Stimulation of aerobic degradation of bentazone, mecoprop and dichlorprop by oxygen addition to aquifer sediment

Biostimulation with oxygen and electron donors supports micropollutant biodegradation in an experimentally simulated nitrate-reducing aquifer

The availability of suitable electron donors and acceptors limits micropollutant natural attenuation in oligotrophic groundwater. This study investigated how electron donors with different biodegradability (humics, dextran, acetate, and ammonium), and different oxygen concentrations affect the biodegradation of 15 micropollutants (initial concentration of each micropollutant = 50 μg/L) in simulated nitrate reducing aquifers. Tests mimicking nitrate reducing field conditions showed no micropollutant biodegradation, even with electron donor amendment. However, 2,4-dichlorophenoxyacetic acid and mecoprop were biodegraded under (micro)aerobic conditions with and without electron donor addition. The highest 2,4-dichlorophenoxyacetic acid and mecoprop biodegradation rates and removal efficiencies were obtained under fully aerobic conditions with amendment of an easily biodegradable electron donor. Under microaerobic conditions, however, amendment with easily biodegradable dissolved organic carbon (DOC) inhibited micropollutant biodegradation due to competition between micropollutants and DOC for the limited oxygen available. Microbial community composition was dictated by electron acceptor availability and electron donor amendment, not by micropollutant biodegradation. Low microbial community richness and diversity led to the absence of biodegradation of the other 13 micropollutants (such as bentazon, chloridazon, and carbamazepine). Finally, adaptation and potential growth of biofilms interactively determined the location of the micropollutant removal zone relative to the point of amendment. This study provides new insight on how to stimulate in situ micropollutant biodegradation to remediate oligotrophic groundwaters as well as possible limitations of this process.

Effect of dissolved organic carbon on micropollutant biodegradation by aquifer and soil microbial communities

Groundwater, a major source of drinking water worldwide, is often contaminated with micropollutants. Although microbial communities in aquifers and soils have the capability to biodegrade some micropollutants, this process is limited in situ. Biostimulation with dissolved organic carbon (DOC) is known to promote micropollutant biodegradation, but the role of DOC biodegradability is still poorly understood. This study investigated how three DOC types with different biodegradability (humics, dextran and acetate) affect the biodegradation of 15 micropollutants by aquifer and soil microbial communities under aerobic and nitrate reducing conditions. Although originating from different environments, both communities were able to biodegrade the same 4 micropollutants under aerobic conditions - 2,4-D, MCPP, chloridazon (CLZ) and chloridazon-desphenyl. However, DOC addition only affected MCPP biodegradation, promoting MCPP biodegradation regardless of DOC biodegradability. Biodegradation of 2,4-D, MCPP and CLZ under aerobic conditions was observed after a lag phase, whose duration differed per compound. 2,4-D was biodegraded first and fully. Aquifer community was able to degrade about half of the initial MCPP concentration (removal efficiency of 49.3 ± 11.7%). CLZ was fully biodegraded by the aquifer community, but not by the soil community, possibly due to substrate competition with organics originating from the inoculum. Therefore, the natural organic carbon present in the inocula and in environmental systems can influence micropollutant biodegradation. Under nitrate reducing conditions micropollutant biodegradation was not observed nor biostimulated by DOC addition. The results also highlight the importance of sufficient exposure time to trigger in situ micropollutant biodegradation.

Influence of redox condition and inoculum on micropollutant biodegradation by soil and activated sludge communities

Micropollutant biodegradation is selected by the interplay among environmental conditions and microbial community composition. This study investigated how different electron acceptors, and different inocula with varying microbial diversity, pre-exposed to distinct redox conditions and micropollutants, affect micropollutant biodegradation. Four tested inocula comprised of agricultural soil (Soil), sediment from a ditch in an agricultural field (Ditch), activated sludge from a municipal WWTP (Mun AS), and activated sludge from an industrial WWTP (Ind AS). Removal of 16 micropollutants was investigated for each inoculum under aerobic, nitrate reducing, iron reducing, sulfate reducing, and methanogenic conditions. Micropollutant biodegradation was highest under aerobic conditions with removal of 12 micropollutants. Most micropollutants were biodegraded by Soil (n = 11) and Mun AS inocula (n = 10). A positive correlation was observed between inoculum community richness and the number of different micropollutants a microbial community initially degraded. The redox conditions to which a microbial community had been exposed appeared to positively affect micropollutant biodegradation performance more than pre-exposure to micropollutants. Additionally, depletion of the organic carbon present in the inocula resulted in lower micropollutant biodegradation and overall microbial activities, suggesting that i) an additional carbon source is needed to promote micropollutant biodegradation; and ii) overall microbial activity can be a good indirect indicator for micropollutant biodegradation activity. These results could help to develop novel micropollutant removal strategies.

Combining sediment management and bioremediation in muddy ports and harbours: A review

This paper reviews two important sources of innovation linked to the maritime environment and more importantly to ports: the potential coupling of sediment management and (bio)remediation. The detrimental effects of dredging are briefly considered, but the focus here is on a sustainable alternative method of managing the problem of siltation. This technique consists of fluidizing the sediment in situ, lowering the shear strength to maintain a navigable under-keel draught. Preliminary investigations show that through this mixing, aeration occurs, which results in a positive remediation effect as well. An overview of port contamination, remediation, and the recent research on aerobic (bio)degradation of port contaminants is made in order to show the potential for such innovative sediment management to reduce dredging need and remediate contaminated mud in ports. This review also highlights the lack of full-scale field applications for such potential remediation techniques, that remain largely confined to the laboratory scale.

