Treatment of Electroplating Wastewater Using NF pH-Stable Membranes: Characterization and Application

Industrial adoption of nanofiltration (NF) for treatment of low-pH wastewater is hindered by the limited membrane lifetime at strongly acidic conditions. In this study, the electroplating wastewater (EPWW) filtration performance of a novel pH-stable NF membrane is compared against a commercial NF membrane and a reverse osmosis (RO) membrane. The presented membrane is relatively hydrophobic and has its isoelectric point (IEP) at pH 4.1, with a high and positive zeta potential of +10 mV at pH 3. A novel method was developed to determine the molecular weight cut-off (MWCO) at a pH of 2, with a finding that the membrane maintains the same MWCO (~500 Da) as under neutral pH operating conditions, whereas the commercial membrane significantly increases it. In crossflow filtration experiments with simulated EPWW, rejections above 75% are observed for all heavy metals (compared to only 30% of the commercial membrane), while keeping the same pH in the feed and permeate. Despite the relatively lower permeance of the prepared membrane (~1 L/(m2·h·bar) versus ~4 L/(m2·h·bar) of the commercial membrane), its high heavy metals rejection coupled with a very low acid rejection makes it suitable for acid recovery applications.

Using Additives for Fouling Control in a Lab-Scale MBR; Comparing the Anti-Fouling Potential of Coagulants, PAC and Bio-Film Carriers

This study investigates the effect of different additives, such as coagulants/flocculants, adsorption agents (powdered activated carbon, PAC), and bio-film carriers, on the fouling propensity of a lab-scale membrane bio-reactor (MBR) treating synthetic municipal wastewater. The coagulation agents FO 4350 SSH, Adifloc KD 451, and PAC1 A9-M at concentrations of 10 mg/L, 10 mg/L, and 100 mg Al/L, respectively, and PAC at a concentration of 3.6 ± 0.1 g/L, exhibited the best results during their batch-mode addition to biomass samples. The optimal additives FO 4350 SSH and Adifloc KD 451 were continuously added to the bioreactor at continuous-flow addition experiments and resulted in increased membrane lifetime by 16% and 13%, respectively, suggesting that the decrease of SMPc concentration and the increase of sludge filterability is the dominant fouling reduction mechanism. On the contrary, fouling reduction was low when PAC1 A9-M and PAC were continuously added, as the membrane lifetime was increased by approximately 6%. Interestingly, the addition of bio-film carriers (at filling ratios of 40%, 50%, and 60%) did not affect SMPc concentration, sludge filterability, and trans-membrane pressure (TMP). Finally, the effluent quality was satisfactory in terms of organics and ammonia removal, as chemical oxygen demand (COD), biochemical oxygen demand (BOD)5, and NH 4 + -N concentrations were consistently below the permissible discharge limits and rarely exceeded 30, 15, and 0.9 mg/L, respectively.

Free-Standing Lipid Bilayers Based on Nanopore Array and Ion Channel Formation

Integrated nanopores are novel and versatile single-molecule sensors for individual label-free biopolymer detection and characterization. However, their studies and application requires a stable lipid bilayer to maintain protein function. Herein, we describe a method for producing lipid bilayers across a nanopore array on a silicon nitride substrate. We used a painting technique commonly used with Teflon films to embed α-hemolysin (α-HL) into bilayer lipid membranes (BLMs) to form an ion channel. This was carried out in nanofluid developed in our lab. The membrane formation process, stability of BLMs and ion channel recordings were monitored by patch clamp in real-time. BLM formation was demonstrated by electrical recording (<10 pS conductance) of suspended lipid bilayers spanning a nanopore in the range of ±100 mV. Membrane resistance (Rm) and capacitance (Cm) of the device with the bilayer were assessed by membrane test as above 1.0 GΩ and ~20±2 pF, respectively. The silicon nitride surface and aperture edge were smooth at the nanometer lever leading to remarkable membrane stability. The membrane lifetime was 5–24 h. A single α-HL channel inserted in 30–60 min applied a potential of +100 mV. The α-HL channel currents were recorded at ~100±10 pA. Such integrated nanopores enable analysis of channel functions under various solution conditions from the same BLM. This will open up a variety of applications for ion channels including high-throughput medical screening and diagnosis.

Hyperbranched poly(ionic liquid) functionalized poly(ether sulfone) membranes as healable antifouling coatings for osmotic power generation

Membrane fouling and membrane deterioration are two major concerns since they greatly worsen membrane performance in pressure retarded osmosis (PRO) and shorten the membrane lifetime.

Investigations of Alkaline and Enzymatic Membrane Cleaning of Ultrafiltration Membranes Fouled by Thermomechanical Pulping Process Water

The pulp and paper industry is one of the most important industrial sectors worldwide, and has considerable potential for the sustainable fractionation of lignocellulosic biomass to provide valuable compounds. Ultrafiltration (UF) is a suitable separation technique for the profitable production of hemicelluloses from process water from thermomechanical pulping (ThMP), but is limited by membrane fouling. Improvements in cleaning protocols and new alternative cleaning agents are required to ensure a long membrane lifetime, and thus a sustainable process. This study, therefore, focuses on the cleaning of polymeric UF membranes after the filtration of ThMP process water, comparing alkaline with enzymatic cleaning agents. The aim was to develop a cleaning procedure that is efficient under mild conditions, resulting in a lower environmental impact. It was not possible to restore the initial permeability of the membrane when cleaning the membrane with enzymes alone, but the permeability was restored when using a two-step cleaning process with enzymes in the first step and an alkaline cleaning agent in the second step. Scanning electron microscopy gave a deeper inside into the cleaning efficiency. Attenuated total reflectance Fourier-transform infrared spectroscopy analysis confirmed that not only polysaccharides, but also extractives are adsorbed onto the membrane surface.

Factors Affecting Membrane Distillation Process for Seawater Desalination

Membrane distillation (MD), a process based on the thermal principle, is a combination of distillation and membrane separation in the same unit. There are many factors that can affect the MD performance, but the membrane characteristics are the most important in this process. The changes in the membrane properties affect the process efficiency, the permeate flux as well as the membrane lifetime. Some of the membrane properties mentioned in this paper include liquid entry pressure (LEP), contact angle, pore size, porosity, thickness, thermal conductivity, support layer, tortuosity, etc. This review paper aims to evaluate the membrane properties in order to reduce membrane wetting and to improve desalination efficiency. From this review, it can be seen that the LEP and contact angle are the important factors which directly affect the hydrophobicity of the membrane. When LEP and the contact angle increase, the hydrophobicity of the membrane increases. Thus, the membrane is durable and the MD system works efficiently. The remaining factors indirectly affect the operation of the MD system through LEP and contact angle (hydrophobicity).