Immobilization of Acidithiobacillus ferrooxidans on cotton gauze for biological oxidation of ferrous ions in a batch bioreactor

Simplification of the Acidithiobacillus ferrooxidans Culture Process for Expanding the Field of Biomachining

Biomachining is an eco-friendly metal processing method with broad application potential. Nevertheless, the bacterial culture methods that are currently involved in biomachining require the intensive use of chemical reagents, especially FeSO4, specialized equipment, and professional-level skills in the field of biology. Herein, the differences between two cultures with and without sterilization were evaluated. Acidithiobacillus ferrooxidans was cultured with iron instead of FeSO4 in the culture medium. The chemical and biochemical parameters of the culture were analyzed by studying the area of exposed iron and continuously regulating the pH. Eliminating the sterilization and sterile inoculation of the medium is feasible for culturing A. ferrooxidans. The key to achieving a high bacterial density in culture with iron was to maintain the solution pH. The possibility of mass culturing A. ferrooxidans with steel cuttings was evaluated in a custom bioreactor, and the bacterial concentration reached 9 × 107 cells/mL.

Odor reduction using hydrogen sulfide-removing bacteria in sludge filtration systems: Ferrous-oxidizing bacteria and sulfur-oxidizing bacteria

The preconditioning of digested sludge in sludge filtration systems produces hydrogen sulfide (H₂S), a major odor-causing source. This study evaluated the effects of adding H₂S-removing bacteria to sludge-filtration systems. Ferrous-oxidizing bacteria (FOB) and sulfur-oxidizing bacteria (SOB) were mass-cultivated in a hybrid bioreactor equipped with an internal circulation system. In this bioreactor, FOB and SOB effectively removed >99% of H₂S; however, the acidic conditions created by adding a coagulant during digested sludge preconditioning were more favorable for FOB than for SOB. In batch tests, SOB and FOB removed 94 ± 1.1% and 99 ± 0.1% of H₂S, respectively; therefore, digested sludge preconditioning proved more suitable for FOB activity than SOB activity. The results revealed that the optimal FOB addition ratio was 0.2%, validated using a pilot filtration system. Moreover, the 57.5 ± 2.9 ppm H₂S generated in the sludge preconditioning step was reduced to 0.01 ± 0.01 ppm after adding 0.2% FOB. Therefore, the results of this study will be useful because they provide a process for biologically removing odor-causing sources without affecting the dewatering efficiency of the filtration system.

Immobilized Microbial Catalytic Oxidation Preparation and Application of Biopolymeric Ferric Sulfate

A novel inorganic polymer flocculant, biopolymeric ferric sulfate (BPFS), was prepared by immobilization technology of microorganisms and by oxidation of ferrous sulfate using domestic Thiobacillus ferrooxidans (T. f) under acidic condition. T. f was isolated on the agarose single-plate medium, which exhibited an unusual trait on the utilization of low concentration of the nitrogen source and phosphorus as the nutrient substance. Under the optimal conditions, the microorganism could grow and reproduce normally and maintain the strong catalytic oxidation activity to Fe2+. The immobilization of T. f on the polyurethane as the support matrix was investigated. Cycling batch operation was applied to the preparation of 40 kg/m3, 60 kg/m3, and 80 kg/m3 BPFS when the optimal conditions are pH value of 1.8, circulation flow rate of 0.28–0.30 L/h, and reaction temperature of 28 ± 1°C. When the prepared BPFS and SPFS (solid biopolymeric ferric sulfate) were used to dispose Songhua River water, the removal rate of turbidity and CODMn of BPFS was slightly better than that of SPFS. The removal efficiencies of turbidity and CODMn by BPFS could reach 93.9% and 79.7%, respectively. The result suggests that the BPFS has good flocculating activity.