The performance and mechanism of simultaneous removal of calcium and heavy metals by Ochrobactrum sp. GMC12 with the chia seed (Salvia hispanica) gum as a synergist

A bacterium Ochrobactrum sp. GMC12, capable of biomineralization and denitrification, was employed to investigate the performance and mechanism of heavy metals removal. A chia seeds (Salvia hispanica) gum was proposed as a synergist for the first time. The results showed that strain GMC12 reduced Ca²⁺, Cd²⁺, Zn²⁺, and nitrate by 83.38, 98.89, 98.95, and 100% (2.09, 0.29, 0.55, and 0.79 mg L^-1 h^-1), respectively, over 96 h continuous determination experiments. The concentration gradient test revealed that strain GMC12 would effectively remove Cd²⁺ and Zn²⁺ by 99.80 and 99.91% (0.67 and 1.35 mg L^-1 h^-1), respectively, under the synergistic effect of gum (1.0%, w/v). The SEM-EDS and XRD manifested that Ca²⁺, HMs ions, and anionic groups coated on the bacteria surface to form CaCO₃, Ca₅(PO₄)₃OH, CdCO₃, Cd₅(PO₄)₃OH, ZnCO₃, and Zn₂(PO₄)OH. The fluorescence spectrometry and fourier transform infrared (FTIR) spectra illustrated that extracellular polymeric substance (EPS) was the key product for the nucleation site of bacteria, and the gum promoted the accumulation of bio-precipitates and accelerated the removal of HMs. In this research, Ochrobactrum sp. GMC12 exhibited great potential in wastewater treatment and chia seeds gum would go deep into material preparation and wastewater treatment due to its non-toxic nature, high viscosity, and advantageous morphology.

Application of an electrochemical treatment for EDDS soil washing solution regeneration and reuse in a multi-step soil washing process: Case of a Cu contaminated soil

Soil washing is an extensively used process for remediation of heavy metals contaminated soils. However the amount of fresh washing solution to be used represents a significant economical drawback of this process. This paper investigates the application of an electrochemical process (Fe/Fe electrodes couple) for the regeneration of a spent EDDS solution, containing Cu and major competitor cations (Ca, Fe, Mg, and Mn). The effect of current density, pH and conductivity of the washing solution on the recovery process performances was investigated. Current density showed the highest influence on Cu, Mg and Mn removal yields. Maximum removal yields reached 99% for Cu, 77% for Mn and 49% for Mg. No influence of the investigated parameters on Ca removal was observed, while an increase of Fe concentration due to anode dissolution occurred. Characterization of sludge produced from the 2 h electrochemical test (5 mA cm(-2), pH = 8, 8 mS cm(-1)) displayed concentrations of 2.8 g kg(-1) for Ca, 0.4 g kg(-1) for Cu, 535.6 g kg(-1) for Fe, 2.6 g kg(-1) for Mg. TCLP tests at pH 2.88 and 4.93 showed a low leaching percentage (Ca, 10-21%; Cu, 6-12%; Fe, 0.22% Mg, 27-36%). Multi-washing tests were carried out to assess the decrease of the chelating ability of the regenerated washing solution and the Cu extraction efficiency.