Physical and Chemical Characterization of Sustainable Green Adhesives Derived from Municipal Treatment Plant Sludges

Adhesive formulations derived from sustainable feedstocks, like waste-activated sludge and biosolids from wastewater treatment plants, are developed due to protein-based adhesives receiving attention for their low-cost, resourcefulness, and minimal ecological footprint. The protein composition and associated dynamic changes of the adhesive formulations were studied via gel permeation chromatography, which detailed a molecular size distribution of 8.72 × 105 g/mol for the adhesive formulation and 6.89 × 103 g/mol for the dewatered biosolid base fraction, which confirms the formation of multiple protein functional groups combining to form the larger adhesive molecules. Further analysis determined the types of proteins present in the dewatered biosolids as glutelin, prolamin, globulin, and albumin proteins, with the glutelin proteins as the most prevalent, as thus likely responsible for adhesive formation. The rheological properties of the novel protein adhesive were also studied to interpret the structure of the adhesives, which detailed the findings of viscoelastic properties and flow behaviors of each adhesive in relation to the wastewater treatment plant sample location, which yielded higher flow points, storage moduli, and loss moduli for the dewatered biosolids in comparison to the waste-activated sludge and biosolid adhesives, which correlates with the higher solids content of the dewatered biosolids and potentially cell rupturing when exposed to filtration stress.