Jingyi Hu

Comparison of the Effects of Extracellular and Intracellular Organic Matter Extracted From Microcystis aeruginosa on Ultrafiltration Membrane Fouling: Dynamics and Mechanisms

Algae organic matter (AOM), including intracellular organic matter (IOM) and extracellular organic matter (EOM), are major membrane foulants in the treatment of algae-polluted water. In this study, the effects of EOM and IOM (at dissolved organic concentrations of 8 mg/L) on the fouling of a poly(ether sulfone) ultrafiltration (UF) membrane were investigated using a dead-end down-flow UF unit. Changes in the membrane pore geometry and the interaction energy between the membrane and foulants were analyzed based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The data (relative standard deviation within 10%) showed that UF was able to retain 57% and 46% of IOM and EOM respectively, while the corresponding membrane fluxes rapidly reduced to 28% and 33% of their respective initial values after a specific filtration volume of only 3.75 mL/cm(2). The fouling model implied that cake formation was the major mechanism. Specifically, IOM foulant had a much greater free energy of cohesion (-59.08 mJ/m(2)) than EOM foulant (3.2 mJ/m(2)), leading to the formation of a compacted cake layer on the membrane surface. In contrast, small molecules of hydrophobic EOM tended to be adsorbed into the membrane pores, leading to significant reduction of the pore size and membrane flux. Therefore, the overall fouling rates caused by EOM and IOM were comparable when both of the above-mentioned mechanisms were considered.

Tight ceramic UF membrane as RO pre-treatment: The role of electrostatic interactions on phosphate rejection

Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems.

Effect of PAC dosage in a pilot-scale PAC-MBR treating micro-polluted surface water.

To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC-MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2g/L performed the best among 0, 1, 2 and 3g/L PAC-MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1g/L PAC-MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC system. The accumulation of organic matter in the bulk mixture of 3g/L PAC-MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2g/L PAC-MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21 days operation.

Reuse of spent granular activated carbon for organic micro-pollutant removal from treated wastewater

Spent granular activated carbons (sGACs) for drinking water treatments were reused via pulverizing as low-cost adsorbents for micro-pollutant adsorption from a secondary treated wastewater effluent. The changes of physicochemical characteristics of the spent carbons in relation to the fresh carbons were determined and were correlated to the molecular properties of the respective GAC influents (i.e. a surface water and a groundwater). Pore size distribution analysis showed that the carbon pore volume decreased over a wider size range due to preloading by surface water, which contains a broader molecular weight distribution of organic matter in contrast to the groundwater. However, there was still considerable capacity available on the pulverized sGACs for atrazine adsorption in demineralized water and secondary effluent, and this was particularly the case for the groundwater spent GAC. However, as compared to the fresh counterparts, the decreased surface area and the induced surface acidic groups on the pulverized sGACs contributed both to the lower uptake and the more impeded adsorption kinetic of atrazine in the demineralized water. Nonetheless, the pulverized sGACs, especially the one preloaded by surface water, was less susceptible to adsorption competition in the secondary effluent, due to its negatively charged surface which can repulse the accessibility of the co-present organic matter. This suggests the reusability of the drinking water spent GACs for micro-pollutant adsorption in the treated wastewater.

Influence of activated carbon preloading by EfOM fractions from treated wastewater on adsorption of pharmaceutically active compounds

In this study, the preloading effects of different fractions of wastewater effluent organic matter (EfOM) on the adsorption of trace-level pharmaceutically active compounds (PhACs) onto granular activated carbon (GAC) were investigated. A nanofiltration (NF) membrane was employed to separate the EfOM by size, and two GACs with distinct pore structures were chosen for comparison. The results showed that preloading with EfOM substantially decreased PhAC uptake of the GACs; however, comparable PhAC adsorption capacities were achieved on GACs preloaded by feed EfOM and the NF-permeating EfOM. This indicates that: (1) the NF-rejected, larger EfOM molecules with an expectation to block the PhAC adsorption pores exerted little impact on the adsorbability of PhACs; (2) the smaller EfOM molecules present in the NF permeate contributed mainly to the decrease in PhAC uptake, mostly due to site competition. Of the two examined GACs, the wide pore-size-distributed GAC was found to be more susceptible to EfOM preloading than the microporous GAC. Furthermore, among the fourteen investigated PhACs, the negatively charged hydrophilic PhACs were generally subjected to a greater EfOM preloading impact.

Pharmaceutical adsorption from the primary and secondary effluents of a wastewater treatment plant by powdered activated carbon

AbstractThis study investigated the powdered activated carbon (PAC) adsorption of 13 pharmaceuticals from the primary (and secondary) effluents of a wastewater treatment plant. In addition to fresh PAC, PAC that was previously used for pharmaceutical elimination from the secondary effluent was also examined for its reuse potential in the primary effluent. The results showed a comparably negligible pharmaceutical uptake by fresh and used PACs in the primary effluent, in contrast to a substantial uptake by both PACs in the secondary effluent. This result indicated a severe adsorption competition induced from the primary effluent organic matter, i.e. the considerably higher constituents of low molecular and hydrophobic components. Furthermore, the competition effect even resulted in a desorption of the negatively charged pharmaceuticals from the used PAC into the primary effluent. It was concluded that adding fresh PAC to the secondary effluent is preferred and that recycling the used PAC into the activated ...