Speciation Efficiency Indices (SEI) and Readily-Biodegradable Indices (RBI) for Optimising Ligand Control of Environmental and Associated Industrial Processes

Abstract

Two new concepts, termed Speciation Efficiency Index (SEI) and Readily-Biodegradable Index (RBI) have been introduced as markers of the efficiency of agents to form a species and to biodegrade, when applied to process-specific roles; these are illustrated using data from two industrial-environmental studies. Chelating agents such as EDTA and DTPA have been employed in many industrial and environmental processes to sequester specific metal ions that have deleterious effects upon the process itself. These two agents do not comply with the most recent international criteria for ready-biodegradability. Hence, several chelating agents (S,S′-EDDS, IDS and NTA) have been assessed in terms of their SEI, using the Joint Expert Speciation System, with particular reference (a) to replacing EDTA in the pulp and paper-making industry, and (b) to judge the transuranic decontamination effects of EDTA, S,S′-EDDS, NTA and citrate in the nuclear industry. For both pulp processing and for radionuclide decontamination, both SEI and RBI values lead to the conclusion that the best agent is S,S′-EDDS.