Deciphering effects of humic acid in landfill leachate on the simultaneous nitrification, anammox and denitrification (SNAD) system from performance, electron transfer and microbial community

• Published in: The Science of the total environment Vol. 809; p. 151178
• Main Authors: Liu, Yinuo, Han, Yi, Zhang, Jianbing, Hou, Yanan, Song, Yuanyuan, Lu, Caicai, Li, Haibo, Guo, Jianbo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 25.02.2022
• Subjects: Anaerobic Ammonia Oxidation; Bioreactors; Denitrification; Electron transfer; Electrons; Humic acid; Humic Substances; Landfill leachate; Microbial community; Microbiota; Nitrification; Nitrogen; Oxidation-Reduction; SNAD; Water Pollutants, Chemical; SNAD; Electron transfer; Landfill leachate; Humic acid; Microbial community
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.151178

Simultaneous nitrification, anammox and denitrification (SNAD) system is effective for landfill leachate treatment. However, humic acid (HA) as both an organic pollutant and electron shuttle in landfill leachate, its effects on the SNAD system remain unknown. This study demonstrated that HA initially inhibited NH4+-N removal efficiency due to HA inhibition on anammox bacteria (the lowest fell to 90.89% from 100%), but the HA inhibition was released after adaption in the SNAD system. Hence, the mechanism of releasing HA inhibition in the SNAD system was established from performance, electron transfer and microbial community. Firstly, HA could be effectively removed by an adsorption-biodegradation process in the SNAD system, which avoided deteriorated performance caused by HA accumulation. Electrochemical analysis demonstrated that HA stimulated riboflavin and flavin mononucleotide (FMN) secretion to promote electron transfer efficiency. With the improved electron transfer efficiency, ETSA and ATP values significantly increased, indicating that HA enhanced the microbial metabolism activity of the SNAD system. Further analysis by enzymatic activity assay showed that the HAO (39.68 to 69.53 U/L), AMO (242.94 to 308.36 U/L), HZO (133.73 to 169.65 U/mL), NXR (24.63 to 54.52 U/L), NAR (94.40 to 114.36 U/L) and NIR (104.40 to 123.74 U/L) activities were improved with the HA increased from 0 to 200 mg/L, manifesting that HA enhanced nitrogen metabolism in the SNAD system. Besides, more reasonable metabolic division of labor in functional bacterial and enrichment of heterotrophic bacteria achieved efficient simultaneous removal of HA and nitrogen. Overall, efficient HA biodegradation, faster electron transfer efficiency and better metabolic division of microbial communities released HA inhibition, making the SNAD system more resistant to HA stress. This study shed light on the effects of HA on the SNAD system and provided a new insight for the SNAD system to landfill leachate treatment. [Display omitted] •Performance of the SNAD system temporarily declined due to humic acid inhibition.•Humic acid was removed in the SNAD system by an adsorption-biodegradation progress.•Humic acid promoted the electron transfer efficiency of the SNAD system.•Humic acid made better microbial communities metabolic division of the SNAD system.•Positive effects of humic acid on the SNAD system released humic acid inhibition.