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After fermentation, activated sludge contains many acid-producing bacteria and their metabolites, which have a good reducing effect. Various active groups (e.g., hydroxyl, amino, carboxyl, and phosphate) on microbial cell surfaces can adsorb heavy metals through complexation or chelation, forming heavy metal precipitates and thereby reducing the toxicity of heavy metals. However, the effects and mechanisms of using sludge after anaerobic fermentation to remove Cr(VI) are unclear, such as the dominance of direct versus indirect biological reduction, the contribution of abiotic effects, and the influence of fermentation conditions. This paper compares Cr(VI) removal in fermented and unfermented sludges. After fermentation for 24 h, 99.9% of the Cr(VI) (50 mg/L) in anaerobic sludge was removed within 7 h, which was twice the rate in unfermented activated sludge. A series of comparative experiments demonstrated that Cr(VI) removal primarily occurred through biological effects (about 92%), which included biological reduction and biosorption. 16SrRNA gene sequencing revealed that Cr(VI) transformation primarily occurred through direct biological reduction, with the related genera being Trichococcus, Acetobacter, Aeromonas, and Tolumonas. Fourier-transform infrared (FTIR) spectroscopy results showed that the C = O and C–O functionalities on sludge were likely involved in the Cr(VI) conversion. Majority of the Cr(VI) in the system was reduced to Cr(III) and existed in the suspension, with a small amount deposited on the sludge surface. The X-ray photoelectron spectroscopy (XPS) results indicated that the majority of Cr was present as reduced Cr(III) on the sludge. These results demonstrate that after fermentation in an aqueous environment, activated sludge is an effective medium for the remediation of Cr(VI). These results are useful for designing a green and sustainable bioreduction system for the remediation of Cr(VI)-polluted water. [ABSTRACT FROM AUTHOR]

Strain NB-1, which can efficiently degrade nitrobenzene, was identified as Pseudomonas frederiksbergensis. NB-1 was resistant to cold and alkali with the widest temperature (4–35 °C) and pH (5–11) adaptive range, compared with other reported nitrobenzene-degrading microorganisms. Based on the Haldane-Andrews model, the real maximum specific growth rate μm', specific affinity aA, and inhibition coefficient Ki were used in response surface methodology (RSM) simultaneously for the first time to guide NB-1 to treat nitrobenzene wastewater. According to the RSM model, the environmental factors (temperature, pH, salinity) corresponding to the optimal values of μm', aA, and Ki were determined. By comparing the specific growth rates corresponding to the optimal values of μm', aA, and Ki, respectively, the optimum growth conditions of NB-1 were determined under different nitrobenzene concentrations. The study of μm', aA, and Ki by RSM provided a new approach for a more accurate optimization of biological wastewater treatment conditions. [ABSTRACT FROM AUTHOR]

The formation of mine-contaminated groundwater as a result of acidic mine drainage from the oxidation of sulfur-containing minerals entering the groundwater. Biological permeable reactive barrier (Bio-PRB) technology is excellent for the remediation of mine-contaminated groundwater. Usually, the organic substrates utilized in Bio-PRB are a combination of rapid initiators, which are readily bioavailable, and long-lasting nutrients, which are more difficult to degrade. Herein, we investigated the effectiveness of three rapid initiators and three long-lasting nutrients to remove sulfate from simulated mine-contaminated groundwater via simulated column experiments. The rapid initiators comprised crude glycerol, sodium acetate, and industrial syrup (IS), and the long-lasting nutrients included biodiesel emulsified oil, soybean oil emulsified oil, and high-carbon alcohol emulsified oil (HO). Microorganisms were stimulated using IS to create a sulfate reduction system owing to its high total organic carbon content (24.30 g L -1 ), achieving optimal sulfate removal rate (1.69 mmol dm -3 d -1 ). The fastest (2.93 mmol dm -3 d- 1 ) and highest (88%) sulfate removal rates were achieved using HO, which is probably associated with the ability of HO to provide the most suitable C/N ratio (111.75) and induce the growth of sulfate-reducing bacteria (SRB) for substrate degradation. Conversely, a high concentration of sulfate reduction products inhibited SRB growth in the HO column. The addition of organic materials promoted SRB growth and various organic substrate-degrading bacteria. Furthermore, the competitive growth of methanogens (86.6%) may be responsible for the decrease in the relative abundance of SRB during the later stages of the experiment in the HO column.