•The TNRE is stable at approximately 85% for a long time at a C/N ratio of 1–2.•Both PNA and nitrification-denitrification contributes to intensifying denitrogen.•Regulating the DO partition and C/N ...ratio leads to a dynamic microbial balance.•Organic matter has a greater impact on the single-stage denitrogen than AR.
Current research focuses on efficient single-stage nitrogen removal from organic matter wastewater using the partial nitritation-anammox (PNA) process. In this study, we constructed a single-stage partial nitritation-anammox and denitrification (SPNAD) system using a dissolved oxygen-differentiated airlift internal circulation reactor. The system was operated continuously for 364 days at 250 mg/L NH4+–N. During the operation, the COD/NH4+–N ratio (C/N) was increased from 0.5 to 4 (0.5, 1, 2, 3, and 4), and the aeration rate (AR) gradually increased. The results showed that the SPNAD system maintained efficient and stable operation at C/N = 1–2 and AR = 1.4–1.6 L/min, with an average total nitrogen removal efficiency of 87.2%. The removal pathways of pollutants in the system and the interactions between microbes were revealed by analyzing the changes in sludge characteristics and microbial community structure at different phases. As the influent C/N increased, the relative abundance of Nitrosomonas and Candidatus Brocadia decreased, and that of denitrifying bacteria, such as Denitratisoma, increased to 44%. The nitrogen removal pathway of the system gradually changed from autotrophic nitrogen removal to nitrification-denitrification. At the optimum C/N, the SPNAD system synergistically removed nitrogen through PNA and nitrification-denitrification. Overall, the unique reactor configuration facilitated the formation of dissolved oxygen compartments, providing a suitable environment for different microbes. An appropriate organic matter concentration maintained the dynamic stability of microbial growth and interactions. These enhance microbial synergy and enable efficient single-stage nitrogen removal.
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Digestate recirculation is often considered an important way to improve system stability (system acidification, ammonia inhibition, hydrolysis limitations, etc.) and gas production performance. ...However, it is not clear how the promotion of biohythane production works in anaerobic co-digestion with digestate recirculation of rice straw (RS) and pig manure (PM). Two sets of laboratory-scale two-stage continuous stirred tank reactors were operated continuously for 95 d to investigate the performance of biohythane production in the first/second phase under mesophilic (M)/thermophilic (T) and digestate recirculation conditions. Firstly, biohythane was not produced by PM with RS under digestate recirculation. The main reasons were: 1) Digestive recirculation promoted the growth of hydrogenotrophic methanogenic bacteria; and 2) limitations in hydrolysis. Secondly, digestate recirculation has positive effects on the removal rates (removal rates of TS, VS, polysaccharide, protein and TCOD increased by 30.4%, 22.3%, 9.9%, 31.4%, and 11.9%, respectively) and energy yield (up to 68.7%). Finally, there was a higher abundance of hydrogen-producing bacteria (Fervidobacterium 44.9% and Coprothermobacter 18.8%) in T2, accounting for >80% of the total, and of which the huge hydrogen production potential cannot be ignored. The results provide new ideas for alleviating the energy crisis and developing green energy in the future.
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•Anaerobic co-digestion with digestate recirculation produced no biohythane.•Digestate recirculation improved system stability, removal rate, and energy yield.•Digestive recirculation promoted hydrogenotrophic methanogenic bacteria growth.•M1-T1 and T2-M2 were hydrolysis-limited.•The thermophilic acid-producing phase showed strong hydrogen production potential.
The concept of partial nitritation-anammox (PN/A) process has been proposed for many years, however seasonal temperatures and low ammonia concentrations under mainstream conditions always challenge ...the application in practical engineering. Thus, we operated a PN/A moving bed biofilm reactor (PN/A-MBBR) for treating 50 mg-NH4/L wastewater at various temperatures of 35 °C, 25 °C, and 15 °C. The effect of temperature reduction on biofilm system was investigated from process performance, microbial community and activity, to metabolic pathways. The results showed that total nitrogen removal efficiency declined from 76.6 % to 48.6 % as the temperature was reduced from 35 °C to 15 °C, while nitrogen removal rate decreased to 0.28 kg-N/m3/d. Low temperature stimulated the secretion of polysaccharide in loosely bound-EPS and protein in tightly bound-EPS. Meanwhile, specific activity of anammox declined from 1.53 to 0.56 g-N/g-VSS/d, and the relative abundance of Candidatus Brocadia dropped from 20.1 % to 9.4 %. Temperature reduction had significant effect on the expression of functional genes (hzsA and hdh) for anammox reaction. Nitrification-denitrification process was enhanced during low temperatures and recovery phases. Biofilm system might respond to temperature reduction by the decline of substance transport and energy consumption, as well as the enhancement of biofilm formation and diversity of nitrogen removal pathways. The findings of this study provide a deep insight into the effect of temperature reduction on PN/A process, also promote the practical applications of mainstream PN/A in the future.
