An Algal-Bacteria Symbiosis Rapidly Developed in a Phototrophic-Biotrickling Filter: Dual Purification-Carbon Fixation Performance Evaluation and Symbiotic Mechanism Analysis

Abstract

Conventional biological treatment of ester-type volatile organic compounds (VOCs) is challenged by low mineralization rates or uncontrolled CO2 emissions when high mineralization occurs. In this study, an algal-bacterial symbiosis (ABS) system with a high carbon fixation rate and bidirectional interaction was successfully established in a phototrophic-biotrickling filter (PBTF), enabling low-carbon treatment of VOCs. Metabolic reconstruction based on metagenomic and metatranscriptomic analyses suggested that endogenous indole-3-acetic acid (IAA) may contribute to synergistic interactions between microalgae and bacteria. The concentration of endogenous IAA reached 446.16 ± 40.03 mg/m3 (packing material), with the expression of IAA-related genes exhibiting a 3.23-fold increase; this resulted in highly active cross-kingdom signal transduction between microalgae and bacteria. Consequently, the biosynthesis of extracellular polymeric substances (EPSs) increased to 973.52 ± 277.36 mg/m3 (packing material), leading to the formation of a dense EPS-derived physical barrier that protected ABS from n-butyl acetate-induced toxicity. Additionally, the presence of microalgae increased the abundance of phototrophic bacteria (e.g., Leptolyngbya) and the expression of associated carbon-related genes (rbcL/S) by 2.54-fold. As a result, the synergistic ABS mode ensured efficient n-butyl acetate removal (99.43 ± 0.50%) and CO2 fixation (705.33 ± 17.70 g/(m3 packing material·d), thus maintaining the stability of the PBTF. Overall, the dual-enhancement system of ABS in a PBTF presents an effective low-carbon VOC removal strategy, paving the way for broader, stable applications of this system in the treatment of ester-type VOCs.