Microbial ecology dynamics of a partial nitritation bioreactor with Polar Arctic Circle activated sludge operating at low temperature

Enhancement of the reactivation process of long-term starved anammox granular sludge with gravel balls: Microbial succession and metabolic impact

Anaerobic ammonium oxidation (Anammox) process is an economical and energy-efficient method of wastewater nitrogen removal. However, they are highly susceptible to starvation stress caused by sudden environmental changes. Rapid reactivation of starved anammox sludge is a crucial method to address seed sludge shortages and expand practical applications. This study investigated the impact of gravel balls on the reactivation of long-term starved anammox granular sludge (628 days). The results showed that gravel balls enhanced the recovery of nitrogen removal performance in starved anammox sludge, with nitrogen removal efficiency being 19.88% higher than the control group at the end of the recovery phase. The gravel balls also increased extracellular polymeric substance (EPS) secretion, contributing to the stability of the anammox system. Furthermore, the gravel balls promoted the proliferation of anammox bacteria, with the relative abundance of anammox bacteria reaching 38.25% on the 80th day. The analyses of microbial functions indicated that gravel balls facilitated cross-feeding and co-metabolism among microbes, while enhancing quorum sensing associated with anammox bacteria, forming a multifunctional community network centered on anammox bacteria. This indicates that gravel balls can effectively accelerate the reactivation process of long-term starved anammox sludge, aiding the reutilization of long-term starved anammox sludge.

Key microbial taxa play essential roles in maintaining soil muti-nutrient cycling following an extreme drought event in ecological buffer zones along the Yangtze River

Climatic extremes, especially extreme droughts, are occurring more frequently and profoundly impacting biogeochemical processes. However, the relative importance of microbial communities on soil nutrient cycling and community maintenance under natural extreme drought events remains elusive. During a record-breaking drought in the Yangtze River Basin (YRB) in the summer of 2022, we collected ambient soils and drought-affected bare and vegetated soils in ecological buffer zones from two sites with similar soil and vegetation characteristics along the YRB, and examined the relative contribution of soil bacterial communities in supporting multi-nutrient cycling index (MNCI) involving carbon-, nitrate- and phosphorus-cycling and their associations with microbial network. Extreme drought decreased (p < 0.05) bacterial α-diversity but increased MNCI in vegetated soils at both sites, while both remained unchanged (p > 0.05) in bare soils, possibly as a result of vegetation releasing rhizodeposits under drought which selectively recruited bacterial communities. Bacterial community compositions were shifted (p < 0.05) only in vegetated soils, and they exerted more influence than α-diversity on soil MNCI. Notably, the Anaerolineae, identified as a biomarker enriched in vegetated soils, had close associations with enzyme activities and soil MNCI at both sites, suggesting their potential recruitment by vegetation to withstand drought. Furthermore, key ecological clusters (Module 1) in bacterial co-occurrence networks at both sites supported (p < 0.05) higher MNCI, despite no substantial variation in network structure due to drought. Specifically, the most important taxa within Module 1 for predicting soil MNCI revealed by random forest modeling analysis (R2 = 0.44 - 0.63, p < 0.001), such as B1-7BS, SBR1031 and Nocardioides, could be deeply involved in soil nitrogen-cycling, suggesting an essential role of specialized interactions of bacterial communities in maintaining soil multifunctionality. Overall, this study demonstrates that changes in biomarkers and functional taxa under extreme drought may better reflect the biological mechanisms involved in microbial communities impacting ecosystem function, which may aid in forecasting the ecological consequences of ongoing climate change in the ecological buffer zones along the YRB.

Optimizing carbon sources regulation in the biochemical treatment systems for coal chemical wastewater: Aromatic compounds biodegradation and microbial response strategies

