Optimization of photocatalytic ceramic membrane filtration by response surface methodology: Effects of hydrodynamic conditions on organic fouling and removal efficiency.

The effects of the operating conditions, including the applied pressure, feed organic concentration, and recirculation flowrate along the TiO2-coated ceramic membrane, on the normalized membrane permeability and organic removal efficiency were systematically investigated by operating a photocatalytic membrane reactor (PMR). Response surface methodology (RSM) was conducted to better understand the interactive effect of operational conditions as well as their individual and combined effects to control membrane performance. Our results showed that the applied pressure and feed organic concentration, as single parameter, affected the normalized membrane permeability and organic removal efficiency more dominantly than the recirculation flowrate. The polynomial performance equations generated by RSM successfully predicted the membrane performance of the PMR. The responses to the normalized membrane permeability and organic removal efficiency with respect to the operational conditions were less sensitive to any combination of operational conditions than to their individual impacts. The combined effects of the operating conditions were less pronounced in promoting the catalytic performance of organic contaminants on the TiO2 surface. Our RSM analysis based on experimental observations designed by Box-Behnken Design (BBD) suggested that 1.3 bar of applied pressure, 44 mg/L of feed organic dye concentration and 0.8 L/min as recirculation flowrate as optimum conditions achieved more than 98% of organic removal efficiency and less than 5% of decline in normalized membrane permeability. This research shows that the RSM provides effective tool to optimize operational conditions to determine fouling rate and organic removal in PMR.

Identification of Membrane Fouling with Greywater Filtration by Porous Membranes: Combined Effect of Membrane Pore Size and Applied Pressure.

Membrane fouling caused by complex greywater synthesized by personal care products and detergents commercially available for household applications was investigated using dead-end microfiltration (MF) and analyzed systematically by a multistage Hermia blocking model as a first attempt. The highest flux decline was associated with the smallest pore size of the membrane (0.03 µm). This effectiveness was more pronounced at higher applied pressures to the membrane. A cake layer was formed on the membrane consisting mainly of silica particles present as ingredients in greywater. Although organic rejection was low by the porous MF membrane, the organic compound contributed to membrane fouling in the filtration stage. With a 0.03 µm pore size of the membrane, dominant fouling mechanisms were classified into three stages as applied pressure increased, such as complete pore blocking, intermediate pore blocking, and cake layer formation. Specifically, during the early stage of membrane filtration at 1.5 bar, membrane fouling was determined by complete pore blocking in the 0.10 µm pore size of the membrane. However, the later stage of membrane fouling was controlled mainly by intermediate pore blocking. Regardless of the applied pressure, pore constriction or standard blocking played an important role in the fouling rate with a 0.45 µm pore size of the membrane. Our results also support that complex formation can occur due to the concentration of organic and inorganic species present in simulated greywater. Thus, strategic approaches such as periodic, chemically enhanced backwashing need to be developed and tailored to remove both organic and inorganic fouling from MF membranes treating greywater.

Functional Constipation is Associated with a Decline in Word Recognition 2 Years Later in Community-Dwelling Older Adults: The Korean Frailty and Aging Cohort Study.

BACKGROUND: Consumption and cognitive impairment are the most common health problems among older adults. This study aimed to determine the effects of functional constipation on cognitive decline in community-dwelling older adults. METHODS: This was a 2-year longitudinal analysis of Korean Frailty and Aging Cohort Study data, including 851 community-dwelling residents who participated in both the baseline and follow-up surveys. A neuropsychological test, the Consortium to Establish a Registry for Alzheimer's Disease Assessment Battery (CERAD-K), and the Korean version of the Frontal Assessment Battery (FAB) were used to evaluate cognitive function. Functional constipation was defined according to the ROME IV criteria. An analysis of covariance was used to identify the association between functional constipation and cognitive decline. RESULTS: Among the 851 participants, 8.9% had functional constipation. The patients in the constipation group were more likely to have low physical activity (15.8% vs. 8.8%), polypharmacy (61.8% vs. 45.5%), and depression (30.3% vs. 17.4%) than the non-constipation group. After adjusting for potential confounding factors, including age, sex, education years, low physical activity, polypharmacy, type 2 diabetes mellitus, depression, and baseline Cognitive Function Test score, the mean changes in Word Recognition test scores from 2018 to 2020 were -0.07 and -0.54 in the non-constipation and constipation groups, respectively (p=0.007). Other cognitive function tests (Mini-Mental State Examination, word list memory, word list recall, digit span, trail-making test, and FAB) did not show any difference in decline between the two groups (p>0.05). CONCLUSIONS: Functional constipation at baseline was associated with a decline in word recognition after 2 years.

