Le déploiement de processus biologiques intensifiés s’accélère en traitement des eaux usées au regard des volumes importants à traiter et des avantages apportés : compacité, temps de traitement et qualité d’eaux. Cependant, cette intensification se fait souvent au détriment d’une consommation importante d’énergie qui reste le principal défi à relever. Pour cela, deux systèmes intensifs ont été analysés: un bioréacteur à membrane (BàM, 64000 eqH) et un procédé de boues activé conventionnel (BAC24000 eqH). Dans un premier temps, toutes les dépenses énergétiques de ces stations ont été quantifiées puis sectorisées, pour ensuite, définir des coûts de référence et proposer des stratégies de réduction d’énergie. L’audit énergétique pour ces deux stations confirme que l’aération est le poste le plus consommateur (Pour le BAC, la consommation totale de la station vaut 0.82 kWh/m3traité dont 44% sont dus à l’aération).Si de nombreux postes de dépenses énergétiques s’avèrent immuables, plusieurs facteurs influencent cependant ces consommations: La capacité hydraulique, la température, l’âge des boues... L’analyse des stations sur plus de trois ans de fonctionnement souligne les facteurs influençant cette consommation spécifique (kWh/m3traité) : débit entrant (saisonnalité) et concentrations en MES dans les bassins biologiques. Ainsi, une optimisation énergétique a été faite en mixant les données terrains avec des simulations sous GPS-X. Les résultats ont ainsi permis de relier les dépenses énergétiques (demande en oxygène) avec la production de boue. L’introduction d’un paramètre  permet de trouver en fonction des contraintes locales (Couts du kWh et de l’évacuation des boues) la concentration en MES dans les bassins qui minimise les coûts globaux. / Intensive biological processes are increasingly used in wastewater field due to their principles to operate on a reduced surface and produce good quality waters. However, studies show that intensification and high energy consumption go hand in hand, pointing out the value of energy benchmarking. In this work, two intensive systems have been studied: a membranebioreactor, MBR, (64000 p.e.) and a conventional active sludge, CAS, (24000 p.e.).Our objectives were to know where and why this energy is consumed, what factors influence these consumptions, and to give tools to optimize the energy efficiency. A three years energy audit was done for both stations confirming that aeration is the major energy expense (more than 44% of the total plant consumption:0.82kWh/m3). Several factors influence this energy were identified: hydraulic capacity, temperature andsludge age... High energy consumption has been noted in case of low hydraulic loading underlining the seasonal consumption. Moreover, the impact of Suspended Solid (SS) concentration on the energy consumption and on the overall treatment cost was determined at different SS concentration (ranged from 1 to 8 gSS/L) by software simulation (GPS-X) and data analysis. Simulation results showed that an increase of SS leads to an increase in oxygen demand (increased energy cost) but leads also to a decrease of sludge production (reduction of sludge disposal cost).In a full scale plant based on CAS process, the SS concentration must be carefully chosen in order to find the best compromise between the levels of treatment required, the energy demand to ensure biological activity and the sludge disposal cost while minimizing overall costs.

abstract: To address sustainability issues in wastewater treatment (WWT), Siemens Water Technologies (SWT) has designed a "hybrid" process that couples common activated sludge (AS) and anaerobic digestion (AD) technologies with the novel concepts of AD sludge recycle and biosorption. At least 85% of the hybrid's AD sludge is recycled to the AS process, providing additional sorbent for influent particulate chemical oxygen demand (PCOD) biosorption in contact tanks. Biosorbed PCOD is transported to the AD, where it is converted to methane. The aim of this study is to provide mass balance and microbial community analysis (MCA) of SWT's two hybrid and one conventional pilot plant trains and mathematical modeling of the hybrid process including a novel model of biosorption. A detailed mass balance was performed on each tank and the overall system. The mass balance data supports the hybrid process is more sustainable: It produces 1.5 to 5.5x more methane and 50 to 83% less sludge than the conventional train. The hybrid's superior performance is driven by 4 to 8 times longer solid retention times (SRTs) as compared to conventional trains. However, the conversion of influent COD to methane was low at 15 to 22%, and neither train exhibited significant nitrification or denitrification. Data were inconclusive as to the role of biosorption in the processes. MCA indicated the presence of Archaea and nitrifiers throughout both systems. However, it is inconclusive as to how active Archaea and nitrifiers are under anoxic, aerobic, and anaerobic conditions. Mathematical modeling confirms the hybrid process produces 4 to 20 times more methane and 20 to 83% less sludge than the conventional train under various operating conditions. Neither process removes more than 25% of the influent nitrogen or converts more that 13% to nitrogen gas due to biomass washout in the contact tank and short SRTs in the stabilization tank. In addition, a mathematical relationship was developed to describe PCOD biosorption through adsorption to biomass and floc entrapment. Ultimately, process performance is more heavily influenced by the higher AD SRTs attained when sludge is recycled through the system and less influenced by the inclusion of biosorption kinetics. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2011

