Rapid start-up and stable operation of an aerobic/oxic/anoxic simultaneous nitrification, denitrification, and phosphorus removal reactor with no sludge discharge

Simultaneous removal of nitrogen and phosphorus by aerobic denitrifying Paracoccus versutus JUST-3

Strain JUST-3, exhibiting high-efficiency simultaneous nitrogen and phosphorus removal under aerobic conditions, was isolated and identified as Paracoccus versutus based on 16S rDNA gene sequencing and comprehensive physiological and biochemical analysis. The strain demonstrated optimal performance when cultured with sodium acetate as carbon source under the following conditions: C/N ratio of 10, P/N ratio of 0.2, 35 °C, and pH of 8.0. The variations in intermediate metabolites, the activity of functional enzymes, and the nitrogen/phosphorus balance experiments elucidated the pathways in nitrogen and phosphorus removal under aerobic conditions. Exogenous signal molecules (＜50 nmol/L) could promote growth, enhance aerobic denitrification, and improve simultaneous nitrogen and phosphorus performance. The identification of signaling molecules represents a significant breakthrough, revealing novel regulatory mechanisms in microbial quorum-sensing systems and enabling precise control of microbial community behaviors. This study expands the application of aerobic denitrification and phosphorus removal technology, laying the foundation for wastewater treatment.

Optimizing operation strategy to improve storage of intracellular carbon sources in anaerobic/oxic/anoxic system: Enhanced nitrogen removal by endogenous denitrification

Endogenous denitrification (ED) can make full use of the carbon sources and avoid replenishment of it. However, strengthening the storage of intracellular carbon sources is an important factor in improving ED efficiency. In this study, employed batch experiments using real domestic wastewater in the anaerobic/oxic (A/O) process. The anaerobic and oxic processes were run for 4 h under ambient conditions with the dissolved oxygen (DO) concentrations in the oxic stage controlled at 0.5, 1.0, 1.5, and 3.0 mg/L, respectively. The results showed that the content of poly-β-hydroxyalkanoates (PHA) reached its peak at 60 min (1.25 mmolC/L). And with DO concentrations of 1.5 mg/L, the contents of glycogen (Gly) were 27.74 mmolC/L. Subsequently, the AOA-SBR was established to investigate its effect on the long-term nitrogen removal performance of domestic wastewater by optimizing the anaerobic time and DO concentrations. The results showed that at an anaerobic time of 60 min and DO concentration of 1.5 mg/L, the storage of the intracellular carbon sources was highest and the total nitrogen (TN) removal efficiency increased to 82.12%. In addition, Candidatus Competibacter dominated gradually in the system as the strategy was optimized.

Synchronous in-situ sludge reduction and enhanced denitrification through improving electron transfer during endogenous metabolisms with Fe(Ⅱ) addition

The creation of large amounts of excess sludge and residual nitrogen are critical issues in wastewater biotreatment. This study introduced Fe(II) into an oligotrophic anaerobic reactor (OARFe) that was implemented to modify an anoxic-oxic process to motivate in-situ sludge reduction and enhance denitrification under an effective electron shuttle among organic matter, nitrogen, and Fe. The addition of 15 mg L-1 Fe(II) resulted in a sludge reduction efficiency reached 32.0% with a decreased effluent nitrate concentration of 33.3%. This was mostly attributed to the electron transfer from Fe(II) to organic matters and nitrogen species in OARFe. The participation of Fe(II) led to the upregulation of Geothrix and Terrimonas, which caused active organic matter hydrolysis and cell lysis to stimulate the release of extracellular polymeric substances (EPS) and substance transfer between each layer of EPS. The higher utilization of released bioavailable dissolved organic matter improved endogenous denitrification, which can be combined with iron autotrophic denitrification to realize multiple electron donor-based nitrogen removal pathways, resulting in an increased nitrate removal rate of 58.2% in the absence of external carbon sources. These functional bacteria associated with the transformation of nitrogen and carbon and cycling between ferrous and ferric ions were enriched in OARFe, which contributed to efficient electron transport occurred both inside and outside the cell and increased 2,3,5-triphenyltetrazolium chloride electronic transport system activity by 46.9%. This contributed to the potential operational costs of chemical addition and sludge disposal of Fe-AO being 1.9 times lower than those of conventional A2O processes. These results imply that the addition of ferrous ions to an oligotrophic anaerobic zone for wastewater treatment has the potential for low-cost pollution control.