The complex composition of coal chemical wastewater (CCW), marked by numerous highly toxic aromatic compounds, induces the destabilization of the biochemical treatment system, leading to suboptimal treatment efficacy. In this study, a biochemical treatment system was established to efficiently degrade aromatic compounds by quantitatively regulating the dosage of co-metabolized substrates (specifically, the chemical oxygen demand (COD) Glucose: COD Sodium acetate = 3:1, 1:3, and 1:1). The findings demonstrated that the system achieved optimal performance under the condition that the ratio of COD Glucose to COD Sodium acetate was 3:1. When the co-metabolized substrate was added to the system at an optimal ratio, examination of pollutant removal and cumulative effects revealed that the removal efficiencies for COD and total organic carbon (TOC) reached 94.61 % and 86.40 %, respectively. The removal rates of benzene series, nitrogen heterocyclic compounds, polycyclic aromatic hydrocarbons, and phenols were 100 %, 100 %, 63.58 %, and 94.12 %, respectively. Research on the physiological response of microbial cells showed that, under optimal ratio regulation, co-metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, the contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) for proteins in the optimal group were 7.12 mg/g-SS and 152.28 mg/g-SS, respectively. Meanwhile, the ratio of α-Helix / (β-Sheet + Random coil) and the proportion of intermolecular interaction forces were also increased in the optimal group. At system completion, the ratio of α-Helix / (β-Sheet + Random coil) reached 0.717 (LB-EPS) and 0.618 (TB-EPS), respectively. Additionally, the proportion of intermolecular interaction forces reached 74.83 % (LB-EPS) and 55.03 % (TB-EPS). An in-depth analysis of the metabolic regulation of microorganisms indicated that the introduction of optimal ratios of co-metabolic substrates contributed to a noteworthy upregulation in the expression of Catechol 2,3-dioxygenase (C23O) and Dehydrogenase (DHA). The expression levels of C23O and DHA were measured at 0.029 U/mg Pro·g MLSS and 75.25 mg TF·(g MLSS·h)-1 (peak value), respectively. Correspondingly, enrichment of aromatic compound-degrading bacteria, including Thauera, Saccharimonadales, and Candidatus_Competibacter, occurred, along with the upregulation of associated functional genes such as Catechol 1,2-dioxygenase, Catechol 2,3-dioxygenase, Protocatechuate 3,4-dioxygenase, and Protocatechuate 4,5-dioxygenase. Considering the intricate system of multiple coexisting aromatic compounds in real CCW, this study not only obtained an optimal ratio for carbon source addition but also enhanced the efficient utilization of carbon sources and improved the capability of the system to effectively degrade aromatic compounds. Additionally, this paper established a theoretical foundation for metabolic regulation and harmless treatment within the biochemical treatment of intricate systems, exemplified by real CCW.

Robust rehabilitation of anammox system by granular activated carbon under long-term starvation stress: Microbiota restoration and metabolic reinforcement

This article investigates the buffering capacity and recovery-enhancing ability of granular activated carbon (GAC) in a starved (influent total nitrogen: 20 mg/L) anaerobic ammonium oxidation (anammox) reactor. The findings revealed that anammox aggregated and sustained basal metabolism with shorter performance recovery lag (6 days) and better nitrogen removal efficiency (84.9 %) due to weak electron-repulsion and abundance redox-active groups on GAC's surface. GAC-supported enhanced extracellular polymeric substance secretion aided anammox in resisting starvation. GAC also facilitated anammox bacterial proliferation and expedited the restoration of anammox microbial community from a starved state to its initial-level. Metabolic function analyses unveiled that GAC improved the expression of genes involved in amino acid metabolism and sugar-nucleotide biosynthesis while promoted microbial cross-feeding, ultimately indicating the superior potential of GAC in stimulating more diverse metabolic networks in nutrient-depleted anammox consortia. This research sheds light on the microbial and metabolic mechanisms underlying GAC-mediated anammox system in low-substrate habitats.

Mitigating the inhibition of antibacterial agent chloroxylenol on nitrification system-The role of Rhodococcus ruber in a bioaugmentation system

The chloroxylenol (PCMX) degrading strain was successfully isolated from sludge and identified as Rhodococcus ruber (R. ruber). Afterwards, a bioaugmentation system was constructed by seeding R. ruber into nitrifying sludge to fasten degradation efficiency of highly toxic PCMX from wastewater. Results showed that R. ruber presented high PCMX-degrading performance under aerobic conditions, 25 °C, pH 7.0 and inoculum sizes of 4% (v/v). These optimized conditions were used in subsequent bioaugmentation experiment. In bioaugmentation system, R. ruber could detoxify nitrifiers by degrading PCMX, and the content of polysaccharide in extracellular polymeric substances increased. The quantitative polymerase chain reaction results exhibited that the absolute abundance of 16S rRNA gene and ammonia oxidizing bacteria (AOB) slightly elevated in bioaugmentation system. After analyzing the results of high-throughput sequencing, it was found that the loaded R. ruber can colonize successfully and turn into dominant strains in sludge system. Molecular docking simulation showed that PCMX had a weaker suppressed effect on AOB than nitrite oxidizing bacteria, and R. ruber can alleviate the adverse effect. This study could provide a novel strategy for potential application in reinforcement of PCMX removal in wastewater treatment.

