Ionic fluid as a novel cleaning agent for the control of irreversible fouling in reverse osmosis membrane processes.

While a variety of chemical cleaning strategies has been studied to control fouling in membrane-based water treatment processes, the removal of irreversible foulants strongly bound on membrane surfaces has not been successful. In this study, we firstly investigated the diluted aqueous solutions of ionic fluid (IF, 1-ethyl-3-methylimidazolium acetate) as a cleaning agent for three model organic foulants (humic acid, HA; bovine serum albumin, BSA; sodium alginate, SA). The real-time monitoring of cleaning progress by optical coherence tomography (OCT) showed that fouling layer was dramatically swelled by introducing IF solution and removed by shear force exerted during cleaning. This phenomenon was induced due to the pre-existing interactions between organic foulants were weakened by the intrusion of IF into the fouling layer, which was analyzed by the measurement of adhesion forces using atomic force microscopy (AFM). In the experiments with model foulants and wastewater effluent, IF was added to alkaline cleaning agents (NaOH) to verify the applicability to be supplemented in commercial cleaning agents, and resulted in the significantly enhanced control of irreversible membrane fouling. Implication of utilizing recyclable IF with negligible volatility is that environmental effects of membrane cleaning solutions could be minimized by decreasing usage of cleaning chemicals, while increasing the cleaning efficiency.

Incorporation of iron (oxyhydr)oxide nanoparticles with expanded graphite for phosphorus removal and recovery from aqueous solutions.

In this work, iron (oxyhydr)oxide nanoparticle-doped expanded graphite (IO/EG-1 and IO/EG-2) was prepared via a hydrothermal reaction and applied for the phosphorus adsorption in the aqueous solutions. The analysis of scanning electron microscopy (SEM) and X-ray diffraction (XRD) verified the successful fabrication of IO/EGs, and iron (oxyhydr)oxide nanoparticles became more crystalized according to the calcination at high temperature (IO/EG-2). The maximum adsorption capacity of IO/EG-1 was considerably higher (7.30 mg/g) than that of IO/EG-2 (0.70 mg/g) mainly due to the electrostatic interaction between the negatively charged phosphate ions with iron (oxyhydr)oxides. At the neutral pH, IO/EG-1 exhibited more positively charged than IO/EG-2, which the iso-electric points (IEP) were pH of 9.1 and 6.0, respectively. The thermodynamic study also suggested that the phosphorus adsorption energy of IO/EG-1was considerably favorable (-12.13 kJ/mol) than that of IO/EG-2 (-7.43 kJ/mol). The regeneration of IO/EG-1 were efficiently achieved by a simple extraction using an alkaline solution such as NaOH. Overall, our study suggested that the prepared IO/EGs could be used as good adsorbents for the phosphorus recovery from aqueous solutions.

Enhanced Anaerobic Digestion of Long Chain Fatty Acid by Adding Magnetite and Carbon Nanotubes.

This study investigated the impact of stimulating direct interspecies electron transfer (DIET), by supplementing nano-sized magnetite (nFe3O4, 0.5 g Fe/g VSS) and carbon nanotubes (CNT, 1 g/L), in anaerobic digestion of oleic acid (OA) at various concentrations (0.10 - 4.00 g chemical oxygen demand(COD)/L). Both supplementations could enhance CH4 production, and its beneficial impact increased with increased OA concentration. The biggest improvements of 114% and 165% compared to the control were achieved by nFe3O4 and CNT, respectively, at OA of 4 g COD/L. The enhancement can be attributed to the increased sludge conductivity: 7.1 ± 0.5 (control), 12.5 ± 0.8 (nFe3O4-added), and 15.7 ± 1.1 µS/cm (CNT-supplemented). Dissolved iron concentration, released from nFe3O4, seemed to have a negligible role in improving CH4 production. The excretion of electron shuttles, i.e., humic-like substances and protein-like substances, were found to be stimulated by supplementing nFe3O4 and CNT. Microbial diversity was found to be simplified under DIET-stimulating conditions, whereby five genera accounted for 88% of the total sequences in the control, while more than 82% were represented by only two genera (Methanotrix concilli and Methanosarcina flavescens) by supplementing nFe3O4 and CNT. In addition, the abudance of electro-active bacteria such as Syntrophomonas zehnderi was significantly increased from 17% to around 45%.

Increased biodegradability of low-grade coal wastewater in anaerobic membrane bioreactor by adding yeast wastes.

