Shuai Liang

Engineering application of membrane bioreactor for wastewater treatment in China: Current state and future prospect

China has been the forerunner of large-scale membrane bioreactor (MBR) application. Since the first large-scale MBR (⩾ 10 000 m3·d−1) was put into operation in 2006, the engineering implementation of MBR in China has attained tremendous development. This paper outlines the commercial application of MBR since 2006 and provides a variety of engineering statistical data, covering the fields of municipal wastewater, industrial wastewater, and polluted surface water treatment. The total treatment capacity of MBRs reached 1 × 106 m3·d−1 in 2010, and has currently exceeded 4.5 × 106 m3·d−1 with ∼75% of which pertaining to municipal wastewater treatment. The anaerobic/anoxic/aerobic-MBR and its derivative processes have been the most popular in the large-scale municipal application, with the process features and typical ranges of parameters also presented in this paper. For the treatment of various types of industrial wastewater, the configurations of the MBR-based processes are delineated with representative engineering cases. In view of the significance of the cost issue, statistics of capital and operating costs are also provided, including cost structure and energy composition. With continuous stimulation from the environmental stress, political propulsion, and market demand in China, the total treatment capacity is expected to reach 7.5 × 106 m3·d−1 by 2015 and a further expansion of the market is foreseeable in the next five years. However, MBR application is facing several challenges, such as the relatively high energy consumption. Judging MBR features and seeking suitable application areas should be of importance for the long-term development of this technology.

A ten liter stacked microbial desalination cell packed with mixed ion-exchange resins for secondary effluent desalination.

The architecture and performance of microbial desalination cell (MDC) have been significantly improved in the past few years. However, the application of MDC is still limited in a scope of small-scale (milliliter) reactors and high-salinity-water desalination. In this study, a large-scale (>10 L) stacked MDC packed with mixed ion-exchange resins was fabricated and operated in the batch mode with a salt concentration of 0.5 g/L NaCl, a typical level of domestic wastewater. With circulation flow rate of 80 mL/min, the stacked resin-packed MDC (SR-MDC) achieved a desalination efficiency of 95.8% and a final effluent concentration of 0.02 g/L in 12 h, which is comparable with the effluent quality of reverse osmosis in terms of salinity. Moreover, the SR-MDC kept a stable desalination performance (>93%) when concentrate volume decreased from 2.4 to 0.1 L (diluate/concentrate volume ratio increased from 1:1 to 1:0.04), where only 0.875 L of nonfresh water was consumed to desalinate 1 L of saline water. In addition, the SR-MDC achieved a considerable desalination rate (95.4 mg/h), suggesting a promising application for secondary effluent desalination through deriving biochemical electricity from wastewater.

Carbon filtration cathode in microbial fuel cell to enhance wastewater treatment

A homogeneous carbon membrane with multi-functions of microfiltration, electron conduction, and oxygen reduction catalysis was fabricated without using noble metals. The produced carbon membrane has a pore size of 553nm, a resistance of 6.0±0.4Ωcm(2)/cm, and a specific surface area of 32.2m(2)/g. After it was assembled in microbial fuel cell (MFC) as filtration air cathode, a power density of 581.5mW/m(2) and a current density of 1671.4mA/m(2) were achieved, comparable with previous Pt air cathode MFCs. The filtration MFC was continuously operated for 20days and excellent wastewater treatment performance was also achieved with removal efficiencies of TOC (93.6%), NH4(+)-N (97.2%), and total nitrogen (91.6%). In addition, the carbon membrane was much cheaper than traditional microfiltration membrane, suggesting a promising multi-functional material in wastewater treatment field.

Fluorescence properties of dissolved organic matter as a function of hydrophobicity and molecular weight: case studies from two membrane bioreactors and an oxidation ditch

Dissolved organic matter (DOM) plays a substantial role in wastewater treatment systems. Fluorescence is an important property of DOM and its use is promising for DOM characterization, but has rarely been extended to probing the basic physicochemical properties such as hydrophobicity and molecular weight. This study explores the possible linkages between the fluorescence properties and hydrophobicity/molecular weight of DOM, through case studies from three wastewater treatment plants (two membrane bioreactors and one oxidation ditch). The fluorescence properties of different hydrophobic/hydrophilic and molecular-weight fractions of DOM were obtained using excitation–emission matrix (EEM) spectroscopy and size-exclusion chromatography with fluorescence detection. The EEM spectra were interpreted using techniques of fluorescence regional integration, parallel factor analysis, fluorescence spectroscopic indices, and a novel energetic mapping based on fluorophore energy levels. It was found that for all the three plants, the hydrophobic fractions of DOM had a higher fluorescence intensity per UV absorbance (indicating a higher quantum yield) as well as a larger Stokes shifts than the hydrophilic fraction. The lower-molecular-weight fractions generally exhibited a higher fluorescence intensity per total organic carbon (indicating a higher fluorophore density), with the fluorescence distribution at slightly smaller excitation and emission wavelengths. These phenomena were explained via analysis of the fluorophore energy state during the excitation/emission process. The scale of the π-conjugated system in DOM molecules may serve as an intermediate factor in the correlations between the hydrophobicity/molecular weight and the fluorescence properties. These correlations may assist in developing fluorescent probes for the DOM characteristics during the process monitoring of wastewater treatment plants.

