Response of sulfur-metabolizing biofilm to external sulfide in element sulfur-based denitrification packed-bed reactor.

Dosing sulfide into the sulfur-packed-bed (S0PB) has great potential to enhance the denitrification efficiency by providing compensatory electron donors, however, the response of sulfur-metabolizing biofilm to various sulfide dosages has never been investigated. In this study, the S0PB reactor was carried out with increasing sulfide dosages by 3.6 kg/m3/d, presenting a decreasing effluent nitrate from 14.2 to 2.7 mg N/L with accelerated denitrification efficiency (k: 0.04 to 0.27). However, 6.5 mg N/L of nitrite accumulated when the sulfide dosage exceeded 0.9 kg/m3/d (optimum value). The increasing electron export contribution of sulfide a maximum of 85.5% illustrated its competition with the in-situ sulfur. Meanwhile, over-dosing sulfide caused serious biofilm expulsion with significant decreases in the total biomass, live cell population, and ATP by 90.2%, 86.7%, and 54.8%, respectively. This study verified the capacity of dosing sulfide to improve the denitrification efficiency in S0PB but alerted the negative effect of exceeded dosing.

Mitigating nitrite accumulation during S0-based autotrophic denitrification: Balancing nitrate-nitrite reduction rate with thiosulfate as external electron donor.

This study was carried out to determine the effect of influent nitrate loading on nitrite accumulation during elemental-sulfur based denitrification process, and proposed to enhance the nitrogen removal efficiency by mitigating nitrite accumulation with thiosulfate as external electron donor. Along with increasing the nitrate influent loading (from 0.09 kg N/m3/d to 1.73 kg N/m3/d) by shortening the empty bed contact time (EBCT) (from 5 h to 0.25 h), the nitrate removal loading increased from 0.08 to 0.83 kg N/m3/d. Meanwhile, the raise of the nitrate influent loading obviously aggravated the nitrite accumulation. Herein, nitrite began to accumulate since the nitrate influent loading was over 0.86 kg N/m3/d, and a maximum nitrite accumulation of 2.39 mg/L was observed under the 0.25 h of EBCT and 15 mg/L of nitrate influent concentration condition. Thiosulfate was used as the external electron donor to accelerate the nitrite reduction rate in order to mitigate the nitrite accumulation. As a result, the nitrite accumulation significantly decreased from 2.39 mg/L to 0.17 mg/L with the thiosulfate dosage of 13.36 mg/L. However, the nitrite accumulation bounced with the on-going increase of the thiosulfate dosage, indicating that the nitrate reduction rate and nitrite reduction rate were accelerated alternatively. After dosing thiosulfate, the relative abundances of sulfurimonas and ferritrophicum grew up significantly.

[Effect of N2O produced by indigenous denitrifiers in oil reservoir on the physical properties of crude oil]. / 油藏本源反硝化功能菌的产气作用(N2O)及对原油物性的影响.

The success of microbial enhanced oil recovery (MEOR) relies on complex microbial processes. Nevertheless, the contribution and mechanism of in-situ denitrification to microbial oil recovery remain unclear. In this study, eight denitrifying bacterial strains, designated T1, D1, D44, D46, D15, S1, S2 and S6, were isolated from the produced water of Xinjiang Oilfield, China, by a double layered plate method. The16S rDNA gene sequences of these denitrifying strains shared 100% similarity with Pseudomonas stutzeri (T1, D1, and D44), Pseudomonas putida (D46 and D15), and Pseudomonas aeruginosa (S1, S2, S6), respectively. The N2O production effects of these strains on the physical properties of crude oil were evaluated with batch experiment. Results showed that the highest total gas yield was observed with sucrose as carbon source, and the maximal concentration of N2O occurred with glycerol as carbon source. The denitrification process by these bacterial strains led to volume expansion and viscosity reduction of crude oil. Crude oil expansion rate was positively correlated with the concentration of N2O, with a correlation coefficient of 0.983, but not correlated with the volume of total gas production. Strain S1, S2, and S6 produced 530-730 mg·L-1 of surfactant using glycerol as ole carbon source, which could reduce surface tension and emulsify crude oil. However, these surfactant-producing strains produced less N2O, exhibited weaker effects on oil swelling and viscosity reduction, compared to the none-surfactant-producing denitrifying strains. Our results suggested that more attention should be paid to the ability of N2O production by denitrifying bacteria when exploiting microbial resources towards enhancing oil recovery.

[Simulation and prediction of water environmental carrying capacity in Liaoning Province based on system dynamics model].

By the methods of system dynamics, a water environmental carrying capacity (WECC) model was constructed, and the dynamic trend of the WECC in Liaoning Province was simulated by using this model, in combining with analytical hierarchy process (AHP) and the vector norm method. It was predicted that under the conditions of maintaining present development schemes, the WECC in this province in 2000-2050 would be decreased year after year. Only increasing water resources supply while not implementing scientific and rational management of water environment could not improve the regional WECC, and the integration of searching for new and saving present water resources with controlling wastewater pollution and reducing sewage discharge would be the only effective way to improve the WECC and the coordinated development of economy, society, and environment in Liaoning.