Ammonia, thiocyanate, and cyanate removal in an aerobic up-flow submerged attached growth reactor treating gold mine wastewater.

The objective of the study was to investigate the nitrification process, as well as the bio-chemical removal of cyanate and thiocyanate, while treating gold mining wastewater using an aerobic up-flow SAGR. A total of six SAGRs, each packed with locally sourced pea gravel (estimated specific surface area of 297 m-2 m-3), were operated at various HRTs and tested on both low- and high-strength gold mining wastewaters. The two sets of three SAGRs were operated at HRTs of 0.45 days, 1.20 days, and 2.40 days. Nitrification was successfully achieved in all six SAGRs regardless of the wastewater strength or HRT examined. The steady-state, 20 °C surface area loading rate was determined to be 1.2 g-TAN m-2 d-1 in order to comply with an effluent discharge limit at 10 mg-TAN L-1 (i.e., with the wastewater sources examined). At all ammonia loading rates, thiocyanate was successfully removed, and residual concentrations were below 2 mg-SCN-N L-1. Cyanate appeared to be hydrolyzed and subsequently nitrified. Acute toxicity tests conducted on both daphnia and trout revealed the effluent to be safe for direct discharge.

Development of four-stage moving bed biofilm reactor train with a pre-denitrification configuration for the removal of thiocyanate and cyanate.

Two trains (A and B) of four-stage moving bed biofilm reactors (MBBRs) were developed for the degradation of thiocyanate (SCN(-)), cyanate (OCN(-)) and ammonia (NH3). A pre-denitrification configuration was established in the first-stage reactor of the B train using SCN(-) and OCN(-) as the sole carbon source. SCN(-), OCN(-) and NH3 were completely removed in both trains. The highest removal of total nitrogen equivalent (total-N) occurred at a loading rate of 5.6 mg-N L(-1) h(-1). The pre-denitrification configuration resulted in increased total-N removal in the B train (62.6%) compared to the A train (38.5%). Thiobacillus spp. were the predominant bacteria in all MBBRs. Bacteria related to bioprocesses involving anaerobic ammonium oxidation were present in the B train, suggesting that part of nitrogen removal occurs via this pathway. Our results showed that the pre-denitrification configuration increases the efficiency of removal of total-N compounds in the SCN(-)/OCN(-)-degrading MBBR process.

Active single-drop microextraction for the determination of gaseous diisocyanates.

This paper presents a novel application of active single-drop microextraction (SDME) for the determination of mixtures of four gaseous diisocyanates: 2,4- and 2,6-toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI). The optimised simultaneous extraction, preconcentration and derivatization method utilizes a 2.3-microL Milli-Q water drop containing dibutylamine (DBA) as a derivatization reagent and phenylisocyanate (PHI) as an injection standard. A type III screening design, combined with Box-Behnken surface modelling and Simplex optimisation was applied to optimise the method. Several SDME approaches--standard SDME, automatic organic solvent film (OSF) and use of a supported-drop (SD) device--were compared with solid-phase microextraction (SPME) in terms of sensitivity and robustness under varied conditions. Of these SDME alternatives, SD proved to be the most suitable for diisocyanate sampling. The detection limits using SDME followed by UPLC-MS-MS analysis were 0.9 and 0.8 microg m(-3) for 2,4- and 2,6-TDI, respectively, 1.0 microg m(-3) for HDI and 0.2 microg m(-3) for MDI.

Possible use of constructed wetland to remove selenocyanate, arsenic, and boron from electric utility wastewater.

Wetland microcosms were used to evaluate the ability of constructed wetlands to remove extremely high concentrations of selenocyanate (SeCN-), arsenic (As), and boron (B) from wastewater generated by a coal gasification plant in Indiana. The wetland microcosms significantly reduced the concentrations of selenium (Se), As, B, and cyanide (CN) in the wastewater by 64%, 47%, 31%, and 30%, respectively. In terms of the mass of each contaminant, 79%, 67%, 57%, and 54% of the Se, As, B, and CN, respectively, loaded into the microcosms were removed from the wastewater. The primary sink for the retention of contaminants within the microcosms was the sediment, which accounted for 63%, 51%, and 36% of the Se, As, and B, respectively. Accumulation in plant tissues accounted for only 2-4%, while 3% of the Se was removed by biological volatilization to the atmosphere. Of the 14 plant species tested, cattail, Thalia, and rabbitfoot grass were highly tolerant of the contaminants and exhibited no growth retardation. Environmental toxicity testing with fathead minnow (Pimephales promelas) larvae confirmed that the water treated by the wetland microcosms was less toxic than untreated water. The data from the wetland microcosms support the view that constructed wetlands could be used to successfully reduce the toxicity of aqueous effluent contaminated with extremely high concentrations of SeCN-, As, and B, and that a pilot-scale wetland should therefore be constructed to test this in the field. Cattail, Thalia, and rabbitfoot grass would be suitable plant species to establish in such wetlands.

Removal of selenocyanate from water using elemental iron.

Batch experiments were conducted to investigate the removal of selenocyanate (SeCN-) from oil refinery wastewater and artificial wastewater with elemental iron [Fe(0)]. The chemical forms of selenium in the reacted solids were determined with X-ray photoelectron spectroscopy (XPS) and a sulfite extraction procedure. SeCN- was effectively removed from the wastewater with Fe(0) filings when the water pH was controlled at approximately 6. SeCN- was removed by Fe(0) through the formation of elemental selenium [Se(0)] and ferrous selenide. The possible chemical reactions between SeCN- and Fe(0) included deselenation of SeCN- and electrochemical reduction of Se(0) to selenide. A cost-effective process may be developed for the treatment of SeCN- in wastewater using Fe(0).

Purification and properties of the inducible enzyme cyanase.

Cyanase (cyanate hydrolase EC 3.5.5.3) has been purified 270-fold to a high state of purity from Escherichia coli B. The native enzyme has a molecular weight of approximately 150 000 as estimated by sucrose density gradient centrifugation and gel-filtration chromatography on Bio-Gel P-300. The enzyme is an oligomer composed of apparently identical subunits which have a molecular weight of approximately 15 000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amino acid analyses showed that the enzyme contains no tryptophan and a single histidine residue, based on a subunit molecular weight of 14 661. Catalytic hydrolysis of cyanate was found to be dependent on the patience of bicarbonate and to be affected by ionic strength. The concentration of bicarbonate required to give half-maximal activity in the presence of 2 mM potassium cyanate was 0.1 mM. The apparent Km for cyanate in the presence of 3 mM bicarbonate is 0.6 mM. The initial product of the reaction is carbamate (or a related, unstable compound and/or carbamate precursor) which subsequently decomposes to ammonia and bicarbonate.