Academic literature on the topic 'Fouling precursors'

Transparent exopolymer particles (TEP) and their precursors have been identified as critical causal factors in fouling of desalination and other water treatment membranes. TEP and the fractions thereof are composed of a wide variety of organic constituents and size fractions and have conventionally been only quantified by an operational method, specifically, Alcian Blue measurement. For fouling control and mitigation purposes, it is important to accurately measure the amount of both TEP and TEP precursors, their fouling capacity, and their response to cleaning. However, these issues are not well understood nor are there generally accepted methods for undertaking comparative studies to address this lack of understanding. In this study, a three-stage research study was undertaken to evaluate (1) TEP and TEP precursors quantification methods, (2) TEP and TEP precursors fouling potential on seawater reverse osmosis (SWRO) membranes, and (3) hydrogen peroxide (H2O2) cleaning performance on TEP fouled SWRO membranes. It was found that the concentrations of TEP may only represent ~10% of the total mass; while TEP precursors represent ~80% of the total TEP. This highlights the importance of measuring, reporting, and operationally considering both TEP and TEP precursors for membrane biofouling studies. A reliable, adaptable statistical method using the T-test was developed to quantify and develop a criterion for differentiating fouling behaviour of different TEP surrogates and TEP fractions. Similar fouling potential was measured with total TEP, TEP, and TEP precursors at the same concentrations. Therefore, TEP concentrations rather than TEP sizes were correlated to membrane fouling. It highlighted the importance of developing new advanced pre-treatment techniques for TEP precursors removal. H2O2 cleaning enhanced water flux, possibly due to re-compaction/re-attachment of xanthan gum on the membrane surface following its breakdown into smaller fragments. The hypothesis of membrane degradation due to exposure to H2O2 during cycles of fouling and cleaning-in-place (CIP) was not supported by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), salt flux, and salt rejection results. The work strongly suggests peroxide cleaning be further evaluated with field trials as an alternative to commonly used, but more destructive, cleaning techniques.

碩士<br>國立臺灣大學<br>環境工程學研究所<br>92<br>The effect of humic acid size distribution as electric enhanced membrane process under various membrane pressure and electric voltage was investigated. Humic acid solution was divided into three groups, namely G1-25,000~3,000 Da, G2-3,000~500 Da and G3-500〜50 Da, by means of gel filtration chromatography according to their apparent molecular weight. Ultrafiltration behaviors were analyzed by the resistance-in-series model. The results showed that flux declined to the extend of initial flux 85%, 78% and 72% with pressure under 47 kPa, 74 kPa and 98 kPa, respectively. Resistance in series model also revealed that irreversible resistance raised from 6 % to 21%. Besides, humic acid removal efficiency decreased with pressure increase. While treating various molecular size solution at pressure 98 kPa. The order of flux decline was G3> G2 >G1≒ unfractionated solution. It was believed that smaller solute with stronger adsorption to the membrane pores caused serious membrane fouling and flux decline. Smaller molecular could easily pass through 100k Da membrane, thus UV254 and DOC removal efficiency was only 70 % and 47 %, respectively. However, the reversible and weak reversible resistance of the smaller molecule was 33 %, which was higher than 12 % of G1 group. Thus, frequent backwash was a promising way to deal with smaller solute. When operating the electric enhanced membrane process, electrophoresis and electroosmosis are the main mechanism to enhance the filtration process. Adding 25 V to the system could keep the flux greater than 80 % of initial flux without electric enhanced. Besides, it has capability to reduce NOM precursors containing in permeate. As a result, the electrical enhanced membrane process has the potential for drinking water treatment.

Recently, treatment plants have adopted biofiltration to compliment conventional treatment and ozonation. Previous literature has focused on passive applications of biofiltration. In this study, several pilot-scale biofiltration trains were designed in parallel to conventional treatment to investigate the impact of nutrient addition (nitrogen and phosphorus), use of hydrogen peroxide, aluminum sulphate (alum), and different filtration media (anthracite vs. granular activated carbon (GAC)) on biofiltration performance. Parameters measured included organic removal, reduction of DBP precursor, improvements in filter runtimes and ultrafiltration (UF) fouling control. Nutrient addition did not improve biofiltration performance. Supplementing hydrogen peroxide (<1 mg/L) decreased headloss, DBP formation potentials while adversely affecting UF fouling. In-line alum addition (<0.5 mg/L) improved biofilter’s ability to control fouling and DBP precursor without adversely impacting headloss. GAC provided superior performance when compared to anthracite. Conventional treatment provided higher DOC, and DBP precursor removal, as well as better UF fouling control compared to biofiltration.