Fangshu Qu

Ultrafiltration membrane fouling by extracellular organic matters (EOM) of Microcystis aeruginosa in stationary phase: influences of interfacial characteristics of foulants and fouling mechanisms.

This paper focused on the membrane fouling caused by extracellular organic matters (EOM) which was extracted from lab-cultured Microcystis aeruginosa in stationary phase. The characteristics of EOM such as molecular weight distribution, hydrophobicity and fluorescence were measured. It was found that high molecular weight (MW) and hydrophilic organics accounted for the major parts of algal EOM which was comprised of protein-like, polysaccharide-like and humic-like substances. Ultrafiltration (UF) experiments were carried out in a stirring cell and hydrophobic polyethersulfone (PES) membranes which carried negative charge were used. Prefiltration, calcium addition and XAD fractionation were employed to change the interfacial characteristics of EOM. Then the effects of these interfacial characteristics on flux decline, reversibility and mass balance of organics were compared. Algal EOM proved to cause serious membrane fouling during UF. The fraction of algal EOM between 0.45 μm and 100 kDa contributed a significant portion of the fouling. Hydrophobic organics in EOM tended to adhere to membrane surface causing irreversible fouling, while the cake layer formed by hydrophilic organics caused greater resistance to water flow due to hydrophilic interaction such as hydrogen bond and led to faster flux decline during UF. The results also indicated that the algal EOM was negatively charged and the electrostatic repulsion could prevent organics from adhering to membrane surface. In term of fouling mechanisms, cake layer formation, hydrophobic adhesion and pore plugging were the main mechanisms for membrane fouling caused by algal EOM.

Characterization of dissolved extracellular organic matter (dEOM) and bound extracellular organic matter (bEOM) of Microcystis aeruginosa and their impacts on UF membrane fouling

Extracellular organic matter (EOM) of cyanobacteria was classified into the dissolved EOM (dEOM) which was released into culture solution and the bound EOM (bEOM) which surrounded the cells. The dEOM and bEOM extracted from Microcystis aeruginosa in stationary phase were used to study their characteristic differences and then their impacts on ultrafiltration (UF) membrane fouling. Component analyses showed that dEOM was comprised of proteins, polysaccharides and humic-like substances, while that bEOM contained only proteins and polysaccharides. Additionally, polysaccharides dominated in dEOM with a polysaccharide/DOC ratio of 1.11 mg mg(-1), while proteins were the primary components of bEOM with a protein/DOC ratio of 1.08 mg mg(-1). Results of size fractionation and XAD resin fractionation revealed that bEOM was mainly distributed in the high-MW and hydrophobic fractions, while that dEOM was more hydrophilic. Result of UF experiments indicated that dEOM which had a higher organic content and stronger hydrophilicity caused more severe flux decline and reversible fouling, and that bEOM led to slower flux decline but more irreversible fouling due to less electrostatic repulsive and more hydrophobic adhesion. The impacts of these two kinds of EOM on the UF fouling caused by cyanobacterial cells were also investigated. It was found that both flux decline and irreversible membrane fouling caused by the cells were aggravated when cells were together with EOM, especially for bEOM which might increase the surface hydrophobicity of the cells.

Relationship between soluble microbial products (SMP) and effluent organic matter (EfOM): Characterized by fluorescence excitation emission matrix coupled with parallel factor analysis

Effluent organic matter (EfOM) originating from wastewater treatment plant (WWTP) is of significant concern, as it not only influences the discharge quality of WWTP but also exerts a significant effect on the efficiency of the downstream advanced treatment facilities. Soluble microbial products (SMP) is a major part of EfOM. In order to further understand the relationship between soluble microbial products (SMP) and EfOM, and in turn, to propose measures for EfOM control, the formation of SMP and EfOM in identical activated sludge sequencing batch reactors (SBR) with different feed water was investigated using fluorescence excitation and emission spectroscopy matrix coupled with parallel factor analysis (EEM-PARAFAC) as well as other organic matter quantification tools. Results showed that EfOM contained not only SMP but also a considerable amount of allochthonous organic matter that derived not merely from natural organic matter (NOM). Four components in EfOM/SMP were identified by EEM-PARAFAC. Tyrosine-like substances in EfOM (Component 3, λex/em=270/316 nm) were mainly originated from utilization associated products (UAP) of SMP. Tryptophan-like substances (Component 2, λex/em=280/336 nm) as well as fulvic-like and humic-like substances in EfOM (Component 1, λex/em=240(290)/392 nm and Component 4, λex/em=260(365)/444 nm) were majorly derived from the refractory substances introduced along with the influent, among which Component 2 was stemmed from sources other than NOM. As solid retention time (SRT) increased, Component 2 and polysaccharides in SMP/EfOM decreased, while Component 4 in SMP increased.

