Improved sulfur autotrophic denitrification using supplementary bovine serum albumin

Excess nitrate presented in natural water body and drinking water has been a challenge for maintaining safe ecosystem and human health. Sulfur autotrophic denitrification is proved a feasible technology to remove nitrate from water environment. However, comparatively low rate of sulfur autotrophic denitrification needs to be addressed before wide application of this technology, which is a result of the low solubility of elemental sulfur. Therefore, this study employed bovine serum albumin (BSA) as a supplementary material to modify the elemental sulfur for improved sulfur autotrophic denitrification rate. Artificial biofilm of Thiobacillus denitrificans was prepared and employed in experiments. By testing different amount of BSA applied in both elemental sulfur and the biofilm, including 1 %, 2 % and 4 % mass ratios, it was found that larger employment of BSA had significant effect in increasing the denitrification rate. Particularly when 4 % BSA was added into elemental sulfur, the highest denitrification rate reached 26.8 mg-N/(L·d), 3.7 times of the control group. Meanwhile, the largest reaction rate constant was achieved, 4.13 mg^0.5/(L^0.5·d), 2.78 times of the control group. This effect was attributed to promoted conversion of elemental sulfur to polysulfide that was easily utilized by sulfur-oxidizing bacteria. A long-term operation (14 days) of packed bed reactor filled with sulfur particles and 1 % BSA delivered a much faster start-up than the control and outperformed it with better denitrification performance all-through the experiment. This result evidenced again that BSA could make a highly effective supplement in sulfur autotrophic denitrification.