Response surface methodology to investigate the effects of operational parameters on membrane fouling and organic matter rejection in hard-shell encased hollow-fiber membrane.

The response surface methodology (RSM) was found useful statistical tool for understanding combined effect of filtration, backwashing time and dosage of sodium hypochlorite (NaOCl) added into backwash water as three operational parameters on transient behavior of transmembrane pressure (TMP) and organic rejection efficiency. Here, encased, hollow-fiber ultrafiltration (UF) system was developed for treating synthetic humic acid (HA) solution. To carry out RSM analysis, experimental matrix was designed by Box-Behnken model. Results showed that the NaOCl dosage for the chemical enhanced backwashing (CEB) as single parameter played most dominant role in fouling mitigation. Effect of hydraulic cleaning by applying the permeate backwashing only without performing the CEB was almost negligible to flush the fouling layer from membrane. Considering two correlated parameters, backwashing time combined with NaOCl dosage was found much more important than combination of other parameter such as filtration time to reduce fouling rate. Regardless of the operational parameters, the organic rejection efficiency was maintained 30% only. The RSM analysis also found that 40.1 min of filtration, 1.1 min of backwashing and 834 mg/L of NaOCl were optimum operating parameters to enhance both permeate recovery and fouling mitigation.

Phytate-mediated phosphorylation of maize, rice, and potato starches at different pH conditions.

Maize, rice, and potato starches were dispersed with phytate at pH 7, 9, and 11, and were subjected to dry-heating at 130 °C for 12 h. The residual phosphorus content and structural characteristics revealed that the treatment resulted in starch phosphorylation. Further, pasting viscosity, clarity, solubility, and swelling power were analyzed to determine the physicochemical properties of the phosphorylated starch. These heat-treated starches retained phosphorus mainly in the form of monostarch monophosphate. Phosphorylation increased the peak viscosity and decreased the pasting temperature in maize and rice starches, but not in potato starch. Paste clarity, solubility, and swelling power were also increased in phosphorylated maize and rice starches. Phosphorus content, paste clarity, solubility, and swelling power were the highest at pH 7, but the maximum paste viscosity was at pH 9. These results indicate that phytate can be used for starch phosphorylation, with the reaction efficiency based on the botanical source of the starch and the reaction pH.

Membrane fouling by sodium alginate in high salinity conditions to simulate biofouling during seawater desalination.

This study aims to better understand biofouling by algal organic matters (AOM) during seawater pretreatment by microfiltration (MF). To simulate AOM biofouling, sodium alginate (SA) solutions with three different concentrations (2, 20 and 50ppm) were filtered in dead-end mode with MF membrane. A modelling approach with blocking laws was used to identify the fouling mechanisms behind flux decline with time. The effect of SA concentration and cations such as Na+ (0.6M) and Ca2+ (0.015M) addition to SA solution on fouling mechanisms was studied. While for low SA concentration (2ppm), fouling occurs within two phases: a pore constriction phase followed by cake formation phase, for high SA concentration (50ppm), fouling occurs within only one phase controlled by cake formation. The addition of Na+ (0.6M) or Ca2+ (0.015M) to SA solution mitigates membrane fouling, however, the addition of both cations enhances fouling by formation of dense cake layer on membrane.