Membrane BioReactor (MBR) is a wastewater treatment method which combine both biological and physical cleaning. In the membrane tank there is membrane fibres which physically separate wastewater from containing organic material. This causes the membrane fibres to easily build fouling. A measure that can describe membrane fouling, is the pressure across the fiber membranes (transmembrane pressure). The higher the pressure, the dirtier the fiber membranes. Therefore the fiber membranes need to be cleaned frequently. A current applying cleaning method, membrane air scouring, works by releasing air bubbles from the bottom of the tank to remove organic fouling from the membrane fibres. Membrane air scouring accounts for a big part of the total energy consumption. Therefore research is needed to find development opportunities to counteract membrane fouling and to make membrane air scouring more energy efficient. In this master thesis, two different air scouring strategies are used in the membrane tank to reduce the development of the membrane fouling. The first aeration strategy, with lower air supply, was operated at a constant air supply of 5.04 m3air/m3permeate. The second aeration strategy, with higher air supply, varied instead the air supply linearly with increased incoming flow. The different aeration strategies were then compared with each other, and it was looked at which aeration strategy is the most energy efficient regarding energy consumption per permeate volume produced, to reduce membrane fouling.For three weeks, each aeration strategy was applied in the pilot plant at Himmerfjärdsverket. During the strategies, maintenance cleaning was done with oxalic acid, as the commonly used chemical sodium hypochlorite was not available. The transmembrane pressure in the membrane tank was analysed during the aeration strategies to investigate how the membrane fouling developed. The sludge properties of the water in the pilot plant were also analysed, to see if these had any influence on the membrane fouling. Energy calculations were also done to for quantify the energy consumption from the membrane air scouring.The thing that had the biggest impact on energy consumption was the size of the incoming flow. Then irreversible fouling of inorganic substances that clog the membrane pores. Finally, reversible fouling of organic material that forms cakelayers on the fibres. The investigation showed that the aeration strategy with the lowest air supply was enough to successfully suppress the membrane fouling and maintain a high permeability. In pilot-scale, consumed the air strategy with lower air supply 74 Wh/m3, while the higher air supply aeration strategy consumed 92 Wh/m3for the pilot-scale membrane air cleaning. At full scale, the aeration strategy with lower air supply is expected to consume 46 Wh/m3. In full scale, more frequent maintenance cleaning may need to be done, which means poorer filtration performance during washing periods. The recommendation is to test the aeration strategy with lower air supply and at the same time have more frequent maintenance cleaning, to investigate whether it is the most energy efficient option in the long term. / Membrane BioReactor (MBR) är en vattenreningsteknik som tillämpar både biologisk och fysisk vattenrening. I membrantanken finns det membranfibrer som fysiskt separerar avloppsvattnet från det innehållande organiska materialet. Detta får membranfibrerna att lätt bli nedsmutsade. Ett mått som kan beskriva membrannedsmutsningen är trycket över membranfibrerna (transmembrantrycket). Ju smutsigare membranfibrerna är, desto sämre genomsläpplighet får de och trycket som krävs att suga vattnet igenom dem ökar. Membranfibrerna behöver därmed rengöras ofta. I dagsläget görs det med hjälp av luftbubblor som skaver bort smutsen som finns på fibrerna. Att lufta membrantanken kallas membranluftrengöring och står för en stor del av reningsteknikens totala energiförbrukning. För att göra MBR-processen till en mer energieffektiv vattenreningsteknik, behöver kunskapen öka om hur nedsmutsningen av membranen kan motverkas och membranluftrengöringen bli mer effektiv.I detta examensarbete tillämpas två olika strategier för att lufta membrantanken. Den första luftningsstrategin, med en lägre lufttillförsel, drevs med en konstant lufttillförsel på 5,04 m3luft/m3permeat. Den andra luftningsstrategi, med en högre lufttillförsel, varierade istället lufttillförseln linjärt vid ökat inkommande flöde av avloppsvatten. De olika luftningsstrategierna jämfördes sedan med varandra med avseende på vilken luftningsstrategi som är mest energieffektiv med avseende på energiförbrukning per producerad permeatvolym.I tre veckor tillämpades varsin luftningsstrategi i pilotanläggningen på Himmerfjärdsverket. Under tiden utfördes det underhållsrengöring, dock med oxalsyra, eftersom den vanligtvis använda kemikalien natriumhypoklorit inte var tillgänglig. Transmembrantrycket i membrantanken analyserades under luftningsstrategierna för att utreda hur membrannedsmutsningen utvecklat sig. Slamegenskaperna för vattnet i pilotanläggningen analyserades också, för att se om dessa hade någon påverkan på membrannedsmutsningen. Det gjordes därefter energiberäkningar för att ta reda på membranluftrengöringens energiförbrukning.Det som hade störst påverkan på energiförbrukningen visade sig vara storleken pådet inkommande flödet. Därefter irreversibel nedsmutsning som igensätter membranporerna. Sist kom reversibel nedsmutsning av organiskt material som bildar beläggningar på fibrerna. Utredningen visade att luftningsstrategin med lägst lufttillförsel var tillräcklig för att lyckas dämpa membrannedsmutsningen och bibehålla en hög genomsläpplighet. I pilotanläggningen förbrukade luftningsstrategin med lägre lufttillförsel 74 Wh/m3, medan luftningsstrategin med högre lufttillförsel förbrukade 92 Wh/m3. I fullskala förväntas luftningsstrategin med lägre lufttillförsel förbruka 46 Wh/m3. I fullskala kan mer frekvent underhållsrengöring behöva göras, vilket innebär sämre filtreringsprestanda under tvättperioderna. Rekommendationen är att testa luftningsstrategin med lägre lufttillförsel och samtidigt ha mer frekvent underhållsrengöring, för att utreda om det är det mest energieffektiva alternativet på lång sikt.

