Measurement of Foam Quality of Activated Sludge in MBR Process

Abstract

Sludge in MBR ProcessSystems Engineering, Faculty of Science and Engineering, MBR (membrane bioreactor) process has been applied to wastewater treatment plants Ritsumeikan University, recently. It is well known that the most important point of the optimum maintenance is 1-1-1 Nojihigashi, control of membrane clogging in the process. Suitable indices for operation and mainteKusatsu, 525-8577, Japan nance in MBR are desired to predict the timely cleaning period and carry out the effective cleaning of the membrane. A large amount of foam is sometimes produced in MBR facilities. Some foam seems to be produced by extracellular protein that is known to cause the membrane clogging. Therefore measurement methodology of foam quality produced by activated sludge in MBR process and characteristics of its extracellular polymer substances (EPS) were studied. The conclusions were: (1) EPS was able to be extracted by steaming treatment on the optimum condition at 105°C for 30 minutes. (2) Bingham viscosity and yield stress of activated sludge were measured. The yield stress was contributed by EPS and this suggested that EPS was one important factor for foaming. (3) The measurement of foam quality using a video camera showed good performance. The foaming power and the foam stability increased proportionally with the concentration of protein in EPS. It was clear that the protein concentration in EPS was strongly related to the foam quality and quantity. (4) The foaming power decreased by addition of MLSS. This decrease was caused by adsorption of EPS to MLSS. Foaming in an aeration tank will be an index for membrane cleaning requirement. Bestimmung der Schaumqualität von Belebtschlamm in Membranbioreaktoren

Evaluating the Measurement of Activated Sludge Foam Potential

“…Foaming power is a test which concentrates on what happens during foam production rather than the volume or stability of the foam produced. Albumin and EPS were extracted from mixed liquor samples taken from the MBR process and the foaming power due to these components was determined as the sample volume consumed during foam production [10]. Foaming power was found to increase proportionally to the protein content within the EPS.…”

“…In large volumes foam can result in a multitude of operational problems including: reduction in plant performance, physical hazard to operators from exposure to pathogens and walkway obstruction [2][3][4][5], blockage of pipes [1], reduction in oxygen transfer [6], interference with essential plant monitoring equipment [2], and risk to consent failure thorough solids loss from the final settlement stage of the treatment process [7][8][9]. Recently, the presence of foam has also been recognised in systems which employ advanced wastewater treatment such as membrane bioreactors (MBR) [10].…”

“…The exact mechanism of how foaming is initiated and then stabilized still remains unanswered [6,10,11]. In general terms, the formation of foam initially involves the dispersion of a gas in a liquid [6].…”

“…One widely recognized theory behind activated sludge foaming is that the hydrophobic filaments attach themselves to surfaces of solid particles to create what is described as 'three-phase foams [20]'. Following this, the floc particles then have the ability to adhere to the surface of gas bubbles, causing them rise and form a stable froth on the surface of aeration basins [10,14]. These hydrophobic filaments are also believed to perform an additional role of producing extra bio-surfactants [21] as well as stabilizing foam bubbles by bridging the interspatial water layer, forming a dam which then prevents liquid drainage and film thinning [19,22].…”

“…These hydrophobic filaments are also believed to perform an additional role of producing extra bio-surfactants [21] as well as stabilizing foam bubbles by bridging the interspatial water layer, forming a dam which then prevents liquid drainage and film thinning [19,22]. Within MBRs the occurrence of foams has been linked to the presence of extracellular polymeric substances (EPS) in the form of extracellular proteins [10]. These have the characteristics of surface active agents and can come from sources other than filamentous bacteria [23].…”