Continuous-flow Membrane Bioreactor Research Articles

Insights into the life-cycle of aerobic granular sludge in a continuous flow membrane bioreactor by tracing its heterogeneous properties at different stages

This work gave insights into the life-cycle of aerobic granular sludge (AGS) by tracing its heterogeneity in the basic properties at different stages in a closed system (a continuous flow membrane bioreactor, MBR), including physical and chemical characteristics and microbial communities. The results indicate that the entire life-cycle consists of the following four stages, namely, the initial, growing, mature and cleaved stages, where multiple AGS properties synergistically affect the rheological properties of the AGS over its life-cycle. The storage modulus (G') of AGS reached its maximum value at the mature stage, whose value was significantly and positively correlated with the protein (PN) in extracellular polymeric substances (EPS) and granule size, specifically the peak area of granule size distribution, but this value was strongly and negatively correlated with the roughness. The AGS at the mature stage would be more vulnerable to be destroyed than that at other stages under the condition of higher shear strain, such as γ = 50%, which was associated with larger granule size and fewer polysaccharide (PS)-related functional groups (especially in the soluble microbial products (SMPs) in the outermost layer of AGS), and the decrease in PS was correlated with a higher relative abundance of Chloroflexi. Additionally, the value of shear strain that AGS was subjected to had a good linear correlation (R2=0.993) with the Young's modulus, which indicated the ability of AGS to resist deformation improved with increasing values of shear strain.

Continuous-flow membrane bioreactor enhances enrichment and culture of autotrophic nitrifying bacteria by removing extracellular free organic carbon.

An activated sludge system can be inoculated with enriched nitrifying bacteria to enhance NH4+-N removal, or enriched nitrifying bacteria can be added directly to a river to remove NH4+-N. However, the enrichment culture is still generally inefficient and the technical bottleneck has not been clarified. Previous studies have shown that extracellular free organic carbon (EFOC) inhibits the growth of some autotrophic bacteria, and separating EFOC during culture with a membrane bioreactor (MBR) promotes the continuous growth of autotrophic bacteria and CO2 fixation. However, whether a membrane bioreactor can also be used to enrich and culture autotrophic nitrifying bacteria by separating EFOC has not been verified. In this study, an MBR was constructed to separate EFOC during the culture of nitrifying bacteria in activated sludge to confirm that the MBR better enriches and cultures nitrifying bacteria than a sequencing batch reactor (SBR). Our results showed that after culture for 34days, the rate of NH4+-N removal and the nitrification rate by nitrifying bacteria in the MBR were 2.20-fold and 1.42-fold higher than in the SBR, respectively. The abundance of Nitrospira in the MBR was also 7.23-fold greater than in the SBR at the end of the experimental period. After 34days, the average concentration of EFOC and the average EFOC/bacterial organic carbon ratio in the MBR were only 53% and 37% of those in the SBR, respectively. A correlation analysis suggested that the timely removal by the MBR of the EFOC generated during the culture process may be an important factor in promoting the growth of autotrophic nitrifying bacteria. The possible mechanism by which the MBR separates EFOC to the growth of promote autotrophic nitrifying bacteria is discussed from the perspective of the inhibitory effect of EFOC on cbb gene transcription. Our experimental results suggest a new approach to enhancing the enrichment of autotrophic nitrifying bacteria and extending the application of MBRs.

Main components of free organic carbon generated by obligate chemoautotrophic bacteria that inhibit their CO2 fixation.

Chemoautotrophic bacteria play an important role in combating the rise in global CO2. However, recently it was found that extracellular free organic carbon (EFOC) generated by chemoautotrophic bacteria inhibits their CO2 fixation. Although continuous-flow membrane bioreactor can remove EFOC and enrich bacteria, it may also remove beneficial bio-factors for bacterial growth. Finding out the main inhibitory factors and inhibitory mechanisms in EFOC can provide theoretical guidance for the development of targeted inhibitory component removal technology. The results show a significant negative correlation between the increasing proportion of small-molecule EFOC and the decreasing trend of CO2 fixation efficiency, and simulation experiments confirm that the small molecule organics such as amino acids and organic acids are the main components of EFOC that inhibit CO2 fixation by inhibiting ribulose bisphosphate carboxylase/oxygenase (RuBisCO) gene (cbb) transcription efficiency. Therefore, amino acids and organic acids are suggested to be recovered to promote efficient CO2 fixation of autotrophic bacteria.

