improvement of bioremediation performance for the degradation of petroleum hydrocarbons in contaminated sediments

Microcosm bioremediation strategies were applied to sediments contaminated with hydrocarbons. Experiments were performed in aerobic conditions in a single-step treatment and in a two-step anaerobic-aerobic treatment. In aerobic conditions, either inorganic nutrients or composts were added to the microcosms, while, in the first anaerobic phase of the two-step experiment, acetate and/or allochthonous sulfate-reducing bacteria were used. After the treatment under anaerobic conditions, samples were exposed to aerobic conditions in the presence of compost. In the aerobic treatments, 81% hydrocarbon biodegradation was observed after 43 days in the presence of inorganic nutrients. In aerobic conditions in the presence of mature compost, hydrocarbon biodegradation was 51% after 43 days of treatment, whereas it was 47% after 21 days with fresh compost. The two-step experiment allowed us to obtain a hydrocarbon degradation of 91%, after a first anaerobic step with an inoculum of sulfate-reducing prokaryotes

Extraction of Zinc and Manganese from Alkaline and Zinc-Carbon Spent Batteries by Citric-Sulphuric Acid Solution

The paper is focused on the recovery of zinc and manganese from alkaline and zinc-carbon spent batteries. Metals are extracted by sulphuric acid leaching in the presence of citric acid as reducing agent. Leaching tests are carried out according to a24full factorial design, and empirical equations for Mn and Zn extraction yields are determined from experimental data as a function of pulp density, sulphuric acid concentration, temperature, and citric acid concentration. The highest values experimentally observed for extraction yields were 97% of manganese and 100% of zinc, under the following operating conditions: temperature40∘C, pulp density 20%, sulphuric acid concentration 1.8 M, and citric acid 40 gL-1. A second series of leaching tests is also performed to derive other empirical models to predict zinc and manganese extraction. Precipitation tests, aimed both at investigating precipitation of zinc during leaching and at evaluating recovery options of zinc and manganese, show that a quantitative precipitation of zinc can be reached but a coprecipitation of nearly 30% of manganese also takes place. The achieved results allow to propose a battery recycling process based on a countercurrent reducing leaching by citric acid in sulphuric solution

End-of-Life Liquid Crystal Display Recovery: Toward a Zero-Waste Approach

End-of-life liquid crystal displays (LCD) represent a possible source of secondary raw materials, mainly glass and an optoelectronic film composed of indium (90%) and tin (10%) oxides. A strong interest for indium, classified as critical raw material, pushed research towards the development of high-efficiency recycling processes. Nevertheless, a deepened study of the technological innovation highlighted that only a small number of treatments included use of whole waste. Furthermore, these processes often need high temperatures, long times, and raw materials that have a significant environmental impact. In this context, this article shows an approach developed in accordance with the "zero waste" principles for whole, end-of-life LCD panel recycling. This process includes preliminary grinding, followed by cross-current acid leaching and indium recovery by zinc cementation, with efficiencies greater than 90%. A recirculation system further increases sustainability of the process. To enhance all waste fractions, glass cullets from leaching are used for concrete production, avoiding their disposal in landfill sites. Considering the achieved efficiencies, combined the simple design suitable for real-scale application (as confirmed by the related patent pending), this process represents an excellent example of implementing circular economy pillars

Continuous biosorption of copper and lead in single and binary systems using Sphaerotilus natans cells confined by a membrane: experimental validation of dynamic models

Biosorption of heavy metals using membrane reactors as confining devise for free cells is an alternative process to remove these metallic pollutants from aqueous solution. In this paper, experimental data and modelling of heavy metal biosorption onto Sphaerotilus natans cells confined by a ultrafiltration/microfiltration (UF/MF) membrane reactor are reported. Biosorption tests using single and binary metallic solutions (Cu, Pb and Cu-Pb) denoted the biomass affinity (Pb>Cu), the competition among metals simultaneously present in the system, the filtrate flux decline and the change of metal retention coefficient on the membrane for pore plugging by cell fragments. Dynamic modelling is developed considering the unsteady mass balances of the metal in the system and the equilibrium parameters obtained by biosorption batch tests using Langmuir models. Experimental validation of the dynamic models denoted the importance of partial degradation of cells, which is specifically considered in modelling by introducing a time-depending profile for the biomass concentration. (C) 2004 Elsevier B.V. All rights reserved

Biogeochemical Interactions In The Application Of Biotechnological Strategies To Marine Sediments Contaminated With Metals

Sediment contamination in coastal areas with high anthropogenic pressure is a widespread environmental problem. Metal contaminants are of particular concern, since they are persistent and cannot be degraded. Microorganisms can influence metal mobility in the sediment by several direct and indirect processes. However, the actual fate of metals in the environment is not easily predictable and several biogeochemical constraints affect their behaviour. In addition, the geochemical characteristics of the sediment play an important role and the general assumptions for soils or freshwater sediments cannot be extended to marine sediments. In this paper we analysed the correlation between metal mobility and main geochemical properties of the sediment. Although the prediction of metal fate in sediment environment, both for ex-situ bioleaching treatments and in-situ biostimulation strategies, appears to require metal-specific and site-specific tools, we found that TOM and pH are likely the main variables in describing and predicting Zn behaviour. Arsenic solubilisation/increase in mobility appears to correlate positively with carbonate content. Cd, Pb and Ni appear to require multivariate and/or non-linear approaches