PCE dissolution and simultaneous dechlorination by nanoscale zero-valent iron particles in a DNAPL source zone

While the capability of nanoscale zero-valent iron (NZVI) to dechlorinate organic compounds in aqueous solutions has been demonstrated, the ability of NZVI to remove dense non-aqueous phase liquid (DNAPL) from source zones under flow-through conditions similar to a field scale application has not yet been thoroughly investigated. To gain insight on simultaneous DNAPL dissolution and NZVI-mediated dechlorination reactions after direct placement of NZVI into a DNAPL source zone, a combined experimental and modeling study was performed. First, a DNAPL tetrachloroethene (PCE) source zone with emplaced NZVI was built inside a small custom-made flow cell and the effluent PCE and dechlorination byproducts were monitored over time. Second, a model for rate-limited DNAPL dissolution and NZVI-mediated dechlorination of PCE to its three main reaction byproducts with a possibility for partitioning of these byproducts back into the DNAPL was formulated. The coupled processes occurring in the flow cell were simulated and analyzed using a detailed three-dimensional numerical model. It was found that subsurface emplacement of NZVI did not markedly accelerate DNAPL dissolution or the DNAPL mass-depletion rate, when NZVI at a particle concentration of 10g/L was directly emplaced in the DNAPL source zone. To react with NZVI the DNAPL PCE must first dissolve into the groundwater and the rate of dissolution controls the longevity of the DNAPL source. The modeling study further indicated that faster reacting particles would decrease aqueous contaminant concentrations but there is a limit to how much the mass removal rate can be increased by increasing the dechlorination reaction rate. To ensure reduction of aqueous contaminant concentrations, remediation of DNAPL contaminants with NZVI should include emplacement in a capture zone down-gradient of the DNAPL source.     

Anaerobic dechlorination and redox activities after full-scale Electrical Resistance Heating (ERH) of a TCE-contaminated aquifer

The effects of Electrical Resistance Heating (ERH) on dechlorination of TCE and redox conditions were investigated in this study. Aquifer and groundwater samples were collected prior to and after ERH treatment, where sediments were heated to approximately 100 degrees C. Sediment samples were collected from three locations and examined in microcosms for 250 to 400 days of incubation. Redox activities, in terms of consumed electron acceptors, were low in unamended microcosms with field-heated sediments, although they increased upon lactate-amendment. TCE was not dechlorinated or stalled at cDCE with field-heated sediments, which was similar or lower compared to the degree of dechlorination in unheated microcosms. However, in microcosms which were bioaugmented with a mixed anaerobic dechlorinating culture (KB-1) and lactate, dechlorination past cDCE to ethene was observed in field-heated sediments. Dechlorination and redox activities in microcosms with field-heated sediments were furthermore compared with controlled laboratory-heated microcosms, which were heated to 100 degrees C for 10 days and then slowly cooled to 10 degrees C. In laboratory-heated microcosms, TCE was not dechlorinated and redox activities remained low in unamended and lactate-amended sediments, although organic carbon was released to the aqueous phase. In contrast, in field-heated sediments, high aqueous concentrations of organic carbon were not observed in unamended microcosms, and TCE was dechlorinated to cDCE upon lactate amendment. This suggests that dechlorinating microorganisms survived the ERH or that groundwater flow through field-heated sediments carried microorganisms into the treated area and transported dissolved organic carbon downstream.     

Utilization of urban sewage sludge: Chinese perspectives

Purpose

Urbanization and industrialization in China has resulted in a dramatic increase in the volume of wastewater and sewage sludge produced from wastewater treatment plants. Problems associated with sewage sludge have attracted increasing attention from the public and urban planners. How to manage sludge in an economically and environmentally acceptable manner is one of the critical issues that modern societies are facing.

Methods

Sludge treatment systems consist of thickening, dewatering, and several different alternative main treatments (anaerobic digestion, aerobic digestion, drying, composting, and incineration). Agricultural application, landfill, and incineration are the principal disposal methods for sewage sludge in China. However, sewage sludge disposal in the future should focus on resource recovery, reducing environmental impacts and saving economic costs.

Results

The reuse of biosolids in all scenarios can be environmentally beneficial and cost-effective. Anaerobic digestion followed by land application is the preferable options due to low economic and energy costs and material reuse.

Conclusion

It is necessary to formulate a standard suitable for the utilization of sewage sludge in China.     