Rapid granulation of aerobic granular sludge and maintaining its stability by combining the effects of multi-ionic matrix and bio-carrier in a continuous-flow membrane bioreactor

The present investigation aimed at providing a novel approach to promote the rapid granulation and stability of aerobic granular sludge (AGS) in a continuous-flow membrane bioreactor (MBR). By operating two identical MBRs with or with no bio-carrier for 125 days, it was found that the combination of multi-ionic matrix and bio-carrier could promote the rapid formation and maintain the long-term stability of AGS. The primary AGS was first observed inside the reactor on day 14, and the mature AGS appeared soon and kept stable for more than 4 months (its average size still was about 800 μm on day 125). Suitable filling ratio of bio-carrier was beneficial to form a stable and regular circulating water flow inside, and adding divalent metal ions quickly reduced the negative charges of tiny sludge particles, which were two essential factors leading to the rapid granulation of AGS and maintaining its stability. The multi-ionic matrix not only enhanced the biological aggregation process, but also facilitated the expansion of the cultivated AGS into a new multi-habitat system of Mn-AGS, in which, complex microbial communities with rich bio-diversity robustly promoted the efficient removal of organic pollutants and nutrients.

N-Acyl-homoserine lactone-mediated quorum sensing of aerobic granular sludge system in a continuous-flow membrane bioreactor

The investigation aimed at revealing the N-acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) of aerobic granular sludge (AGS) system in a membrane bioreactor (MBR) with internal circulation. During the experimental period, the MBR was operated under a continuous-flow mode, in which, AGS was cultivated directly. The specific AHL molecules were determined and the correlation between the AHL-mediated QS, extracellular polymeric substance (EPS) production and microbial community was explored. Two kinds of specific signaling molecule, N-octanoyl-dl- homoserine lactone (C8-HSL) and N-tetradecanoyl-dl-homoserine lactone (C14-HSL), were detected in the cultivated AGS, but C14-HSL was the major one, which was detected to be ranging from 86.58 ng/gMLSS to 594.00 ng/gMLSS among all samples. Most importantly, the concentration of C14-HSL was positively correlated to the production of LB-EPS and TB-EPS (r > 0.906, P < 0.034, minimum ‘r’ and maximum ‘p’), which demonstrated it’s a crucial component in the formation of AGS and determined its stability. The results indicated that the structure of microbial community showed weak correlation with the content of AHLs and EPS if without the pressure of microbial selection. But, the conditions within the bioreactor determined the microbial community, and the contained functional bacteria released signaling molecules to promote the granulation.

Microbial extracellular polymeric substances (EPS) acted as a potential reservoir in responding to high concentrations of sulfonamides shocks during biological wastewater treatment

Extracellular polymeric substances (EPS), one of the main components of activated sludge, could complex with pollutants and thus influence their fate in wastewater treatment system. In this work, the roles of EPS in resisting sulfamethazine (SMZ) shocks were investigated in a continuous flow membrane bioreactor. Results show that SMZ could be intercepted in the EPS of activated sludge during the lag phase of biodegradation. EPS acted as a potential reservoir against SMZ shocks, guaranteeing undetectable SMZ in the effluent. The increased production of EPS in responding to SMZ shocks improved the binding capability of EPS to SMZ. The critical roles of microbial EPS in removing bio-refractory contaminants such as sulfonamides are probably underestimated previously.

Continuous removal of the model pharmaceutical chloroquine from water using melanin-covered Escherichia coli in a membrane bioreactor.