Impact of dataset diversity on accuracy and sensitivity of parallel factor analysis model of dissolved organic matter fluorescence excitation-emission matrix.

Parallel factor (PARAFAC) analysis enables a quantitative analysis of excitation-emission matrix (EEM). The impact of a spectral variability stemmed from a diverse dataset on the representativeness of the PARAFAC model needs to be examined. In this study, samples from a river, effluent of a wastewater treatment plant, and algae secretion were collected and subjected to PARAFAC analysis. PARAFAC models of global dataset and individual datasets were compared. It was found that the peak shift derived from source diversity undermined the accuracy of the global model. The results imply that building a universal PARAFAC model that can be widely available for fitting new EEMs would be quite difficult, but fitting EEMs to existing PARAFAC model that belong to a similar environment would be more realistic. The accuracy of online monitoring strategy that monitors the fluorescence intensities at the peaks of PARAFAC components was examined by correlating the EEM data with the maximum fluorescence (Fmax) modeled by PARAFAC. For the individual datasets, remarkable correlations were obtained around the peak positions. However, an analysis of cocktail datasets implies that the involvement of foreign components that are spectrally similar to local components would undermine the online monitoring strategy.

Effect of granular activated carbon addition on the effluent properties and fouling potentials of membrane-coupled expanded granular sludge bed process

To mitigate membrane fouling of membrane-coupled anaerobic process, granular activated carbon (GAC: 50 g/L) was added into an expanded granular sludge bed (EGSB). A short-term ultrafiltration test was investigated for analyzing membrane fouling potential and underlying fouling mechanisms. The results showed that adding GAC into the EGSB not only improved the COD removal efficiency, but also alleviated membrane fouling efficiently because GAC could help to reduce soluble microbial products, polysaccharides and proteins by 26.8%, 27.8% and 24.7%, respectively, compared with the control system. Furthermore, excitation emission matrix (EEM) fluorescence spectroscopy analysis revealed that GAC addition mainly reduced tryptophan protein-like, aromatic protein-like and fulvic-like substances. In addition, the resistance distribution analysis demonstrated that adding GAC primarily decreased the cake layer resistance by 53.5%. The classic filtration mode analysis showed that cake filtration was the major fouling mechanism for membrane-coupled EGSB process regardless of the GAC addition.

Comparison of Hydrophilicity and Mechanical Properties of Nanocomposite Membranes with Cellulose Nanocrystals and Carbon Nanotubes

The inherent properties of hydrophilicity and mechanical strength of cellulose nanocrystals (CNCs) make them a possible alternative to carbon nanotubes (CNTs) that may present fewer objections to application water-treatment membranes. In this work, the hydrophilicity and mechanical properties of CNCs and CNTs nanocomposite poly(ether sulfone) (PES) membranes were characterized and compared. Membrane pore geometry was analyzed by scanning electron microscopy (SEM). Overall porosity and mean pore radius were calculated based on a wet-dry method. Results showed that PES polymers were loosely packed in the top layer of both the CNC- and CNT-composite membranes (CNC-M and CNT-M). The porosity of the CNC-M was greater than that of the CNT-M. Membrane hydrophilicity, measured by water-contact angle, free energy of cohesion, and water flux, was increased through the addition of either CNCs or functionalized CNTs to an otherwise hydrophobic polymer membrane. The hydrophilicity of the CNC-M was greater than the CNT-M. In addition, the Youngs modulus and tensile strength was enhanced for both the CNC-M and CNT-M. While smaller concentrations of CNTs were required to achieve an equal increase in Youngs modulus compared with the CNCs, the elasticity of the CNC-composite membranes was greater.