Simultaneous nitrification, denitrification and phosphorus removal: What have we done so far and how do we need to do in the future?

Nitrogen and phosphorus contamination in wastewater is a serious environmental concern and poses a global threat to sustainable development. In this paper, a comprehensive review of the studies on simultaneous nitrogen and phosphorus removal (SNPR) during 1986-2022 (538 publications) was conducted using bibliometrics, which showed that simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) is the most promising process. To better understand SNDPR, the dissolved oxygen, carbon to nitrogen ratio, carbon source type, sludge retention time, Cu²⁺ and Fe³⁺, pH, salinity, electron acceptor type of denitrifying phosphorus-accumulating organisms (DPAOs), temperature, and other influencing factors were analyzed. Currently, SNDPR has been successfully implemented in activated sludge systems, aerobic granular sludge systems, biofilm systems, and constructed wetlands; sequential batch mode of operation is a common means to achieve this process. SNDPR exhibits a significant potential for phosphorus recovery. Future research needs to focus on: (1) balancing the competitiveness between denitrifying glycogen-accumulating organisms (DGAOs) and DPAOs, and countermeasures to deal with the effects of adverse conditions on SNDPR performance; (2) achieving SNDPR in continuous flow operation; and (3) maximizing the recovery of P during SNDPR to achieve resource sustainability. Overall, this study provides systematic and valuable information for deeper insights into SNDPR, which can help in further research.

Impact and microbial mechanism of continuous nanoplastics exposure on the urban wastewater treatment process

Contamination by nanoplastics in urban water has aroused increasing concern. The impact of nanoplastic exposure on the wastewater treatment process in the long term is still unclear. This study investigated the effect of continuous nanoplastic exposure (R1:0, R2:10, R3:100, and R4:1000 μg/L) on the nitrification and denitrification processes for over 200 days in a sequencing batch reactor (SBR). The results revealed that nanoplastic exposure does not demonstrate significant inhibition of total nitrogen removal. The ammonia oxidation rate (19.24 ± 0.01 mgN/gMLVSS/h, p < 0.05) and denitrification rate (11.78 ± 0.11 mgN/ gMLVSS/h, p < 0.05) in R4 was significantly lower than the control (R1: 0 μg/L). The maximal reaction velocities of N₂O reduction (Vmax) were improved after long-term exposure to nanoplastics in high concentrations. The R3 demonstrated the highest Vmax value-six times higher than R4 and approximately 20 times higher than R1 and R2. The microbial structure largely varied with the exposure to nanoplastics, where the exposure to a high concentration largely suppressed the nitrifier and selectively enriched the denitrifier. The percentage of the top 20 genera of denitrifiers increased from 31.76% to 63.42%, and the nitrifiers decreased from an initial 12.40% to 2.83% for R4. The predominant genera were found to be Thauera, Azoarcus, and Defluviicoccus in R4 and R3 which indicated their tolerance to nanoplastics. The function prediction results indicated that the membrane transport function was significantly enhanced and the lipid metabolism function was significantly reduced in R4 as compared with the control (R1, p<0.05). This may be attributed to the adsorption of nanoplastics on bacteria. Observation under a scan electronic microscope demonstrated that the nanoplastics were firmly attached to the microbe surface and aggregated in activated sludge at high nanoplastics dosed reactor. These results deepen the understanding of the effect of nanoplastics on the urban wastewater treatment process and provide valuable information for the management of nanoplastic contamination in urban wastewater.

