Wastewater sludge dewaterability enhancement using hydroxyl aluminum conditioning: Role of aluminum speciation

Abstract

a b s t r a c tChemical conditioning is one of the most important processes for improve the performance of sludge dewatering device. Aluminum salt coagulant has been widely used in wastewater and sludge treatment. It is generally accepted that pre-formed speciation of aluminum salt coagulants (ASC) has an important influence on coagulation/flocculation performance. In this study, the interaction mechanisms between sludge particles and aluminum salt coagulants with different speciation of hydroxy aluminum were investigated by characterizing the changes in morphological and EPS properties. It was found that middle polymer state aluminum (Al b ) and high polymer state aluminum (Al c ) performed better than monomer aluminum and oligomeric state aluminum (Al a ) in reduction of specific resistance to filtration (SRF) and compressibility of wastewater sludge due to their higher charge neutralization and formed more compact flocs. Sludge was significantly acidified after addition Al a , while pH was much more stable under Al b and Al c conditioning due to their hydrolysis stability. The size of sludge flocs conditioned with Al b and Al c was small but flocs structure was denser and more compact, and floc strength is higher, while that formed from Al a is relatively large, but floc structure was loose, floc strength is relatively lower. Scanning environmental microscope analysis revealed that sludge flocs conditioned by Al b and Al c (especially PAC 2.5 and Al 13 ) exhibited obvious botryoidal structure, this is because sludge flocs formed by Al b and Al c were more compact and floc strength is high, it was easy generated plentiful tiny channels for water release. In addition, polymeric aluminum salt coagulant (Al b , Al c ) had better performance in compressing extracellular polymeric substances (EPS) structure and removing sticky protein-like substances from soluble EPS fraction, contributing to improvement of sludge filtration performance. Therefore, this study provides a novel solution for improving sludge dewatering property by controlling aluminum speciation.

Comprehensive insights into the inorganic coagulants on sludge dewatering: comparing aluminium and iron salts

“…Meanwhile, the iron coagulants achieved better sludge dewaterability than the aluminium coagulants. Compared with previous studies, our study further confirmed this result using the high pressure filtration system.…”

“…Compared with the previous studies, sludge dewaterability was significantly related to EPS composition (i.e. TTAC, TTPN, and PS), and functional groups (i.e.…”

“…It remains impossible to determine whether there is any advantage in selecting one of the two inorganic coagulants over the other as a pretreatment method (aluminium vs iron). For example, some authors have concluded that aluminium coagulants conditioning is superior to iron when considering sludge dewaterability . However, compared with aluminium coagulants, iron coagulants were better able to improve the sludge dewaterability in another study .…”

“…In recent years, of the different pretreatment methods, the application of conventional inorganic coagulants (aluminium and iron salts) as a chemical pretreatment method has raised research attention, because these methods further enhance sludge dewaterability . Many studies have been conducted to compare aluminium and iron salt pretreatments . However, their conclusions are inconsistent.…”

Improvement of wastewater sludge dewatering performance using titanium salt coagulants (TSCs) in combination with magnetic nano-particles: Significance of titanium speciation

“…The market price of TiCl 4 was 8000 yuan per ton, while that of the commonly used inorganic salts -polymeric aluminum chloride (PACl) was around 2000 yuan per ton. According to our study, the optimal dosages of TSCs and PACl were 0.003 gTi/gTSS and 0.05gAl/gTSS for sludge conditioning respectively (Cao et al, 2016). The dosage of PACl is nearly ten times as much as that of titanium salt to achieve the same dewatering efficiency.…”