On line monitoring local fouling behavior of membrane filtration process by in situ hydrodynamic and electrical measurements

© 2019 The hollow fiber ultrafiltration (UF) membrane has been widely applied in the water treatment industry, however, the membrane fouling is the core reason and limiting factor in terms of its industrial application. In the constant flux process, hollow fiber membranes (HFM) non-uniform fouling varies along the axis direction, which is the basic mechanism of HFM fouling. In this paper, the local membrane fouling behaviors and verities are investigated using electrical impedance (EI) and zeta potential (ZP) to capture the feedback signals of membrane fouling behaviors. The results are then, integrated with Hermia's model and an equivalent circuit model. As the fitting results show, both the EI and ZP can be employed as indicators of different membrane fouling states. This work defines the different stages of membrane fouling depending on the alternating relationship between EI and ZP in the membrane filtration process. Furthermore, the behavior of cake layer compaction is defined from the perspective of the membrane fouling mechanism. Therefore, this study provides an effective means for accurate identification of membrane fouling behavior. In addition, the EI and ZP exhibit great potential to identify the fouling distributions and proceedings in HFM fouling. Doing so successfully confirms that the characteristics of non-uniform fouling of HFM are reflected in the spatiotemporal difference of the fouling process

Evaluation of energy-distribution of a hybrid microbial fuel cell-membrane bioreactor (MFC-MBR) for cost-effective wastewater treatment

© 2015 Elsevier Ltd. A low-cost hybrid system integrating a membrane-less microbial fuel cell (MFC) with an anoxic/oxic membrane bioreactor (MBR) was studied for fouling mitigation. The appended electric field in the MBR was supplied by the MFC with continuous flow. Supernatant from an anaerobic reactor with low dissolved oxygen was used as feed to the MFC in order to enhance its performance compared with that fed with synthetic wastewater. The voltage output of MFC maintained at 0.52 ± 0.02 V with 1000 Ω resister. The electric field intensity could reach to 0.114 V cm-1. Compared with the conventional MBR (CMBR), the contents rather than the components of foulants on the cake layer of fouled MFC-MBR system was significantly reduced. Although only 0.5% of the feed COD was translated into electricity and applied to MBR, the hybrid system showed great feasibility without additional consumption but extracting energy from waste water and significantly enhancing the membrane filterability

Performance of a microbial fuel cell-based biosensor for online monitoring in an integrated system combining microbial fuel cell and upflow anaerobic sludge bed reactor

© 2016. A hybrid system integrating a microbial fuel cell (MFC)-based biosensor with upflow anaerobic sludge blanket (UASB) was investigated for real-time online monitoring of the internal operation of the UASB reactor. The features concerned were its rapidity and steadiness with a constant operation condition. In addition, the signal feedback mechanism was examined by the relationship between voltage and time point of changed COD concentration. The sensitivity of different concentrations was explored by comparing the signal feedback time point between the voltage and pH. Results showed that the electrical signal feedback was more sensitive than pH and the thresholds of sensitivity were S = 3 × 10-5 V/(mg/L) and S = 8 × 10-5 V/(mg/L) in different concentration ranges, respectively. Although only 0.94% of the influent COD was translated into electricity and applied for biosensing, this integrated system indicated great potential without additional COD consumption for real-time monitoring

Microbial community characteristics during simultaneous nitrification-denitrification process: effect of COD/TP ratio

© 2015, Springer-Verlag Berlin Heidelberg. To evaluate the impact of chemical oxygen demand (COD)/total phosphorus (TP) ratio on microbial community characteristics during low-oxygen simultaneous nitrification and denitrification process, three anaerobic-aeration (low-oxygen) sequencing batch reactors, namely R1, R2, and R3, were performed under three different COD/TP ratios of 91.6, 40.8, and 27.6. The community structures of each reactor were analyzed via molecular biological technique. The results showed that the composition of ammonia-oxidizing bacteria (AOB) was affected, indicated by Shannon indexes of the samples from R1, R2, and R3. Nitrosomonas was identified to be the dominant AOB in all SBRs. Moreover, the copy numbers of nitrifiers were more than those of denitrifiers, and the phosphorus-accumulating organisms to glycogen-accumulating organisms ratio increased with the decrease of COD/TP ratio

Effect of phosphorus load on nutrients removal and N<inf>2</inf>O emission during low-oxygen simultaneous nitrification and denitrification process

Three laboratory scale anaerobic-aerobic (low-oxygen) SBRs (R1, R2 and R3) were conducted at different influent phosphorus concentration to evaluate the impacts of phosphorus load on nutrients removal and nitrous oxide (N2O) emission during low-oxygen simultaneous nitrification and denitrification (SND) process. The results showed that TP and TN removals were enhanced simultaneously with the increase in phosphorus load. It was mainly caused by the enrichment of polyphosphate accumulating organisms (PAOs) under high phosphorus load and low COD/P ratio (<50), which could use nitrate/nitrite as electron acceptors to take up the phosphorus. N2O emission was reduced with increasing phosphorus load. N2O-N emission amount per cycle of R3 was 24.1% lower than that of R1. It was due to the decrease of N2O yield by heterotrophic denitrification. When the phosphorus load increased from R1 to R3, heterotrophic denitrification (D) ranged from 42.6% to 36.6% of the N2O yield. © 2013 Elsevier Ltd