Achieving simultaneous nitrification, denitrification, and phosphorus removal in pilot-scale flow-through biofilm reactor with low dissolved oxygen concentrations: Performance and mechanisms

In this pilot-scale study, a flow-through biofilm reactor (FTBR) was investigated for municipal wastewater treatment. The removal efficiencies for ammonium, total nitrogen, total phosphorus, and chemical oxygen demand were 87.2 ± 17.9%, 61.1 ± 13.9%, 83.5 ± 11.9%, and 92.6 ± 1.7%, respectively, at low dissolved oxygen concentrations (averaged at 0.59 mg/L), indicating the feasibility and robustness of the FTBR for a simultaneous nitrification, denitrification, and phosphorous removal (SNDPR) process. The co-occurrence network of bacteria in the dynamic biofilm was complex, with equivalent bacterial cooperation and competition. Nevertheless, the bacterial interactions in the suspended sludge were mainly cooperative. The presence of dynamic biofilms increased bacterial diversity by creating niche differentiation, which enriched keystone species closely related to nutrient removal. Overall, this study provides a novel FTBR-based SNDPR process and reveals the ecological mechanisms responsible for nutrient removal.

High concentration powder carrier bio-fluidized bed process: A new perspective for domestic wastewater treatment

The nitrogen removal mechanism of the high concentration powder carrier bio-fluidized bed (HPB) process was investigated with actual domestic wastewater. The micron-size (10-70 μm) powder carriers were diatomite and Fe-C. Results showed diatomite enriched the relative abundances of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, accordingly increasing the rate of nitrification. Even a 100% increase of genes associated with the ammonia oxidation was achieved. Fe-C enhanced the rate of substrate utilization mainly by increasing the activity of the electron transfer system. Hydrocyclone separator, as a key device of HPB, was able to recover the carriers with high efficiency (recovery efficiency of 72.66 ─ 82.50% after 75 days), thus, indirectly improving the functionality of the carriers. Furthermore, it could renew the surface of microbial aggregations, consequently improving the adsorption capacity to substrates. HPB could provide the feasibility of shortening the hydraulic retention time and expanding the capacity of wastewater treatment plants.

Architecture of HAP-anammox granules contributed to high capacity and robustness of nitrogen removal under 7°C

The anaerobic ammonium oxidation (anammox) process is an autotrophic nitrogen removal process with great potential as a cost-effective and highly efficient technology in the wastewater treatment field. The main challenges yet to be overcome in this new frontier technology are operating at lower temperatures and achieving a high and stable nitrogen removal efficiency. In this study, an up-flow expanded bed reactor with hydroxyapatite (HAP)-anammox granules was operated for more than 200 days at 7°C. The nitrogen loading rate (NLR) was improved from 1.0 g-N/L/d to 3.6 g-N/L/d, together with a high-level nitrogen removal efficiency of 84-92%, which is the highest to date at extremely low temperatures in a continuous experiment. Candidatus Kuenenia was revealed to be the only dominant anammox genus, with a relative abundance of 35.3-37.5%. The optimal operational temperature was around 35°C and the apparent activation energy (E_a) was calculated as 78.37 kJ/mol. The three-layers architecture and architectural evolution of HAP-anammox granules into HAP-cores and peeling biofilms with outstanding settling performance were characterized. Under 7°C, the high capacity of nitrogen removal with robust removal efficiency using HAP-anammox granules was achieved.

Evaluating the nitrogen-contaminated groundwater treatment by a denitrifying granular sludge bioreactor: effect of organic matter loading

A sequential bed granular bioreactor was adapted to treat nitrate-polluted synthetic groundwater under anaerobic conditions and agitation with denitrification gas, achieving very efficient performance in total nitrogen removal at influent organic carbon concentrations of 1 g L^-1 (80-90%) and 0.5 g L^-1 (70-80%) sodium acetate, but concentrations below 0.5 g L^-1 caused accumulation of nitrite and nitrate and led to system failure (30-40% removal). Biomass size and settling velocity were higher above 0.5 g L^-1 sodium acetate. Trichosporonaceae dominated the fungal populations at all times, while a dominance of terrestrial group Thaumarchaeota and Acidovorax at 1 and 0.5 g L^-1 passed to a domination of Methanobrevibacter and an unclassified Comamonadaceae clone for NaAc lower than 0.5 g L^-1. The results obtained pointed out that the denitrifying granular sludge technology is a feasible solution for the treatment of nitrogen-contaminated groundwater, and that influent organic matter plays an important role on the conformation of microbial communities within it and, therefore, on the overall efficiency of the system.

