Simultaneous bio-reduction of nitrate and Cr(VI) by mechanical milling activated corn straw

Abundant lignocellulose waste is an ideal energy source for environmental bioremediation, but its recalcitrance to bioavailability makes this a challenging prospect. We hypothesized that the disruption of straw's recalcitrant structure by mechanochemical ball milling would enhance its availability for the simultaneous bioreduction of nitrate and Cr(VI). The results showed that the ball-milling process increased the quantity of water-soluble organic matter released from corn straw and changed the composition of organic matter by strongly disrupting its lignocellulose structure. The increase in ball-milling time increased the specific surface area of the straw and favored the adhesion of microorganisms on the straw surface, which enhanced the bioavailability of the energy in the straw. Substantially increased removal of NO3--N (206.47 +/- 0.67 mg/g) and Cr(VI) (37.62 +/- 0.09 mg/g) was achieved by using straw that was ball milled for 240 min, which validated that ball milling can improve the utilization efficiency of straw by microorganisms. Cellular and molecular biological analyses showed that ball-milled straw increased microbial energy metabolism and cellular activity related to the electron transport chain. This work offers a potential way to achieve the win-win goal of utilizing agricultural wastes and remediating environmental pollution.

Automated summary

In this study, ball milling was used to disrupt the structure of straw, enhancing its availability for the simultaneous bioreduction of nitrate and Cr(VI). The ball milling process changed the composition of organic matter in the straw and increased the release of water-soluble organic matter. Increasing the ball milling time increased the surface area of the straw, promoting microbial adhesion and improving the bioavailability of the energy in the straw.