BIOORGANOCLAY · Use of organoclays in bioremediation of contaminated soils and groundwater

Final Activity Report Summary - BIOORGANOCLAY (Use of organoclays in bioremediation of contaminated soils and groundwater)

The immobilisation and elimination of contaminants from polluted groundwaters are an objective of increasing importance. Reactive barriers are one of the effective techniques to prevent spreading of pollutants in groundwater. The function of reactive barriers can be based on physicochemical and biological processes such as adsorption and biodegradation. Recent studies have suggested that surfactant/clay complexes (partially modified organo-montmorillonite) represent a new and promising class of materials for bioremediation. The low exchanged surfactant amount has several advantages in soil remediation due to their balanced hydrophilic/hydrophobic surface properties: higher compatibility with soils as well as bacteria and their lower manufacturing costs. The role of the type and amount of cationic surfactant in the sorption behaviour of partially modified clays and the applicability of a partially modified organoclay/aquifer mixtures for bioremediation of 2,4 dichlorophenol were studied in batch and flow system. As pure organoclays have low hydraulic permeability and they cannot thus be used in a column system, the organoclay was mixed with an aquifer material which had no significant sorption capacity for organic pollutants of low polarity but was mostly able to retard colloidal-size organoclay particles under flow condition. In order to adjust the sorption capacity of these organoclay (2C18-35-MM)/aquifer mixtures the DCP adsorption isotherms were determined. The 2,4-dichlorophenol sorption on aquifer was negligible. On organoclay/aquifer mixtures (0.5-5.0 %(w/w)) the sorption capacity increased with increasing organoclay content and the adsorption isotherms were non-linear and could be fitted by the Freundlich equation. When the adsorbed amount of DCP was normalised on the carbon content of these mixtures the adsorption isotherms coincided, consequently the sorption capacity of these mixtures appears to be mostly dependent on adsorbed amount of surfactant. The biodegradation tests with Ralstonia eutropha were carried out in batch system at initially toxic and non-toxic DCP concentrations in pure aquifer without organoclay and organoclay/aquifer mixtures. The fact that both the free and the initially sorbed amount of DCP were mineralised is indicative of the completely reversible sorption process of DCP on organoclay. In general, 2C18 35-MM had no negative effects on microorganisms. It could therefore serve as a suitable component of biodegradation plants. The adsorption behaviour of DCP on organoclay(2C18-35-MM)/aquifer mixtures at different compositions were further studied under flow conditions. Applying 0.1 mL/min flow rate (0.46 m/day specific flux) the organic content of the organoclay/aquifer mixture did not change significantly and the lost mass of the packing material was about 1 % after 700 pore volumes which can be attributed to the natural porous structure and filtering capability of the aquifer material used. Since 0.46 m/day groundwater specific flux corresponds to an average one, no significant loss is to be expected in the application of organoclay/aquifer mixtures. The characterisation of the water flow regime in the packed column with organoclay/aquifer mixtures was carried out by breakthrough measurements with the conservative tracer D2O. The dispersivity of the column material increased with the organoclay content. The organoclay content apparently increased the variations in microscopic pore water velocities which is represented by a larger dispersivity length at the column scale. In the column filled with organoclay/aquifer mixtures the 2,4-dichlorophenol retardation was proportional to the organoclay content up to 1 %(w/w). Above 1.5 - 2.0 %(w/w) organoclay content the permeability of the column material decreased. The measured breakthrough curves of DCP on organoclay/sediment mixtures were modelled by the CDE equation and the sorption characteristic of the column was compared to batch sorption results. The measured breakthroughs were forward simulated by Hydrus1D using the Freundlich parameters determined in batch system and inverse modelled from the measured data assuming a kinetic effect, which was only observed under flow condition. In order to optimise the DCP and bacteria transport for biodegradation using partially modified organoclay/aquifer mixture materials the Ralstonia eutropha transport behaviour was investigated under flow condition. The results show that with increasing organoclay content up to 1.0 % (w/w) the bacterial breakthrough is strongly retarded. The bacterial distribution curves in the column show that bacterial growth is significant inside the column material, especially at the top of the column.

Data: CORDIS, © European Union