Impact of Natural Organic Matter on Floc Size and Structure Effects in Membrane Filtration

Abstract

Hematite (10 mg of Fe/L) floc-humic acid assemblages have been formed at pH 4 either by first aggregating hematite particles with salt (100 mM KCl) and then adding humic acid (salt-particle-organic or SPO assemblages) or by suspending the hematite particles in humic acid solutions and then adding salt to induce aggregation (organic-particle-salt or OPS assemblages). The behavior of these assemblages upon deposition on microfiltration (MF) membranes has then been investigated. In the OPS case, the fractal dimension (dF) of the assemblages formed varied dramatically depending upon the extent of charge neutralization by added fulvic acid with dF values typical of diffusion-limited cluster aggregates at low (0.1-0.2 mg/L) humic acid concentrations and dF values typical of reaction-limited cluster aggregates either in the absence of humic acid or concentrations greater than 0.4-0.6 mg/L. In the SPO case, dF values on the order of 2.1 were initially observed and were found to decrease to around 1.8-1.9 for humic acid concentrations greater than 0.6-0.8 mg/L. OPS assemblages with low fractal dimensions were found to be highly compressible once deposited on MF membranes with significantly higher specific cake resistances than was the case for SPO assemblages at transmembrane pressures of 50 kPa and above. These results highlight the importance of both the choice of coagulant (e.g., preformed vs formed in situ) and the transmembrane pressure to which a membrane filtration process might be allowed to rise prior to removal of the fouling layer.

Influence of floc structure on coagulation–microfiltration performance: Effect of Al speciation characteristics of PACls

“…The fractal dimension results showed no much difference between different Al species-dominant PACls. This is consistent with the understanding that reaction-limited aggregation (RLA, in a low salt environment) leads to compact floc (higher dF, in the range of 2.3-2.5) [4].…”

“…The hybrid coagulation-microfiltration process such as submerged membrane systems or direct membrane filtration processes which do not require to include settling processes are becoming more popular in the water industry [3]. There is also a tendency to use deadend MF or UF systems rather than pumped cross-flow systems to reduce energy consumption [4]. However, membrane fouling in dead-end mode has been known as the major problem.…”

Effect of aluminum speciation and pH on in-line coagulation/diatomite microfiltration process: Correlations between aggregate characteristics and membrane fouling

“…Cho et al [8,10] claimed that flocs with a high fractal dimension (D f ) had low compressibility, leading to low membrane permeability. Other studies, however, reported that aggregates of relatively low D f were highly compressible after their deposition on the MF membrane surface, resulting in pronouncedly increase in the specific cake resistances (higher than 50 kPa as trans-membrane pressure) [9,11]. Up to now, findings on the relationship of floc characteristics to membrane performance are not consistent, although it is believed that the structure of the cake layer plays an important role in membrane permeability.…”

Characterizations of Nanofluid Heat Transfer Enhancements

“…This membrane is commonly used to study microfiltration [65][66][67]. Shown in the Figure 10 are a schematic and photograph of the experimental apparatus used for dead end membrane filtration.…”