Engineering Seminar Series 1_2010: Benefit of Lignite for Dewatering of Digested Sewage Sludge Demonstrated in Pilot Scale Trials

Dr. Emma Qi, Research fellow at Department of Chemical Engineering, Monash University, Victoria, Australia

Date: 2010-01-26
Time: 11:00 to 12:00
Venue: 9-5-05


Sewage sludge contains as high as 99 wt% water and dewatering is often made difficult by the presence of colloidal organic matters. The result is low dewatering rates or low solids contents of the final product. In pressure filtration processes, it is often necessary to use physical conditioners such as carbon powders and coals as filter aids in conjunction with chemical conditioners (e.g. flocculants and coagulants) to improve the strength of the solid structures and permeability of the filter cake and hence to improve the sludge dewaterability.

Lignite, a low-rank coal, has been investigated in laboratory scale mechanical compression and vacuum filtration tests performed on a digested sewage sludge as a physical conditioner and demonstrated to be able to improve sludge dewatering rate significantly when used in conjunction with polyelectrolytes for flocculation. In the present study, pilot scale sludge dewatering using a plate-frame filter press was carried out. The dewaterability of lignite-conditioned sludge as affected by the flocculant dose was evaluated using Specific Resistance to Filtration (SRF) as well as percentage sludge water removal and product solids content. Using the high molecular weight polymer ZETAG8125 at two third of the dose for ZETAG7501 achieved similar sludge water removal and lower SRF during dewatering. When conditioning the sludge with the lignite at ratios of 0.5 and 1 part lignite to 1 part sludge solids, the Net Sludge Yield (YN) was found to increase from 1.2 kgm-2h-1 without lignite conditioning to 5.2 and 7.8 kgm-2h-1, respectively. Higher doses of the lignite did not result in any further increase in the sludge yield due to the low mass fraction of the sludge solids in the cake.

About the Speaker

2004 - PhD in School of Chemistry at Monash University, Australia.
2004 - 2005: Post doctoral research associate in University of Newcastle, working with Forensic Services, Australian Federal Police, on drug profiling
2006 - present: Research fellow at Department of Chemical Engineering, Monash University, Victoria, Australia, working in waste water cleanup, dewatering processes and biofuels areas