In order to study the performance and mechanisms of excess sludge reduction in the activated sludge that incorporates the Cannibal™ Process, laboratory activated sludge systems incorporating an anaerobic bioreactor into the sludge recycle stream were operated. In this study, the solids production in the Cannibal system was about 35-40% of the conventional system under steady state conditions. The reduction in waste sludge was optimized when the interchange rate, (the ratio of sludge fed from the activated sludge system to the bioreactor compared to the total mass in the activated sludge system) was set at about 10%. It was found that the release of protein from the anaerobic bioreactor was greater than that from the aerobic bioreactor. The SOUR data suggested that the released protein from the anaerobic bioreactor was easily degraded when the sludge was returned to the activated sludge system. It was also found that when the proportion of sludge added to the anaerobic bioreactor in batch tests was approximately 10%, the protein release was about 30 mg/L. When the proportion of sludge added was increased to 26 to 41%, the release was reduced to 10 and 6 mg/L, respectively. Within 30 hours, the protein release was complete. This suggests that there is an optimum or maximum amount of recycle or interchange (~10%) for the process to function best. / Master of Science

Detta examensarbete behandlar det biologiska reningssteget vid Stora Enso Fors AB kartongfabrik. Examensarbetet omfattar 20 p och ingår i slutskedet av Magisterutbildningen, 60 p, i Kemiteknik med inriktning industriell ekologi vid Kungliga Tekniska Högskolan i Stockholm. Stora Enso Fors AB är en kartongfabrik som är lokaliserat i Fors strax nordost om Avesta. Tillverkning sker av både mekanisk massa samt kartong. Fabriken har ett eget reningsverk som tar hand om avloppsvattnet från processen. De biologiska anläggningarnas utformning har under årens lopp utvecklats främst genom bättre syresättning i luftningsbassängerna samt förändringar i avloppsvattnets sammansättning. För att klara av dessa förändringar kan styrparametern slamhalten behöva ersättas med andra alternativa styrsätt. Examensarbetets syfte är just att studera möjligheten att styra det biologiska reningssteget vid Fors kartongpappersbruk efter nyckeltalet nettoslamproduktionen. Projektet innefattar även att undersöka hur COD-reduktionen och mikroflorans sammansättning påverkas av denna styrparameter. Litteraturstudier av reningsteknikens processer har utförts samt den befintliga reningsanläggningen i Fors har studerats. Det första steget i projektet var att besluta vilket målvärde som skulle användas på nettoslamproduktionen som skulle användas under en försöksperiod där den biologiska reningen skulle styras efter nettoslamproduktionen. För varje dygn under tre olika tidsperioder ( period 1, period 2 och period 3) har driftsdata samlats in och sammanställdes och därefter beräknades nettoslamproduktionens dygnsvärde. Driftsdata för period 1 och halva period 2 har använts som underlag för att kunna bestämma målvärdet för nettoslamproduktionen. Den bestämdes att vara 0,46 kg SS/kg reducerad COD som användes i ett fullskaleförsök, s.k. period 3. Värdena har sedan analyserats för att försöka finna effekter och samband för styrning av reningsverket efter styrningsparametern nettoslamproduktionen, jämfört med det tidigare sättet att styra efter slamhalten. Detta för att se om nettoslamproduktionen skulle kunna vara en ny bättre styrparameter. Resultatet visade bl.a.: - Att period 2 och 3 övervägande hade ett högt flöde som överskrider värdet på 14 000 m3/dygn som reningsanläggningen är dimensionerad efter. - Att medelvärdet för nettoslamproduktionen för period 3 låg på 0,5 kg SS/kg reducerad COD - På en jämnare och lägre COD-halt ut från kemfällningen för period 3 jämfört med perioderna 1 och 2, (ett undantag den 9 februari). - Att period 3 hade en hög och jämn COD-reducering. - Att period 3 verkade ha en bättre biologisk process än perioderna 1 och 2, bl. a. för att antalet hjuldjur, klockdjur var högre och att antalet trådbakterier var lägre och perioden hade också bättre flockbetyg. När det gäller en del samband så verkar det finnas en tendens för alla tre perioderna att när nettoslamproduktionen är hög så ger