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●NRR dropped from 0.46 to 0.28 kg-N/m3/d as the temperature decreased to 15 °C.●Low temperature could stimulate the secretion of protein in T-EPS.●Temperature reduction significantly affected genes expression (hzsA and hdh).●Performance recovery was incomplete due to NOB proliferation.
To investigate the complex inhibitions leading to the deterioration of reactor performance in anaerobic treatment of monosodium glutamate (MSG) wastewater under low COD/sulfate ratios, a ...comprehensive assessment of the overall reactor performance, sludge characteristics and microbial community characteristics was conducted in this study. The COD removal rate of the reactor was maintained above 90% throughout the experiment, but the gas yield decreased by 52% due to the complex competition between sulfate-reducing bacteria (SRB) and methane-producing archaea (MPA) resulting in a decreasing number of MPA. The sludge characteristics and microbial community features indicated that the complex competition between SRB and MPA included competition for hydrogen and survival space in the reactor. In addition, the competitive advantage of SRB for electrons led to the production of more sulfides in the reactor, further inhibiting the activity of MPA. Therefore, the complex inhibition within the reactor for anaerobic treatment of MSG wastewater with low COD/sulfate ratios, including sulfide toxicity inhibition, competition between SRB and MPA for substrate and space, not only led to a reduction in gas production, but also affected microbial activity and glutamate degradation.
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•The COD removal rate was approximately 90% at a low COD/sulfate ratio.•Complex competitions between SRB and MPA deteriorated the gas production performance.•Toxic inhibition of sulfides is an important factor in the decline of methanogens.•More than 50% of the electrons flow to SRB when COD/sulfate ratio was 0.667.
To better understand performance recovery and its mechanism, after the deterioration of an anaerobic ammonia oxidation (anammox) process, experiments were conducted in a UASB reactor. A two-stage ...anammox reaction was conducted in the reactor, and long-term continuous operation was conducted for 202 d. The mechanism of performance recovery was studied by adjusting the total nitrogen (TN) concentration and hydraulic retention time (HRT) of the influent. The results showed that after the long-term continuous operation, the TN removal efficiency decreased from 88.22 % before deterioration to 11.68 %, and then recovered to 80.63 %. The nitrogen loading rate decreased from 2.25 kg-N/m3/d before deterioration to 0.26 kg-N/m3/d and then recovered to 2.79 kg-N/m3/d. Nitrogen removal load (NRR) decreased from 1.98 kg-N/m3/d to 0.26 kg-N/m3/d before deterioration and recovered to 2.25 kg-N/m3/d. Microbial diversity was analyzed by high-throughput sequencing. During the operation, the dominant anammox strains changed from Candidatus Kuenenia (24.19 %) before deterioration to Candidatus Brocadia (11.90 %) after recovery. The influent TN concentration and HRT were the key factors that affected performance recovery. Reducing the influent TN concentration and shortening the HRT can effectively avoid the inhibition of anammox by the substrate and enable the rapid recovery of nitrogen removal performance. As the microorganisms in the reactor recovered their activity through enrichment, the influent TN gradually increased, and produced NRR higher than the pre-deterioration level, so the reactor performance was fully restored. This study provides a scientific support for recovering the two-stage anammox process performance after deterioration.
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•Anammox reactor performance was recovered after 148 d of regulation.•The performance was regulated by reducing HRT and adjusting TN concentration.•NRE recovered from 11.68 % to 80.6 % and NRR from 0.26 kg-N/m3/d to 2.25 kg-N/m3/d.•Candidatus Brocadia replaced Candidatus Kuenenia as dominant bacteria after recovery.•TN concentration had the greatest impact on the performance recovery.
•A transient process optimization control strategy for Marine hybrid propulsion system is proposed.•The evaluation function of the transient process is established.•Adaptive Perturbation Quantum wave ...whale optimization algorithm is presented.
