Biological waste treatment technology is currently the world's largest application process, and its functional achievement mainly relies on complex microbial communities. However, the microbial system in such engineered ecosystems has been considered a "black box." Over the past decade, with the development of molecular biotechnology and next-generation sequencing technologies, the exploration of such "black boxes" has gradually deepened. In particular, the role of ecological forces in uncovering and regulating microbial communities has been largely recognized and has provided novel insights into the link between microbial communities and engineering objectives. However, the study of community ecology in engineered ecosystems is still in its early infancy and faces grand challenges in bridging engineering principles with microbial ecology theory. In this review, we discuss recent advances in the understanding of microbial community behavior in biological waste treatment systems, including biodiversity and its influencing factors, the role of neglected rare species, microbial interactions, and community assembly mechanisms. We emphasize the importance of these ecological perspectives in revealing and regulating microbial communities and functions, such as the enhancement of contaminant removal and operational stability in engineered ecosystems. In particular, cross-validation of the microbial community analysis results is necessary to yield valid real information to guide the improvement and stability of engineering ecosystem performance. Multi-omics approaches and synthetic community biology are preferred ways to link ecological theory and engineering objectives.

Stochastic and deterministic processes are the major themes governing microbial community assembly; however, their roles in bioreactors are poorly understood. Herein, the mechanisms underlying microbial assembly and the effect of rare taxa were studied in biofilters. Phylogenetic tree analysis revealed differences in microbial communities at various stages. Null model analysis showed that stochastic processes shaped the community assembly, and deterministic processes emerged only in the inoculated activated sludge after domestication. This finding indicates the dominant role of stochastic factors (biofilm formation, accumulation, and aging). The Sloan neutral model corroborated the advantages of stochastic processes and mainly attributed these advantages to rare taxa. Cooccurrence networks revealed the importance of rare taxa, which accounted for more than 85% of the keystones. Overall, these results provide good foundations for understanding community assembly, especially the role of rare taxa, and offer theoretical support for future community design and reactor regulation.

Quorum sensing is widespread in the microbial world; however, the role of this population behavior at low temperatures (<15 degrees C) remains poorly understood. Here, the effects of quorum sensing in wastewater treatment processes at low temperatures are revealed using both microcosm experiments and global surveys. Quorum- sensing bacteria act as pioneers to facilitate microorganism migration from the species pool to the carrier surface during biofilm colonization at 15 degrees C. A high biofilm formation rate is accompanied by significant enrichment of quorum-sensing bacteria and upregulation of gene expression. By analyzing the global activated sludge microbiome data, we find that quorum-sensing bacteria exhibit a typical temperature-dependent distribution pattern. The performance of the process is strongly linked to the content of quorum-sensing bacteria. Our findings elucidate a potential response mechanism of the microbial community to environmental stress and provide implications for the enhancement of the wastewater biotreatment process at low temperatures.

Biofilms are widespread in natural and engineering environments and are being increasingly used for pollutant treatment. However, low temperature is one of the major challenges in practice. Here, we developed an alternative strategy to enhance biofilm formation and biofilter startup at 15 degrees C by supplementing with spermidine, an essential substance for cell growth. A significantly increased biofilm biomass was observed in the treatment group (with spermidine), accompanied by a higher live cell ratio and biofilm matrix excretion as compared with the control (without spermidine). The bacterial communication ability, including quorum sensing and the second messenger system, was found to be enhanced in the treatment group. The bacterial secretion system and quorum sensing pathway were also significantly enriched in differential genes, and most of these genes were up-regulated in the treatment group. Robustness and null model analysis revealed that spermidine bolstered microbial community stability and mitigated the dispersal limitation process, which would be conducive to biofilm development. The application of spermidine in biofilters enhanced the biomass accumulation rate and performance. Overall, our results highlighted the importance of the microbial community on biofilm formation regulation and provided a feasible strategy for the enhancement of biofilm formation in low-temperature environments.

Starvation disturbance due to nutrient limitation is a common problem in bioreactors. However, an understanding of how microbial systems respond to starvation remains in its infancy. Here the metabolic response mechanism of a biofilm community to starvation was investigated using a well-controlled gaseous toluene treatment biofilter through interruption of its operation. It was found that metabolic characteristics showed significant differences before and after starvation. The dominant carbon source utilization type shifted from amino acids and carboxylic acids to esters and carbohydrates after starvation, which is more conducive to improving energy production. Metagenomic sequencing analysis supported that the changes in the dominant metabolic substrate, enhanced metabolic stability, and flexibility in the mode of energy metabolism could be the main ways to guarantee functional resilience in ecosystems after starvation. The results highlight the microbial metabolic response to starvation, which would be beneficial to the understanding of functional resilience and bioreactor stability.

