Heterogeneity of Counter-Diffusional Biofilm Achieved Simultaneous Organic-Fermentation and Nitrogen-Removal of Nitrophenol by Microaeration: Metabolic Pathways and Microbial Ecological Mechanisms

Abstract

Counter-diffusional biofilm driven by hydrophobic membrane offers opportunities for sustainable environmental remediation. However, how the heterogeneity of counter-diffusional biofilms affects internal redox function, bacterial ecology and metabolic metabolism remains unknown. Addressing this, we herein report a counter-diffusional biofilm coupled with microaeration hydrolysis-acidification system for 2,4-dinitrophenol (2,4-DNP) degradation to explore the role of heterogeneity and reveal the metabolic mechanisms. We achieve a novel 2,4-dinitrophenol (2,4-DNP) degradation pathway with simultaneous organic-fermentation and nitrogen-removal by affiliating counter-diffusional biofilm for enhancing hydrolysis acidification, resulting in 99.54 ± 0.03% removal over 20% higher than the conventional biotreatment processes. The enhanced pathways were nitroreduction, deamination, carboxylation, cleavage, and fermentation, as well as simultaneous nitrification and denitrification. Such an enhancement effect is largely dependent on a more hospitable redox microenvironment with a dissolved oxygen (DO) gradient of 0–0.4 mg/L along cross heterogeneity of counter-diffusional biofilm. Furthermore, reduction-related, nitrogen removal-related, fermentative, and oxidation-related bacteria were dominantly distributed in the outer, middle, and inner layers of the biofilm, respectively, exhibiting redox biostructural stratification along with biofilm depth. Ultimately, a synergistic metabolism between carbon and nitrogen through energy metabolism and electron transfer within the biofilm was revealed, thus generating a synergistic interaction between the functional bacteria at cross heterogeneous stratifications. This study offers novel insights into the role of heterogeneity in biofilm systems, expanding the fundamental understanding of biofilm heterogeneity and microbial interactions and facilitating the application of the counter-diffusional biofilm process for wastewater treatment.

Keywords: Counter-diffusional biofilm, heterogeneity, hydrolysis acidification, bacterial ecology, synergistic mechanisms