New insights on destruction mechanisms of waste activated sludge during simultaneous thickening and digestion process via forward osmosis membrane

This study delved into the efficacy of sludge digestion and the mechanisms involved in sludge destruction during the implementation of forward osmosis process for sludge thickening and digestion (FO-MSTD). Utilizing a lab-scale FO membrane reactor for the thickening and digestion of waste activated sludge (WAS), the investigation explored the effects of sludge thickening and digestion in FO-MSTD processes using draw solutions of varying concentrations. The findings underscored the significance of hydraulic retention time (HRT) as a pivotal parameter influencing the swift thickening or profound digestion of sludge. Consequently, tailoring the HRT to specific processing objectives emerged as a key strategy for achieving desired treatment outcomes. In the investigation, the use of a 1 M NaCl draw solution in the FO-MSTD process showcased enhanced thickening and digestion capabilities. This specific setup raised the concentration of mixed liquor suspended solids (MLSS) to over 30 g/L and achieved a 42.7% digestion efficiency of mixed liquor volatile suspended solids (MLVSS) within an operational timeframe of 18 days. Furthermore, the research unveiled distinct stages in the sludge digestion process of the FO-MSTD system, characterized by fully aerobic digestion and aerobic-local anaerobic co-existing digestion. In the fully aerobic digestion stage, the sludge digestion rate exhibited a steady increase, leading to the breakdown of sludge floc structures and the release of a substantial amount of nutrients into the sludge supernatant. The predominant microorganisms during this stage were typical functional microorganisms found in wastewater treatment systems. Transitioning into the aerobic-local anaerobic co-existing digestion stage, both MLSS concentration and MLVSS digestion efficiency continued to rise, accompanied by a decreasing dissolved oxygen (DO) concentration. More organic matter was released into the supernatant, and sludge microbial flocs tended to reaggregate. The localized anaerobic environment within the FO-MSTD reactor fostered an increase in the relative abundance of bacteria with nitrogen and phosphorus removal functions, thereby positively impacting the mitigation of total nitrogen (TN) and total phosphorus (TP) concentrations in the sludge supernatant. The results of this research enhance comprehension of the advanced FO-MSTD technology in the treatment of WAS.

Comparison of treatment performance and microbial community evolution of typical dye wastewater by different combined processes

The degradation of typical dye wastewater is a focus of research in the printing and dyeing industry. In this study, a combined micro-electrolysis and microbial treatment method was established to treat refractory dye wastewater, and the pivotal factors in the microbial treatment were optimized. In the series and coupled modes, the removal rates of chroma reached 98.75% and 92.50%, and the removal rates of chemical oxygen demand (COD) reached 96.17% and 82.29%, respectively. The high-throughput sequencing results showed that the microbial communities in the microbial system varied at different treatment stages. From the culture stage to the domestication stage, the dominant phylum was Proteobacteria; however, the community abundance of microorganisms decreased. A combination of micro-electrolysis and biological methods can alter the characteristics of the microbial community, increase the number of dominant phyla, and increase the abundance of microorganisms. The degradation effect of the series mode and the overall strengthening effect of micro-electrolysis on the microorganisms were better than those of the coupled mode. In actual wastewater, the maximum removal rates of chroma, COD, total nitrogen (TN), ammonia nitrogen (NH3-N), and total phosphorus (TP) are 97.50%, 98.90%, 94.35%, 93.95%, and 91.17%, respectively. Three-dimensional fluorescence spectrum analysis showed that microbial processes could significantly degrade fluorescent components in wastewater, and methanogenic active enzymes in anaerobic processes could continue to react. The combined process can realize the efficient treatment of toxic dye wastewater by reducing the toxicity of wastewater and efficiently degrading organic matter, which has important guiding significance for the treatment of refractory dye wastewater.

Towards a better understanding of the anaerobic/oxic/anoxic-aerobic granular sludge process (AOA-AGS) for simultaneous low-strength wastewater treatment and in situ sludge reduction from ambient to winter temperatures

The new anaerobic/oxic/anoxic-aerobic granular sludge (AOA-AGS) merits the advantages of effective carbon utilization and low-carbon treatment. However, low temperature poses stressing concerns and the resisting mechanism remains much unknown. Herein, an AOA-AGS process was configured for simultaneous nitrification, denitrification and phosphorus removal (SNDPR) with low-strength wastewater from ambient (>15 °C) to winter temperatures (<15 °C). Results showed that simultaneously advanced nutrients removal, and dramatic in situ sludge reduction (Yobs of 0.093 g MLSS/g COD) were gained regardless of seasonally decreasing temperatures. Winter temperatures even amplified Candidatus Competibacter predominating from 20.11% to 34.74%, which laid the core basis for endogenous denitrification, sludge minimization and temperature resistance. A removal model was thus proposed given the observed functional groups, and doubts were also raised for future investigations. This study would aid a better understanding on the microbial ecology and engineering aspects of the new AOA-AGS process treating low-strength wastewater at low temperatures.

