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COUPLING A-STAGE TECHNOLOGY with DISSOLVED AIR FLOTATION (DAF) for INCREASED ORGANICS REMOVAL and COMPACT SLUDGE PRODUCTION at PILOT SCALE Aantal Woorden: 22531

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COUPLING A-STAGE TECHNOLOGY with DISSOLVED AIR FLOTATION (DAF) for INCREASED ORGANICS REMOVAL and COMPACT SLUDGE PRODUCTION at PILOT SCALE Aantal Woorden: 22531 COUPLING A-STAGE TECHNOLOGY WITH DISSOLVED AIR FLOTATION (DAF) FOR INCREASED ORGANICS REMOVAL AND COMPACT SLUDGE PRODUCTION AT PILOT SCALE Aantal woorden: 22531 Stijn Decru Stamnummer: 01202687 Promotor: Prof. Dr. ir. Korneel Rabaey Prof. Dr. ir. Bart De Gusseme Copromotor: dr. ir. Jo de Vrieze, ir. Cristina Cagnetta Masterproef voorgelegd voor het behalen van de graad Master of Science in de bio- ingenieurswetenschappen: milieutechnologie Academiejaar: 2016 - 2017 Copyright “The author and the promoter give the permission to use this thesis for consultation and to copy parts of it for personal use. Every other use is subject to the copyright laws, more specifically the source must be extensively specified when using results from this thesis.” “De auteur en de promotor geven de toelating deze scriptie voor consultatie beschikbaar te stellen en delen ervan te kopiëren voor persoonlijk gebruik. Elk ander gebruik valt onder de beperkingen van het auteursrecht, in het bijzonder met betrekking tot de verplichting de bron te vermelden bij het aanhalen van resultaten uit deze scriptie.” Gent, juni 2017 De promotoren, De auteur, Prof. dr. ir. Korneel Rabaey Stijn Decru Prof. dr. ir. Bart De Gusseme Dr. ir. Jo de Vrieze Cristina Cagnetta i ii Acknowledgements The year that lies behind me is one in which I learned a tremendous amount of things. The experience I gained during the HRAS-DAF pilot work told me that you should never expect anything to work properly from the beginning and that really anything can fail. The problem solving was challenging but kept everyone closely involved to the project. Working in the lab gave me insights in the chemical analyses that are necessary to run a biotechnological plant. First of all I would like to thank Cristina for her enthusiasm and patience she showed towards me. She was always available for questions and if something wasn’t clear from the first time, she would eagerly explain it to me twice. She steered me in the good way and gave me the critical insights that were necessary to build the story of my thesis. I am grateful to Jo Devrieze for the advice he gave me on the anaerobic digestion of A-stage sludge and for reading my thesis. He was also the one who supplied me with vacutainers without which I couldn’t have brought a single gas sample safely back to the faculty for analysis. I remember feeling like an engineer for the first time when I attended Professor Rabaey courses on environmental technology during the third year. It was during these courses that he awakened my interest in biotechnological processes for wastewater treatment and made me choose one of his topics. His advice was always to the point and helped a lot to keep the focus and define the paths to take. My first encounter with professor De Gusseme was during the course ‘microbial resource recovery’. I admired his practical approach and strong link with the industry and his involvement was an enriching complement to the story of the thesis. To the people from Aquafin. Thank you Bart & Francis for sustaining the HRAS-DAF pilot together with me and answering my questions and Marjolein for guiding this project. Special thanks to Francis for bringing samples several times from Aartselaar to the lab in Gent. Thank you Marc, Solo (Souleymane), Kris (Christiaan) and Eric who were there to come up with fast and practical solutions if there was a mechanical problem with the HRAS-DAF pilot. To the people from Nijhuis for making this thesis possible by providing the DAF unit and doing necessary adaptions to make everything work. iii Further, I would like to thank everyone from CMET. The people I could chat or have fun with during my work in the lab, have a coffee together or provide me with answers to my questions. My fellow leaders at the youth movement (chiro), I would like to thank you for letting me do one extra year, knowing that I would be less closely involved because of the thesis. Once again we had fantastic moments, and you tolerated the many times I was absent. It’s like Timmy Simons once said, it’s better to quit to late than to early. Finally, to my parents, sister and smaller brother, I am grateful that you pushed me through the last weeks of the thesis. You supported me when I needed it and gave me courage to go further. iv Abstract Current wastewater treatment processes such as the conventional activated sludge process (CAS) focus solely on the removal of organics and nutrients and are therefore not sustainable. The organics present in the wastewater possesses an abundant resource potential and the focus should shift from solely environmental protection