Thermodynamics and effectiveness of biomolecules and electron-acceptors in an ecologically engineered wetland – implications for the design and optimisation

Abstract In this study redox models were developed for each of the three sample sites to calculate the most effective biomolecule-electron acceptor pairs as a function of pH. The study effectively demonstrated the importance of considering biomolecular substrates available in ecologically engineered wetland systems in conjunction with the specific electron acceptors and redox reaction products in optimising specific wetland functions e.g., denitrification. The study indicated that the pH of the wetland water column and soil pore water is an important factor in controlling which biomolecules are most effectively oxidised by which specific electron donors. The pH intersect point can be calculated and observed on Eh-pH diagrams of the electron acceptors oxidising the various biomolecules input into the model and of biomolecules reducing various electron acceptors input into the model. Wetland water quality monitoring data thus is important in managing ecologically engineered wetlands, so the correct biomolecular substrates are added to optimise specific redox reactions e.g., denitrification. The model also indicated that Fe(OH) 3 as an electron acceptor is more or less effective depending on the reaction products of the reaction e.g., magnetite, more effective, or Fe 2+ , less effective. This observation indicates that the effectiveness of the various redox reaction in ecologically engineered wetland systems may be highly dependent on the specific reaction products that form from these reactions. This implies a foreknowledge of the products that could form in redox reactions in specific engineered wetlands, underlining the importance of geochemical modelling in the design and optimisation of ecologically engineered wetland systems.