Effect of adding wood chips on sewage sludge dewatering in a pilot-scale plate-and-frame filter press process

The addition of wood chips combined with cationic polyacrylamide (CPAM) and polymeric aluminium chlorides (PACl) to sewage sludge was investigated to enhance the dewatering in a pilot-scale plate-and-frame filter press. The results indicated that the chemical coagulation significantly affected the moisture content (MC) and specific resistance to filtration (SRF) of the sludge in bench-scale tests. The lowest MC and SRF were 87.93% and 0.31 × 1011 m kg−1, respectively, for CPAM and PACl dosages of 0.04% and 4%, respectively. However, when the wood chips were combined with chemical coagulation conditioning, minimal improvements were noted in the sludge dewatering ability compared to the coagulation conditioning alone. Moreover, the addition of wood chips was effective for the subsequent plate-and-frame filter press dewatering process. The wood chips acted as skeleton builders during this high-pressure dewatering (1.0 MPa). The lowest MC was 50.3% when the dosages of CPAM, PACl and wood chips were 0.05%, 4% and 100%, respectively. Furthermore, a wood chip dosage of 100% increased the high heat value (HV) and low HV of the products by 20% and 150%, respectively, compared to the control. Several subsequent disposal options, such as landfilling, incineration and bio-composting, are proposed as a result of the low MC and high low HV of the products.

Biofouling control by biostimulation of quorum-quenching bacteria in a membrane bioreactor for wastewater treatment.

Bacterial quorum quenching (QQ) has been shown to be effective in controlling biofouling in membrane bioreactors (MBRs) for wastewater treatment. However, the encapsulation of a sufficient level of QQ bacteria is complicated and difficult. In plant research, gamma‐caprolactone (GCL), which is structurally similar to the quorum signal, N‐acyl homoserine lactone (AHL), was successfully used to specifically stimulate AHL‐degrading bacteria (biostimulation) in hydroponic systems to control blackleg and soft rot diseases in potato. In this study, the feasibility of enriching QQ bacteria from activated sludge by GCL was examined, and the effect of biostimulation on biofouling control in MBR treating domestic wastewater was investigated. The results showed that after enrichment with GCL, activated sludge could effectively degrade AHLs, and a QQ gene (qsdA) was augmented. The proposed biostimulation QQ strategy, by introducing and continuously dosing GCL, could significantly increase QQ activity, decrease AHL, control the secretion of extracellular polymeric substances (EPS), and thus, effectively control biofouling in an MBR. This biostimulation QQ strategy provides a more convenient option for biofouling control in MBR applications. Biotechnol. Bioeng. 2016;113: 2624–2632.

Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition

As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl2 solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na(+) or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca(2+) in backwash water significantly decreased the backwash efficiency. Moreover, Ca(2+) played an important role in foulant removal, and the residual HA content closely related to the residual Ca(2+) content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na(+) and HA, respectively.

Effect of quorum quenching on biofouling and ammonia removal in membrane bioreactor under stressful conditions

Quorum quenching (QQ) has been used to control biofouling in membrane bioreactors (MBRs), but the effect of QQ on the performance of MBR has not been systematically studied. This study investigated the effect of QQ on ammonia removal in MBR especially in some stressful conditions. The results showed that membrane fouling was effectively alleviated by QQ in all conditions. For the short HRT (3.94 h), the ammonia removal in QQ-MBR was fluctuating. In the presence of nitrification inhibitors (acetonitrile and allylthiourea) or at low temperature (10 °C), QQ induced much more significant suppression on nitrification in batch test and MBR. The number of the ammonia oxidizing bacteria (AOB) was not decreasing in these situations, which indicated that QQ only suppressed the activity of AOB. In all, comprehensive considerations should be taken into account when applying a QS tuning strategy to a bioreactor.