Zhihui Yang

The anaerobic granular sludge from an Internal Circulation (IC) reactor of a paper mill wastewater treatment plant were seeded in an Anammox upflow anaerobic sludge blanket reactor. After 185 days operation, the reactor was finally started up by increasing the influent ammonium and nitrite concentrations to 224 mg/L and 255 mg/L, respectively, with volumetric nitrogen removal rate increasing to 3.76 kg/(m3·d). The physicochemical characteristics of the cultivated Anammox granules were observed by scanning electron microscope, transmission electron microscope and Fourier Transform infrared spectroscopy (FTIR). Results suggested that during the start-up course, the granular sludge initially disintegrated and then re-aggregated. FTIR spectra results revealed that the Anammox granular sludge contained abundant functional groups, indicating that it may also possess good adsorption properties. The ecological structure of the granular sludge, analyzed by the metagenomic sequencing methods, suggested that the relative abundance of the dominant bacterial community in the seeding sludge, i.e., Proteobacteria, Firmicutes, Bacteroidetes, significantly reduced, while Planctomycetes which contains anaerobic ammonium oxidation bacteria remarkably increased from 1.59% to 23.24% in the Anammox granules.

As part of our efforts to find effective methods to the drinking water risk management, the health risk assessment of arsenic and cadmium in groundwater near Xiangjiang River was analyzed. The results suggest that although the arsenic and cadmium concentrations in 97% of groundwater sources are less than the requirement of Water Quality Standards for Drinking Water (GB5749-2006) in China, the residents served by almost all of the investigated centralized drinking water sources have a significant potential health risk by consumption, especially cancer risk. It is justified through analyses that risk assessment is an effective tool for risk management, and the maximum permissible concentration of arsenic and cadmium in drinking water (0.01 and 0.005 mg L^-1, respectively) is suitable for China at present, considering the current economic status of China. Risk managers develop cleanup standards designed to protect against all possible adverse effects, which should take into account highly exposed individuals, effects of mixtures of toxic substances, attendant uncertainties, and other factors such as site-specific (or generic) criteria, technical feasibility, cost–benefit analyses, and sociopolitical concerns.

Though there exists a wide spectrum of sulfur‐oxidizing microorganisms in soils, the oxidation rate of soil‐applied elemental sulfur (S⁰) is regularly limited because of a restricted population size. An incubation experiment was conducted to determine the effect of repeated S⁰ applications on different microbial populations, sulphate (SO₄ ²⁻)‐S concentration, and soil pH. Elemental sulfur was applied repeatedly at a rate of 15 mg S g⁻¹ soil in a 15‐day interval cycle of 7 times. After each cycle, 7.5 mg lime (CaCO₃) g⁻¹ soil was applied to adjust the soil pH to an optimum range. Soil pH and 0.025 M potassium chloride (KCl)–extractable SO₄ ²⁻‐S were determined every 3 days. The population of Thiobacillus spp. and aerobic heterotrophic sulfur‐oxidizing bacteria were counted 3 and 15 days after each S⁰ application. The results showed that the soil pH decreased rapidly from an initial value of 7.6 to 5.3, 15 days after the first S⁰ application. Lime applications successfully counterbalanced the acidifying effect of S⁰ oxidation, and soil pH values were maintained in the optimum range with a pH of about 6.4. The 0.025 M KCl–extractable SO₄ ²⁻‐S content increased with repeated applications of S⁰, showing a maximum value of 3,800 mg S kg⁻¹ soil after the sixth S⁰ application. Thereafter, the SO₄ ²⁻‐S concentration decreased significantly. The Thiobacillus spp.count increased consistently with repeated S⁰ applications. The number of Thiobacillus spp. at the first application of S⁰ was significantly lower than the count after all other applications. A maximum Thiobacillus spp. count of 1.0 · 10⁸ g⁻¹ soil was observed after the seventh application of S⁰. The fastest S⁰ oxidation rate was found after the second application of S⁰. The population of aerobic heterotrophic sulfur‐oxidizing bacteria increased also with repeated S⁰ applications, showing a maximum count of 5.0 · 10⁴ g⁻¹ soil after the fourth S⁰ application. Thereafter, the population declined steadily. Significant relationships between SO₄ ²⁻‐S concentration and count of Thiobacillus spp. (R²=0.85, p2=0.63, p0 applications decrease soil pH, increase Thiobacillus spp. counts, and thus increase extractable SO₄ ²⁻‐S concentration in soils. The results further suggest that soils that receive regular S⁰ applications have a higher Thiobacillus spp. count and thus have conjecturally a higher S⁰ oxidation potential than soils that have never received S⁰. This again indicates a priming effect of S⁰ oxidation by Thiobacillus spp., which needs to be confirmed under field conditions.