Uranium removal from groundwater via in situ biostimulation: Field-scale modeling of transport and biological processes

During 2002 and 2003, bioremediation experiments in the unconfined aquifer of the Old Rifle UMTRA field site in western Colorado provided evidence for the immobilization of hexavalent uranium in groundwater by iron-reducing Geobacter sp. stimulated by acetate amendment. As the bioavailable Fe(III) terminal electron acceptor was depleted in the zone just downgradient of the acetate injection gallery, sulfate-reducing organisms came to dominate the microbial community. In the present study, we use multicomponent reactive transport modeling to analyze data from the 2002 field experiment to identify the dominant transport and biological processes controlling uranium mobility during biostimulation, and determine field-scale parameters for these modeled processes. The coupled process simulation approach was able to establish a quantitative characterization of the principal flow, transport, and reaction processes based on the 2002 field experiment, that could be applied without modification to describe the 2003 field experiment. Insights gained from this analysis include field-scale estimates of the bioavailable Fe(III) mineral threshold for the onset of sulfate reduction, and rates for the Fe(III), U(VI), and sulfate terminal electron accepting processes.     

ICS-1500离子色谱仪在地下水检测中的应用

采用ICS-1500离子色谱仪与淋洗液自动发生器联用,等浓度淋洗,用AS40自动进样,同时测定地下水中氟化物、氯化物、硫酸盐和硝酸盐氮。该方法简便快捷,灵敏度高,极大提高了分析的效率,适用于地下水中四项阴离子的检测。     

Formation of secondary inorganic aerosol in a frigid urban atmosphere

•Harbin showed relatively high threshold RH (80%) for apparent increase of SOR. •The observed SOR were at the lower end of the ratios from Beijing’s winter. •Temperature-dependent increase of NOR was sharper than that of SOR. • NOR increased with stronger biomass burning impact but SOR was largely unchanged. Formation of secondary inorganic aerosol (SIA) was investigated during a six-month long heating season in Harbin, China. Enhanced sulfate formation was observed at high relative humidity (RH), with the same threshold RH (80%) for both colder and warmer measurement periods. Compared to wintertime results from Beijing, the threshold RH was considerably higher in Harbin, whereas the RH-dependent enhancement of sulfur oxidation ratio (SOR) was less significant. In addition, the high RH events were rarely encountered, and for other periods, the SOR were typically as low as ~0.1. Therefore, the sulfate formation was considered inefficient in this study. After excluding the several cases with high RH, both SOR and the nitrogen oxidation ratio (NOR) exhibited increasing trends as the temperature increased, with the increase of NOR being sharper. The nitrate to sulfate ratio tended to increase with increasing temperature as well. Based on a semi-quantitative approach, this trend was attributed primarily to the temperature-dependent variations of precursors including SO₂ and NO₂. The influence of biomass burning emissions on SIA formation was also evident. With stronger impact of biomass burning, an enhancement in NOR was observed whereas SOR was largely unchanged. The different patterns were identified as the dominant driver of the larger nitrate to sulfate ratios measured at higher concentrations of fine particulate matter.     

Temperature and feed strategy effects on sulfate and organic matter removal in an AnSBB

The objective of this work was to analyze the interaction effects between temperature, feed strategy and COD/[SO(4)(2-)] levels, maintaining the same ratio, on sulfate and organic matter removal efficiency from a synthetic wastewater. This work is thus a continuation of Archilha et al. (2010) who studied the effect of feed strategy at 30 °C using different COD/[SO(4)(2-)] ratios and levels. A 3.7-L anaerobic sequencing batch reactor with recirculation of the liquid phase and which contained immobilized biomass on polyurethane foam (AnSBBR) was used to treat 2.0 L synthetic wastewater in 8 h cycles. The temperatures of 15, 22.5 and 30 °C with two feed strategies were assessed: (a) batch and (b) batch followed by fed-batch. In strategy (a) the reactor was fed in 10 min with 2 L wastewater containing sulfate and carbon sources. In strategy (b) 1.2 L wastewater (containing only the sulfate source) was fed during the first 10 min of the cycle and the remaining 0.8 L (containing only the carbon source) in 240 min. Based on COD/[SO(4)(2-)] = 1 and on the organic matter (0.5 and 1.5 gCOD/L) and sulfate (0.5 and 1.5 gSO(4)(2-)/L) concentrations, the sulfate and organic matter loading rates applied were 1.5 and 4.5 g/L.d, i.e., same COD/[SO(4)(2-)] ratio (=1) but different levels (1.5/1.5 and 4.5/4.5 gCOD/gSO(4)(2-)). When reactor feed was 1.5 gCOD/L.d and 1.5 gSO(4)(2-)/L.d, gradual feeding (strategy b) showed to favor sulfate and organic matter removal in the investigated temperature range, indicating improved utilization of the electron donor for sulfate reduction. Sulfate removal efficiencies were 87.9; 86.3 and 84.4%, and organic matter removal efficiencies 95.2; 86.5 and 80.8% at operation temperatures of 30; 22.5 and 15 °C, respectively. On the other hand, when feeding was 4.5 gCOD/L.d and 4.5 gSO(4)(2-)/L.d, gradual feeding did not favor sulfate removal, indicating that gradual feeding of the electron donor did not improve sulfate reduction.     