Biological ammonium and sulfide oxidation in a nitrifying sequencing batch reactor: Kinetic and microbial population dynamics assessments

A kinetic study was carried out in a sequencing batch reactor (SBR) (125 mg NH₄⁺-N/L) inoculated with a physiologically stable nitrifying sludge not previously acclimated to sulfur compounds and fed at different initial sulfide concentrations (2.5-20.0 mg HS^--S/L). Up to 10.0 mg HS^--S/L, the nitrifying process kept stable and complete, reaching an ammonium consumption efficiency (E_NH4+) of 100% and a nitrate yield (Y_NO3-) of 0.95 ± 0.03 mg NO₃^--N/mg NH₄⁺-N consumed. At 15.0 and 20.0 mg HS^--S/L, after an initial alteration in the nitrite oxidizing process, the Y_NO2- was decreasing throughout the cycles and the Y_NO3- increasing, obtaining in the last cycle at 20.0 mg HS^--S/L, an E_NH4+ of 100%, a Y_NO2- of zero, and a Y_NO3- of 0.80 mg NO₃^--N/mg NH₄⁺-N consumed. At the end of the period at 20.0 mg HS^--S/L, the specific rates of ammonium consumption and nitrate formation were 15 and 55% lower than their respective values in the control period without sulfide addition, showing that the sludge had a better metabolic adaptation for ammonium oxidizing activity than for nitrite oxidizing activity. The sludge acquired a higher sulfide oxidation capacity along the cycles. Bacterial population dynamics assessment indicated that the ammonium oxidizing bacteria (AOB) community was more diverse and stable than the nitrite oxidizing bacteria (NOB) community. The use of consortia with a previously stabilized nitrifying activity in SBR may constitute an alternative for eliminating simultaneously ammonium by nitrification and sulfide by sulfide oxidation and be implemented for the treatment of wastewater with ammonium and sulfide.

Robustness of an aerobic granular sludge sequencing batch reactor for low strength and salinity wastewater treatment at ambient to winter temperatures

Acclimation performances and characteristics of aerobic granular sludge to salt and temperature were investigated in a sequencing batch reactor (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR). The aerobic granular SNDPR system was firstly subjected to low salinity (0.5%, w/v) at moderate temperature (> 15 ℃) and subsequent low temperature (< 15 ℃). The shock loading of salinity temporarily deteriorated biological phosphorus removal, while dual stresses of salinity and low temperature induced temporary inhibition on both nitrogen and phosphorus removal. Both salinity and low temperature stimulated the settleability of aerobic granules, accompanied with decreased ratios of protein to polysaccharide (PN/PS). Illumina MiSeq sequencing revealed that salinity rarely affected bacterial richness, but significantly decreased the diversity. Whereas low temperature strengthened both bacterial richness and diversity. Phyla Proteobacteria, Chloroflexi and their sub-groups acted as the main halophilic bacteria while Proteobacteria was also psychrophilic. The functional bacteria such as nitrifiers, denitrifiers, and phosphorus removal bacteria exhibited greater tolerance to salt and low temperature than glycogen accumulating organisms (GAOs). Overall, the present study demonstrated the resilience and robustness of aerobic granular sludge toward salinity and low temperature, which could aid the knowledge of saline wastewater treatment by aerobic granular sludge.

Enhancement of the ANAMMOX bacteria activity and granule stability through pulsed electric field at a lower temperature (16 ± 1 °C)

The effects of different frequencies of pulsed electric field (PEF) on the ANAMMOX process were investigated. The results showed that the intermediate frequency could dramatically enhance both the ANAMMOX bacterial activity and granule sludge stability at 16 ± 1 °C The nitrogen removal efficiency of R1 (intermediate frequency) was significantly enhanced by 62.24% and 79.51% compared to R2 (lower frequency) and R3 (higher frequency), with a nitrogen loading rate of 6.84 kg Nm^-3 d^-1. In addition, the intermediate frequency could stimulate cells to secrete more extracellular polymeric substances (EPS) to sustain the granule sludge stability. The granule sludge disintegrated on days 55 and 35 in R2 and R3. The protein (PN)/polysaccharide (PS) ratios of R1 were 28.46% and 54.20% higher than R2 and R3, which was beneficial to granule sludge stability. This study showed that PEF could solve the problem of decreased ANAMMOX bacterial activity and granule stability at lower temperatures.