This thesis describes the rejection efficiency and the fouling behaviour of calcium sulphate solutes in a 1 nm tubular ceramic titanium dioxide nanofiltration membrane. Calcium sulphate is considered as one of the greatest scaling potential inorganic salts that responsible for membrane fouling which represents a main challenge in the expansion of membrane processes for desalination of brackish and saline water. The surface charge type and magnitude for the composite amphoteric TiO_2 membrane were characterised using streaming potential measurements. Electrokinetic membrane experiments were conducted in a background electrolyte comprising 0.01 M (NaCl). The zeta potential was estimated from the measured streaming potential using the Helmoholtz-Smoluchowski equation and the surface charge density was subsequently calculated using the Gouy-Chapman and Graham equations. The experimental results showed that the membrane was negatively charged at neutral pH and its iso-electrical point (i.e.p) was at pH of 4.0. The rejection behaviour of calcium sulphate at three different initial concentrations (0.001, 0.005 and 0.01 M) were investigated compared to other naturally occurring minerals (NaCl, Na_2 SO_4, CaCl_2) in single salt solutions. The rejection experiments were conducted at five different applied trans-membrane pressures ranged from 1.0 to 5.0 bars. Salt retention measurements showed that the rejection sequence was R (CaSO_4) > R (Na_2 SO_4) > R (CaCl_2) > R (NaCl). This rejection sequence behaviour showed an inverse relationship with the diffusion coefficients of the four salts. The salt with the lowest diffusion coefficient (CaSO_4) showed the highest rejection (43.3%), whereas that with the highest diffusion coefficient showed the lowest rejection. The rejection of calcium sulphate solution at saturation concentration was also conducted after a suspension solution of 0.015 M (CaSO_4) was prepared and filtered. The ionic analysis for calcium sulphate permeates indicated that, for the negatively charged TiO_2 membrane, the rejection for bivalent anion (SO_4^(2-) ) was higher than that of the bivalent cation (Ca^(2+) ).The critical flux (CF) experiments were carried out at six trans-membrane pressure ranged from 1.0 to 6.0 bars to identify the form and the onset of calcium sulphate fouling (as gypsum) using different concentrations below saturation concentration (0.001, 0.005, 0.01 M) and at saturation concentration. Two different flux-pressure techniques have been applied and compared to determine the critical flux values; these are: step by step technique and standard stepping technique. The obtained critical flux results from both measuring techniques (for all the four sessions) confirmed that the critical flux was reached and exceeded. The present work indicated that the resulting critical flux values from both measuring procedures were decreased as the ionic strengths of the calcium sulphate solutes were increased. A mathematical model has been proposed to identify the key parameters that affect the transport performance inside the TiO_2 nanofiltration membrane. The original Donnan steric pore model (DSPM) was used to simulate the rejection of 0.01 M sodium chloride as a reference solution. The membrane effective pore radius was estimated using two different transport models, both of these models depend on the permeation test of uncharged solute (glucose). The Donnan potential was determined based on the membrane effective fixed charge density which was determined by supposing that the membrane surface charge was uniformly distributed in the void volume of cylindrical pores. The theoretical rejection of NaCl solute for the present DSPM model was found to be in agreement with the experimental data.