Enhanced denitrification performance of granular sludge for the treatment of waste brine from ion exchange resin process

Ion exchange resin process is a widely used process in wastewater treatment plants, but its waste brine is characterized by high salinity and nitrate concentration, leading to costly treatment. This study innovatively explored the use of an up-flow anaerobic sludge bed (USB) for the treatment of waste brine from ion exchange resin process, following a pilot-scale ion exchange resin process. Specifically, the D890 ion exchange resin was employed for nitrate removal from secondary effluent, with resin regeneration using 4% NaCl solution. The USB was inoculated with anaerobic granular sludge and acclimated under various single-factor conditions, which revealed the optimal pH range of 6.5-9, salt concentration of 2%, hydraulic retention time of 12 h, C/N ratio of 3.3, and up-flow velocity of 1.5 m/h for reactor operation. This study provides a novel approach for the cost-effective treatment of waste brine from ion exchange resin process. The study found that the denitrification efficiency was highest when the NO3--N concentration was around 200 mg/L, with NO3--N and TN removal rates exceeding 95% and 90%, respectively, under optimal operating conditions. Characterization of the granular sludge during different phases of the operation revealed a significant increase in proteobacteria and gradually became the dominant species over time. This study presents a novel, cost-effective approach to treat waste brine from ion exchange resin process, and the long-term stable operation of the reactor offers a reliable option for resin regeneration wastewater treatment.

Advanced low-strength wastewater treatment, side-stream phosphorus recovery, and in situ sludge reduction with aerobic granular sludge

Modern paradigm has upgraded wastewater treatment plants (WWTPs) to water resources recovery facilities (WRRFs), where aerobic granular sludge (AGS) is a sewage treatment technology with promising phosphorus recovery (PR) potential. Herein, the AGS-based simultaneous nitrification, denitrification, and phosphorus removal coupling side-stream PR process (AGS-SNDPRr) was developed with municipal wastewater. Results revealed that AGS always maintained good structural stability, and pollutant removal was unaffected and effective after 40 days of anaerobic phosphorus-rich liquid extraction (fixed rate of 30%). The AGS-SNDPRr achieved a stable phosphorus recovery efficiency of 63.40%, and the side-stream PR further exaggerated in situ sludge reduction by 7.7-10%. Apart from responses of extracellular polymeric substances (EPS), the Matthew effect of typical denitrifying glycogen accumulating organisms (DGAOs) Candidatus_Competibacter up to 67.40% mainly contributed to enhanced performance of this new process. This study demonstrated a new approach for simultaneous advanced wastewater treatment, phosphorus recovery, and excess sludge minimization.

Changes in microbial community during hydrolyzed sludge reduction

In this study, the effects of different enzymes (lysozyme, α-amylase and neutral protease) on sludge hydrolysis efficiency and microbial community in sequencing batch reactor (SBR) were introduced. The results showed that the hydrolysis efficiencies of the three enzymes were 48.5, 22.5 and 31%, respectively, compared with the accumulated sludge discharge of the blank control group. However, it has varying degrees of impact on the effluent quality, and the denitrification and phosphorus removal effect of the system deteriorates. The lysozyme that achieves the optimal sludge hydrolysis effect of 48.5% has the greatest impact on the chemical oxygen demand (COD), total nitrogen (TN), and nitrate nitrogen (NO3--N) of the effluent. The sludge samples of the control group and the groups supplemented with different enzyme preparations were subjected to high-throughput sequencing. It was found that the number of OTUs (Operational Taxonomic Units) of the samples was lysozyme > α-amylase > blank control > neutral protease. Moreover, the abundance grade curve of the sludge samples supplemented with lysozyme and α-amylase was smoother, and the community richness and diversity were improved by lysozyme and α-amylase. The species diversity of the sludge supplemented with lysozyme and neutral protease was great, and the community succession was obvious. The introduction of enzymes did not change the main microbial communities of the sludge, which were mainly Proteobacteria, Actinobacteria and Bacteroidetes. The effects of three enzyme preparations on sludge reduction and microbial diversity during pilot operation were analyzed, the gap in microbial research was filled, which provided theoretical value for the practical operation of enzymatic sludge reduction.

