Biological Manganese Removal by Novel Halotolerant Bacteria Isolated from River Water

Manganese-oxidizing bacteria have been widely investigated for bioremediation of Mn-contaminated water sources and for production of biogenic Mn oxides that have extensive applications in environmental remediation. In this study, a total of 5 Mn-resistant bacteria were isolated from river water and investigated for Mn removal. Among them, Ochrobactrum sp. NDMn-6 exhibited the highest Mn removal efficiency (99.1%). The final precipitates produced by this strain were defined as a mixture of Mn2O3, MnO2, and MnCO3. Optimal Mn-removal performance by strain NDMn-6 was obtained at a temperature range of 25–30 °C and the salinity of 0.1–0.5%. More interestingly, strain NDMn-6 could be resistant to salinities of up to 5%, revealing that this strain could be possibly applied for Mn remediation of high salinity regions or industrial saline wastewaters. This study also revealed the potential of self-detoxification mechanisms, wherein river water contaminated with Mn could be cleaned by indigenous bacteria through an appropriate biostimulation scheme.

Biofiltration field study for cold Fe(II)- and Mn(II)-rich groundwater: accelerated Mn(II) removal kinetics and cold-adapted Mn(II)-oxidizing microbial populations

Removal of Mn(II) from Fe(II)- and Mn(II)-rich groundwater in cold regions is challenging, due to slow Mn(II) removal kinetics below 15 °C. This study demonstrated onset, acclimation, and acceleration of Mn(II) removal in a two-stage pilot-scale biofilter (Fe and Mn filters) at varying low on-site temperatures (8–14.8 °C). Mn(II) removal commenced at 8 °C in the Mn filter after Fe(II) removal. A shift in redox-pH conditions favored biological Mn(II) removal and Mn(II)-oxidizing bacteria increased. The Mn filter reached steady-state functioning after 97 days, exhibiting high removal efficiencies (97 ± 0.9%). Yet, first-order rate constants (k) for Mn(II) removal were low (10−6–10−5 min−1; t1/2 = ∼40 d). After consecutive backwashes and filter inoculation with backwashed sludge, k remarkably accelerated to 0.21 min−1 (t1/2 = 3.31 min at 11 ± 0.6 °C). The cold-adapted microbial consortium (51 genera), including Pseudomonas, Leptothrix, Flavobacterium, and Zoogloea, cultured from the field-aged biofilter rapidly produced biogenic Mn oxides at 8 °C, confirmed by electron paramagnetic resonance spectroscopy. Birnessite and pyrolusite detected by synchrotron-based powder X-ray diffraction, and a repetitive birnessite-like surface morphology on ripened filter materials, reflected autocatalytic oxidation. Shifting in k indicated the vertical progress of biofilter ripening, which was not limited by low temperature.

Role of extracellular polymeric substances (EPS) from <i>Pseudomonas putida</i> strain MnB1 in dissolution of natural rhodochrosite

Microbially mediated oxidation of Mn(II) to Mn oxides have been demonstrated in previous studies, however, the mechanisms of bacteria how to dissolve and oxidize using a solid Mn(II) origin are poorly understood. In this study, we examined the role of extracellular polymeric substances (EPS) from P. putida strain MnB1 in enhancing dissolution of natural rhodochrosite. The results showed that P. putida strain MnB1 cell can effectively dissolve and oxidize natural rhodochrosite to generate Mn oxides, and EPS were found to play an important role in increasing dissolution of natural rhodochrosite. Compared with EPS-free treatment, dissolution rate of natural rhodochrosite in the presence of bacterial EPS was significantly increased with decreasing initial pH and increasing EPS concentration, ionic strength and rhodochrosite dosage (p < 0.05). The fourier-transform infrared spectroscopy (FTIR) analysis implies that the functional groups like N-H, C=O and C-H in EPS contributed to the dissolution of natural rhodochrosite. This study is helpful for understanding the mechanisms of the formation of biogenic Mn oxides using a solid Mn(II) origin.

Removal of Indigo Carmine by Bacterial Biogenic Mn Oxides

Indigo carmine (IC) is one of the oldest, most important and highly toxic dyes used and released in the effluents of many industries, such as textile, paper and plastics. Biogenic Mn oxides (BMO) were prepared by culturingMarinobactersp. MnI7-9 in presence of Mn (II). The Point of Zero Charge (PZC) of the BMO is 7.5 by salt titration method. The surface area (BET) is 27.68 m2g-1by the nitrogen adsorption-desorption method. The adsorption kinetics of low concentration IC (5 mg L-1) on the BMO fit the pseudo-first order model, while the adsorption kinetics of higher concentration IC (20 mg L-1) fit the pseudo-second order model. Intra-particle diffusion is an important rate-controlling step. The equilibrium adsorption data fit well in the Langmuir isotherm equation. The maximal adsorption capacity is 115.61 mg g-1at 25¡æ. A larger IC removal amount can be obtained when the amount of the BMO is 2 g L-1at pH 6.5. These results suggest that the BMO can be used as an efficient material for IC removal from aqueous solution.