Removal of taste and odor model compound (2,4,6-trichloroanisole) by tight ultrafiltration membranes

Taste and odor causing organic compounds of concern to the general public are produced at low concentrations (i.e., ng/L) in surface water. Bench-scale membrane filtration experiments were conducted with 2,4,6-trichloroanisole (TCA), which is of special interest as a model compound due to its very low odor threshold level (i.e., 10 ng/L). Four different tight ultrafiltration (UF) membranes, with different molecular weight cutoffs (MWCO) and hydrophobicities were investigated. The removal of TCA decreased with increasing permeability for all of the UF membranes tested. Relatively hydrophobic UF membranes, even those with higher MWCO and permeability values, exhibited much higher TCA removal efficiencies than relatively hydrophilic UF membranes, both in the presence and absence of hydrophobic natural organic matter (Suwannee River NOM). The adsorption of TCA onto the membrane surfaces/pores through the hydrophobic interaction was found to be important for the efficient removals of TCA by hydrophobic UF membranes, especially those with greater hydrophobicities. The removals of TCA by the tight-UF membranes were affected by two major mechanisms: (1) a convection mechanism for the transmission of TCA through the membrane pores and (2) the adsorption of TCA onto the membrane surfaces/pores through hydrophobic interactionsclose141

Intermittent chlorination shifts the marine biofilm population on reverse osmosis membranes

The influence of chlorine on marine bacterial communities was examined in this study. A non-chlorine-adapted marine bacterial community (NCAM) and a chlorine-adapted bacterial community (CAM, bacterial community treated with 0.2 mg-Cl-2/L chlorine) were cultivated for 1 month. A distinct difference was observed between the NCAM and CAM, which shared only eight operational taxonomic units (OTUs), corresponding to 13.1% of the total number of identified OTUs. This result suggested that chlorine was responsible for the changes in the marine bacterial communities. Kordiimonas aquimaris was found to be a chlorine-resistant marine bacterium. The effect of intermittent chlorination on the two marine biofilm communities formed on the reverse osmosis (RO) membrane surface was investigated using various chlorine concentrations (0, 0.2, 0.4, 0.6 and 0.8 mg Cl-2/L). Although the average number of adherent marine bacteria on the RO membrane over a period of 7 weeks decreased with increasing chlorine concentration, disinfection efficiencies showed substantial fluctuations throughout the experiment. This is due to chlorine depletion that occurs during intermittent chlorination. These results suggest that intermittent chlorination is not an effective disinfection strategy to control biofilm formation

Nitrification stability and membrane performance under different water permeation intensity of an osmotic membrane bioreactor

The effects of water permeation intensity on nitrifying bacterial activity, forward osmosis (FO) membrane performance, and bacterial community structure were investigated in an osmotic membrane bioreactor (OMBR). Ammonia was partially oxidized by controlling acidification buffer concentration. Then, the FO module was externally integrated with a nitrifying bioreactor to examine nitrifying bacterial activity in response to the increased salinity. The salinity gradually increased from 2.7 to 45.7 g.L-1 total dissolved solids (TDS). Inhibition of nitrite-oxidizing activity was initiated at a salt concentration of 36.2 g.L-1 TDS. Complete ammonia-oxidizing bacteria inhibition occurred at 45.7 g.L-1 TDS. Illumina high-throughput sequencing revealed that the bacterial community responded to the operational conditions such as the ammonia loading rate and salt concentration. Only two species, Nitrosomonas eutropha and Nitrobacter winogradskyi, were responsible for nitrification in the OMBR. The cellulose triacetate FO membrane showed poor rejection efficiencies for ammonia, nitrite, and nitrate. The FO module was capable to maximally recover 107.8% water in the OMBR. However, the water permeation intensity should be appropriately adjusted to avoid nitrification failure by maintaining the optimal salinity as lower than 35 g.L TDS, which is equivalent to water permeation efficiency of 107.8% in this study

Negligible seeding source effect on the final ANAMMOX community under steady and high nitrogen loading rate after enrichment using poly(vinyl alcohol) gel carriers

This study investigated the effect of seeding source on the mature anaerobic ammonia oxidation (ANAMMOX) bacterial community niche in continuous poly(vinyl alcohol) (PVA) gel systems operated under high nitrogen loading rate (NLR) condition. Four identical column reactors packed with PVA gels were operated for 182 d using different seeding sources which had distinct community structures. The ANAMMOX reaction was achieved in all the bioreactors with comparable total and ANAMMOX bacterial 16S rRNA gene quantities. The bacterial community structure of the bioreactors became similar during operation; some major bacteria were commonly found. Interestingly, one ANAMMOX species, "Candidatus Brocadia sinica", was conclusively predominant in all the bioreactors, even though different seeding sludges were used as inoculum source, possibly due to the unique physiological characteristics of "Ca. Brocadia sinica" and the operating conditions (i.e., PVA gel-based continuous system and 1.0 kg-N/ (m(3)center dot d) of NLR). The results clearly suggest that high NLR condition is a more significant factor determining the final ANAMMOX community niche than is the type of seeding source. (C) 2018 Elsevier Ltd. All rights reserved

