Enhanced digestion and alginate-like- exopolysaccharides extraction from Nereda sludge

Aerobic granular sludge/Nereda technology has proven to be more beneficial compared to activated sludge systems. Until now not much research has been spend on treatment of Nereda excess sludge (NES). In this study the biodegradability of NES is investigated, combined with thermal pressure hydrolysis (TPH) as pre-treatment method and the application of an up-flow digester concept. The maximal biodegradability is estimated at 50% volatile solids (VS) (VS content of raw sludge is 80%). In a conventional CSTR digester 42% VS is converted, whereas TPH increased this to 48% (HRT=20 days). The up-flow digester performed slightly better than the conventional system: 43% VS is converted. Modelling of the CSTR systems showed to yield well fitting results; modelling of up-flow digesters yielded results which deviated a lot from the measured values. Besides anaerobic digestion, the extraction procedure of alginate-like-exopolysaccharides (ALE) is optimized and the mutual influence of digestion and ALE extraction is researched. Extraction of ALE can be done with a lower amount of chemicals as the initial procedure. ALE seems to be slowly biodegraded during anaerobic digestion, although the amount of ALE recovered from digested sludge did not differ from undigested sludge. ALE extraction applied prior to digestion could be a synergistic hybrid, as the extraction procedure can act as a pre-treatment method to reduce sludge volume and increase biodegradability rate. The optimal combination is however not yet found. Finally the influence of ALE-extraction method and protein content is investigated. ALE seems to contain a significant fraction of protein (20-40%), although large differences were observed between protein detection methods and ALE extraction methods. II Preface This thesis is the result of my graduation research project, performed at the Sanitary Engineering Section at the faculty of Civil Engineering and Geosciences of Delft University of Technology and in the laboratory of RoyalHaskoningDHV in Amersfoort. The subjects of this study are various aspects of Nereda excess sludge treatment.