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

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 (NH4+-N) and nitrite nitrogen (NO2−-N) in the effluent by 1.63 and 4.85-fold, respectively, and increased considerably nitrate nitrogen (NO3−-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.

Insights into the influences of biochar on the fate and transport of pesticides in the soil environment: a critical review

“…Typically, the large surface area of biochar promotes an adsorptive activity. Several scanning electron microscopy studies have confirmed that biochar adsorbs contaminants on its surface area (Cederlund et al 2016;Bai et al 2023).…”