• Environmental Engineering Research
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• v.20 no.3
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• pp.223-229
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• 2015

The application of coagulation for feed water pretreatment prior to microfiltration (MF) process has been widely adopted to alleviate fouling due to particles and organic matters in feed water. However, the efficiency of coagulation pretreatment for MF is sensitive to its operation conditions such as pH and coagulant dose. Moreover, the optimum coagulation condition for MF process is different from that for rapid sand filtration in conventional drinking water treatment. In this study, the use of response surface methodology (RSM) was attempted to determine coagulation conditions optimized for pretreatment of MF. The center-united experimental design was used to quantify the effects of coagulant dose and pH on the control of fouling control as well as the removal organic matters. A MF membrane (SDI Samsung, Korea) made of polyvinylidene fluoride (PVDF) was used for the filtration experiments. Poly aluminum chloride (PAC) was used as the coagulant and a series of jar tests were conducted under various conditions. The flux was $90L/m^2-h$ and the fouling rate were calculated in each condition. As a result of this study, an empirical model was derived to explore the optimized conditions for coagulant dose and pH for minimization of the fouling rate. This model also allowed the prediction of the efficiency of the coagulation efficiency. The experimental results were in good agreement with the predictions, suggesting that RSM has potential as a practical method for modeling the coagulation pretreatment for MF.

• Journal of Biosystems Engineering
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• v.33 no.1
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• pp.30-37
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• 2008

Dynamic excitation and response analysis is an acceptable method to determine some of physical properties of agricultural product for quality evaluation. There is a difference in the internal viscoelasticity between sound and defective fruits due to the difference of geometric structures, thereby showing different vibration characteristics. This study was carried out to develop a portable piezoelectric film-based glove sensor system that can separate internally damaged watermelons from sound ones using an acoustic impulse response technique. Two piezoelectric sensors based on polyvinylidene fluoride (PVDF) films to measure an impact force and vibration response were separately mounted on each glove. Various signal parameters including number of peaks, energy ratio, standard deviation of peak to peak distance, zero-crossing rate, and integral value of peaks were examined to develop a regression-estimated model. When using SMLR (Stepwise Multiple Linear Regression) analysis in SAS, three parameters, i.e., zeros value, number of peaks, and standard deviation of peaks were selected as usable factors with a coefficient of determination ($r^2$) of 0.92 and a standard error of calibration (SEC) of 0.15. In the validation tests using twenty watermelon samples (sound 9, defective 11), the developed model provided good capability showing a classification accuracy of 95%.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.1
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• pp.95-106
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• 2011

Even though MBR processes have many advantages such as high quality effluents, a small footprint and convenience for operation compared to conventional activated sludge processes, there are some shortcomings in terms of the cost and potential fouling incident that keeps MBR (Membrane bioreactor) processes from being widely applied. To reduce these problems, PTFE (Polytetrafluoroethylene) flat sheet membranes that have excellent permeability and durability were tested instead of PVDF (Polyvinylidene fluoride) membrane which is being used widely in water treatment. Low concentration of sodium hydroxide (NaOH) was also added into the membrane modules in order to prevent the membrane fouling as well as to provide the alkalinity. With conditions mentioned above, a pilot-scale MBR system based on the MLE (Modified Ludzack Ettinger) process was operated at flux of 40 $L/m^{2}/hr$ and over 15,000 mg/L MLSS concentration for about 8 months. And coagulant(alum) was added into the membrane tank to remove phosphorus. Although the more coagulant is added the more effectively phosphorus is removed, that can lead to fouling for a long operation(Ronseca et al.,2009). By the way there is a research that fouling grow up after stopping injection of coagulant(Holbrook, 2004). Stable operation of MBR systems was achieved without major chemical cleaning and the effluent quality was found to be good enough to comply with the treated waste water quality regulations of the Korea.

• Membrane and Water Treatment
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• v.13 no.5
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• pp.235-243
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• 2022

The paper presents the effect of operating temperatures and flow rates on the distillate flux that can be obtained from a hydrophobic membrane having the characteristics: pore size of 0.15 ㎛; thickness of 130 ㎛; and 85% porosity. That membrane in the present investigation could be the direct contact (DCMD) or the air-gap membrane distillation (AGMD). To model numerically the membrane distillation processes, the two-dimensional computational fluid dynamic (CFD) is used for the DCMD and AGMD cases here. In this work, DCMD and AGMD models have been validated with the experimental data using different flows (Parallel and Counter-current flows) in non-steady-state situations. A good agreement is obtained between the present results and those of the experimental data in the literature. The new approach in the present numerical modeling has allowed examining effects of the nature of materials (Polyvinylidene fluoride (PVDF) polymers, copolymers, and blends) used on thermal properties. Moreover, the effect of the area surface of the membrane (0.021 to 3.15 ㎡) is investigated to explore both the laminar and the turbulent flow regimes. The obtained results found that copolymer P(VDF-TrFE) (80/20) is more effective than the other materials of membrane distillation (MD). The mass flux and thermal efficiency reach 193.5 (g/㎡s), and 83.29 % using turbulent flow and an effective area of 3.1 ㎡, respectively. The increase of feed inlet temperatures and its flow rate, with the reduction of cold temperatures and its flow rate are very effective for increasing distillate water flow in MD applications.