Selenium removal

Hansen D., Duda P.J., Zayed A. Terry N. Selenium removal by constructed wetlands role of biological volatilization. Environ Sc Technol 1998 32 591-597. 

Nurdogan, Y. Schroeder, R.P. Meyer, C.L. Selenium removal from petroleum refinery wastewater. Proceedings, 49th Purdue Industrial Waste Conference, West Lafayette, IN, 1994. 

A solution of 1.0 g of 3,17-androstandione in 50 ml of methanol and containing 1 g of selenium dioxide, was allowed to remain in an ice-chest overnight. The formed 3,3-dimethoxyandrostan-17-one was not separated. 1 g of solid potassium hydroxide and 2.5 g of sodium borohydride in 2.5 ml of water were added and the mixture allowed to react at room temperature for 24 hours. The solution was then poured into a large excess of water, extracted with methylene chloride, the organic layer dried and evaporated to a residue. The residue was dissolved in ether, and a small amount of selenium removed by filtration. The ether was boiled off and the organic material dissolved in 100 ml of boiling acetone. 25 ml of diluted hydrochloric acid were added, the solution boiled for 5 minutes and then allowed to cool. Upon crystallization,... 

Lin, Z.-Q. and Terry, N. 2003. Selenium removal by constructed wetlands. Quantitative importance of biological volatilization in the treatment of Se-laden agricultural drainage water. Environmental Science and Technology, 37 606-15. 

Agnihotri, R., Chauk, S., Mahuli, S., and Fan, L.S., 1998. Selenium removal using ca-based sorbents reaction kinetics. Environ. Sci. Technol., 32, 1841-1846. 

ABSTRACT Particular elements can, even at trace levels, intact product quality, deposit formation, and regulatory compliance. Characterization of trace and ultra-trace level constituents in aqueous and/or organic matrices has often required the need to employ more than one analytical technique. In recent years, improvements in ICP-MS technologies have made it a preferred technique for multi-element trace level characterization in a variety of matrices. Coupling ICP-MS with various liquid chromatography techniques has enabled a unique capability to speciate organo-metallics at ppb levels. This paper will show how ICP-MS has been successfully used to measure ppb levels in refinery effluent streams. It will demonstrate how hyphenated ICP-MS techniques assisted in development of bioremediation options for selenium removal in wastewater treatment plants. 

Building upon a study that was performed for the Western States Petroleum Association (WSPA) [1] to optimize iron-based selenium removal processes, a scheme was developed to measure total selenium, and the individual selenium species present in the SSW and aqueous streams. Total selenium was measured by ICP-MS after a peroxide/acid digestion pretreatment of the samples. Speciation of the selenium was accomplished using an anionic ion chromatographic separation followed by quantification of the selenite, selenate, and selenocyanate using ICP-MS. 

Elemental speciation using mass spectrometry in conjunction with ICPAES is a latest advance in atomic spectroscopy, which is becoming popular in analytical research labs. Mason et al. ExxonMobil Research and Engineering) show how linking ICP-MS to various liquid chromatographic techniques has enabled determination of ppm levels of metals in hydrocarbons to ppb level measurements in refinery effluent streams. Hyphenated ICP-MS techniques were used to provide speciation information on nickel and vanadium in crude oils and assist in development of bioremediation options for selenium removal in wastewater treatment plants. Similar ICP-MS technique without sample demineralization was used by Lienemann, et al. Institut Francais du Petrole) to determine the trace and ultra-trace amounts of metals in crude oils and fractions. 

Murphy A. P. (1989) A water treatment process for selenium removal. J. Water Pollut. Control Fed. 61, 361-362. Neal R. H. and Sposito G. (1989) Selenate adsorption on alluvial soils. Soil Sci. Soc. Am. J. 53, 70-74. 

NurdogaN Y., Schroeder R. P. and Meyer C. L. (1994) Selenium removal from petroleum r nery wastewater, 49th Purdue Industrial Waste Conference Proceedings. Lewis Pubhshers, Chelsea, MI. 

WSPA (1995) Selenium Removal Technology Study Project Final Report. Western State Petroleum Association,... 

DEVELOPMENT, TESTING AND FULL-SCALE OPERATION OF A NEW TREATMENT METHOD FOR SELENIUM REMOVAL FROM ACIDIC EFFLUENTS... 

From that perspective, the joint work by Noranda Inc., CEZinc Division and its parent research agency, the Noranda Technology Center (NTC), brings a useful contribution to the search for better treatment technologies for selenium removal. The engineering company, SNC-Lavalin Inc., also contributed to this work, in particular in the areas of engineering, cost estimating and full-scale implementation. 

It is also known that the above treatment technologies can hardly achieve selenium removals below 1 mg/1 in the treated effluents (not considering dilution by other process effluents). For liquid effluents with initial selenium concentrations in the range of 1 to 10 mg/1, the USEPA (7) treatability database reports selenium removal performance in the range of 1 to 3 mg/1. No performance results are reported by the treatability database for liquid streams containing selenium concentrations above 10 mg/1. 

The joint Noranda/NTC R D program on selenium removal really entered into a new area of research. A literature review, contacts within the industry and contacts with treatment equipment suppliers indicated that no treatment technology had ever been applied at full-scale specifically for removing selenium from acidic liquid effluents. 

Table I - Summary of Technology Evaluations for Selenium Removal... 

Figure 1 presents a conceptual process flow diagram of the new selenium removal unit. 

Figure 1 - Block Flow Diagram for the Full Scale Selenium Removal Unit...

Commissioning and start-up of the full-scale selenium removal unit took place in December 1998. Once the unit reached close to normal, steady-state operation, an intensive performance evaluation program was undertaken over 18 different treatment batches. Twelve parameters were measured daily at various points along the treatment process chain. 

MBR processes is usually low since the As species remain in soluble form. Few cases showed how major role was played by the problematic layers such as fouling and clogging layers. Consequently, other processes should be integrated if enhanced As removal is required. Fluoride removal in urban wastewater is variable depending on the operating conditions of the urban wastewater treatment plant. Research data concerning the fate and removal of trace U in urban wastewater is very limited. Selenium removal by MBR is moderate to low. Both U and Se are met in very low concentrations in municipal wastewater. 

To develop an effective, optimized ELM process for selenium removal, it is necessary to understand the forms of the selenium ions present in contaminated aqueous streams. Selenium can exist in several oxidation states -II, 0, IV, and VI (13). In naturally occurring ground or surface waters, inorganic selenium is found in the IV (selenite) and VI (selenate) states (14). In petroleum refinery wastewater effluents, the form of selenium depends on the process stream. In stripped sour water the selenium exists primarily in the Se(-II) oxidation state as either organoselenium compounds or selenocyanate. In the final biotreated effluent, selenium exists primarily as selenite [Se(IV)] and selenate [Se(VI)] oxyanions (1). 

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