Development of a molasses wastewater treatment system equipped with a biological desulfurization process

Biogas purification and ammonia load reduction in sewage treatment by two-stage down-flow hanging sponge reactor

In this study, a two-stage down-flow hanging sponge (TSDHS) reactor was used as biotrickling filter for biogas desulfurization by utilizing the anaerobic digester supernatant (ADS) of sewage sludge of an activated sludge process (ASP). The reactor comprises a closed-type first-stage down-flow hanging sponge (1st DHS) and an open-type second-stage down-flow hanging sponge (2nd DHS) reactors. In the 1st DHS, hydrogen sulfide in biogas was dissolved into the ADS, and then it was oxidized into elemental sulfur and sulfate by microbe using dissolved oxygen and nitrite in the ADS. More than 99.9 % of hydrogen sulfide was removed within 400 s of empty bed residence time, and >50 % of removed hydrogen sulfide was oxidized into elemental sulfur and accumulated at the surface of the sponge carrier in the 1st DHS. The 1st DHS effluent was fed into the 2nd DHS for nitrogen removal via nitrification and sulfur-based denitrification with the recirculation of the 2nd DHS effluent under nonaeration condition. In the 2nd DHS, 36.8 % of ammonia and 5.3 % of total inorganic nitrogen were removed. Sulfurimonas and Halothiobacillus were increased and contributed to the sulfur-based denitrification as well as the accumulation of elemental sulfur in the 1st DHS, respectively. In the 2nd DHS, Nitrosococcus, Nitrobacter, and Sulfuritalea were considered as the contributors of nitrogen removal via nitrification and sulfur-based denitrification. Further, this study shows that a TSDHS reactor can achieve not only desulfurization of biogas in the 1st DHS but also a 3.5 %-15 % reduction of the ammonia load in the 2nd DHS by effective utilization of the ADS during sewage treatment, assuming that the ADS is returned to the ASP.

Efficient removal of dextran in sugar juice by immobilized α-dextranase from Chaetomium gracile

Dextran problem restricts the development of the sugar industry. Although the enzymatic treatment based on α-dextranase from Chaetomium gracile (α-dextranase (CG)) has been effective in solving this issue, the lack of immobilization products hinder its industrial applications. This research described a novel and suitable method to immobilize α-dextranase (CG). The purified α-dextranase (CG) was immobilized via cross-linking using modified chitosan as carriers. In addition, this study used a deep eutectic solvent that greatly improved the enzymatic properties of immobilized α-dextranase (CG). α-dextranase (CG) was immobilized by adding deep eutectic solvent (DES-IM-α-dextranase (CG)) showed better temperature tolerance and storage properties than free and ordinary immobilized counterparts. It can eliminate dextran by 59.71% in mixed sugarcane juice and 38.71% in clarified sugarcane juice. The achieved results were considerably better than those obtained using free and other immobilized enzymes. Altogether, these findings confirmed that DES-IM-α-dextranase (CG) displayed great potential in solving the dextran problem.

Production and characteristics of elemental sulfur during simultaneous nitrate and sulfide removal

The production and characteristics of elemental sulfur were examined during simultaneous sulfide and nitrate removal, with abiotic assays as control. The biotic assay showed good sulfide and nitrate removal, with the respective removal percentage of which were 90.67-96.88% and 100%. Nitrate reduction resulted in the production of nitrogen gas, while sulfate formed due to sulfide oxidation. The concentration of elemental sulfur in the effluent was greater than that in the sludge, which accounted for 73.70-86.28% of total elemental sulfur produced. Furthermore, the elemental sulfur of the effluent and sludge from the biotic assays was orthorhombic crystal S₈. Elemental sulfur was normally distributed in the effluent, but its average diameter increased with the increasing influent sulfide concentration (60-300 mg S/L), where the average diameter increased from 10 (60 mg S/L) to 29 μm (300 mg S/L).