to the recovery of energy and materials. High rate activated sludge (HRAS) systems such as the A-stage or high rate contact stabilisation (HiCS) process are able to capture a significant fraction of these organics and transfer them to the sludge. Although some energy is lost via microbial respiration, most of it is captured in the sludge. Part of the energy stored in the sludge can be recovered under the form of biogas (CH4) via anaerobic digestion (AD). The high rate activated sludge is more biodegradable and conversion efficiencies during AD are up to 2.5 times higher than for excess sludge produced during CAS. Unfortunately, the high food to microorganism ratios specific to these high rate systems lead to a poor settling sludge. Solid/liquid separation of HRAS via conventional settling generates diluted sludge (± 10 g L- 1). Further thickening is thus required prior to AD. Moreover, a considerable part of the organics (up to 50 %) are not separated in the settler and leave with the effluent. In the view of optimal energy recovery, a more efficient technique for solid/liquid separation is needed. During this thesis dissolved air flotation (DAF) was applied for solid/liquid separation and it was shown that the HRAS-DAF combination is feasible at pilot scale but needs close monitoring. The HRAS-DAF pilot was able to obtain high organics removal and produce concentrated sludge (21 – 47 g COD L-1). The sludge was anaerobically digested to recover the energy present in the sludge under the form of biogas. When a single polymer was used to assist flocculation, conversion efficiencies to methane were 58 – 68 %. This is comparable to a conventional HRAS where settling is used for the solids separation. When a dual polymer system was used conversion efficiencies were lower, 40 – 42 %. This was likely due to phosphorous or trace elements depletion or to the polymers interfering with hydrolysis and digestion of sludge during AD. v Nederlandse samenvatting De huidige technieken voor waterzuivering zoals het actief slib proces (CAS) richten zich enkel op de verwijdering van organisch materiaal en nutriënten en zijn daarom niet duurzaam. De aanwezige organische stoffen in het afvalwater beschikken over een overvloedig potentieel voor grondstof recuperatie en de focus moet overgaan van enkel milieubescherming naar het terugwinnen van energie en materialen. Hoog belast geactiveerd slib (HRAS) systemen, zoals de A-trap (A-stage) of het hoog belast contact stabilisatie proces (HiCS), kunnen een significante fractie van deze organische stoffen opnemen en overbrengen naar het slib. Hoewel sommige energie via microbiële respiratie verloren gaat, wordt het grootste deel in het slib vastgelegd. Een deel van de energie die in het slib wordt opgeslagen, kan vervolgens worden teruggewonnen onder de vorm van biogas (CH4) via anaerobe vergisting. Het hoog belaste geactiveerd slib is beter biologisch afbreekbaar en de omzettingsefficiënties tijdens anaerobe vergisting zijn maximaal 2,5 keer hoger dan voor slib geproduceerd tijdens CAS. Helaas leiden de hoge ‘feed tot micro-organismen’-verhoudingen (F/M) die specifiek zijn voor deze hoog belaste systemen tot een slecht bezinkbaar slib. Vast/vloeistof scheiding van HRAS slib via conventionele sedimentatie zorgt voor laag geconcentreerd slib (± 10 g L-1). Verdere verdikking is dus vereist voorafgaand aan anaerobe vergisting (AD). Bovendien wordt een aanzienlijk deel van de organische stoffen (tot 50%) niet gescheiden in de bezinkingstank maar meegenomen in het effluent. Met het oog op optimale energieherwinning is er een efficiëntere techniek voor vast/vloeistof scheiding nodig. Tijdens deze thesis werd opgeloste lucht flotatie (DAF) toegepast voor vast/vloeistof scheiding en het bleek dat de HRAS-DAF combinatie haalbaar is op pilootschaal mits nauwkeurige opvolging. De HRAS-DAF piloot kon hoge organische verwijdering verkrijgen en geconcentreerd slib produceren (21 - 47 g COD L-1). Het slib werd anaeroob vergist om de aanwezige energie in het slib in de vorm van biogas te recupereren. Wanneer enkel anionisch polymeer werd gebruikt voor flocculatie, was de conversie efficiëntie naar methaan 58 – 68%. Dit is vergelijkbaar met een conventionele HRAS, waar bezinking gebruikt werd voor de vaste-stofafscheiding. Wanneer een dubbel polymeer systeem werd gebruikt, was de conversie-efficiëntie lager, 40 – 42%. Dit was waarschijnlijk te wijten aan de uitputting van fosfor of sporenelementen of aan de polymeren die interfereren met hydrolyse en vertering van slib tijdens AD. vi Table of contents Copyright ..................................................................................................................................... i Acknowledgements ................................................................................................................... iii Abstract .....................................................................................................................................
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