Physical and biochemical changes in sludge upon Tubifex tubifex predation

Physical and biochemical changes in sludge upon Tubifex tubifex predation

de Valk, S.L. (TU Delft Sanitary Engineering)
Khadem, A.F. (TU Delft Sanitary Engineering)
Foreman, Christine M. (Montana State University - Bozeman)
van Lier, J.B. (TU Delft Sanitary Engineering)
de Kreuk, M.K. (TU Delft Sanitary Engineering)

2016

Worm predation (WP) on activated sludge leads to increased sludge degradation rates, irrespective of the type of worm used or reactor conditions employed. However, the cause of the increased sludge degradation rates remains unknown. This paper presents a comparative analysis of the physical and biochemical aspects of predated sludge, providing insight into the hydrolytic mechanisms underlying WP. To this end, the sessile worm Tubifex tubifex was used as a model oligochaete and was batch cultivated in an 18-L airlift reactor. Predation on activated sludge showed an average reduction rate of 12 ± 3.8%/d versus 2 ± 1.3%/d for endogenous respirated sludge. Sludge predation resulted in an increased release of inorganic nitrogen, phosphate and soluble chemical oxygen demand (sCOD). The sCOD consisted mainly of polysaccharides; however, fluorescence excitation emission matrix spectroscopy analysis also revealed the presence of Tryptophan-protein-like substances. Results suggest that the released polysaccharides contain a protein-like element. Additionally, soluble iron increased slightly in concentration after WP. The extent of hydrolysis seemed to reach an average plateau of about 40% volatile solids (VS) reduction after 4 days, which is substantially higher than the 29% VS reduction for endogenous decay of activated sludge after 30 days. Furthermore, T. tubifex predominantly consumed the protein fraction of the extracellular polymeric substances. Results suggest that that the worms specifically target a fraction of the sludge that is predominantly biodegradable under aerobic conditions, albeit at significantly higher degradation rates when compared to the endogenous decay of waste activated sludge.

biodegradability
Oligochaeta
sludge reduction
Tubifex
WAS
Worm predation

http://resolver.tudelft.nl/uuid:ca1aa0b4-9418-4430-bdc1-33f0a487f364

https://doi.org/10.1080/09593330.2016.1236150

0959-3330

Environmental Technology, 38 (12), 1524-1538

Institutional Repository

journal article

© 2016 S.L. de Valk, A.F. Khadem, Christine M. Foreman, J.B. van Lier, M.K. de Kreuk