Wastewater

Bacteria

Biology

Pyrolysis

Denitrification

Nitrogen

Heterotroph

Genetics

Biochar

Environmental engineering

Organic chemistry

Nitrous-oxide reductase

Environmental chemistry

Nitrite reductase

Environmental science

Nitrite

Denitrifying bacteria

Chemistry

Nitrate reductase

Aerobic denitrification

Nitrate

Bioresource Technology

Biochar is widely used in water treatment because of its porous structure, however, the effects of biochars on denitrification remain unclear. Here, we combined molecular biological and electrochemical techniques to investigate effects of biochars (formed at 300 °C, 500 °C and 800 °C) on denitrification. Results showed that biochar at 300 °C increased total nitrogen removal by 415% and decreased N2O accumulation by 78%. Mechanistic research demonstrated that it achieved the highest electron transfer efficiency and denitrifying enzyme activities. Further study evidenced that biochar at 300 °C increased the abundance of denitrifiers such as Pseudomonas. Correlation analysis indicated that nitrate reductase and nitrite reductase activities were the key factors influenced by biochar during denitrification. Overall, this study suggested that biochar at 300 °C could act as the bio-engineer of electron shuttle and the stimulator of denitrification, achieving high rate nitrogen removal and significant reduction of N2O accumulation from high-strength wastewater.

Highly efficient nitrate removal in a heterotrophic denitrification system amended with redox-active biochar: A molecular and electrochemical mechanism