Justin Chun-Te Lin

Application of nanosilver surface modification to RO membrane and spacer for mitigating biofouling in seawater desalination

Biofouling is one the most critical problems in seawater desalination plants and science has not yet found effective ways to control it. Silver compounds and ions are historically recognized for their effective antimicrobial activity. Nanosilver particles have been applied as a biocide in many aspects of disinfection, including healthcare products and water treatment. This study proposes an innovative biofouling control approach by surface modification of the RO membrane and spacer with nanosilver coating. A chemical reduction method was used for directly coating nanosilver particles on the membrane sheet and spacer. The surface-modified membrane and spacer were tested for their antifouling performance in a cross-flow flat-sheet membrane cell, which is a part of a pilot plant in Wukan desalination plant. The silver-coating membranes and spacers, along with an unmodified membrane sheet, were tested in the membrane cell and compared on the basis of their antifouling performance. Permeate flux decline and salt rejection was continuously monitored through the testing period. Meanwhile regrowth of microbial populations on the membrane cell was quantified by a unique microbial counting every three to four days. The results showed that both silver-coated membrane (Ag-cM) with uncoated spacer and silver-coated spacer (Ag-cS) with uncoated membrane performed better than the unmodified membrane and spacer (Un-MS), in terms of much slower decrease in permeate flux and TDS rejection. However, the effect of silver-coated spacer on antimicrobial activity was more lasting. In the silver-coated spacer test, there was almost no multiplication of cells detected on the membrane during the whole testing period. Besides, the cells adhering to the membrane seemed to lose their activity quickly. According to the RO performance and microbial growth morphology, the nanosilver coating technology is valuable for use in biofouling control in seawater desalination.

Membrane Fouling Mitigation: Membrane Cleaning

Fouling is an inevitable hurdle limiting flux and performance of membrane processes. This paper reviewed the literature studies on physical cleaning methods and chemical cleaning and commented on the indices for cleaning efficiencies therein used in literature works.

Water Coagulation Using Electrostatic Patch Coagulation (EPC) Mechanism

Coagulation of fine particles to form large flocs is an essential step to reach efficient dewatering of wet materials. The electrostatic patch coagulation (EPC) mechanism was applied in this study to remove turbidity and natural organic matters in water using four different dosing-mixing schemes. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit removal of turbidity. The EPC mechanism could only efficiently remove organic matters of molecular weight of 7500–10,000 Da. Only sufficient rapid mixing is relevant to organic matter removal. The mechanisms for natural organic matters (NOM) removal are proposed to be complexation of ions and NOM to form insoluble aggregates to be separated by membrane filtration.

Pre-Treatment of Natural Organic Matters Containing Raw Water using Coagulation

Coagulation is a commonly adopted process as a pretreatment step for minimizing membrane fouling. Three coagulants, polyaluminum chloride (PACl), alum, and FeCl3 were tested under four mixing-settling schemes for turbidity and natural organic matters (NOM) removal. The organic matters in the raw waters were fractionated by high performance size exclusion chromatography (HP-SEC) system and were characterized using the excitation-emission matrix (EEM) fluorescence spectra. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit turbidity removal using PACl or FeCl3 under “electrostatic patch coagulation” (EPC) mechanism. The EPC mechanism is not efficient for alum coagulation. At higher coagulant doses, the NOM removal is not affected by mixing condition. Intensive rapid mixing alone benefits NOM removal using PACl or FeCl3. Alum is a poor coagulant for NOM removal under EPC mechanism.

Low density supercritical fluids precipitation of 9-cis and all trans-β-carotenes enriched particulates from Dunaliella salina

In this study, supercritical anti-solvent (SAS) pulverization coupled with reverse phase elution chromatography was employed to isolate 9-cis and trans-β-carotenes from Dunaliella salina. Total concentration of 9-cis (134.7mg/g) and trans-β-carotene (204.2mg/g) was increased from 338.9mg/g of the ultrasonic extract to 859.7mg/g (338.9 for 9-cis and 520.8 for trans) of the elution fraction. The SAS pulverization of the collected fraction further produced submicron-sized particulates containing 932.1mg/g (355.6 for 9-cis and 576.5 for trans) of total β-carotenes with a recovery of 86.3% (83.9% for cis and 87.8% for trans). Effects of two SAS operational conditions on the purity, recovery of total β-carotenes, mean size and morphology of the precipitates were obtained from an experimentally designed method. Generation of micronized particulates enriched with 9-cis and trans-β-carotenes by low-density SAS was proved to be feasible and environmental benign.