Environmental risk assessment of veterinary pharmaceuticals: development of a standard laboratory test with the dung beetle Aphodius constans

The environmental risk assessment of veterinary pharmaceuticals for dung beetles is required if the substance is an anti-parasiticide for the treatment of pasture animals. However, the demonstration of the environmental safety of those substances for dung fauna is hampered by the fact that no standardized laboratory test system is currently available. Here a test system using the temperate dung beetle species Aphodius (Agrilinus) constans (Scarabaeidae: Aphodiinae) Duftschmidt is described. The survival of first instar larvae of A. constans exposed to a model substance, dimethoate, spiked into formulated (i.e. dried, formulated and re-wetted) or fresh dung was measured over a period of three weeks. Larvae performed better in formulated dung which also proved to be more suitable for mixing-in test substances homogenously. Dimethoate caused significant larval mortality with LC50 values within a range of 1.3-2.8 mg a.s./kg dung (d.w.), depending on the dung type. Based on the data presented here, it is recommended to incorporate this new test system in the risk assessment process for veterinary pharmaceuticals. However, an international ringtest should to be performed beforehand to ensure adequate validation of the method.     

Vertical small scale variations of sorption and mineralization of three herbicides in subsurface limestone and sandy aquifer

Vertical variation in sorption and mineralization potential of mecoprop (MCPP), isoproturon and acetochlor were investigated at low concentrations (μg-range) at the cm-scale in unsaturated sub-surface limestone samples and saturated sandy aquifer samples from an agricultural catchment in Brévilles, France. From two intact core drills, four heterogenic limestone sections were collected from 4.50 to 26.40m below surface (mbs) and divided into 12 sub-samples of 8-25cm length, and one sandy aquifer section from 19.20 to 19.53m depth divided into 7 sub-samples of 4-5cm length. In the sandy aquifer section acetochlor and isoproturon sorption increased substantially with depth; in average 78% (acetochlor) and 61% (isoproturon) per 5cm. Also the number of acetochlor and isoproturon degraders (most-probable-number) was higher in the bottom half of the aquifer section (93->16000/g) than in the upper half (4-71/g). One 50cm long limestone section with a distinct shift in color showed a clear shift in mineralization, number of degraders and sorption: In the two brown, uppermost samples, up to 31% mecoprop and up to 9% isoproturon was mineralized during 231 days, the numbers of mecoprop and isoproturon degraders were 1300 to >16000/g, and the sorption of both isoproturon and acetochlor was more than three times higher, compared to the two deeper, grayish samples just below where mineralization (≤4%) and numbers of degraders (1-520/g) were low for all three herbicides. In both unsaturated limestone and sandy aquifer, variations and even distinct shifts in both mineralization, number of specific degraders and sorption were seen within just 4-15cm of vertical distance. A simple conceptual model of herbicides leaching to groundwater through a 10m unsaturated limestone was established, and calculations showed that a 30cm active layer with the measured sorption and mineralization values hardly impacted the fate of the investigated herbicides, whereas a total thickness of layers of 1m would substantially increase natural attenuation.     

Dechlorination after thermal treatment of a TCE-contaminated aquifer: laboratory experiments

A microcosm study was conducted to evaluate dechlorination of trichloroethene (TCE) to ethene and survival of dechlorinating bacteria after a thermal treatment in order to explore the potential for post-thermal bioremediation. Unamended microcosms containing groundwater and aquifer material from a contaminated site dechlorinated TCE to cis-1,2-dichloroethene (cDCE), while lactate-amended microcosms dechlorinated TCE to cDCE or ethene. A thermal treatment was simulated by heating a sub-set of microcosms to 100 degrees C for 10d followed by cooling to 10 degrees C over 150 d. The heated microcosms demonstrated no dechlorination when unamended. However, when amended with lactate, cDCE was produced in 2 out of 6 microcosms within 300 d after heating. Dechlorination of TCE to cDCE thus occurred in fewer heated (2 out of 12) than unheated (10 out of 12) microcosms. In unheated microcosms, the presence of dechlorinating microorganisms, including Dehalococcoides, was confirmed using nested PCR of 16S rRNA genes. Dechlorinating microorganisms were detected in fewer microcosms after heating, and Dehalococcoides were not detected in any microcosms after heating. Dechlorination may therefore be limited after a thermal treatment in areas that have been heated to 100 degrees C. Thus, inflow of groundwater containing dechlorinating microorganisms and/or bioaugmention may be needed for anaerobic dechlorination to occur after a thermal treatment.     

