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Halogenated organic solvents such as chlorobenzenes (CBs) are frequent groundwater contaminants due to legacy spills. When contaminated anaerobic groundwater discharges into surface water through wetlands and other transition zones, aeration can occur from various physical and biological processes at shallow depths, resulting in oxic-anoxic interfaces (OAIs). This study investigated the potential for 1,2,4-trichlorobenzene (1,2,4-TCB) biodegradation at OAIs. A novel upflow column system was developed to create stable anaerobic and aerobic zones, simulating a natural groundwater OAI. Two columns containing (1) sand and (2) a mixture of wetland sediment and sand were operated continuously for 295 days with varied doses of 0.14-1.4 mM sodium lactate (NaLac) as a model electron donor. Both column matrices supported anaerobic reductive dechlorination and aerobic degradation of 1,2,4-TCB spatially separated between anaerobic and aerobic zones. Reductive dechlorination produced a mixture of di- and monochlorobenzene daughter products, with estimated zero-order dechlorination rates up to 31.3 μM/h. Aerobic CB degradation, limited by available dissolved oxygen, occurred for 1,2,4-TCB and all dechlorinated daughter products. Initial reductive dechlorination did not enhance the overall observed extent or rate of subsequent aerobic CB degradation. Increasing NaLac dose increased the extent of reductive dechlorination, but suppressed aerobic CB degradation at 1.4 mM NaLac due to increased oxygen demand. 16S-rRNA sequencing of biofilm microbial communities revealed strong stratification of functional anaerobic and aerobic organisms between redox zones including the sole putative reductive dechlorinator detected in the columns, Dehalobacter. The sediment mixture column supported enhanced reductive dechlorination compared to the sand column at all tested NaLac doses and growth of Dehalobacter populations up to 4.1 × 10 8 copies/g (51% relative abundance), highlighting the potential benefit of sediments in reductive dechlorination processes. Results from these model systems suggest both substantial anaerobic and aerobic CB degradation can co-occur along the OAI at contaminated sites where bioavailable electron donors and oxygen are both present., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

Traveling bacterial waves are capable of improving contaminant remediation in the subsurface. It is fairly well understood how bacterial chemotaxis and growth separately affect the formation and propagation of such waves. However, their interaction is not well understood. We therefore perform a modeling study to investigate the coupled effects of chemotaxis and growth on bacterial migration, and examine their effects on contaminant remediation. We study the waves by using different initial electron acceptor concentrations for different bacteria and substrate systems. Three types of traveling waves can occur: a chemotactic wave due to the biased movement of chemotactic bacteria resulting from metabolism-generated substrate concentration gradients; a growth/decay/motility wave due to a dynamic equilibrium between bacterial growth, decay and random motility; and an integrated wave due to the interaction between bacterial chemotaxis and growth. Chemotaxis hardly enhances the bacterial propagation if it is too weak to form a chemotactic wave or its wave speed is less than half of the growth/decay/motility wave speed. However, chemotaxis significantly accelerates bacterial propagation once its wave speed exceeds the growth/decay/motility wave speed. When convection occurs, it speeds up the growth/decay/motility wave but slows down or even eliminates the chemotactic wave due to the dispersion. Bacterial survival proves particularly important for bacterial propagation. Therefore we develop a conceptual model to estimate the speed of growth/decay/motility waves., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Abstract: It is important to determine the behavior of constituents in treated sewage during soil aquifer treatment for water recycling. A collaborative project with Herman Bouwer published in 1984 documented the fate and occurrence of Priority Pollutants during groundwater recharge using wastewater with application to water reuse and agricultural systems. New compounds are continually being manufactured and released to the environment. The interest today has shifted to the behavior of emerging contaminants. One important class of emerging contaminants is pharmaceuticals and personal care products (PPCPs). The hazards to the environment and human health of trace levels of PPCPs in water supplies are poorly understood. A multi compound method using solid phase extraction and chemical derivatization with pentafluorobenzylbromide, followed by analysis via gas chromatography/mass spectrometry was used to study the occurrence and removals of 18 PPCPs in a local wastewater treatment plant (WWTP). Overall, 16 out of the 18 selected PPCPs, which span a range of therapeutic classes and some commonly used personal care products, were detected in raw sewage samples collected from the Baltimore Back River WWTP. Ten of the 18 selected PPCPs were detected in the treated sewage effluent, signifying incomplete removal for the majority of the PPCPs during the wastewater treatment processes. The majority of the target analytes were detected in both the influent and effluent WWTP samples at μg/L levels, although some PPCPs (e.g., naproxen and ibuprofen) were encountered at μg/L levels. Biodegradation is an important process for wastewater and soil aquifer treatment. Aerobic batch biodegradation (using activated sludge as microbial inocula) experiments were conducted to gain insight into the biodegradation behavior of our target PPCPs at initial concentrations of 50, 10, and 1μg/L. Sterile control studies showed no loss of our target PPCPs during the entire incubation period, and sorption to the biomass was found to be negligible for all testing conditions. Biodegradation results were not sensitive to the initial concentration and showed that 13 of the 18 PPCPs tested exhibited biotransformations greater than 80% after 50 days of incubation. Phenytoin, 5-fluorouracil, and diclofenac were the only three compounds with removals less than 60%. The occurrence study revealed the presence of PPCPs in sewage effluents, and the biodegradation study suggests that biotransformation is a possible removal mechanism for PPCPs during groundwater recharge or soil aquifer treatment for water recycling. [Copyright &y& Elsevier]

