Valorization of sewage sludge organic matter for polyacrylamide-based greener hydrogel production with good salt resistance and high permeability

Many efforts have been made to realize the sewage sludge (SS) valorization. Due to the low duration of polyacrylamide (PAM) under high temperatures and high salinity conditions in oilfields, a new organic cross-linking agent, SS extract (SE), has been developed to enhance the PAM cross-linking strength. PAM-SE exhibits excellent temperature and salinity resistance. Due to the disruption of the alpha-helix structure of proteins in SE, the released -OH and -NH2 could react with acrylamide to enhance hydrogen bonding and covalent bonding (transamidation and dehydration), resulting in increasing thermal stability of PAM-SE. The PAM-SE exhibits high plugging capacity (93.93 %) in high-permeability fractures. The breakthrough pressure is 2.73 MPa. The pressure gradient is 27.3 MPa/m. CaCl2 plays a key role in PAM-SE, leading to excellent salt resistance and high thermal stability due to cross-linking network formation. The key reason for the high-temperature and high-salt resistance of PAM-SE is that: i) SE is a cross-linking agent that can react with AM during polymerization to enhance cross-linking; ii) Ca2 + in formation water could cross-link SE and carboxylic acid in polymer to form a stable gel due to the presence of proteins in SE. The unique properties of PAM-SE provide a new approach to increasing hydrogel stability under high-salinity conditions and at high temperatures. It paves a new way for resource utilization of SS.