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.
Highlights
Shortcomings of existing conventional biological processes for wastewater treatment, such as poor effluent quality, particulates in their outflow, low volumetric and organic loading rates, high sludge production, high footprint, reduced nitrogen nitrification, low efficient in dye removal and high requirements for disinfection of the wastewater treated, have forced the community to find new treatment methods, such as those membrane bioreactors (MBRs) could offer [1,2,3,4]
The domestic wwt had 5.5 times more soluble microbial products (SMPs) proteins and 11 times more SMP carbohydrates compared to the synthetic wwt, which are attributed to higher F/M
Growth in the two wwt types, it resulted that the domestic wwt had 5.5 times more SMP proteins and 11 times more SMP carbohydrates compared to the synthetic wwt
Summary
Shortcomings of existing conventional biological processes for wastewater treatment, such as poor effluent quality, particulates in their outflow, low volumetric and organic loading rates, high sludge production, high footprint, reduced nitrogen nitrification, low efficient in dye removal and high requirements for disinfection of the wastewater treated, have forced the community to find new treatment methods, such as those membrane bioreactors (MBRs) could offer [1,2,3,4]. Despite the many advantages of MBRs, membrane fouling caused by interactions between activated sludge suspension and membrane still remains their main disadvantage, limiting their expanded application [3,5,6]. Fouling could be attributed to the adhesion of activated sludge components, such as soluble microbial products (SMPs), extracellular polymeric substances (EPSs) and colloids on the surface of the membrane or within the inner surface of pores, causing deposition in the form of biofilm and/or complete pore blockage, respectively [7,8]. According to Mesquita et al (2010) [9] when the temperature is low their concentration is decreased, whereas temperature fluctuations cause biomass stress and increase SMP and EPS.
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