Characterization of acetochlor degradation and role of microbial communities in biofilters with varied substrate types

Northeast China has a large area of cultivated land, and the application of various chemical herbicides is very high. As a high-efficiency herbicide widely used in dry fields, its residue in the environment is also concern. Therefore, low-cost and high efficient control measures are urgently needed. Twelve Biofilter simulation devices were designed to investigate the efficiency and mechanism of removing acetochlor under low-temperature conditions. Biochar (Bio-BF), ceramsite (CER-BF), and gravel (GRA-BF) were chosen to be substrates to compare the effect of substrate type on the removal of acetochlor. The results showed that the biochar (Bio-BF) treatment had the shortest onset time (<1 h), The gravel (GRA-BF) treatment had the longest onset of action (more than 8 h), but the removal effect was essentially the same as the biochar treatment. The 16S rRNA gene sequencing results revealed that different bacterial communities are formed due to different substrates. Proteobacteria and Actinobacteria are the dominant phyla in the three biofilters. Four metabolites, 2-ethyl-6-methyl-N-(ethoxymethyl) acetanilide, N-(2-ethyl-6-methyl phenyl) acetamide, N-(2-ethyl-6-methyl phenyl) formamide, and (2-ethyl-6-methyl phenyl) carbamic acid, were identified using gas phase mass spectrometry. The analysis and prediction of the degradation pathways of acetochlor revealed that Ferribacterium, Klebsiella, and Comamonadaceae belonging to the phylum Proteobacteria and Rhodococcus belonging to the phylum Actinobacteria were the key microorganisms involved in the degradation of acetochlor in the biofilter. Redundancy analysis (RDA) further indicates that dissolved oxygen and temperature are key environmental factors affecting the development of key microbial communities within the biofilter, and that future design of biofilters in Northeast China should focus on how to improve oxygen content and temperature.