China
Africa
Explore chapters and articles related to this topic
Advances in Remediation of PFAS-impacted Waters
Published in David M. Kempisty, LeeAnn Racz, Forever Chemicals, 2021
John Anderson, Pingping Meng, Tim Sidnell, Ian Ross
Nanofiltration membranes are often marketed based on a molecular weight cut off (MWCO), typically ranging from 200 to several thousand Daltons (Da). Appleman et al. (2013) demonstrated greater than 94% removal for PFCA and PFSA of chain lengths, varying from C4 to C9 for both deionized and artificially generated groundwater matrices using a NF membrane with a MWCO of 270 Da. Subsequent testing by Franke et al. (2019) indicated that PFAS with molecular weights below 270 Da were concentrated, indicating a likelihood that size exclusion was not the only mechanism for removal, and suggesting that electrostatic repulsion and diffusion into the membrane polymer could be responsible for short-chain PFAS removal. Much of the work presented was performed with the same commercial NF membrane. Additional research indicates that fabricated NF membranes designed for PFAS selectivity may provide effective capacity while increasing water recovery rates (Boo et al. 2018). However, while NF is a fully developed technology for drinking and wastewater treatment, much of the characterized PFAS-related work for NF remains on the bench-scale with implications of these developments unclear for field-scale application. NF is considered a highly implementable technology commercially and is sometimes combined with reverse osmosis (RO) as part of a more complex treatment train.
An Insight into Various Approaches toward Flux Enhancement and Fouling Mitigation of Membranes during Nano and Ultrafiltration
Published in Sundergopal Sridhar, Membrane Technology, 2018
On the other hand, the primary removal mechanism in UF is size exclusion, although the electrical charge and surface chemistry of the particles or membrane may affect the purification efficiency. UF pore ratings range from approximately 1,000 to 500,000 Da, thereby making UF more permeable than NF (2,001,000 Da). Since only high-molecular weight species are removed in UF, the osmotic pressure differential across the membrane surface is negligible. Low applied pressures are therefore sufficient to achieve high flux rates from an UF membrane. In conventional UF configurations, the process solution is pressurized, typically between 10 to 70 psi, while in contact with a supported semipermeable membrane. Solutes smaller than the molecular weight cut-off (MWCO), emerge as ultrafiltrate and retained molecules are concentrated on the pressurized side of the membrane.
Characterization Techniques
Published in Mihir Kumar Purkait, Randeep Singh, Membrane Technology in Separation Science, 2018
Mihir Kumar Purkait, Randeep Singh
Molecular weight cut-off (MWCO) is a notation used to characterize the pore size of the membranes. The MWCO of a membrane is defined as the molecular weight that is 90% rejected by the membrane [1]. For example, a membrane with 68000 MWCO means solutes of molecular weight more than or equal to 68000 Da will be 90% rejected by the membrane. The different types of MWCOs of a membrane, that is, sharp or diffuse, are shown in Figure 4.19. In this method the membrane is characterized for its MWCO by using different molecular weight solute particles, such as poly(ethylene glycol), poly(vinyl pyrrolidone), and dextran. The solutions of these different molecular weight solutes are prepared and permeated through the membrane. The solute molecular weight for which the membrane gives at least 90% rejection is taken as the MWCO of the membrane and the solute rejection is given by
Impacts of composite flocculant in coagulation/ultrafiltration hybrid process for treatment of humic acid water: the role of basicity
Published in Environmental Technology, 2021
Chenghui Yu, Baoyu Gao, Xue Shen, Fan Bu, Bo Jin, Qinyan Yue
The coagulation samples were gently decanted from the coagulation apparatus to a 300 mL cylindrical stirred beaker (MSC050, Mosu, China) for ultrafiltration. The molecular weight cut-off (MWCO) of the UF membrane (Mosu Science Equipment Co., Ltd., Shanghai, China) used in this study was 100 kDa. Permeate mass was measured by the electronic balance. The distribution of membrane resistance was used to analyse membrane fouling. Membrane resistance was calculated with the following programmes and equations [33,34].
Retention profile on the physicochemical properties of maize cooking by-product using a tight ultrafiltration membrane
Published in Chemical Engineering Communications, 2020
In US, several problems have been recently found according to the waste disposal from agro-food processing industries. Indeed, the maize processing industry produces large amounts of its primary by-product, the cooking water (Nixtamalization wastewaters) which is coming from the Nixtamalization pretreatment (Castro-Muñoz et al., 2019). This typical methodology is applied in order to remove some grain surface parts by the alkaline-thermal treatment (Valderrama-Bravo et al., 2012). As it is well known, this waste is commonly discarded in drainage without any additional treatment. Our research group has recently proposed the membrane technology as an alternative for the treatment of this cooking water (Castro-Muñoz and Yañez-Fernandez, 2015). Firstly, microfiltration (MF) was proposed to reduce the organic load in the bulk extract (Castro-Muñoz et al., 2015). Afterward, an UF step (using a 100 kDa membrane) was then successfully applied to recover the carbohydrates (Castro-Muñoz et al., 2015). Finally, a narrow pore size membrane with nominal molecular weight cutoff (NMWCO) of 1 kDa was used (Castro-Muñoz et al., 2016). The permeate stream coming from this step showed high content of total polyphenols. Basically, a clear permeate free of total soluble solids (TSS), containing low content of total solids, turbidity, carbohydrates, calcium compounds, and total organic carbon (TOC), was obtained (Castro-Muñoz et al., 2016). The recovery of polyphenols was achieved due to the fact that such compounds have a low molecular weight (lower than 700 Da) (Galanakis, 2015); which cannot be rejected for the tight UF membrane. It is needed to provide a better understanding of the retention profile of such tight UF membrane based on such type of membranes are considered in the border of the NF range. Moreover, the separation performance and productivity of these membranes depend on multiple factors, such as membrane material, molecular weight cutoff (MWCO) and operating conditions (e.g. pressure, temperature, feed flow rate, volume reduction factor, etc.) (Cassano et al., 2018). Thereby, the aim of this study is to analyze the retention profile of a tight UF (1 kDa) membrane towards the physicochemical composition of maize cooking waters at different weight reduction factor (WRF) values. For this, the physicochemical properties were determined at each experimental point. The results were analyzed and discussed in detail to provide a clear understanding of the UF process for recovering the polyphenols from maize cooking waters. Finally, a critical analysis of the membrane material used and its role in the recovery is also provided.