Enhancing simultaneous response and amplification of biosensor in microbial fuel cell-based upflow anaerobic sludge bed reactor supplemented with zero-valent iron

© 2017 Elsevier B.V. The development of a convenient and sensitive sensor such as a microbial fuel cell (MFC) to monitor the operation of upflow anaerobic sludge blanket (UASB) is indispensable. However, the biosensor's properties were affected due to excessive acidification and suffocation of the electron transport. In this study, zero-valent iron (ZVI) was applied to restrain excessive acidification and improve the sensing performance. According to the results, the response rate of electrical signal accumulated with the addition of ZVI compared to the control reactor. As well as the electrical signal amplified and the subsidence rate maximum reached 0.059 V/h with 30 mg/L ZVI added that 883% higher than the control one during the stage (COD concentration 500 mg/L–1000 mg/L). With the electrochemical analysis, the internal resistance of ZVI-UASB-MFC decreased and redox activity promoted effectively with ZVI added. During the overloading phase, the fractional content of butyric acid changed from 53% to 31%, while that of acetic acid rose from 18% to 39% after 30 mg/L ZVI addition. These results indicated that adding ZVI to the digestion could retard excessive acidification by promoting butyric acid conversion and accumulating direct interspecies electron transfer simultaneous for enhancing the biosensor's performance. According to the Fe2+ and Fe3+ of effluent were 2.25 mg/L and 0.39 mg/L with 50 mg/L ZVI addition, moderate amount of ZVI was effective for system and safety to the environment. It might helpfully provide a promising way to enhance biosensing

Nitrous oxide emission in low-oxygen simultaneous nitrification and denitrification process: Sources and mechanisms

This study attempts to elucidate the emission sources and mechanisms of nitrous oxide (N2O) during simultaneous nitrification and denitrification (SND) process under oxygen-limiting condition. The results indicated that N2O emitted during low-oxygen SND process was 0.8±0.1mgN/gMLSS, accounting for 7.7% of the nitrogen input. This was much higher than the reported results from conventional nitrification and denitrification processes. Batch experiments revealed that nitrifier denitrification was attributed as the dominant source of N2O production. This could be well explained by the change of ammonia-oxidizing bacteria (AOB) community caused by the low-oxygen condition. It was observed that during the low-oxygen SND process, AOB species capable of denitrification, i.e., Nitrosomonas europaea and Nitrosomonas-like, were enriched whilst the composition of denitrifiers was only slightly affected. N2O emission by heterotrophic denitrification was considered to be limited by the presence of oxygen and unavailability of carbon source. © 2013 Elsevier Ltd

Characterization of fouling layers for in-line coagulation membrane fouling by apparent zeta potential

© The Royal Society of Chemistry. This study investigated the apparent zeta potential of fouled membranes for in-line coagulation membrane fouling monitoring in micro-polluted water treatment. Results show that the apparent zeta potentials are consistent with transmembrane pressures (TMPs) in both a direct filtration process and in-line coagulation ultrafiltration (C-UF). Furthermore, the curve between apparent zeta potential and filtration resistance of C-UF conformed to the form of the Michaelis-Menten equation. The changes of apparent zeta potential along with periodical backwashing were in accordance with the trend of TMP change. As a whole, apparent zeta potential could be a useful indicator for monitoring membrane fouling

Investigation of backwashing effectiveness in membrane bioreactor (MBR) based on different membrane fouling stages

© 2018 Elsevier Ltd In this study the effect of different fouling stages of hollow fiber membranes on effective backwashing length in MBR has been investigated. Computational fluid dynamics (CFD) is imported to simulate backwashing process. A multi-physics coupling model for free porous media flow, convective mass transfer and diluted species transport was established. The laser bijection sensors (LBS) were imported to monitor the backwashing solution position inside fiber lumen. Simulation results indicated that membrane fouling degree could change the velocity of backwash solution inside fiber lumen and make a further effect on effective backwash length. The signal variations of LBS are in accordance with the simulation results. The backwashing process can only play an active role when the filtration pressure is below the critical TMP. It can be concluded that backwash duration in industrial applications need to be set based on changes in TMP

Optimization of hydraulic retention time and organic loading rate for volatile fatty acid production from low strength wastewater in an anaerobic membrane bioreactor

© 2018 Elsevier Ltd This study aims to investigate the production of volatile fatty acids (VFAs) from low strength wastewater at various hydraulic retention time (HRT) and organic loading rate (OLR) in a continuous anaerobic membrane bioreactor (AnMBR) using glucose as carbon source. This experiment was performed without any selective inhibition of methanogens and the reactor pH was maintained at 7.0 ± 0.1. 48, 24, 18, 12, 8 and 6 h-HRTs were applied and the highest VFA concentration was recorded at 8 h with an overall VFA yield of 48.20 ± 1.21 mg VFA/100 mg COD feed . Three different ORLs were applied (350, 550 and 715 mg COD feed ) at the optimum 8 h-HRT. The acetic and propanoic acid concentration maximums were (1.1845 ± 0.0165 and 0.5160 ± 0.0141 mili-mole/l respectively) at 550 mg COD feed . The isobutyric acid concentration was highest (0.3580 ± 0.0407 mili-mole/l) at 715 mg COD feed indicating butyric-type fermentation at higher organic loading rate