Effect of nitrobenzene on the performance and bacterial community in an expanded granular sludge bed reactor treating high-sulfate organic wastewater

Less than 50 mg/L nitrobenzene brought little effect on anaerobic sulfate reduction. Kinetics of sulfate reduction under different nitrobenzene contents was studied. Increased nitrobenzene contents greatly changed the bacterial community structure. Genus Desulfovibrio played the key role in anaerobic sulfate reduction process. Nitrobenzene (NB) is frequently found in wastewaters containing sulfate and may affect biological sulfate reduction process, but information is limited on the responses of sulfate reduction efficiency and microbial community to the increased NB contents. In this study, a laboratory-scale expanded granular sludge bed reactor was operated continuously to treat high-sulfate organic wastewater with increased NB contents. Results successfully demonstrated that the presence of more than 50 mg/L NB depressed sulfate reduction and such inhibition was partly reversible. Bath experiments showed that the maximum specific desulfuration activity (SDA) decreased from 135.80 mg SO₄^2?/gVSS/d to 30.78 mg SO₄^2?/gVSS/d when the NB contents increased from none to 400 mg/L. High-throughput sequencing showed that NB also greatly affected bacterial community structure. Bacteroidetes dominated in the bioreactor. The abundance of Proteobacteria increased with NB addition while Firmicutes presented an opposite trend. Proteobacteria gradually replaced Firmicutes for the dominance in response to the increase of influent NB concentrations. The genus Desulfovibrio was the dominant sulfate-reducing bacteria (SRB) with absence or presence of NB, but was inhibited under high content of NB. The results provided better understanding for the biological sulfate reduction under NB stress.     

Elimination of antibiotic resistance genes and control of horizontal transfer risk by UV-based treatment of drinking water: A mini review

Antibiotic-resistant bacteria and antibiotic resistance genes are in water bodies. UV/chlorination method is better to remove ARGs than UV or chlorination alone. Research on UV/hydrogen peroxide to eliminate ARGs is forthcoming. UV-based photocatalytic processes are effective to degrade ARGs. Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been recognized as one of the biggest public health issues of the 21st century. Both ARB and ARGs have been determined in water after treatment with conventional disinfectants. Ultraviolet (UV) technology has been seen growth in application to disinfect the water. However, UV method alone is not adequate to degrade ARGs in water. Researchers are investigating the combination of UV with other oxidants (chlorine, hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), and photocatalysts) to harness the high reactivity of produced reactive species (Clž·, ClOž·ž, Clž₂·ž⁻, žž·OH, and SOž₄ž·⁻€) in such processes with constituents of cell (e.g., deoxyribonucleic acid (DNA) and its components) in order to increase the degradation efficiency of ARGs. This paper briefly reviews the current status of different UV-based treatments (UV/chlorination, UV/H₂O₂, UV/PMS, and UV-photocatalysis) to degrade ARGs and to control horizontal gene transfer (HGT) in water. The review also provides discussion on the mechanism of degradation of ARGs and application of q-PCR and gel electrophoresis to obtain insights of the fate of ARGs during UV-based treatment processes.     

Broadening of appropriate demulsifier dosage range for latex-containing wastewater by sulfate addition

Investigation of demulsification of polybutadiene latex (PBL) wastewater by polyaluminum chloride (PAC) indicated that there was an appropriate dosage range for latex removal. The demulsification mechanism of PAC was adsorption-charge neutralization and its appropriate dosage range was controlled by zeta potential. When the zeta potential of the mixture was between -15 and 15 mV after adding PAC, the demulsification effect was good. Decreasing the latex concentration in chemical oxygen demand (COD) from 8.0 g/L to 0.2 g/L made the appropriate PAC dosage range narrower and caused the maximum latex removal efficiency to decrease from 95% to 37%. Therefore, more accurate PAC dosage control is required. Moreover, adding 50 mg/L sulfate broadened the appropriate PAC dosage range, resulting in an increase in maximum latex removal efficiency from 37% to 91% for wastewater of 0.2 g COD/L. The addition of sulfate will favor more flexible PAC dosage control in demulsification of PBL wastewater.

