Biochar Amendment in Vermi-Wetland for Enhancing Nitrification during Excess Sludge Recycling

Ting Bai, Gratien Twagirayezu, Zhen Wang, Hui Xia (), Chunlei Sang, Kui Huang and Hongguang Cheng
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Ting Bai: Gansu Research Institute of Chemical Industry Co., Ltd., Lanzhou 730070, China
Gratien Twagirayezu: School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
Zhen Wang: Gansu Research Institute of Chemical Industry Co., Ltd., Lanzhou 730070, China
Hui Xia: School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
Chunlei Sang: School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
Kui Huang: School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
Hongguang Cheng: State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

Sustainability, 2023, vol. 15, issue 24, 1-13

Abstract: Vermi-wetland is a sustainable technology for recycling excess sludge in small-town areas. Although biochar (BC) amendment into the vermi-wetland could considerably boost the effectiveness of treating sludge, its impact on the nitrogen transformation in vermi-wetland remains unclear. Hence, this study aimed to explore the mechanism and performance of BC amendment into the vermi-wetland for enhancing nitrogen transformation during excess sludge recycling. The semi-aquatic plant Acorus calamus and the earthworm Eisenia fetida were planted in the designed vertical vermi-reactor, with corncob BC added to the upper and lower layers of one vermi-reactor, in comparison with the vermi-reactor without BC. The vermi-reactor with BC significantly lowered ( p < 0.05) ammonia nitrogen (NH 4 + -N) and nitrite nitrogen (NO 2 − -N) in the effluent by 1.63 and 4.85-fold, respectively, and increased considerably nitrate nitrogen (NO 3 − -N) in the effluent by 1.5-fold. The numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA) in the vermi-reactor with BC were greatly enriched by 6 and 1.42-fold, compared with their counterparts ( p < 0.05). Moreover, nirS and nirK gene copies in the vermi-reactor with BC were considerably improved ( p < 0.05) by 2.03 and 1.82-fold, respectively. BC significantly enhanced the growth of earthworms by 6.92-fold and promoted plant growth by 1.28-fold. In addition, the AOB members like Nitrosomonas and Nitrosospira and the AOA members like Crenarchaeota and Thaumarchaeota cohabited in BC. Overall, these results suggest that a vermi-reactor amended with BC could enhance the nitrification processes of excess sludge, thereby improving the treatment performance of vermi-wetland.

Keywords: ammonia oxidation; biochar; earthworms; vermicomposting; sludge treatment; wetland plant (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2023
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