The voice of energy saving and environmental protection is increasing, and the regulations on energy efficiency of ships are becoming stricter. It has forced the shipping industry to accelerate the development of marine hybrid propulsion systems (MHPS). However, the direct control of power distribution optimized by advanced intelligent algorithms may lead to ship oscillations and speed fluctuations. This paper presents a transient process optimization control strategy for solving multi-energy switching. A MHPS simulation model is established from the first nature principle and experimental data. A simulation analysis of the critical parameters affecting the switching process, namely the clutch operating oil pressure and the permanent-magnet synchronous motor (PMSM) output torque. From the viewpoint of restraining speed and oscillation, a process evaluation function is designed to include speed tracking, shock mitigation, and slip work reduction. An upgraded version of WOA, namely Adaptive Perturbation Quantum wave whale optimization algorithm (APQWOA), is proposed to solve the optimal control problem. This transient process optimization control scheme was tested in real time operation through experiments. The results show that the APQWOA is reliably evaluated, which significantly reduces the speed fluctuation and shock level.
It is of great significance for intelligent manufacturing to study diagnosis methods to realize the diagnosis of mechanical equipment faults. Multiscale weighted permutation entropy is an effective ...method recently proposed to measure the complexity and dynamic changes of dynamic systems. To solve the shortcoming of multiscale weighted permutation entropy that does not consider high-frequency components, this article proposes hierarchical weighted permutation entropy, which can comprehensively and accurately reflect the low-frequency and high-frequency information of the time series. The simulation signal verifies the effectiveness and superiority of hierarchical weighted permutation entropy. Then, a novel intelligent fault diagnosis method for common rail injectors based on hierarchical weighted permutation entropy and pair-wise feature proximity is proposed. Finally, the proposed method is applied to the common rail injector fault data, and the results verify the effectiveness of the proposed method. Compared with other methods, this method has a higher fault recognition rate and stronger robustness.
The normal operation of high-pressure common rail injector is one of the important prerequisites for the healthy and reliable operation of diesel engines. Therefore, this paper studies the ...high-precision fault diagnosis method for injectors. Firstly, this paper chooses VMD to adaptively decompose the common rail fuel pressure wave. The biggest difficulty in VMD decomposition is the need to manually set the internal combination parameters K and α. In order to overcome this shortcoming, this paper proposes an improved fruit fly search. The variational mode decomposition method of the algorithm, with the energy growth factor e as the objective function, can adaptively decompose the multi-component signal into superimposed sub-signals. In addition, based on the analytic hierarchy process and dispersion entropy, hierarchical dispersion entropy is proposed to obtain a comprehensive and accurate complexity estimation of time series. Then, a fault diagnosis scheme for high-pressure common rail injector based on IFOA-VMD and HDE is proposed. Finally, using the engineering test data, the method is compared with other methods. The proposed method appears, based on the numerical examples, to be better from both a computational and classification accuracy point of view.
Early fault diagnosis of common rail injectors is essential to reduce diesel engine testing and maintenance costs. Therefore, this paper proposes a new common rail injector early fault diagnosis ...method, which combines the Maximum Second-order Cyclostationary Blind Deconvolution (CYCBD) optimized by the Seagull Optimization Algorithm (SOA) and Hierarchical Fluctuation Dispersion Entropy (HFDE). First, we use SOA adaptively to seek the optimal filter length of CYCBD and use the optimal CYCBD to filter the fuel pressure signal of the high-pressure fuel pipe. Then, in order to make up for the shortcomings of Multi-scale Fluctuation Dispersion Entropy (MFDE) ignoring high-frequency component information, this paper proposes HFDE to extract the fault characteristics after filtering. Finally, we input the fault characteristics into Least Squares Support Vector Machines (LSSVM) for classification and recognition. Through the analysis of experimental data, the method proposed in this paper can effectively identify the early failure state of the common rail injector. Compared with the existing methods, the proposed method has a higher fault recognition rate.
•Three electrochemical techniques are evaluated for their suitability of continuous monitoring of microbiologically influenced corrosion.•Electrochemical impedance spectroscopy and linear ...polarization resistance significantly inhibit the growth of P. aeruginosa biofilm.•Electrochemical noise measurement does not show adverse impact on the P. aeruginosa biofilm.•Electrochemical noise can be regarded as a suitable technique to continuously monitor biocorrosion.
Different electrochemical techniques and surface analysis methods were used to continuously monitor the corrosion of 2205 duplex stainless steel (DSS) in P. aeruginosa inoculated medium. It was found that linear polarization resistance and electrochemical impedance spectroscopy, significantly inhibited the attachment and growth of the biofilm, due to an internal electric field, leading to lower corrosion rates. In comparison, electrochemical noise as a passive electrochemical measurement technique did not adversely impact the biofilm, and the corrosion rate and the largest pit depth distribution from electrochemical noise were the closest to those from weight-loss data, making it a more suitable technique to monitor MIC by fragile biofilms.
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