Effects of sawdust-CPAM on textile dyeing sludge dewaterability and filter cake properties

Sawdust was used as a filter aid for the textile dyeing sludge dewatering in this study. Results showed that sawdust conditioning in conjunction with cationic polyacrylamide (CPAM) presented much better dewaterability than CPAM alone. The optimal sawdust and CPAM dosage for the best dewaterability was found to be 60 wt.% (mass percent) and 15 kg/t DS (dry solid), the time to filter (TTF) and the yield at 90% degree of the filtration completion (YN90) were 5 s and 15.6 kg/m2 h under the conditions, respectively. TTF and YN90 were more appropriate parameters than specific resistance to filtration (SRF) for assessing the sludge dewaterability as affected by physical conditioners. The moisture content of various filter cake layers gradually became the same with the increase of sawdust dosage. The flocculated sludge cake became relatively incompressible after sawdust conditioning. Sawdust acts to maintain the permeability during the compressed filtration by resisting cake compression.