Key Laboratory of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, PR China.
State Key Laboratory of Urban Water Resource and Environment, School of Environment, Harbin Institute of Technology, Harbin 150090, PR China; State Key Laboratory of Urban Water Resources and Environment, School of Civil and Environmental Engineering, Harbin Institute of Technology Shenzhen, Shenzhen 518055, PR China.
Water Res. 2023 Sep 1;243:120356. doi: 10.1016/j.watres.2023.120356. Epub 2023 Jul 14.
Elemental sulfur packed-bed (SPB) bioreactors for autotrophic denitrification have gained more attention in wastewater treatment due to their organic carbon-free operation, low operating cost, and minimal carbon emissions. However, the rapid development of microbial S-disproportionation (MSD) in SPB reactor during deep denitrification poses a significant drawback to this new technology. MSD, the process in which sulfur is used as both an electron donor and acceptor by bacteria, plays a crucial role in the microbial-driven sulfur cycle but remains poorly understood in wastewater treatment setups. In this study, we induced MSD in a pilot-scale SPB reactor capable of denitrifying over 1000 m/d nitrate-containing wastewater. Initially, the SPB reactor stably removed 6.6 mg-NO-N/L nitrate at an empty bed contact time (EBCT) of 20 mins, which was designated the S-denitrification stage. To induce MSD, we reduced the influent nitrate concentrations to allow deep nitrate removal, resulted in the production of large quantities of sulfate and sulfide (SO:S 3.2 w/w). Meanwhile, other sulfur-heterologous electron acceptors (SHEAs), e.g., nitrite and DO, were also kept at trace levels. The negative correlations between the SHEAs concentrations and the sulfide productions indicated that the absence of SHEAs was a primary inducing factor to MSD. The microbial community drastically diverged in response to the depletion of SHEAs during the switch from S-denitrification to S-disproportionation. An evident enrichment of sulfur-disproportionating bacteria (SDBs) was found at the S-disproportionation stage, accompanied by the decline of sulfur-oxidizing bacteria (SOBs). In the end, we discovered that shortening the EBCT and increasing the reflux ratio could inhibit sulfide production by reducing it from 43.9 mg/L to 3.2 mg/L or 25.5 mg/L. In conclusion, our study highlights the importance of considering MSD when designing and optimizing SPB reactors for sustainable autotrophic sulfur denitrification in real-life applications.
元素硫填充床（SPB）生物反应器因其无有机碳操作、运行成本低和最小碳排放等优点，在废水处理中越来越受到关注。然而，在深度脱氮过程中，SPB 反应器中微生物硫歧化（MSD）的快速发展对这项新技术构成了重大挑战。MSD 是指细菌同时将硫作为电子供体和受体的过程，在微生物驱动的硫循环中起着关键作用，但在废水处理装置中仍了解甚少。在这项研究中，我们在一个能够处理超过 1000 m/d 硝酸盐含量废水的中试规模 SPB 反应器中诱导了 MSD。最初，SPB 反应器在空床接触时间（EBCT）为 20 分钟的情况下稳定地去除了 6.6 mg-NO-N/L 的硝酸盐，这被指定为 S 反硝化阶段。为了诱导 MSD，我们降低了进水硝酸盐浓度以实现深度硝酸盐去除，导致大量硫酸盐和硫化物（SO:S 为 3.2 w/w）的产生。同时，其他硫异源电子受体（SHEAs），如亚硝酸盐和 DO，也保持在痕量水平。SHEAs 浓度与硫化物产量之间的负相关表明，SHEAs 的缺乏是诱导 MSD 的主要因素。当从 S 反硝化切换到 S 歧化时，由于 SHEAs 的消耗，微生物群落发生了剧烈的变化。在 S 歧化阶段，发现硫歧化细菌（SDB）明显富集，同时硫氧化细菌（SOB）减少。最后，我们发现通过缩短 EBCT 和增加回流比可以抑制硫化物的产生，将其从 43.9 mg/L 降低到 3.2 mg/L 或 25.5 mg/L。总之，我们的研究强调了在设计和优化 SPB 反应器时考虑 MSD 的重要性，以便在实际应用中实现可持续的自养硫脱氮。
