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(2004)Journal ArticleIncreasing attention is being paid to health and environmental risk as a result of the presence of trace steroid estrogens in the effluent discharged from municipal sewage treatment plants. This paper focuses on assessment of removal of these trace compounds using H-3-labeled estrone as the model compound. Jar tests over a range of ferric chloride dosages and pH conditions showed that coagulation was ineffective in removal of estrone from secondary effluent. The experiments showed that the combination of powdered activated carbon (PAC) and microfiltration could be effective for removal of trace estrone from water. The rate and extent of estrone removal by PAC are functions of PAC dosage and retention time of PAC in the system. Mathematical analysis of the results using a homogeneous surface diffusion model indicates that the adsorption of estrone on PAC can be limited by film diffusion and internal surface diffusion. The surface and film mass transfer coefficients were determined to be 1.59 x 10(-9) cm(2)/ min and 0.6 cm/min, respectively, under the conditions used.
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(2003)Conference Paper
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(2008)Journal ArticleRelaxation and/or backwashing have been incorporated in most membrane bioreactor (MBR) designs as standard operating strategies to limit fouling. However, to maintain a certain net permeate production, higher instantaneous fluxes have to be applied to compensate for the loss of permeate caused by those modes of operation. To assess the effects of the different operational parameters on fouling for the same water productivity, and to study the fouling mechanisms, three relaxation and five backwashing conditions were applied in a lab-scale aerobic MBR and compared to the continuous filtration mode. Moreover, the fouling behaviour was analyzed in terms of the consequential increase in trans-membrane pressure, resistance fractions and the biopolymeric composition of the fouling layer. The Pearson correlation analysis was applied to identify the major contributor to fouling. From this study, it was found that fouling could be retarded effectively when the appropriate filtration mode was applied. The instantaneous flux applied to compensate for the loss of productivity during backwashing or relaxation periods was the major factor affecting fouling rate for either relaxation or back-washing, which was significantly correlated with the amount of solids and soluble fractions deposited on the membrane surface. The relaxation and backwashing conditions (i.e. duration, interval, strength) also considerably affected the fouling rate. In addition, it was found that pore blocking was more likely to be due to protein rather than carbohydrates and that the cake layer was the major contributor to fouling. (C) 2008 Elsevier B.V. All rights reserved.
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(2008)Journal ArticleA novel filtration mode is presented to reduce fouling propensity in membrane bioreactors (MBR). During this mode, an elevated high instantaneous flux (60 L m-2 h-1) is initially applied for a short time (120 s), followed by a longer filtration (290 s) at lower flux (10.3 L m-2 h-1) and a backwash in each filtration cycle. The mixed mode is expected to limit irreversible fouling as the reversible fouling created during the initial stage appears to protect the membrane. Hydraulic performance and the components of foulants were analyzed and compared with conventional continuous and backwash modes. It was found that the mixed mode featured lower trans-membrane pressure (TMP) after 24 h of filtration when compared to other modes. The mixed mode was effective in preventing soluble microbial products (SMP) attaching directly onto the membrane surface, keeping the cake layer weakly compressed, and reducing the mixed liquor suspended solids (MLSS) accumulation on the membrane. This strategy reduced the resistances of both the cake layer and the gel layer. A factorial experimental design was carried out for eight runs with different conditions to identify the major operational parameters affecting the hydraulic performances. The results showed that the value of the flux in the initial high-flux period had the most effect on the performance of the mixed mode: high initial flux (60 L m-2 h-1) led to improved performance. © 2008 Elsevier Ltd. All rights reserved.
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(2008)Journal ArticleDirect observation (DO) technique allowed the visualisation of fouling deposition and removal in real time and in a non-invasive manner. The DO setup was relatively simple and featured a crossflow hollow fibre membrane module, a microscope and a video camera. Transmembrane pressure (TMP) and fouling height were observed to characterise in detail the mechanisms of fouling deposition. At the end of the bentonite filtration at crossflow velocity (CFV) of 4 mm/s, the fouling thickness was measured as 85 ìm. Specific cake resistance was calculated by taking into account the cake height measurements with this technique. The DO technique also allowed unique insights into the mechanisms related to the fouling removal. The effect of bentonite concentrations were assessed to provide credibility of the technique. © 2008 Elsevier B.V. All rights reserved.
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