The objective of this study was to assess the effectiveness of alkaline hydrolysis as an alternative ex situ technology for remediating groundwater contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Treatment in both batch reactor and continuous stirred tank reactor (CSTR) was investigated. RDX reactivity was strongly dependent on the reaction pH investigated (11–13). The batch system achieved pseudo-first-order RDX reaction rates in the range of (0.8–27.7)×10-3 min-1, corresponding to half-life periods of 17.9 to 0.5 h, respectively. In the CSTR system operated at the initial RDX concentration of 4.5×10-3 mM, 99% RDX removal was achieved with the hydraulic retention time of 2 days and the reaction pH of 11.9. Formate and nitrite were produced as the major hydrolysates in the CSTR system, indicating a simultaneous reaction mechanism involving RDX ring cleavage and elimination of the ring nitrogen. The net OH- demand used only for RDX removal in the CSTR was found to be 1.5, 390, and 130 MOH-/MRDXremoved at pH values of 11.9, 11.5, and 11.0, respectively. A conceptual cost analysis indicated that the expense of alkaline treatment may be comparable to the expense of granular activated carbon treatment for long treatment periods (30 years or more), due to the potentially lower annual operational cost of alkali treatment. [ABSTRACT FROM AUTHOR]

Abstract: The presence of pharmaceuticals and other wastewater-derived micropollutants in surface and groundwaters is receiving intense public and scientific attention. Yet simple GC/MS methods that would enable measurement of a wide range of such compounds are scarce. This paper describes a GC/MS method for the simultaneous determination of 13 pharmaceuticals (acetaminophen, albuterol, allopurinol, amitriptyline, brompheniramine, carbamazepine, carisoprodol, ciclopirox, diazepam, fenofibrate, metoprolol, primidone, and terbinafine) and 5 wastewater-derived contaminants (caffeine, diethyltoluamide, n-butylbenzene sulfonamide, n-nonylphenol, and n-octylphenol) by solid phase extraction (SPE) and derivatization with BSTFA. The method was applied to the analysis of raw and treated sewage samples obtained from a wastewater treatment plant located in the mid-Atlantic United States. All analytes were detected in untreated sewage, and 14 of the 18 analytes were detected in treated sewage. [Copyright &y& Elsevier]