At the same time, rising population and urbanization are causing waste generation at higher quantities yearly, leading to a waste management crisis. If nothing is done in mitigation, waste solids produced from wastewater treatment plants (WWTPs) will progressively overburden current municipal operations and landfills. An exciting technology, produced by the author team, is the generation of wood bioadhesives derived from as-is wastewater treatment sludges (biosolids, waste activated sludge [WAS]) by targeting their proteins for denaturation. This study explored and optimized this novel, innovative protein-based adhesive with and without defatted soy flour as a co-feedstock in addition to other additives. Sustainability of this technology can be achieved through the advantageous reduction of byproducts, diversion of waste from landfills and significant lowering of the carbon footprint through trapping carbon within wood composite materials. This approach not only lessens the environmental impact of traditional adhesives but also enhances resource efficiency, contributing to the advancement of green wood adhesives and the promotion of an efficient circular economy.
Preliminary investigation provided viability of these adhesives with strengths ranging from 180 psi to 425 psi dependent on formulation. Following, a techno-economic analysis of a designed and integrated biorefinery process for three formulations in a 10 MGD WWTP showed promising IRRs ranging from 24.0% - 44.2%, exceeding the 15% hurdle rate set by analysis. Cost of production was estimated for all three formulations at less than $0.20 per pound of adhesive. Commercial protein-based adhesives generally range from $1.20 to $2.00 per pound in production costs, so base formulations fell well within range to incite further investigation. Thus, production of an optimized bioadhesive formulation that can reach shear strengths of >500 psi was achieved for green adhesive formulations that have little to no dependence on petroleum constituents or known carcinogens. A desired reduction in production cost of ≥30% in comparison to the low end of commercial adhesive cost range ($1.20 per pound) was accomplished with the inclusion of changes to adhesive formula from preliminary examination. To accomplish these tasks, a design of experiments (DOE) approach was employed to systematically vary key parameters such as denaturant concentration and curing conditions for base formula optimization. Shear strength testing, as per ASTM D1002-10, was acquired as the response variable, and was obtained by an ultimate testing machine (UTM). Statistical analysis was employed to evaluate the effects of these factors on adhesion strength, ensuring a data-driven optimization process. To further the green technology, leveraging protein co-feedstocks, applying crosslinking additives, and incorporating appropriate modifiers, the adhesive formulations were tailored for enhanced performance and future commercialization. Evaluation of mechanisms utilized analytical testing (i.e. fourier transform infrared spectroscopy (FTIR), liquid chromatography-mass spectrometry (LC-MS), etc.). The final bioadhesives will be applied in the generation of MDF, tested for dry, wet, internal bond, and compressive strengths using the UTM, and assessed against industry standards to validate their feasibility and economic viability.