Increasing global mean temperature influences the hydrologic cycle. In the 21st century, hydrologic change featuring more heavy precipitation events is very likely according to the UN Intergovernmental Panel on Climate Change, IPCC. This change will have a great impact on urban environments and infrastructures. In Sweden, precipitation during the winter will most likely increase by as much as 30 to 50 % by the end of the 21st century, while summer precipitation will decrease in the southern and middle parts of Sweden. Recent years have seen a number of floods caused by heavy rainfalls. With climate change, the problem with floods can be expected to continue and increase. To prevent adverse damage, modelling how the changes in precipitation and temperature will influence the urban drainage systems and how measures can be taken to prevent or reduce the consequences of floods has become increasingly important. The main objective with this thesis is to investigate the hydraulic impact in an urban drainage system due to the presumed increase in intense rainfalls. Regional Climate models produce temperature and precipitation data for the future. The regional climate model RCA3 from Rossby Center at SMHI, produces data with a spatial resolution of 50*50 km and a temporal resolution of 30 min. To be able to use the climate data in urban drainage models, temporal and spatial resolution must be improved. A modification of the so-called Delta change method, where the changes are related to the rainfall intensity level, is presented to transfer the changes in rain characteristics from different future time periods to an observed series. For the study area, the climate model shows an increase of the highest intensities of up to 20 % for the 21st century. Effects of these changes are studied on an urban drainage system in the study area. Results from the urban drainage simulations show that higher water flow- ratios in pipes, longer durations of floods, and more frequent floods can be expected if the climate continues to change with more high intensity rains, as the climate models predict. The maximum water levels in nodes were significantly higher for all future time periods that were simulated. Even in the near future (2011-2040), maximum water levels in nodes were >0,1 m higher compared to today's climate. Since the renewal rate of pipes in the existing urban drainage system is relatively slow, emphasis must not lie only on city development but also on future climate change. Design criteria, therefore, need to be changed according to changes in precipitation. Weak spots in the system must be identified for the adaptation to be as effective as possible. Knowing when, where, and how to put the correct measures when adapting the urban drainage system is essential for efficient management. Climate change also affects urban drainage in different ways, depending on where in Sweden the city lies. In northern Sweden, problems can arise with changing snowmelt patterns, for example. Further research involves an analysis of the consequences that higher water levels, increased max flow, and higher seasonal variations will have and of the adaptation strategies required not only for the urban drainage systems but also for other infrastructures. / En ökad global medeltemperatur påverkar den hydrologiska cykeln och enligt FNs klimatpanel, IPCC, är det väldigt troligt att detta leder till fler häftiga regn under 2000-talet. Förändringen i nederbörd får stor inverkan på den urbana miljön och infrastrukturen. I Sverige ökar nederbörden vintertid med så mycket som 30-50 % i slutet av 2000-talet medan sommarnederbörden minskar i mitten och södra delarna av Sverige. De senaste åren har uppvisat ett antal översvämningar orsakade av häftiga regn. Med klimatförändringen kommer troligtvis problemen med översvämningar fortsätta att öka. Därmed har det blivit ännu viktigare att modellera hur förändringar i nederbörden påverkar det urbana dagvattensystemen och vilka åtgärder som kan sättas in för att förhindra allvarliga översvämningar och skador i framtiden. Huvudsyftet med den här avhandlingen är att undersöka vilken hydraulisk effekt den förändrade nederbörden har på urbana dagvattensystem. Regionala klimatmodeller simulerar bland annat framtida temperatur och nederbördsdata. Den regionala klimatmodellen RCA3 från Rossby Centre på SMHI, producerar data med en spatial upplösning av 50*50 km och en tidsupplösning av 30 min. För att kunna använda klimatdata i en urban dagvattenmodell måste den spatiala och tidsmässiga upplösningen förbättras. En modifiering av den så kallade Delta Change-metoden, där förändringarna är relaterade till intensiteten i nederbörden presenteras för att överföra förändringar i framtida regnkarakteristika