Improved blending strategy for membrane modification by virtue of surface segregation using surface-tailored amphiphilic nanoparticles

Membrane modification is one of the most feasible and effective solutions to membrane fouling problem which tenaciously hampers the further augmentation of membrane separation technology. Blending modification with nanoparticles (NPs), owing to the convenience of being incorporated in established membrane production lines, possesses an advantageous viability in practical applications. However, the existing blending strategy suffers from a low utilization efficiency due to NP encasement by membrane matrix. The current study proposed an improved blending modification approach with amphiphilic NPs (aNPs), which were prepared through silanization using 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) as coupling agents and ZnO or SiO2 as pristine NPs (pNPs), respectively. The Fourier transform infrared and X-ray photoelectron spectroscopy analyses revealed the presence of appropriate organic components in both the ZnO and SiO2 aNPs, which verified the success of the silanization process. As compared with the pristine and conventional pNP-blended membranes, both the ZnO aNP-blended and SiO2 aNP-blended membranes with proper silanization (100% and 200%w/w) achieved a significantly increased blending efficiency with more NPs scattering on the internal and external membrane surfaces under scanning electron microscope observation. This improvement contributed to the increase of membrane hydrophilicity. Nevertheless, an extra dosage of the TMSPMA led to an encasement of NPs, thereby adversely affecting the properties of the resultant membranes. On the basis of all the tests, 100% (w/w) was selected as the optimum TMSPMA dosage for blending modification for both the ZnO and SiO2 types.

Fluorescence quotient of excitation–emission matrices as a potential indicator of organic matter behavior in membrane bioreactors

The potential of using excitation–emission matrix (EEM) fluorescence spectroscopy in revealing organic matter properties has yet to be fully exploited. A fluorescence quotient (FQ) method was established to graphically compare different EEM spectra and hence, reflect the differential properties of organic matter in a wastewater treatment process on the basis of EEM. FQ is defined as a standardized element-wise quotient of two EEM spectra for organic matter in different states (e.g. before and after degradation) or in different forms (e.g. in sludge, in supernatant or on membranes as foulants). This method was applied to two full-scale membrane bioreactors, with multiple FQs calculated among the influent organics, sludge supernatant organics, extracellular polymeric substances and membrane foulants. Statistical analyses confirmed that the distribution of FQ as a function of the fluorescence excitation and emission wavelengths was significantly meaningful in highlighting the differential EEM characteristics, which enabled a clear depiction of the active regions of the different organics on an excitation–emission map. This might therefore indicate the differential propensity for a specific behavior of organic matter (such as biotransformation, sludge/water-phase distribution and membrane fouling) from the perspective of EEM. The FQ method provides a potential tool for EEM data exploitation to reflect organic matter behavior in wastewater treatment processes.

Current state and challenges of full-scale membrane bioreactor applications: A critical review

Membrane bioreactor (MBR) technology for wastewater treatment has been developed for over three decades. Our latest survey shows that MBR applications for wastewater treatment are still in rapid growth today. This review summarizes the pros, cons and progress in full-scale MBR applications. Critical statistics on the capital cost, operating cost, footprint, energy consumption and chemical consumption of full-scale MBRs are provided, and are compared to those of conventional activated sludge (CAS) processes with/without tertiary treatment. The efficiencies in full-scale treatment of ordinary pollutants (C, N and P), pathogens (bacteria and viruses) and emerging pollutants (e.g., trace organic pollutants) are reviewed. The long-term operation stability of full-scale MBRs is also discussed with several examples provided, with special attention placed on the seasonal variation of membrane fouling. Finally, the future challenges of MBR application are outlined from the perspectives of fouling control, pollutant removal, cost-effectiveness and competitiveness in specific fields of application.

Characteristic Regions of Fluorescence Excitation-Emission Matrix (EEM) to Identify Hydrophobic/Hydrophilic Contents of Organic Matter in Membrane Bioreactors

This study systematically investigated the correlations between fluorescence distributions characterized by the excitation-emission matrix (EEM) and hydrophobic/hydrophilic composition of dissolved organic matter (DOM) in membrane bioreactors (MBRs). On the basis of samples from 10 full-scale MBRs, we performed point-to-point comparisons among different components using an EEM fluorescence quotient (FQ) method and obtained a hydrophobic/hydrophilic fluorophore distribution map via Wilcoxon signed rank test. Hydrophobic acids/bases (HOA/HOB) concentrated in the low-wavelength region [excitation wavelength (Ex) < 235 nm], while hydrophilic substances (HIS) were enriched in the region of Ex > 235 nm [especially with emission wavelength (Em) = 300-360 nm]. Quantitatively, EEM regional contribution to whole wavelength fluorescence was found to significantly correlate with the hydrophobic/hydrophilic proportions of DOM, with Pearsons coefficients of 0.94 and 0.78 ( p < 0.01) for HOA and HIS, respectively. We established a linear regression model showing the HOA proportion as a function of the EEM regional contribution at (Ex, Em) = (200-285, 340-465 nm), with R2 = 0.876, which was validated via leave-one-out cross-validation and Monte Carlo simulation. This study shows a statistically hydrophobicity-dependent fluorescence property across different MBRs, and it might be applied to provide a quick estimation of hydrophobic/hydrophilic composition of DOM in wastewater treatment systems based on EEM monitoring.