Combined Effect of Colloids and SMP on Membrane Fouling in MBRs

Abstract

Membrane fouling investigations in membrane bioreactors (MBRs) are a top research issue. The aim of this work is to study the combined effect of colloids and soluble microbial products (SMPs) on membrane fouling. Two lab-pilot MBRs were investigated for treating two types of wastewater (wwt), synthetic and domestic. Transmembrane pressure (TMP), SMP, particle size distribution and treatment efficiency were evaluated. Chemical Oxygen Demand (COD) removal and nitrification were successful for both kinds of sewage reaching up to 95–97% and 100%, respectively. Domestic wwt presented 5.5 times more SMP proteins and 11 times more SMP carbohydrates compared to the synthetic one. In contrast, synthetic wwt had around 20% more colloids in the mixed liquor with a size lower than membrane pore size (<400 nm) than domestic. Finally, the TMP at 36 days reached 16 kPa for synthetic wwt and 11 kPa for domestic. Therefore, synthetic wwt, despite its low concentration of SMPs, caused severe membrane fouling compared to domestic, a result that is attributed to the increased concentration of colloids. Consequently, the quantity of colloids and possibly their special characteristics play decisive and more important roles in membrane fouling compared to the SMP—a novel conclusion that can be used to mitigate membranes fouling.

Performance of a Micro-Scale Membrane Reactor for Greywater Treatment at Household Level

“…Direct membrane filtration can significantly decrease the greywater organic content; however, an important fraction (30% to 50% of COD) still remains in the permeate. The greywater colloidal particles are retained inside the membrane tank and contribute to cake layer formation, while soluble organics will gradually narrow and block the membrane pores [ 24 , 25 ]. To this end, additives can alleviate membrane fouling (at least at short-term) due to the adsorption of soluble compounds [ 26 ].…”

Optimization of Operation Parameters in Ultrafiltration by Experiment Design, Mathematical Modelling and Fouling Characterization of the Membranes Used to Remove Dissolved and Colloidal Substances from a Treated Paper Mill Effluent

“…EPSs and SMPs secretions of microorganisms with high molecular weight, three-dimensional, gel-like form and highly hydrated molecules (Banti et al, 2020).…”

“…Besides that Bound-EPS are further divided into loosely bound EPS (LBEPS), and tightly bound EPS (TBEPS) (Banti et al, 2020;Q. Liu et al, 2020;Wang et al, 2008) and;…”

“…• Yan et al 2019 • SMP have many different origins, i.e, they can be part of the debris of hydrolysed cells released into liquor during the cell lysis process, secreted during substrate metabolism from biomass growth , or even provided by the feed substrate (Banti et al, 2020;Jacquin et al, 2017;Wang et al, 2013). SMP are often classified into two main categories, based on the bacterial phase from which they were derived (Azami et al, 2012;Banti et al, 2020;Ma et al, 2015): (Wang et al, 2008). These species precipitate onto the membrane surface when the concentration of the chemical species exceeds its saturation concentration and due to hydrolysis which leads to pH change, and oxidation (Nakajima, 2013).…”

“…described that the EPS are composed by a wide range of macromolecules, such as of polysaccharides, proteins, extracellular DNA (eDNA), nucleic acids, phospholipids, metal ions and other polymeric compounds. Moreover, several researchers suggests that the proteins and polysaccharides are the major factions in EPS that contribute to biofouling, especially when they are in their soluble form as SMP(Banti et al, 2020).However, other components may also play central roles. Dissolved EPS are also referred to as SMP( Jacquin et al, 2017), more precisely SMP are composed of various organic substances such as volatile fatty acids (VFA), polysaccharides, proteins, humic acids, nucleic acids,enzymes and lipids (Banti et al, 2020;…”