentrations. At total sulfide concentrations above 0.25 mmol L(-1), selectivity for SO(4) (2-) formation approached zero and the end products of H(2)S oxidation were elemental sulfur (S(0)) and S(2)O(3) (2-). Maximum selectivity for S(0) formation (83.3+/-0.7%) during stable reactor operation was obtained at a molar O(2):H(2)S supply ratio of 0.65. Under these conditions, intermediary S(x) (2-) plays a major role in the process. Instead of dissolved sulfide (HS(-)), S(x) (2-) seemed to be the most important electron donor for HA-SOB under S(0) producing conditions. In addition, abiotic oxidation of S(x) (2-) was the main cause of undesirable formation of S(2)O(3) (2-). The observed biomass growth yield under SO(4) (2-) producing conditions was 0.86 g N mol(-1) H(2)S. When selectivity for SO(4) (2-) formation was below 5%, almost no biomass growth was observed.

Since the 1980s, brominated flame retardants (BFRs) have been detected in air, sewage sludge, sediment, fish, shellfish, birds, and mammals, including humans. However, model studies regarding BFR food-chain accumulation are scarce. In the present study, the accumulation of hexabromocyclododecane and brominated diphenyl ethers (BDEs) 47, 153, 154, and 183 in benthivorous barbel (Barbus graellsii) and pelagic bleak (Alburnus alburnus) from four locations in the Ebro river basin in Spain was modeled using a first-order, one-compartment model with sediment interaction. The model accounted for BFR uptake from water, ingested sediment, and food; release via water and feces; growth; and in situ binding of BFRs to black carbon. Rate constants were derived from allometric regressions. For most BFRs, dynamically modeled biota-sediment accumulation factors (BSAFs) were close to measured values, whereas steady-state model BSAFs were too high, especially for BDEs 153, 154, and 183. Differences between BSAFs for individual fish were explained by differences in age, growth, and feeding behavior. On average, modeled BSAFs for barbel were 50% higher than those for bleak because of extra BFR uptake through sediment ingestion and older age of barbel specimens.