posted on 2024-02-23, 17:06authored byYi-Lu Sun, Lin Zhu, Kun Zheng, Zhi-Min Qian, Hao-Yi Cheng, Xue-Ning Zhang, Ai-Jie Wang
Sulfur disproportionation (S0DP) poses a challenge
to
the robust application of sulfur autotrophic denitrification due to
unpredictable sulfide production, which risks the safety of downstream
ecosystems. This study explored the S0DP occurrence boundaries
with nitrate loading and temperature effects. The boundary values
increased with the increase in temperature, exhibiting below 0.15
and 0.53 kg-N/m3/d of nitrate loading at 20 and 30 °C,
respectively. A pilot-scale sulfur-siderite packed bioreactor (150
m3/d treatment capacity) was optimally designed with multiple
subunits to dynamically distribute the loading of sulfur-heterologous
electron acceptors. Operating two active and one standby subunit achieved
an effective denitrification rate of 0.31 kg-N/m3/d at
20 °C. For the standby subunit, involving oxygen by aeration
effectively transformed the facultative S0DP functional
community from S0DP metabolism to aerobic respiration,
but with enormous sulfur consumption resulting in ongoing sulfate
production of over 3000 mg/L. Meanwhile, acidification by the sulfur
oxidation process could reduce the pH to as low as 2.5, which evaluated
the Gibbs free energy (ΔG) of the S0DP reaction to +2.56 kJ, thermodynamically suppressing the S0DP occurrence. Therefore, a multisubunit design along with
S0DP inhibition strategies of short-term aeration and long-term
acidification is suggested for managing S0DP in various
practical sulfur-packed bioreactors.