Alkaline Regeneration Research Articles

Precipitation-Sorption Technology for Purifying the Regeneration Solutions of Condensate-Removal Filters at the Smolensk Nuclear Power Plant

Regeneration solutions from mixed-use filters for condensate removal are one of the main sources of liquid radioactive wastes from nuclear power plants with RBMK reactors. To reduce the amount of liquid radioactive wastes substantially at the Smolensk nuclear power plant, a technology has been developed for removing radionuclides from the regeneration solutions, including mixing of acidic and alkaline regeneration solutions with pH up to 9–10. Copper and iron cations and other ions undergoing hydrolysis, which are present in acidic regenerate as an impurity, precipitate as hydroxides on neutralization by an alkaline regenerate. Cobalt and manganese coprecipitate partially together with the hydroxides. After a holding period, the clarified or filtered solution reaches a stage of ion-selective purification using the radiation-resistant inorganic sorbents Termoksid-3 and Termoksid-35. The filtrate, having a total activity much less than 3·10–10 Ci/liter, is reprocessed as a nonradioactive solution of the salt NaNO3. The results of service-life tests of the technology are presented.

Anion exchange resins for removal of reactive dyes from textile wastewaters

Sorption onto an easily regenerable sorbent in fixed bed filters would be an interesting option for removal of reactive dyes from textile wastewaters. A previous screening with model solutions (Dyes Pigm 51 (2001) 111) had shown two anion exchangers (strong basic S6328a and weak basic MP62, both Bayer) to exhibit good sorption characteristics for reactive dyes. The aim of this study was to evaluate these materials more closely. Thus filter breakthrough, the behavior with original wastewater samples, and the effect of inorganic wastewater parameters as well as regeneration were studied. Breakthrough curves for both materials are relatively unfavorable with a flat gradient, but throughput until breakthrough (100–800 bed volumes) should be sufficient for technical use. With both resins dye uptake is influenced little by competition of inorganic anions (sulfate, carbonate, phosphate) and they perform well in original wastewaters. However, the weak basic type is only efficient up to pH 8. Alkaline regeneration works well for MP62, for S6328a acid regeneration works for most dyes.

Dendrimer-activated solid supports for nucleic acid and protein microarrays.

The generation of chemically activated glass surfaces is of increasing interest for the production of microarrays containing DNA, proteins, and low-molecular-weight components. We here report on a novel surface chemistry for highly efficient activation of glass slides. Our method is based on the initial modification of glass with primary amino groups using a protocol, specifically optimized for high aminosilylation yields, and in particular, for homogeneous surface coverages. In a following step the surface amino groups are activated with a homobifunctional linker, such as disuccinimidylglutarate (DSG) or 1,4-phenylenediisothiocyanate (PDITC), and then allowed to react with a starburst dendrimer that contains 64 primary amino groups in its outer sphere. Subsequently, the dendritic monomers are activated and crosslinked with a homobifunctional spacer, either DSG or PDITC. This leads to the formation of a thin, chemically reactive polymer film, covalently affixed to the glass substrate, which can directly be used for the covalent attachment of amino-modified components, such as oligonucleotides. The resulting DNA microarrays were studied by means of nucleic acid hybridization experiments using fluorophor-labeled complementary oligonucleotide targets. The results indicate that the novel dendrimer-activated surfaces display a surface coverage with capture oligomers about twofold greater than that with conventional microarrays containing linear chemical linkers. In addition, the experiments suggest that the hybridization occurs with decreased steric hindrance, likely a consequence of the long, flexible linker chain between the surface and the DNA oligomer. The surfaces were found to be resistant against repeated alkaline regeneration procedures, which is likely a consequence of the crosslinked polymeric structure of the dendrimer film. The high stability allows multiple hybridization experiments without significant loss of signal intensity. The versatility of the dendrimer surfaces is also demonstrated by the covalent immobilization of streptavidin as a model protein.

Lead metal removal by recycled alum sludge

In this study, alum sludge was recycled using a chemical precipitation process to promote the removal of lead metal in wastewater. To make the process more cost-effective, two different pH ranges were suggested for daily operation, depending on the involvement or otherwise of an aluminum regeneration process at a later stage. If aluminum regeneration was expected, an elevated pH (11.6) was suggested to optimize both the aluminum regeneration and lead removal. Lead hydroxide coprecipitated with alum sludge in alkaline conditions, where the high pH would also facilitate the alkaline regeneration of alum at a later stage. With the use of recycled alum sludge (RAS) in the coagulation process, lead removal rates increased from 79% to 96–98% with 100–180 mg/l of RAS, while the required fresh alum dosage was reduced from 175 mg/l to 50–12.5 mg/l only. If no fresh alum is added to the system, the RAS can still remove up to 94% of lead at low recycling doses (75–100 mg/l), which suggests that the sweep-floc mechanism is crucial to the sludge reuse process. However, if the regeneration of aluminum is not required, a lower initial pH (10.5) should be used to decrease chemical costs.

Repeated use of a hydrophobic ligand-containing porous membrane for protein recovery

A porous hollow-fiber membrane containing a phenyl group as a hydrophobic ligand was prepared by radiation-induced graft polymerization of glycidyl methacrylate, followed by successive ring-opening reactions with phenol and water. Bovine serum albumin (BSA) was bound to the ligand during permeation of a BSA solution in phosphate buffer containing 2M (NH 4) 2SO 4 through the pores of the hollow fiber. Subsequent elution with an (NH 4) 2SO 4-free buffer exhibited an elution percentage of 82%. Repeated cycles of adsorption and elution caused the accumulation of BSA on the pore surface, resulting in a decrease in the binding capacity of BSA with increasing number of cycles. In contrast, by permeating 1 M NaOH after each elution, the binding capacity of BSA was maintained even after ten cycles. This alkaline regeneration was found to be effective in ensuring repeated use of the phenyl-group-containing porous membrane for recovery of proteins.

Optimization of protein G chromatography for biopharmaceutical monoclonal antibodies.

Compared to more stable chromatographic media the use of affinity media with biological ligands such as Protein G Sepharose 4 Fast Flow poses special challenges regarding regeneration and sanitization. This is especially critical for the purification of pharmaceutical proteins, where complete regeneration of the column between runs is of paramount importance. Here, the problems encountered during process development and upscaling of regeneration methods for a Protein G Sepharose Fast Flow column intended for the large-scale purification of pharmaceutical monoclonal antibodies are reported. The initially chosen alkaline regeneration buffer led to an increase in the affinity of Protein G towards antibodies which made elution increasingly difficult. A combination of urea and acetic acid was selected to ensure efficient cleaning of the matrix without affecting ligand properties. Validation experiments were done to demonstrate the functional integrity of the matrix after repeated cycles of use and regeneration, as well as the efficiency of the cleaning process.