Fouling mechanism elucidation in membrane bioreactors by bespoke physical cleaning

Abstract

Cake layer deposition on a membrane surface can determine both external and internal membrane fouling through negatively affecting the total filtration resistance while exerting a positive effect as a pre-filter. Membranes are usually subjected to a periodic cake layer removal through routine physical cleaning, specifically permeate backwashing of hollow fiber membranes, or enhanced cleaning through, for example, chemically-enhanced backwashing. Physical cake layer removal is crucial for sustaining permeability, yet the effect of different physical cleaning modes remains poorly evaluated. The present work attempts to analyze physical cake layer removal through the application of specific cleaning methods and the impact of these on the subsequent resistance. The constituent contributions to the overall resistance are appraised by means of the Resistances In-Series model, with the aim of producing a robust protocol for quantifying these discrete contributors. The results, based in part on published data, show the proposed approach to reliably determine the relative contribution of the different resistance components to within 0.1•10 12 •m-1 across a range of different bench and pilot-scale plants, confirming the resilience of the method.

A Brief Review on the Resistance-in-Series Model in Membrane Bioreactors (MBRs)

“…The experimental observation of different fouling mechanisms can be improved by a complementary analysis of the effects deriving from the periodic cleaning operations of membrane modules, needed for the proper management of MBR systems [ 53 , 54 , 55 , 56 , 57 ]. Indeed, some of the first review papers on membrane cleaning operations have focused their attention on the fouling phenomena and control [ 12 , 58 , 59 , 60 ].…”

Treatment of high strength industrial wastewater with membrane bioreactors for water reuse: Effect of pre-treatment with aerobic granular sludge on system performance and fouling tendency

“…In recent years, membrane bioreactors (MBRs) have attracted growing interest and they have been widely applied for the treatment of municipal as well as industrial wastewater [9,10]. Basically, MBR applies to wastewater treatment processes that integrate a perm-selective membrane with a biological process for the final solid-liquid separation [11].…”

“…Nevertheless, the main drawback associated with MBR operations is represented by membrane fouling [13,14], still hampering the world-wide application of MBRs. Basically, the membrane permeability is strongly influenced by external deposition, referred to as cake layer, as well as internal fouling, usually referred to as pore blocking [9]. The high energy consumption due to membrane aeration (needed to mitigate the extent of membrane fouling), represents another significant drawback of MBRs [15].…”

“…As aforementioned, the RIS model application during membrane cleaning operations enabled to assess the specific fouling mechanisms, according to DiBella et al (2018). The results of RIS model application are summarized inFigure 8.…”

“…In contrast, the percentage contribution of RPB slightly increased from 0.7% to 26.42% from Day 3 to Day 22, indicating that the frequency of chemical cleaning operations should be increased for the treatment of this high strength wastewater and under the explored operational conditions. Indeed, according to literature[9] it was assumed that the resistance due to pore blocking (RPB) is not removable by physical actions (either ordinary or extraordinary), but it can be partially removed through chemical actions only.Referring to Phase II(Figure 9b), it was noticed a different behaviour. Indeed, although the main fouling mechanism remained the RC,irr, it showed a slight decrease throughout experiments and it was also observed a decrease of the pore blocking contribution (from 41.20% to 25.92%) and a significant increase of reversible cake contribution (from 8.95% to 28.52%) at Day 8 and Day 35, respectively.…”