ABSTRACT Microbial community adaptability to pH stress plays a crucial role in biofilm formation. This study aims to investigate the regulatory mechanisms of exogenous putrescine on pH stress, as well as enhance understanding and application for the technical measures and molecular mechanisms of biofilm regulation. Findings demonstrated that exogenous putrescine acted as a switch-like distributor affecting microorganism pH stress, thus promoting biofilm formation under acid conditions while inhibiting it under alkaline conditions. As pH decreases, the protonation degree of putrescine increases, making putrescine more readily adsorbed. Protonated exogenous putrescine could increase cell membrane permeability, facilitating its entry into the cell. Subsequently, putrescine consumed intracellular H + by enhancing the glutamate-based acid resistance strategy and the γ-aminobutyric acid metabolic pathway to reduce acid stress on cells. Furthermore, putrescine stimulated ATPase expression, allowing for better utilization of energy in H + transmembrane transport and enhancing oxidative phosphorylation activity. However, putrescine protonation was limited under alkaline conditions, and the intracellular H + consumption further exacerbated alkali stress and inhibits cellular metabolic activity. Exogenous putrescine promoted the proportion of fungi and acidophilic bacteria under acidic stress and alkaliphilic bacteria under alkali stress while having a limited impact on fungi in alkaline biofilms. Increasing Bdellovibrio under alkali conditions with putrescine further aggravated the biofilm decomposition. This research shed light on the unclear relationship between exogenous putrescine, environmental pH, and pH stress adaptability of biofilm. By judiciously employing putrescine, biofilm formation could be controlled to meet the needs of engineering applications with different characteristics. IMPORTANCE The objective of this study is to unravel the regulatory mechanism by which exogenous putrescine influences biofilm pH stress adaptability and understand the role of environmental pH in this intricate process. Our findings revealed that exogenous putrescine functioned as a switch-like distributor affecting the pH stress adaptability of biofilm-based activated sludge, which promoted energy utilization for growth and reproduction processes under acidic conditions while limiting biofilm development to conserve energy under alkaline conditions. This study not only clarified the previously ambiguous relationship between exogenous putrescine, environmental pH, and biofilm pH stress adaptability but also offered fresh insights into enhancing biofilm stability within extreme environments. Through the modulation of energy utilization, exerting control over biofilm growth and achieving more effective engineering goals could be possible.

Biofilters inoculated with activated sludge are widely used for odor control in WWTP. In this process, biofilm community evolution plays an important role in the function of reactor and is closely related to reactor per-formance. However, the trade-offs in biofilm community and bioreactor function during the operation are still unclear. Herein, an artificially constructed biofilter for odorous gas treatment was operated for 105 days to study the trade-offs in the biofilm community and function. Biofilm colonization was found to drive community evolution during the start-up phase (phase 1, days 0-25). Although the removal efficiency of the biofilter was unsatisfactory at this phase, the microbial genera related to quorum sensing and extracellular polymeric sub-stance secretion led to the rapid accumulation of the biofilm (2.3 kg biomass/m3 filter bed /day). During the stable operation phase (phase 2, days 26-80), genera related to target-pollutant degradation showed increases in relative abundance, which accompanied a high removal efficiency and a stable accumulation of biofilm (1.1 kg biomass/m3 filter bed/day). At the clogging phase (phase 3, days 81-105), a sharp decline in the biofilm accumulation rate (0.5 kg biomass/m3 filter bed /day) and fluctuating removal efficiency were observed. The quorum quenching-related genera and quenching genes of signal molecules increased, and competition for re-sources among species drove the evolution of the community in this phase. The results of this study highlight the trade-offs in biofilm community and functions during the operation of bioreactors, which could help improve bioreactor performance from a biofilm community perspective.

城市异味扰民的问题是目前城市环境信访投诉的主要原因之一,是不可忽视的民生问题.系统梳理了城市异味污染的主要来源,分析了城市异味污染扰民现状及其社会影响,总结了城市异味污染的主要特征,阐明了造成城市异味扰民的主要成因与挑战,并对异味污染控制提出了相应的对策建议,最后结合具体案例介绍了城市异味扰民的解决方案.

Controlling excess biomass accumulation and clogging is important for maintaining the performance of gas biofilters and reducing energy consumption. Interruption of bacterial communication (quorum quenching) can modulate gene expression and alter biofilm properties. However, whether the problem of excess biomass accumulation in gas biofilters can be addressed by interrupting bacterial communication remains unknown. In this study, parallel laboratory-scale gas biofilters were operated with Rhodococcus sp. BH4 (QQBF) and without Rhodococcus sp. BH4 (BF) to explore the effects of quorum quenching (QQ) bacteria on biomass accumulation and clogging. QQBF showed lower biomass accumulation (109 kg/m3) and superior operational stability (85–96%) than BF (170 kg/m3; 63–92%) at the end of the operation. Compared to BF, the QQBF biofilm had lower adhesion strength and decreased extracellular polymeric substance production, leading to easier detachment of biomass from filler surface into the leachate. Meanwhile, the relative abundance of quorum sensing (QS)-related species was found to decrease from 67 (BF) to 56% (QQBF). The QS function genes were also found a lower relative abundance in QQBF, compared with BF. Moreover, although both biofilters presented aromatic compounds removal performance, the keystone species in QQBF played an important role in maintaining biofilm stability, while the keystone species in BF exhibited great potential for biofilm formation. Finally, the possible influencing mechanism of Rhodococcus sp. BH4 on biofilm adhesion was demonstrated. Overall, the results of this study achieved excess biomass control while maintaining stable biofiltration performance (without interrupting operation) and greatly promoted the use of QQ technology in bioreactors.

大庆油田是我国第一大油田,自1959年开采后已有50多年的发展历史,到2020年原油年产量已稳定到3000万吨左右.石油开采过程伴随大量含油污泥的产生,含油污泥属于危险废物,需要寻求安全清洁的处置方式.热解技术在实现无害减量的同时可实现油品资源的高效回收.本文对大庆油田不同来源含油污泥热解特性进行分析,为含油污泥处理方案选择提供理论依据.首先通过热重-红外-质谱(TG-FTIR-MS)联用测试了多源油泥样品的热解特性以及气体产物释放规律;然后采用固定床热解炉在600℃的终温下对多源含油污泥样品进行热解试验,得到三相产率;借助色谱-质谱联用(GCMS)、X射线衍射(XRD)和红外光谱(FTIR)测试对油相产物和固相产物进行详细分析.结果表明热解油以中低链烷烃为主,烯烃和醇含量相对较低,热解渣中主要以SiO2和CaCO3为主.