till en uppmätt regntidsserie. För försöksplatsen visar klimatmodellen en ökning av de högsta intensiteterna med upp till 20 % under 2000-talet. Vilka hydrauliska effekter denna förändring ger upphov till studeras i en modell av ett urbant dagvattensystem från en försöksplats i södra Sverige. Resultaten från simuleringarna visar att större vattenflöde i ledningarna, längre varaktighet vid översvämningar och mer frekventa översvämningar kan förväntas om klimatet fortsätter att förändras i linje med vad klimatmodellerna förutspår. Vattennivåerna i brunnarna var signifikant högre för alla tidsperioder som simulerades. Även i den närmsta perioden (2011-2040) blir den maximala vattennivån i brunnarna 0,1 m högre jämfört med dagens klimat. Eftersom förnyelsetakten för ledningsnäten är relativt långsam så bör man inte bara titta på stads- och befolkningsutvecklingen utan även förändringar i klimatet när åtgärder planeras. Att veta när, var och hur åtgärder ska sättas in för att anpassa systemet är viktigt för en effektiv förvaltning av ledningsnäten. Svaga länkar i systemen måste identifieras för att anpassningen ska bli så effektiv som möjligt. Dimensioneringskriterier behöver ändras i linje med förändringar i nederbörden. Klimatförändringen påverkar också den urbana dräneringen på olika sätt beroende var i Sverige som staden ligger. I norra Sverige kan exempelvis problem uppkomma med förändrade mönster för snöbildning och snösmältning. Mer forskning behövs för att analysera vilka konsekvenser högre vattennivåer, högre flöden och större säsongsvariation får samt vilka anpassningsstrategier som behövs inte bara för det urbana dagvattensystemet utan även för övrig infrastruktur. / Godkänd; 2007; 20070410 (ysko)

The population of Stockholm is increasing and with it the amount of wastewater that needs treatment. To cope with the increase, Henriksdal wastewater treatment plant (WWTP) in Stockholm, Sweden, is currently being expanded into the worlds largest WWTP using membrane bioreactor (MBR) technology. The plant will be controlled to a greater extent by pumps and good control is therefore vital to maintain operational stability and an energy efficient process. To analyse the intricate system of pumps and equalisation in tunnels a dynamic model is required.One reason for expanding Henriksdal WWTP is the decommissioning of Bromma WWTP. Wastewater from Bromma will be diverted to Henriksdal through a large tunnel which can be used for flow equalization. To examine whether flow equalization in the tunnel can even out diurnal variations and extreme rain events, water flow in the tunnel and throughout the WWTP was modelled. Models of the tunnel, pumps and basins were made in the programming language C and then merged with different controllers in Matlab/Simulink. To simulate different scenarios for the year 2040, data for the rainy year of 2012 was increased to match the expected population for 2040.Based on simulations for a scenario with dry weather the possibility for flow equalization could be shown. It required a thought-out control strategy for the control of Bromma pumping station based on flow measurements from several other inflows to the WWTP. The control strategy also proved adequate in handling downpours by increasing the amount of waste water subjected to biological treatment. When simulating snow melt or heavy rain, damming in the Bromma tunnel could help to prevent overflow if no strict boundaries were used for the water level in the tunnel. With a maximum allowed water level of 10 m it was, however, possible to dam the first flush containing high concentrations of pollutants and nutrients.Flow equalization makes it easier to maintain even levels in the basins for the return activated sludge (RAS), which in turn makes it easier to maintain high levels in said basins. Higher levels in the RAS-basins leads to reduced energy consumption. In the event of further development of the model, it is possible to add calculations of energy usage for the pumps, which would facilitate further optimization of controllers and their parameters. / Stockholms befolkning växer och med den även mängden avloppsvatten som behöver renas. För att kunna klara av kapacitetsökningen och samtidigt även möta de förväntade strängare reningskraven i framtiden byggs Henriksdals reningsverk ut med ny membranteknik emedan reningsverket i Bromma ska läggas ned. Det avloppsvatten som idag renas i Bromma reningsverk ska ledas i en 14 km lång tunnel belägen 30–90 m under marken till Henriksdal via en pumpstation i Sickla. I och med detta skapas möjligheten till magasinering av avloppsvatten i tunneln vid kraftiga regn så att bräddning kan undvikas. Även utjämning av dygnsvariationer blir möjlig vilket kan vara bra för de nya