Continuous-flow fractionation of trace metals in environmental solids using rotating coiled columns. Some kinetic aspects and applicability of three-step BCR leaching schemes

The applicability of the three-step BCR leaching scheme to the continuous-flow fractionation of trace metals (TM) using rotating coiled columns (RCC) has been investigated taking soil and sediment reference samples (SRM-2710, CRM-601, BCR-701) as examples. A particulate sample was retained in the rotating column as the stationary phase under the action of centrifugal forces while different eluents, used according to the original and optimised BCR protocols, were continuously pumped through. The whole procedure required 3-4 h instead of at least 50 h needed for the traditional sequential extraction. It has been shown that in comparison with batch sequential extraction procedures (SEP), the recoveries of Cd, Zn, Cu, and Pb at the first stage (most mobile and potentially dangerous acid soluble forms) are somewhat higher, if a dynamic extraction in RCC is used. Nevertheless, the distribution patterns for TM in the first two leachable fractions (acid soluble and reducible forms) are similar in most cases. Since no heating is used in RCC, the recoveries of TM at the third stage (when hydrogen peroxide is applied to oxidize the organic matter) may be incomplete and matrix-dependent. The effect of eluent volume and flow rate on the recovery of TM in different forms has been investigated. It has been shown that the kinetics of heavy metal leaching vary significantly with samples. Hence, investigating the elution profiles can provide additional important information for risk assessment of TM mobilization.     

The need for bioaugmentation after thermal treatment of a TCE-contaminated aquifer: Laboratory experiments

A microcosm study was conducted to evaluate the need for bioaugmentation after a thermal treatment to anaerobically dechlorinate trichloroethene (TCE) to ethene. The microcosms were either: heated to 100 degrees C and slowly cooled to simulate thermal remediation while bioaugmenting when the declining temperature reached 10 degrees C; or kept at ambient groundwater temperatures (10 degrees C) and bioaugmented for comparison. Aquifer samples from three sediment locations within a TCE-polluted source zone were investigated in duplicate microcosms. In biostimulated (5 mM lactate) and heated microcosms, no conversion of TCE was observed in 4 out of 6 microcosms, and in the remaining microcosms the dechlorination of TCE was incomplete to cDCE (cis-dichloroethene). By comparison, complete TCE dechlorination to ethene was observed in 4 out of 6 heated microcosms that were bioaugmented with a highly enriched dechlorinating mixed culture, KB-1, but no electron donor, and also in 4 of 6 microcosms that were augmented with KB-1 and an electron donor (5 mM lactate). These data suggest that electron donor released during heating, was capable of promoting complete dechlorination coincident with bioaugmentation. Heated microcosms demonstrated less methanogenesis than unheated microcosms, even with elevated H2 concentrations and addition of KB-1, which contains methanogens. This suggests that the heating process suppressed the native microbial community, which can decrease competition with the bioaugmented culture and increase the effectiveness of dechlorination following a thermal treatment. Specifically, cDCE removal rates were four to six times higher in heated than unheated bioaugmented microcosms. This study confirms the need for bioaugmentation following a laboratory thermal treatment to obtain complete dechlorination of TCE.     

The change from rifting to thrusting in the Northern Calcareous Alps as recorded in Jurassic sediments

Facies analysis, fossil dating, and the study of the metamorphism in the Late Triassic to Early Cretaceous sedimentary successions in the central part of the Northern Calcareous Alps allow to reconstruct the tectonic evolution in the area between the South Penninic Ocean in the northwest and the Tethys Ocean with the Hallstatt Zone in the southeast. The Triassic as well as the Early and Middle Jurassic sediments were deposited in a rifted, transtensive continental margin setting. Around the Middle/Late Jurassic boundary two trenches in front of advancing nappes formed in sequence in the central part of the Northern Calcareous Alps. The southern trench (Late Callovian to Early Oxfordian) accumulated a thick succession of gravitatively redeposited sediments derived from the sedimentary sequences of the accreted Triassic–Liassic Hallstatt Zone deposited on the outer shelf and the margin of the Late Triassic carbonate platform. During a previous stage these sediments derived from sequences deposited on the more distal shelf (Salzberg facies zone of Hallstatt unit, Meliaticum), and in a later stage from more proximal parts (Zlambach facies zone of Hallstatt unit, Late Triassic reef belt). Low temperature–high pressure metamorphism of some Hallstatt limestones before redeposition is explained by the closure of parts of the Tethys Ocean in Middle to Late Jurassic times and associated subduction. In the northern trench (Late Oxfordian to Kimmeridgian) several hundred meters of sediment accumulated including redeposited material from a nearby topographic rise. This rise is interpreted as an advancing nappe front as a result of the subduction process. The sedimentary sealing by Tithonian sediments, documented by uniform deep-water sedimentation (Oberalm Formation), gives an upper time constraint for the tectonic events. In contrast to current models, which propose an extensional regime for the central and eastern Northern Calcareous Alps in the Late Jurassic, we propose a geodynamic model with a compressional regime related to the Kimmerian orogeny.