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

Abstract

BACKGROUND Extracellular polymeric substances (EPS) play an important role in sludge dewatering. Inorganic coagulants treatment has been widely used to remove the EPS and improve sludge dewaterability. This research evaluates whether there are advantages of selecting one of two chemical coagulation pretreatments, conventional aluminium or iron salts, over the other to enhance sludge dewaterability. The study traced variations in EPS characteristics to understand the mechanisms of sludge dewaterability. RESULTS The results showed that iron coagulants improved dewatering more than aluminium coagulants, by approximately 28.66%. The improved sludge dewaterability was further confirmed in pilot‐scale experiments. Compared with aluminium salts conditioning, iron salts were better able to neutralize stronger charge, formed smaller and more compact flocs, and had a stronger acidification effect. Sludge dewaterability was significantly related to EPS concentrations (i.e. the protein and polysaccharides), EPS composition (i.e. tyrosine/tryptophan amino acid, tyrosine/tryptophan protein, and polysaccharide), and functional groups (i.e. random coil, β‐sheet, and Npr) in the loosely bound EPS (LB‐EPS). A two‐step mechanism was proposed for the iron conditioning process. Moreover, the economic analysis shows iron treatment was more economical than that of aluminium. CONCLUSION Iron salts conditioning removed more LB‐EPS than aluminium salts, thus more significantly improving sludge dewaterability. © 2018 Society of Chemical Industry

Impacts of aluminum‐ and iron‐based coagulants on municipal sludge anaerobic digestibility, dewaterability, and odor emission

“…First, EPSs were believed to be compressed due to surface charge neutralization and adsorption of aluminum-/iron-based coagulants. This formed a compact stable structure fit for a high-pressure dewatering process (Liang et al, 2019). Aluminum-/iron-based coagulants can act as skeleton builders during sludge dewatering (Qi et al, 2011).…”

“…Furthermore, aluminum‐/iron‐based coagulant conditioning improves the sludge dewaterability by decreasing the contents of EPSs (Liang et al, 2019; Shrestha et al, 2019). For example, conditioning by iron coagulants (e.g., FeCl 3 and Fe 2 (SO 4 ) 3 ) removed LB‐EPSs (Liang et al, 2019).…”

“…Furthermore, aluminum‐/iron‐based coagulant conditioning improves the sludge dewaterability by decreasing the contents of EPSs (Liang et al, 2019; Shrestha et al, 2019). For example, conditioning by iron coagulants (e.g., FeCl 3 and Fe 2 (SO 4 ) 3 ) removed LB‐EPSs (Liang et al, 2019). Sludge dewaterability was also found to be related to the compositions (e.g., tyrosine/tryptophan amino acid, tyrosine/tryptophan protein, and polysaccharide) and functional groups (e.g., random coil, β ‐sheet, and N pr ) in the LB‐EPSs (Liang et al, 2019).…”

Electrical and Microwave Characterization of Thermal Annealed Sewage Sludge Derived Biochar Composites

“…This is caused by both residue accumulation during water use and treatments with coagulation and flocculation agents. The most widely used coagulation and flocculation agents are iron and aluminum sulphate [9,10], which are retained in the sludge. The removal of these metals is quite challenging [11,12], expensive and not economically profitable.…”

Investigation of a Gas Hydrate Dissociation-Energy-Based Quick-Freezing Treatment for Sludge Cell Lysis and Dewatering

“…However, as electrolysis needs considerable energy to produce electricity, it has a low energy efficiency. Chemical sludge treatment includes coagulation and acid/base treatment [8,9,10]. During coagulation, cationic ions connect with a negatively charged sludge surface, coagulating the sludge and releasing free and interstitial water.…”