det den effekten att flockbetyget försämras i luftningsbassäng 2. Följande slutsatser av arbetet kan dras: - Att nettoslamproduktionen är den bästa styrparameter för Fors reningsanläggning är svårt att säga efter den korta tidsperiod som försöket utfördes. Men det visar helt klart att det är värt att gå vidare med att styra efter nettoslamproduktionen. - Att använda målvärdet på 0,46 kgSS/kg reducerad COD eventuellt lite högre på 0,50 kg SS/kg reducerad COD skulle kunna vara ett bra riktvärde. - Att styrning efter nettoslamproduktionen skulle kunna ge riktlinjer för hur slamavdragspumpen skall ställas in. Ett fortsatt arbete rekommenderas med att testa styrning av reningsverket efter parametern nettoslamproduktionen med målvärdet, 0,46 kg SS/kg reducerad COD eller möjligen ett högre värde 0,50 kg SS/kg reducerad COD. De fortsatta försöken bör utföras under olika förhållanden. Det är viktigt att bl.a. studera en försöksperiod under en varmare årstid och då jämföra med de perioder som har studerats i detta arbete. Det är också angeläget att testa hur styrningssättet fungerar när reningsverket utsätts för extrema belastningssituationer. / This Master´s thesis discusses the Biological Purification Step at Stora Enso Fors AB cardboard plant. Stora Enso Fors AB is located in Fors just northeast of Avesta. The factory is producing both mechanical pulp and cardboard. The Plant has an own Sewage-Treatment Plant, which take care of the wastewater from the process. The biological construction design has been developed during the last fifteen years and the composition of the wastewater has also been changed. In order to compensate for the changes of the compositions, the old parameter “Sludge content” could be replaced by a new parameter “Net sludge production”. The aim of This Master’s thesis is: - To study the possibility to control the Biological purification step at the Stora Enso Fors AB cardboard plant, by using the parameter Net sludge production. The project will also investigate how COD-reduction and the composition of the micro organisms will be influenced by this parameter. The first step in this project was to determine which target value of the Net sludge production the experiments period should use. The value was decided to 0,46 kg SS/kg reduced COD. Every day during three different periods the productions data has been collected and then analysed. From this material the Net sludge production has been calculated. The first period and half of the second period has been used as basis for determine the target value of the Net sludge production. The target value was decided to be 0,46 kg SS/kg reduced COD and to use this value in a full-scale experiment in the Plant, during the third period. The productions data has been analysed to try to find effects and connections in the Biological purification step when the Sewage-treatment plant is controlled with the new parameter “Net sludge production”. A comparison with the old parameter “Sludge content” has also been done to verify which of the two parameters is the most favourable. The result showed: - That period 2 and 3 predominantly had a high flow which exceed the value 14 000 m3/day, which the Sewage-treatment plant is designed for. - That the average of the Net sludge production for period 3 was 0,5 kg SS/kg reduced COD. - A more even and lower content of COD out from the Chemical step for period 3 compared with the periods 1 and 2 (with the exception on 9 February). - That the reduction of COD was significant and on an even level in period 3. - That period 3 has a tendency to have a better biological process than period 1 and 2. - That the number of higher micro-organism in period 3 increased compared to period 1 and 2. The testimonial of the flocks in the Biological step is also better in this last period. The conclusions of this project are: - Due to the limited time available for this experiment it is difficult to determine if the Net Sludge Production is the most favourable control parameter for Fors Sewage Treatment Plant. However, the experiment clearly shows that is worth to further investigate to control the Sewage Treatment Plant using the parameter Net Sludge Production - To use the target value of the Net sludge production of 0,46 kg SS/kg reduced COD or perhaps a slightly value of 0,50 kg SS/kg reduced COD. - That control based on after the Net Sludge Production could give guidelines for how much sludge the pump should take out from the Biological step. Continued work could be to test to control the Sewage Treatment Plant based on the target value of the Net Sludge Production of 0,46 kg SS/kg reduced COD or 0,50 kg SS/kg reduced COD as mentioned above. Further, the experiment should be performed during different conditions. It is important to study a period during the warmer months of the year and compare the results with the periods, which has been studied in this Master’s thesis. It is also important to test the capacity of the Sewage Treatment Plant during extreme load situations. / www.ima.kth.se