A Maes

Optimization of hydrodynamic treatment regime in the processes of sorption–flocculation water purification from organic contaminants

Abstract The impact of the hydrodynamic treatment on the flocculation process of various fine dispersed sorbents (modified clay minerals, aluminum hydroxide), utilized in the treatment procedures for water purification from dissolved and colloidal organic contaminants has been studied. It has been found that the optimum regime (mode) of hydrodynamic treatment is dependant on the type and disperse composition of contaminants and sorbent, as well as on the method of introducing the latter into the processed mixture. Measurements have been performed to determine the relation of flocculation efficiency versus the level of energy dissipation e , and its corresponding average liquid velocity gradient G and their optimal values have been identified. It has been found that for studied sorbents the optimal regime of hydrodynamic treatment corresponds to conditions of generating developed turbulence, characterized by the values of e =5–18 J kg −1 ·s −1 ( G =2000–4000 s −1 ). It is shown that the increase in hydrodynamic treatment intensity results in decrease in the ratio liquid/solid in flocs.

The lanthanum precipitation method. Part 2: quantification of the conditional interaction constant between technetium(IV) and humic substances.

The interaction between colloidal Tc(IV) species and colloidal Gorleben humic substances (HS) was quantified after application of the La-precipitation method on supernatant solutions obtained under various experimental conditions but at constant ionic strength of the Gorleben groundwater (0.04M). The determined interaction constant LogKHS (2.3+/-0.3) remained unchanged over a large range of Tc(IV) and HS concentrations and was independent of the pH of the original supernatant solution (pH range 6-10), Tc(IV)-HS loading (10(-3)-10(-6)molTcg(-1) HS) and the nature of the reducing surface (Magnetite, Pyrite and Gorleben sand) used for the pertechnetate reduction. The LogKHS value determined by the La-precipitation method is lower than the LogK value obtained from a previous study where the interaction between colloidal Tc(IV) species and Gorleben humic substances was quantified using a modified Schubert approach (2.6+/-0.3). The La-precipitation method allows to accurately determine the amount of Tc(IV) associated with HS but leads to a (small) overestimation of the free inorganic Tc(IV) species.