Jelka Ondruschka

Heavy Metal Removal from Contaminated Sediments by Bacterial Leaching: A Case Study on the Field Scale

Bioleaching experiments on sediments contaminated by heavy metals in the laboratory scale show that leaching rates are related to sulphur content, organic carbon and buffer capacity. Determining these parameters allows the suitability of dredged sediments for the bioleaching process to be assessed. Furthermore, sediment properties can be influenced to a certain extent by the addition of electron donors or a 2-stage reaction under anoxic conditions. The first results from tests in a pilot plant (20 tons of sediment) support the laboratory data. The pilot plant is described.

Bioleaching of heavy metal-contaminated sediments by indigenous Thiobacillus spp : metal solubilization and sulfur oxidation in the presence of surfactants

Abstract The efficiency of surfactant application to improve or inhibit metal solubilization and sulfur oxidation kinetics during the bioleaching of heavy metal-contaminated sediments was studied in suspension-leaching experiments. The river sediment used contained large amounts of fine particles and organic matter. Three types of surfactants were tested: sodium dodecylsulfate (SDS), a C12/14-alkanolethoxylate (Präwozell F1214/5N), and a wettable sulfur (Netz- schwefel 80 WP). Adding 10u2009mmol SDS/l led to transient inhibition of acidification, metal solubilization and sulfur oxidation. Inhibiting bioleaching for just 14u2009days required about ten times more SDS than the amount used for mine waste mitigation. The use of Präwozell resulted in poor inhibition; and using of wettable sulfur did not improve leaching efficiency. The bulk of these surfactants was sorbed onto the solid particles immediately on application, while the remainder in the aqueous phase disappeared within a few days.

Enhanced chitosan production and modeling hyphal growth of Mucor rouxii interpreting the dependence of chitosan yields on processing and cultivation time

Chitosan is a major structural component of fungal cell walls and has diverse medical and other applications. However, cost‐effective culture and extraction methods for fungi need to be developed. Therefore, Mucor rouxii was grown on YPG‐media in both submerged batch and semi‐continuous cultures. Chitosan was extracted from the mycelia to explore strategies to enhance yields and production rates. As observed in earlier studies, M. rouxii is able to adapt to shear stress when cultured semi‐continuously. Modeling the hyphal growth of batch experiments shows that the mycelia were ruptured by shear forces within a short cultivation time shown by a decreased hyphal length. However, an increasing chitosan content was observed with an increasing cultivation period in semi‐continuous cultures, which is an indication for the adaption to shear stress. Semi‐continuous culture resulted in the highest contents of extractable chitosan. The results and models of hyphal growth, including tip extension and branching, suggest that repeated batch cultures may be optimal for chitosan production.

Electrofiltration as a purification strategy for microbial poly-(3-hydroxybutyrate)

The biodegradable polyester poly-(3-hydroxybutyrate) (PHB), produced by Ralstonia eutropha in batch and fed-batch processes, was purified by electrofiltration. The protein film on PHB granules determines their high negative zeta potential, enabling the application of electrofiltration as an integrated technology in the downstream processing of PHB. In order to determine the optimal purification parameters, various pressure and electric field strength conditions were tested. Electrofiltration of PHB at 4bars and 4V/mm provided an up to four times higher concentration factor than conventional filtration. FT-Raman spectroscopy demonstrated that electrofiltration did not result in structural changes to the products. The study demonstrates the efficiency and practical advantages of electrofiltration as a promising downstream step in the PHB production technology.

Filtration kinetics of chitosan separation by electrofiltration.

Downstream processing of chitosan requires several technological steps that contribute to the total production costs. Precipitation and especially evaporation are energy‐consuming processes, resulting in higher costs and limiting industrial scale production. This study investigated the filtration kinetics of chitosan derived from cell walls of fungi and from exoskeletons of arthropods by electrofiltration, an alternative method, thus reducing the downstream processing steps and costs. Experiments with different voltages and pressures were conducted in order to demonstrate the effect of both parameters on filtration kinetics. The concentration of the biopolymer was obtained by the average factor of 40 by applying an electric field of 4 V/mm and pressure of 4 bars. A series of analytical experiments demonstrated the lack of structural and functional changes in chitosan molecules after electrofiltration. These results, combined with the reduction of energy and processing time, define the investigated method as a promising downstream step in the chitosan production technology.