Environmental release and accumulation of pharmaceuticals and personal care products is a global concern in view of increased awareness of ecotoxicological effects. Adsorbent properties make the biopolymer melanin an interesting alternative to remove micropollutants from water. Recently, tyrosinase-surface-displaying Escherichia coli was shown to be an interesting self-replicating production system for melanin-covered cells for batch-wise absorption of the model pharmaceutical chloroquine. This work explores the suitability of these melanin-covered E. coli for the continuous removal of pharmaceuticals from wastewater. A continuous-flow membrane bioreactor containing melanized E. coli cells was used for adsorption of chloroquine from the influent until saturation and subsequent regeneration. At a low loading of cells (10 g/L) and high influent concentration of chloroquine (0.1 mM), chloroquine adsorbed until saturation after 26 ± 2 treated reactor volumes (39 ± 3 L). The average effluent concentration during the first 20 h was 0.0018 mM, corresponding to 98.2% removal. Up to 140 ± 6 mg chloroquine bound per gram of cells following mixed homo- and heterogeneous adsorption kinetics. In situ low-pH regeneration released all chloroquine without apparent capacity loss over three consecutive cycles. This shows the potential of melanized cells for treatment of conventional wastewater or highly concentrated upstream sources such as hospitals or manufacturing sites.

Co-existence of diverse sludge granules in a single membrane bioreactor

This preliminary investigation demonstrated that diverse sludge granules could be cultivated directly in a single continuous-flow membrane bioreactor (MBR) with the same carbon source and nutrients in influent. Results indicated the obtained sludge granules not only had obviously different colors in their appearance, but also exhibited quite diversified microbial compositions. This interesting phenomenon revealed richer microbial diversity occurring in the MBR, which was very beneficial to the stability of the microbial ecosystem within the MBR, and the efficacy of removing organic pollutants and converting nutrients. It was speculated that the main reason leading to the formation of diverse sludge granules was the micro multi-habitat produced by the complex internal circulation within the MBR. Future’s work should be focused on the mechanism, stability and kinetic of forming the diverse sludge granules in MBRs, and further verify the prospective of this novel finding in practical application fields.

Cultivating granular sludge directly in a continuous-flow membrane bioreactor with internal circulation

This research was conducted to cultivate granular sludge directly in a continuous-flow membrane bioreactor and explore the main factors influencing the granulation process. By establishing a suitable internal hydrodynamic circulation in a membrane bioreactor, granular sludge (GS) was successfully cultivated into mature granules with a compact structure and clear shape, in which extracellular polymeric substances played an important role in maintaining its integrity. The results showed that the main factors to determine the cultivation of GS included the total retention of sludge by the membrane module, the internal hydrodynamic circulation, and the entanglement of filamentous bacteria to sludge particles. Filamentous bacteria initiated a granulation process under the action of internal circulation, and maintained the stability of GS for a long period by wrapping biomass aggregates together. Even though filamentous bacteria were the major dominant microbial species in the bioreactor, the microbial community was richly biodiverse, and was responsible for the removal of organic pollutants and nutrients. Overall, the results demonstrated an alternative option for cultivating stable GS directly in a continuous-flow membrane bioreactor.

Study of aerobic granular sludge stability in a continuous-flow membrane bioreactor

A granular continuous-flow membrane bioreactor with a novel hydrodynamic configuration was developed to evaluate the stability of aerobic granular sludge (AGS). Under continuous-flow operation (Period I), AGS rapidly lost their structural integrity resulting in loose and fluffy microbial aggregates in which filamentous bacteria were dominant. The intermittent feeding (Period II) allowed obtaining the succession of feast and famine conditions that favored the increase in AGS stability. Although no further breakage occurred, the formation of new granules was very limited, owing to the absence of the hydraulic selection pressure. These results noted the necessity to ensure, on the one hand the succession of feast/famine conditions, and on the other, the hydraulic selection pressure that allows flocculent sludge washout. This preliminary study shows that the proposed configuration could meet the first aspect; in contrast, biomass selection needs to be improved.

Development of a novel process to mitigate membrane fouling in a continuous sludge system by seeding aerobic granules at pilot plant

The main goal of the current studies was to cultivate granular sludge in a continuous flow membrane bioreactor (CFMBR) to enhance the membrane performance in a pilot-scale reactor. In this regard, CFMBR was operated in two stages for 220 days; stage 1 was run without the addition of aerobic granules, while in stage 2, the aerobic granules synthesized (after a period of regulations) in a granular sludge sequencing batch reactor were seeded in the reactor. The results showed that the particle size in stage 2 was increased to nearly 625µm and SVI5 decreased to 45mL/g from that of 200µm and 145mL/g, respectively, during stage 1. The membrane fouling noted in terms of increase in transmembrane pressure values in CFMBR stage 2 was approximately 8 times lower than that of stage 1 of operation. Membrane cleaning was a regular phenomenon in stage 1, whereas no cleaning was needed during stage 2. The physicochemical analysis showed that a high PN/PS ratio (3.30) of the EPS, approximately 4-fold low soluble microbial products, a high particle size and sludge settleability were the main factors in mitigating this membrane fouling. The characterization of membrane foulants was done using FTIR spectroscopic technique.

