Bioremediation of a polymetallic, arsenic-dominated reverse osmosis reject stream.

The treatment of metal-laden industrial effluents by reverse osmosis is gaining in popularity worldwide due to its high performance. However, this process generates a polymetallic concentrate (retentate) stream in need of efficient post-treatment prior to environmental discharge. This paper presents results on the bioremediation (in batch mode) of a metal-laden, arsenic-dominated retentate using Shewanella sp. O23S as inoculum. The incubation of the retentate for 14 days under anoxic conditions resulted in the following removal yields: As (8%), Co (11%), Mo (3%), Se (62%), Sb (30%) and Zn (40%). The addition of 1 mmol l-1 cysteine increased the removal rate as follows: As (27%), Co (80%), Mo (78%), Se (88%), Sb (83%) and Zn (90%). The contribution of cysteine as a source of H2 S to enhancing the removal yield was confirmed by its addition after 7 days of incubations initially lacking it. Additionally, the cysteine-sourced H2 S was confirmed by its capture onto headspace-mounted Pb-acetate test strips that were analysed by X-ray diffraction. We show that real metal-laden industrial effluents can be treated to medium-to-high efficiency using a biological system (naturally sourced inocula) and inexpensive reagents (yeast extract, lactate and cysteine).

Design and field-scale implementation of an "on site" bioremediation treatment in PAH-polluted soil.

An "on site" bioremediation program was designed and implemented in soil polluted with polycyclic aromatic hydrocarbons (PAHs), especially naphthalene. We began by characterizing the soil's physical and chemical properties. A microbiological screening corroborated the presence of microorganisms capable of metabolizing PAHs. We then analyzed the viability of bioremediation by developing laboratory microcosms and pilot scale studies, to optimize the costs and time associated with remediation. The treatment assays were based on different types of biostimulants, such as a slow or fast-release fertilizer, combined with commercial surfactants. Once the feasibility of the biostimulation was confirmed, a real-scale bioremediation program was undertaken in 900 m(3) of contaminated soil. The three-step design reduced PAH contamination by 94.4% at the end of treatment (161 days). The decrease in pollutants was concomitant with the selection of autochthonous bacteria capable of degrading PAHs, with Bacillus and Pseudomonas the most abundant genera.