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Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis

The photolysis of was studied for the removal of acetic acid in aqueous solution and compared with the H₂O₂/UV system. The radicals generated from the UV irradiation of ions yield a greater mineralization of acetic acid than the OH radicals. Acetic acid is oxidized by radicals without significant formation of intermediate by-products. Increasing system pH results in the formation of OH radicals from radicals. Maximum acetic acid degradation occurred at pH 5. The results suggest that above this pH, competitive reactions with the carbon mineralized inhibit the reaction of the solute with and also OH radicals. Scavenging effects of two naturally occurring ions were tested; in contrast to ions, the presence of Cl⁻ ions enhances the efficiency of the /UV process towards the acetate removal. It is attributed to the formation of the Cl radical and its great reactivity towards acetate.     

pH dependence of persulfate activation by EDTA/Fe(III) for degradation of trichloroethylene

The ability of free ferrous ion activated persulfate (S₂O₈²⁻) to generate sulfate radicals (SO₄⁻) for the oxidation of trichloroethylene (TCE) is limited by the scavenging of SO₄⁻ with excess Fe²⁺ and a quick conversion of Fe²⁺ to Fe³⁺. This study investigated the applicability of ethylene-diamine-tetra-acetic acid (EDTA) chelated Fe³⁺ in activating persulfate for the destruction of TCE in aqueous phase under pH 3, 7 and 10. Fe³⁺ and EDTA alone did not appreciably degrade persulfate. The presence of TCE in the EDTA/Fe³⁺ activated persulfate system can induce faster persulfate and EDTA degradation due to iron recycling to activate persulfate under a higher pH condition. Increasing the pH leads to increases in pseudo-first-order-rate constants for TCE, S₂O₈²⁻ and EDTA degradations, and Cl generation. Accordingly, the experiments at pH 10 with different EDTA/Fe³⁺ molar ratios indicated that a 1/1 ratio resulted in a remarkably higher degradation rate at the early stage of reaction as compared to results by other ratios. Higher persulfate dosage under the EDTA/Fe³⁺ molar ratio of 1/1 resulted in greater TCE degradation rates. However, increases in persulfate concentration may also lead to an increase in the rate of persulfate consumption.     

Formation of secondary inorganic aerosols by power plant emissions exhausted through cooling towers in Saxony

Background, aim, and scope  The fraction of ambient PM₁₀ that is due to the formation of secondary inorganic particulate sulfate and nitrate from the emissions of two large, brown-coal-fired power stations in Saxony (East Germany) is examined. The power stations are equipped with natural-draft cooling towers. The flue gases are directly piped into the cooling towers, thereby receiving an additionally intensified uplift. The exhausted gas-steam mixture contains the gases CO, CO₂, NO, NO₂, and SO₂, the directly emitted primary particles, and additionally, an excess of ‘free’ sulfate ions in water solution, which, after the desulfurization steps, remain non-neutralized by cations. The precursor gases NO₂ and SO₂ are capable of forming nitric and sulfuric acid by several pathways. The acids can be neutralized by ammonia and generate secondary particulate matter by heterogeneous condensation on preexisting particles. Materials and methods  The simulations are performed by a nested and multi-scale application of the online-coupled model system LM-MUSCAT. The Local Model (LM; recently renamed as COSMO) of the German Weather Service performs the meteorological processes, while the Multi-scale Atmospheric Transport Model (MUSCAT) includes the transport, the gas phase chemistry, as well as the aerosol chemistry (thermodynamic ammonium–sulfate–nitrate–water system). The highest horizontal resolution in the inner region of Saxony is 0.7 km. One summer and one winter episode, each realizing 5 weeks of the year 2002, are simulated twice, with the cooling tower emissions switched on and off, respectively. This procedure serves to identify the direct and indirect influences of the single plumes on the formation and distribution of the secondary inorganic aerosols. Results and conclusions  Surface traces of the individual tower plumes can be located and distinguished, especially in the well-mixed boundary layer in daytime. At night, the plumes are decoupled from the surface. In no case does the resulting contribution of the cooling tower emissions to PM₁₀ significantly exceed 15 μgm⁻³ at the surface. These extreme values are obtained in narrow plumes on intensive summer conditions, whereas different situations with lower turbulence (night, winter) remain below this value. About 90% of the PM₁₀ concentrations in the plumes are secondarily formed sulfate, mainly ammonium sulfate, and about 10% originate from the primarily emitted particles. Under the assumptions made, ammonium nitrate plays a rather marginal role. Recommendations and perspectives  The analyzed results depend on the specific emission data of power plants with flue gas emissions piped through the cooling towers. The emitted fraction of ‘free’ sulfate ions remaining in excess after the desulfurization steps plays an important role at the formation of secondary aerosols and therefore has to be measured carefully.