Performance of anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal system overwhelmingly dominated by Candidatus_Competibacter: Effect of aeration time

The anaerobic/oxic/anoxic simultaneous nitrification, denitrification and phosphorus removal process (AOA-SNDPR) is a promising technology for enhanced biological wastewater treatment and in situ sludge reduction. Herein, the effects of aeration time (90, 75, 60, 45, and 30 min, respectively) on AOA-SNDPR were evaluated including simultaneous nutrients removal, sludge characteristics, and microbial community evolution, where the role of a denitrifying glycogen accumulating organisms, Candidatus_Competibacter, was re-explored given its overwhelming dominance. Results revealed that nitrogen removal was more vulnerable, and a moderate aeration period of 45-60 min mostly favored nutrients removal. Low observed sludge yields (Y_obs) were obtained with decreased aeration (as low as 0.02 g MLSS/g COD), while MLVSS/MLSS got increased. The dominance of Candidatus_Competibacter was proven to be the key to endogenous denitrifying and in situ sludge reduction. This study would aid the more carbon- and energy-efficient aeration strategy for AOA-SNDPR systems treating low-strength municipal wastewater.

Enhanced in-situ sludge reduction of the side-stream process via employing micro-aerobic approach in both mainstream and side-stream

Side-stream reactor (SSR), as an in-situ sludge reduction process with high sludge reduction efficiency (SRE) and less negative impact on effluent, has been widely researched. In order to reduce cost and promote large-scale application, the anaerobic/anoxic/micro-aerobic/oxic bioreactor coupled with micro-aerobic SSR (AAMOM) was used to investigate nutrient removal and SRE under short hydraulic retention time (HRT) of SSR. When HRT of SSR was 4 h, AAMOM system achieved 30.41% SRE, while maintaining carbon and nitrogen removal efficiency. Micro-aerobic in mainstream accelerated the hydrolysis of particulate organic matter (POM) and promoted denitrification. Micro-aerobic in side-stream increased cell lysis and ATP dissipation, thus increasing SRE. Microbial community structure indicated that the cooperative interactions among hydrolytic, slow growing, predatory and fermentation bacteria played key roles in improving SRE. This study confirmed that SSR coupled micro-aerobic was a promising and practical process, which could benefit nitrogen removal and sludge reduction in municipal wastewater treatment plants.

Effects of nano metal oxide particles on denitrifying phosphorus removal system: Potential stress mechanism and recovery strategy

The accumulation of nano metal oxide particles (NMOPs) in municipal sewage treatment systems harms the microbial community and its metabolism in activated sludge system, resulting in the degradation of its pollutants removal performance. In this work, the stress effect of NMOPs on the denitrifying phosphorus removal system was systematically investigated in terms of pollutants removal performance, key enzyme activities, microbial community diversity and abundances, and intracellular metabolites. Among the ZnO NPs, TiO₂ NPs, CeO₂ NPs, and CuO NPs, the ZnO NPs showed the most significant impacts with the chemical oxygen demand, total phosphorus, and nitrate nitrogen removal ratio decreased from above 90 % to 66.50 %, 49.13 %, and 57.11 %, respectively. The addition of surfactants and chelating agents could relieve the toxic effect of NMOPs on the denitrifying phosphorus removal system, and the chelating agents were more effective than surfactants in performance recovery. After adding ethylene diamine tetra acetic acid, the removal ratio of chemical oxygen demand, total phosphorus, and nitrate nitrogen under ZnO NPs stress was restored to 87.31 %, 88.79 %, and 90.35 %, respectively. The study provides valuable knowledge to better understand the impacts and stress mechanism of NMOPs on activated sludge systems and provides a solution to recover the nutrients removal performance of denitrifying phosphorus removal system under NMOPs stress.

The disinhibition effect of iron-based particles on anaerobic digestion of florfenicol-containing cow manure: Performance and mechanism

The overuse of antibiotics has caused problems such as environmental pollution, increased antibiotic resistance of pathogenic bacteria, and inhibition of engineered microbial processes such as anaerobic digestion (AD). At present, mitigating the inhibition of antibiotics on the process of microbial recycling of organic matter by using additives has always been a research hotspot. In this study, the effects of the addition of three iron-based particles including zero-valent iron (ZVI), Fe₂O₃ and Fe₃O₄ on the biogas yield during the AD of cow manure containing florfenicol (FLO) were studied. It was found that by alleviating the acid accumulation, the addition of low-concentration ZVI, Fe₂O₃ and high-concentration Fe₃O₄ enhanced the maximum methane production rate of FLO-containing cow manure during AD to 3.5, 1.7 and 3.6 times, respectively, while high concentration of ZVI will lead to the crash of the AD system due to the rise of pH. Within the concentration range of iron-based particles dosed in this study, the Fe₃O₄ dosage showed a significant positive correlation with the cumulative methane production enhancement rate (p < 0.01). The sum of the relative abundances of Limnobacter and Pseudomonas was correlated with the absolute abundance of floR gene with the Pearson correlation coefficient of 0.9457 (p < 0.01), indicating the possibility of these two genera being the potential host bacteria for floR gene.