A biological treatment of industrial wastewaters: Contois kinetics

This paper analyses the steady-state operation of a generalized bioreactor model that encompasses a continuous-flow bioreactor and an idealized continuous-flow membrane bioreactor as limiting cases. A biodegradation of organic materials is modelled using Contois growth kinetics. The bioreactor performance is analysed by finding the steady-state solutions of the model and determining their stability as a function of the dimensionless residence time. We show that an effective recycle parameter improves the performance of the bioreactor at moderate values of the dimensionless residence time. However, at sufficiently large values of the dimensionless residence time, the performance of the bioreactor is independent of the recycle ratio. doi:10.1017/S144618111500005X

A BIOLOGICAL TREATMENT OF INDUSTRIAL WASTEWATERS: CONTOIS KINETICS

This paper analyses the steady-state operation of a generalized bioreactor model that encompasses a continuous-flow bioreactor and an idealized continuous-flow membrane bioreactor as limiting cases. A biodegradation of organic materials is modelled using Contois growth kinetics. The bioreactor performance is analysed by finding the steady-state solutions of the model and determining their stability as a function of the dimensionless residence time. We show that an effective recycle parameter improves the performance of the bioreactor at moderate values of the dimensionless residence time. However, at sufficiently large values of the dimensionless residence time, the performance of the bioreactor is independent of the recycle ratio.

Start-up, influence factors, and the microbial characteristics of partial nitrification in membrane bioreactor

The partial nitrification (PN)–Anammox process was considered as one of the most efficient and economical method to remove ammonia from wastewater without organic carbon consumption. In this process, PN is the key step since it should provide stable effluent with suitable NO2-/NH4+ ratio for the subsequent Anammox. In this study, PN was successfully started-up during 30 d at ambient temperature (25°C) in a continuous flow membrane bioreactor (MBR), by gradually increasing ammonia-loading rate (ALR) under oxygen-limited condition. Finally, the system achieved an ammonia oxidation rate of 0.52 kg m−3 d−1 and an excellent effluent with appropriate NO2-/NH4+ ratio as 1.1–1.3. ALR was indicated as the indispensable controlling factor, and the applied alkalinity with the combination of high ALR inhibition and oxygen limitation provided the selective washout of nitrite-oxidizing bacteria (NOB) and an active aerobic ammonia-oxidizing (AerAOB) population. Techniques of fluorescence in situ hybridization and clone sequencing were utilized simultaneously to study the microbial characteristics in the stable PN system. The results demonstrated that small amounts of NOB were present and not active, while AerAOB predominated in the MBR–PN system, and Nitrosomonas-related AerAOB were considered to be responsible for the satisfactory PN performance.

Advanced analysis of membrane-bioreactor performance with aerobic-anoxic cycling

Mathematical modeling and intensive chemical analysis are used to quantify the relationships among the heterotrophic bacteria, autotrophic bacteria, and key inorganic (NH4+-N and NO3−-N) and organic (COD) compounds of municipal wastewater treated in a pilot-scale membrane bioreactor (MBR) operated with aerobic-anoxic cycles. Key features of the model for MBR are no biomass in the effluent, partial removal of biomass-associated products by the membrane, and D.O. cycling with 9 mg/L during aeration period and 0.5 mg/L for the anoxic period. The model explains the key trends in the cyclic data: NH4+-N is consumed only during aerobic periods and rises steadily during anoxic period; NO3−-N is produced only during aerobic periods, but declines in anoxic periods; The soluble COD in treated water mainly consists of BAP and is relatively constant through the cycle. Advantages of introducing an anoxic cycle to the continuous-flow MBR process are reduction of total effluent nitrogen, oxygen consumption, and sludge production as a consequence of denitrification. On the other hand, the anoxic period causes an increase in the average effluent NH4+-N.