membranen som ska ersätta de nuvarande eftersedimenteringsbassängerna. Utjämning kan även minska behovet av förbigång av biosteget i Henriksdals nya reningsverk vilket leder mindre utsläpp av näringsämnen och föroreningar till Östersjön.För att utreda Brommatunnelns potential till utjämning gjordes modeller över tunneln, pumpstationer och bassänger i Sickla och Henriksdals nya reningsverk i programmeringsspråket C. Modellerna förenklades på olika sätt för att beräkningstiden skulle hållas nere. Dessa modeller kopplades sedan ihop till en större modell i Simulink där även regulatorer till pumpstationerna skapades så att vattenflödet genom reningsverket kunde simuleras. För att kunna simulera tänkbara flöden för 2040 skalades uppmätta flöden från det regniga året 2012 upp till att gälla för den förväntade befolkningsmängden 2040.Utifrån simuleringar av torrt väder kunde det konstateras att det finns goda möjligheter till utjämning av dygnsvariationer med hjälp av smart styrning av pumpstationerna. Simulering av en typisk skyfallstopp visade att även dessa går att utjämna. Vid simulering av snösmältning eller långvariga regn visade det sig att bräddning går att undvika helt om den dämda nivån i Brommatunneln tillåts överstiga 10 m. Med en strikt nivågräns på 10 m var det emellertid möjligt att dämma det initiala flödet, som innehåller mycket näringsämnen och föroreningar, men det registrerades en liten ökning av bräddningen och förbigången av biosteget.Utjämning av flödet gör det lättare att hålla jämna nivåer i returslamtankarna vilket gör det möjligt att hålla nivåerna högre vilket i sin tur leder till minskad energianvändning. Vid en eventuell vidareutveckling av modellen finns möjligheten att lägga till uträkning av energianvändningen för varje simulering vilket skulle underlätta vidare optimering av regulatorer och regulatorparametrar.

This Licentiate Thesis presents a new approach of understanding leakage in agricultural land. Former studies concentrate on long term measurement of different pollutants in nearby watercourses and streams. The new approach is so far only numerically performed, but will soon be complemented by laboratory tests and field measurements. Our hypothesis is that nutrient leakage into groundwater is caused by thermally driven groundwater convection. The maximum density of water occurs at a temperature of near 4oC. Thus, a density increase of the groundwater occurs by heating from about 0oC in the north of Sweden (springtime) and by cooling from about 10oC in the south (autumn). The depth of the convection (leakage) depends on the size of the thermal gradient. This hypothesis consequently explains both why the nutrient leakage occurs during different seasons in the north and south of Sweden and also why the leakage reaches greater depths in the south. The numerical results show that convection is induced by a small horizontal groundwater flow. In the south of Sweden the lowest required permeability for convection to occur was K=6.7∙10-10m2. In this soil the convection cells reached to a maximum depth of 6 meters. The Rayleigh number (Ra) could be as low as 19 for convection to occur, the general critical Ra is 40 in porous media. In northern Sweden a permeability of K=6.1∙10-92 was required. In this soil and climate convection occurred to depths from 0.2 to 0.9 meters. Transient solutions showed that the required time for the convection pattern to fully develop was 22 days. The effect of frost lenses on the groundwater convection was also studied. Small lenses changed the convection rolls slightly, while large obstacles forced the convection rolls to change size and shape. The simulations showed that the required grain size for convection to occur was considerably greater than the grain size in typical agricultural soils. Still vertical groundwater movements exist. Other possible explanations to groundwater convection in agricultural soil in northern Sweden are to be investigated. Unstable groundwater convection or oscillating convection cells, infiltration of rain and melt water, pressure induced convection and the possibility that Coriolis force due to Earth´s rotation could cause secondary currents in groundwater flow. / Godkänd; 2005; 20070102 (haneit)

