Nickel is one of the most dangerous environmental pollutants and its removal from wastewater is an important task. The capacity of a mineral–organic hybrid adsorbent, consisting of Shewanella xiamenensis biofilm and zeolite (clinoptilolite of the Chola deposit), to remove metal ions from nickel-containing batch systems under different experimental conditions was tested. The obtained biosorbent was characterized using neutron activation, SEM, and FTIR techniques. It was established that maximum removal of cations, up to 100%, was achieved at pH 6.0. Several mathematical models were applied to describe the equilibrium and kinetics data. The maximum adsorption capacity of the hybrid biosorbent, calculated using the Langmuir model, varied from 3.6 to 3.9 mg/g. Negative Gibbs energy values and positive ∆H° values indicate the spontaneous and endothermic character of the biosorption process. The effects of several parameters (pH and biosorbent dosage) on Ni(II) removal from real effluent, containing nickel with a concentration of 125 mg/L, were investigated. The optimal pH for Ni(II) removal was 5.0–6.0 and an increase of sorbent dosage from 0.5 to 2.0 led to an increase in Ni(II) removal from 17% to 27%. At two times effluent dilution, maximum Ni(II) removal of 26% was attained at pH 6.0 and sorbent dosage of 1.0 g. A 12-fold effluent dilution resulted in the removal of 72% of Ni(II) at the same pH and sorbent dosage values. The obtained hybrid biosorbent can be used for Ni(II) removal from industrial effluents with low Ni(II) concentrations.

The sorption properties of Shewanella xiamenensis biofilm formed on zeolite (mineral-organic sorbent) as a sorbent have been investigated aiming to determine its suitability for complex zinc-containing effluent treatment. The optimum conditions for metal sorption from synthetic solutions were evaluated by changing the pH, zinc concentration, temperature, and time of sorption. The highest removal of metal ions was attained at pH range 3.0–6.0 within 60–150 min of sorbent-sorbate contact. The results obtained from the equilibrium studies were described using the Langmuir, Freundlich, and Temkin models. Maximum sorption capacity of the sorbent calculated from the Langmuir model changed from 3.4 to 6.5 mg/g. High coefficient of determination values calculated for pseudo-second-order and Elovich models indicate the predominant role of chemisorption in metal removal. Gibbs energy and ∆H° values point at the spontaneous and endothermic character of the sorption. The effect of pH and biosorbent mass on Zn(II) sorption from industrial effluent with an initial Zn(II) concentration of 52.8 mg/L was tested. Maximum removal of zinc ions (85%) was achieved at pH 6.0 by applying a two-step treatment system.

In this paper 31 sediment samples collected from the Danube River, Delta and Black Sea in Romania were investigated by INAA, ICP-MS and CV-AAS techniques for the quantification of 42 elements (Al, Mg, Cl, Ti, Ca, V, Mn, Na, Si, K, Sc, Cr, Fe, Co, Ni, Zn, As, Br, Rb, Sr, Sb, Zr, Mo, Cs, Ba, La, Ce, Sm, Ta, Nd, Eu, Tb, Yb, Lu, Hf, W, Th, U, Cd, Cu, Pb and Hg) and highlighting geochemical peculiarities. Contamination and ecotoxicological risks were evaluated based on single (CF, Er) and complex (PLI, RPLI, RI) indices computed for 26 presumably contaminant elements, suggesting a pollution load in the maritime sector of the Danube and Chilia branch. Significant contribution to the RI had the elements with high toxic response factor, e.g. Hg, rare earth elements (REEs) (Lu having the highest percentage), As, Cd, U, Pb and Sb. Assessment of radiological hazard due to 238U, 232Th and 40K through the absorbed dose rate (ADR), radium equivalent activity index (Raeq), external hazard index (Hex), representative level index (IG), annual effective dose (AED) and excess lifetime cancer risk (ELCR) suggested an elevated radiation exposure of people in the Danube region compared to Black Sea littoral.