Chlorination caused a shift in marine biofilm niches on microfiltration/ultrafiltration and reverse osmosis membranes and UV irradiation effectively inactivated a chlorine-resistant bacterium

The effect of chlorine disinfection on marine biofilm populations and communities formed on membrane surfaces was investigated under two feedwater conditions: raw seawater and deep bed filtration-treated seawater. As a result of chlorination, the structure of the biofilm community on the microfiltration/ultrafiltration and reverse osmosis membrane coupons shifted significantly at the genus level. However, the total bacterial population was not reduced under the two feedwater conditions. This failure to control the biofilm was attributed to the adaptation and survival of selected bacteria under chlorine stress. Phaeobacter caeruleus, isolated from the biofilm, was examined as a representative chlorine-resistant biofilm-forming bacterium. The number of viable P. caeruleus was significantly reduced (as much as 99.8%) after ultraviolet (UV) disinfection. The results indicated that additional disinfection by UV irradiation can inactivate chlorine-resistant bacteria. Therefore, tandem chlorination-UV disinfection may enhance the efficiency of biofouling control in seawater reverse osmosis processes. The synergistic effects of tandem chlorination-UV irradiation on the marine biofilm community should be investigated in future studies

Analysis of Polyvinylidene Fluoride Membranes Fabricated for Membrane Distillation

The optimization of the properties for MD membranes is challenging due to the trade-off between water productivity and wetting tendency. Herein, this study presents a novel methodology to examine the properties of MD membranes. Seven polyvinylidene fluoride (PVDF) membranes were synthesized under different conditions by the phase inversion method and characterized to measure flux, rejection, contact angle (CA), liquid entry pressure (LEP), and pore sizes. Then, water vapor permeability (Bw), salt leakage ratio (Lw), and fiber radius (Rf) were calculated for the in-depth analysis. Results showed that the water vapor permeability and salt leakage ratio of the prepared membranes ranged from 7.76 × 10−8 s/m to 20.19 × 10−8 s/m and from 0.0020 to 0.0151, respectively. The Rf calculated using the Purcell model was in the range from 0.598 μm to 1.690 μm. Since the Rf was relatively small, the prepared membranes can have high LEP (more than 1.13 bar) even at low CA (less than 90.8°). The trade-off relations between the water vapor permeability and the other properties could be confirmed from the results of the prepared membranes. Based on these results, the properties of an efficient MD membrane were suggested as a guideline for the membrane development

Changes in the relative abundance of biofilm-forming bacteria by conventional sand-filtration and microfiltration as pretreatments for seawater reverse osmosis desalination

A pilot-plant to desalinate seawater using reverse osmosis membrane has been in operation for 1.7 years. Two different pretreatment systems, the conventional process with sand-filtration and the membrane-based process of microfiltration with 0.6 mu m pore size, have been used. Besides the physical, chemical, and economic indices needed to evaluate the efficiency of the pretreatment systems, the microbial community structure should be analyzed in order to ensure the removal of bio-foulants, marine biofilm-forming bacteria. In this study, the removal of biofilm-forming bacteria by two seawater reverse osmosis (SWRO) pretreatment systems was qualitatively evaluated through the construction of a 16 S rRNA gene library. The relative abundance of certain member of gamma-proteobacteria, which are responsible for the major pioneering activity in the formation of biofilms by adhesion to surfaces in the marine environment, was calculated. Raw seawater was dominated by biofilm-forming bacteria of Alteromonas (39.2%), Cowellia (7.6%), and Glaciecola (43.0%) genera. The bacterial diversity was significantly changed by the conventional pretreatment system, while microfiltration had little effect on the diversity. The conventional pretreatment system maintained the dominance of biofilm-forming bacteria, but the sum of the relative abundance of biofilm-forming bacteria was decreased from 79.8% to 50.0%. By decreasing the dominance to only 10.0%, microfiltration showed an efficiency superior to that of the conventional pretreatment system for the removal of biofilm-forming bacteria. (C) 2011 Published by Elsevier B.V

Dynamic shift in community structures of biofilm-forming bacteria by the pre-treatment systems of seawater reverse osmosis processes

In this study, the bacterial compositions of raw seawater and permeates from the conventional pre-treatment system and the membrane-based microfiltration system were examined during the seasons of autumn, winter and spring. The biofilm-forming potential was calculated based on the relative abundances of the putative biofilm-forming bacteria for the two seawater reverse osmosis pre-treatment systems. The cloning and sequencing analysis of the 16S rRNA gene reveals the dynamic shift in bacterial community structure to the genera capable of biofilm-formation through the pre-treatments. The highly diverse bacterial community structure of the raw seawater and the permeates hinders the statistical analysis for generalizing the bacterial components according to the sources or the seasons. This study proposes that the operational regimes of pre-treatment systems should be reconsidered based on the target bacterial groups of key biofilm formers. (C) 2013 Published by Elsevier B.V