Dual conditioning of sludge utilizing polyampholyte

Dual conditioning of activated sludge utilizing polyampholyte (T204) in combination with ferric chloride or cationic polyelectrolyte, polydiallyldimethyl ammonium chloride (PDADMAC) was investigated. Capillary suction time, specific resistance to filtration, and settling rate were utilized to assess sludge dewaterability. Floc structure and strength were evaluated. Experimental results indicated that dual conditioning of sludge exhibited better dewaterability at lower doses when compared with single conditioning. Much larger and stronger flocs were formed in dual conditioning. In addition, the sludge dewaterability did not deteriorate significantly when overdosed. It was found that dual polyelectrolytes conditioning (PDADMAC and T204) performed better than the combined use of ferric chloride and T204. It is postulated that in dual conditioning, the negative charge of sludge surfaces was partially neutralized by ferric chloride or PDADMAC, and the relatively more compact primary flocs were formed. The later added T204 could then become adsorbed either onto positively charged patch, or onto the un-neutralized part of the primary flocs. The enhanced flocculation is attributed to the interactions between PDADMAC and T204 that results in the improved dewaterability. The advantages of PDADMAC over ferric chloride as applied in dual conditioning in combination with T204 are discussed. Journal of Environmental Engineering © ASCE.