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The thesis concludes that microalgae may improve wastewater treatment in ponds in cold climate, from a treatment perspective as well as a sustainability perspective. A literature review revealed that the microalgae biomass produced may find economic use, depending on what species will come to dominate, since there are many possible products from microalgae biomass. Laboratory experiments showed that microalgae collected in the Mid Sweden region can grow readily in wastewater from the same region also under cold climatic conditions. During spring and autumn conditions - between 5-10 Centigrades - the doubling times of the fastest growing cultures in the experiments were below 2 days. A microalgal treatment plant model were considered having a better position for sustainable development, than a conventional three-step wastewater treatment plant and a mechanical-chemical plant complemented with a constructed wetland, when sustainability was evaluated with a socio- ecological method (Holmberg et al. 1996), and emergy evaluation (Odum 1996). / Godkänd; 2002; 20070224 (ysko)

When constructing large borehole heat exchanger (BHE) systems, bedrock and borehole thermal properties are vital for a good design. Today's design programs presume conductive heat transfer in both borehole and bedrock. In groundwater-filled boreholes, however, convective flow will be induced in the groundwater due to the occurring temperature gradients. The resulting more efficient heat transfer lowers the borehole thermal resistance. A 3 m long borehole was numerically studied to investigate the effect of heat injection on natural convection in a groundwater-filled borehole heat exchanger in impermeable bedrock. A convective flow with rising water close to the U-pipe and descending water at the borehole wall was induced. The flow rates in the groundwater are determined by the temperature gradient in the borehole. A higher injection rate results in a larger convective heat transfer, lowering the borehole thermal resistance. An equivalent radius model was also constructed in order to examine possible model simplifications. Using an annulus instead of a more complex U-pipe geometry may radically decrease the required computer capacity and calculation time. The result shows that for a solid bedrock model, borehole mean heat transfer patterns are similar for both models. Therefore, it may be possible to use the simpler equivalent radius model to simulate the convective heat transfer in borehole heat exchangers. Thermal response tests in boreholes were also conducted to investigate the effect of different power and temperature levels on convective heat transfer. A decrease in borehole thermal resistance is seen for higher fluid temperatures. A cold injection test was also performed. The resulting lower temperatures in the borehole increase the borehole thermal resistance, and leading to the formation of ice in the borehole. These tests indicate the importance of using different borehole thermal resistances in BHE design calculations, if the system should operate under several power levels. Thermal response test while drilling was investigated as an alternative method to the standard thermal response test. With this new method, bedrock conductivity would be continuously determined along the borehole. Therefore, bedrock anomalies such as fractures may be detected. The method is investigated for water driven down-the-hole hammers. A numerical model was developed to investigate the thermal response to heat release during drilling. The results show that by providing measurements of high accuracy and precision, occurring small changes in conductivity may be detectable. This licentiate thesis is the first part of a PhD thesis. It summarises the results of the study on the effect of natural convection on BHEs, as well as theoretical investigation of a new thermal response test method. To fulfil the PhD, the influence of groundwater movement on thermal response tests will be further studied with numerical models and field tests. The goal is to implement the result in BHE design calculation programs and TRT analysis. This licentiate thesis includes two submitted journal articles and one conference paper. / <p>Godkänd; 2006; 20070109 (haneit)</p>

Godkänd; 1998; 20070404 (ysko)

Many substances derived from human activity end up in wastewater systems at some point. A large number of different substances - up to 30,000 - are present in wastewater. Some of them are valuable, such as nitrogen and phosphorus, but there are also hazardous substances such as heavy metals and anthropogenic organic substances. To be able to utilise the wastewater nutrients on arable land (agriculture, forestry or other alternatives), it is of great importance to investigate the sources of hazardous substances in wastewater and the human activities and attitudes that brings these different substances into the wastewater systems. For management of wastewater residues it is therefore important to be able to assess both the benefits and the risks from such products. Residues from wastewater are complex mixtures of substances, which demand a multi-sided approach for solving the problem as a whole. / Godkänd; 2001; 20070225 (ysko)