A comparative study on stabilization of available As in highly contaminated hazardous solid waste.

The stabilization of available As was conducted by chemical fixation after Fenton process in a solid waste residual (SWR) from organic arsenic industry. Single as well as combined fixation treatments by using ferric sulfate (FS), magnesium chloride (MC) and calcium hydroxide (CH) were carried out to assess and to evaluate the fixation effect through toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and sequential extraction procedure (SEP). The effect of aging treatment on the fixation of available As in SWR was also investigated. Experimental result showed that the optimal molar ratios for Fe:As, Mg:As and Ca:As were 2:1, 3:1 and 2:1, respectively, and the combination fixation FS+MC+CH was found to be the optimal fixation treatment. With respect to the leaching behavior and the speciation migration of As in SWR after stabilization, TCLP, SPLP and SEP represent a pertinent and inseparable system for the fixation effect evaluation. The fixation treatment of available As in SWR could be evaluated directly after 3 days and the aging treatment is not needed though it can further enhance the fixation effect.

[Cloning and expression in Pichia pastoris of an alkaline mannanase gene].

A strain containing alkaline mannanase gene was isolated from soil by functional plates and the genome library was constructed. From it a mannanase gene TM1 was acquired and was sequenced. The BLAST analysis showed a lower-than-60% similarity of the amino acid sequence to those in GenBank and proved TM1 to be a new mannanase gene (GenBank accession number AY623903). The new gene without signal peptide was cloned into the Pichia pastoris expression vector pHBM905C. The recombinant plasmid pHBM1201 was digested by Sal I and transformed into Pichia pastoris KM71, GS115, SMD1168, respectively. All of the recombinant Pichia pastroris strains containing pHBM1201 secreted functional beta-mannanase. Because of its high mass of expression, the recombinant Pichia pastoris SMD1168-3 containing pHBM1201 was induced at shake flasks. The optimal temperature and pH of the beta-mannanase produced by the recombinant strains were 55 degrees C and 7.5, respectively. The enzymatic activity for konjak powder reached 41.8 with a half life of one hour. After keeping at 80 degrees C for 5 min, the enzymatic activity declined from 77% to 11% and the enzymatic activity could recover up to more than 60% when the temperature descended to 55 degrees C.