Demineralization is required in upgrading low-grade coal to serve as an alternative energy resource for the production of fuel and valuable chemicals but generates a large amount of low-grade coal wastewater (LCWW). The objective of this study was to investigate the effects of a co-substrate on an anaerobic membrane bioreactor (AnMBR) treating LCWW. CH4 was not produced during the operation fed by LCWW alone. When yeast wastes (YW) were supplemented, there was a gradual increase in the biodegradability of LCWW, achieving 182 CH4 mL/g COD with 58% COD removal efficiency. The analysis of physicochemical characteristics in the effluent of AnMBR, done by excitation-emission matrix (EEM) and size exclusion chromatography (SEC), showed that the proportion of soluble microbial products (SMPs) and aromatic group with high-molecular weight (>1 kDa) increased. Microbial analysis revealed that the increased dominance of bacteria Comamonas, Methanococcus, and Methanosarcina facilitated biodegradation of LCWW in the presence of YW.

Role of extracellular polymeric substances (EPS) in biofouling of reverse osmosis membranes.

This study elucidates the mechanisms by which extracellular polymeric substances (EPS) impact permeate water flux and salt rejection during biofouling of reverse osmosis (RO) membranes. RO fouling experiments were conducted with Pseudomonas aeruginosa PAO1, EPS extracted from PAO1 biofilms, and dead PAO1 cells fixed in formaldehyde. While a biofouling layer of dead bacterial cells decreases salt rejection and permeate flux by a biofilm-enhanced osmotic pressure mechanism, the EPS biofouling layer adversely impacts permeate flux by increasing the hydraulic resistance to permeate flow. During controlled fouling experiments with extracted EPS in a simulated wastewater solution, polysaccharides adsorbed on the RO membranes much more effectively than proteins (adsorption efficiencies of 61.2-88.7% and 11.6-12.4% for polysaccharides and proteins, respectively). Controlled fouling experiments with EPS in sodium chloride solutions supplemented with 0.5 mM calcium ions (total ionic strength of 15 mM) indicate that calcium increases the adsorption efficiency of polysaccharides and DNA by 2- and 3-fold, respectively. The increased adsorption of EPS onto the membrane resulted in a significant decrease in permeate water flux. Corroborating with these calcium effects, atomic force microscopy (AFM) measurements demonstrated that addition of calcium ions to the feed solution results in a marked increase in the adhesion forces between a carboxylated particle probe and the EPS layer. The increase in the interfacial adhesion forces is attributed to specific EPS-calcium interactions that play a major role in biofouling of RO membranes.

Behaviors of intercellular materials and nutrients in biological nutrient removal process supplied with domestic wastewater and food waste.

A four-stage biological nutrient removal (BNR) process was operated to investigate the effect of anaerobically fermented leachate of food waste (AFLFW) as an external carbon source on nutrient removal from domestic wastewater having a low carbon-to-nitrogen ratio. The BNR system that was supplemented with AFLFW showed a good performance at a sludge retention time (SRT) of 30 days, despite low temperature. With this wastewater, average removal efficiencies of soluble chemical oxygen demand (COD), total nitrogen (T-N), and total phosphorus (T-P) were 88 to 93%, 70 to 74%, and 63 to 68%, respectively. In this study, several kinds of poly-hydroxyalkanoates (PHAs) were observed in cells. These included 24% poly-3-hydroxybutyrate (PHB), 41% poly-3-hydroxyvalerate (PHV), 18% poly-3-hydroxyhexanoate (PHH), 10% poly-3-hydroxyoctanoate (PHO), 5% poly-3-hydroxydecanoate (PHD). and 2% poly-3-hydroxydodecanoate (PHDD), indicating that microorganisms could store various PHAs through the different metabolic pathways. However, breakdown of the enhanced biological phosphorus removal (EBPR) mechanism was observed when SRT increased from 30 to 50 days for the enhancement of nitrification. To study the effect of SRT on EBPR, a sequencing batch reactor (SBR) system that was supplied with glucose was operated at various SRTs of 5, 10, and 15 days. Nitrification and denitrification efficiencies increased as SRT increased. However, the content of intracellular materials such as PHAs, glycogen. and poly-P in cells decreased. From these results, it was concluded that SRT should be carefully controlled to increase nitrification activity and to maintain biological phosphorus removal activity in the BNR process.