Propionic Acid: Method of Production, Current State and Perspectives

During the past years, there has been a growing interest in the bioproduction of propionic acid by Propionibacterium. One of the major limitations of the existing models lies in their low productivity yield. Hence, many strategies have been proposed in order to circumvent this obstacle. This article provides a comprehensive synthesis and review of important biotechnological aspects of propionic acid production as a common ingredient in food and biotechnology industries. We first discuss some of the most important production processes, mainly focusing on biological production. Then, we provide a summary of important propionic acid producers, including Propionibacterium freudenreichii and Propionibacterium acidipropionici, as well as a wide range of reported growth/production media. Furthermore, we describe bioprocess variables that can have impact on the production yield. Finally, we propose methods for the extraction and analysis of propionic acid and put forward strategies for overcoming the limitations of competitive microbial production from the economical point of view. Several factors influence the propionic acid concentration and productivity such as culture conditions, type and bioreactor scale; however, the pH value and temperature are the most important ones. Given that there are many reports about propionic acid production from glucose, whey permeate, glycerol, lactic acid, hemicelluloses, hydrolyzed corn meal, lactose, sugarcane molasses and enzymatically hydrolyzed whole wheat flour, only few review articles evaluate biotechnological aspects, i.e. bioprocess variables.

Occurrence and transformation of phenoxy acids in aquatic environment and photochemical methods of their removal: a review

The article presents the behavior of phenoxy acids in water, the levels in aquatic ecosystems, and their transformations in the water environment. Phenoxy acids are highly soluble in water and weakly absorbed in soil. These highly mobile compounds are readily transported to surface and groundwater. Monitoring studies conducted in Europe and in other parts of the world indicate that the predominant phenoxy acids in the aquatic environment are mecoprop, 4-chloro-2-methylphenoxyacetic acid (MCPA), dichlorprop, 2,4-dichlorophenoxyacetic acid (2,4-D), and their metabolites which are chlorophenol derivatives. In water, the concentrations of phenoxy acids are effectively lowered by hydrolysis, biodegradation, and photodegradation, and a key role is played by microbial decomposition. This process is determined by the qualitative and quantitative composition of microorganisms, oxygen levels in water, and the properties and concentrations of phenoxy acids. In shallow and highly insolated waters, phenoxy acids can be decomposed mainly by photodegradation whose efficiency is determined by the form of the degraded compound. Numerous studies are underway on the use of advanced oxidation processes (AOPs) to remove phenoxy acids. The efficiency of phenoxy acid degradation using AOPs varies depending on the choice of oxidizing system and the conditions optimizing the oxidation process. Most often, methods combining UV radiation with other reagents are used to oxidize phenoxy acids. It has been found that this solution is more effective compared with the oxidation process carried out using only UV.

Hydrolysis and photolysis of bentazone in aqueous abiotic solutions and identification of its degradation products using quadrupole time-of-flight mass spectrometry

Hydrolysis and photolysis of bentazone in abiotic aqueous solutions were examined under laboratory conditions. Hydrolysis was studied in different buffer solutions (pH 4.0 ± 0.1, 7.0 ± 0.1, and 9.0 ± 0.1), at different temperatures (15 °C ± 2 °C, 25 °C ± 2 °C, 35 °C ± 2 °C, and 45 °C ± 2 °C), and at different Fe³⁺ concentrations (1, 5, and 10 mg/L). Photolysis was assessed in different buffer solutions and at different solvent (methanol and ethyl acetate) concentrations (10%, 20%, and 30%) or Fe³⁺ (1, 5, and 10 mg/L) concentrations and under mercury or xenon light irradiation. Hydrolysis half-lives ranged 46-99 days at three different conditions. Photolysis half-lives ranged 2.3-7.5 h in three different conditions under mercury and xenon irradiation. Hydrolysis and photolysis of bentazone were accelerated by both alkaline conditions and elevated temperatures, and solvents and Fe³⁺ strongly enhanced bentazone degradation. Photodecomposition was much faster under a mercury lamp than under a xenon lamp. N-methyl bentazone and 6-OH bentazone/8-OH bentazone were identified as degradation products using UPLC-Q-TOF-MS. The data generated from this study could be useful for risk assessment of pesticides in the environment.

Behaviour of bentazon as influenced by water and tillage management in rice-growing conditions

Bentazon is a widely used herbicide in rice agroecosystems that has commonly been found in water resources. To assess how tillage and water regimes affect sorption/desorption, dissipation and leaching of bentazon in Mediterranean rice-growing conditions, field experiments were carried out using tillage and flooding (TF), tillage and sprinkler irrigation (TS), no-tillage and sprinkler irrigation (NTS) and long-term no-tillage and sprinkler irrigation (NTS7). After 3 years, the K_d values in TS were 2.3, 1.6 and 1.7 times lower than the values in NTS7, NTS and TF respectively. Greater sorption of bentazon was related to higher contents in total organic carbon and, although to a lesser extent, in humic acids and dissolved organic carbon. The persistence of bentazon was significantly greater under anaerobic (half-life DT₅₀ = 94.1-135 days) than under aerobic (DT₅₀ = 42.4-91.3 days) incubation conditions for all management regimes. Leaching losses of bentazon were reduced from 78 and 74% in TS and TF to 61 and 62% in NTS7 and NTS respectively. The mid- and long-term implementation of sprinkler irrigation in combination with no-tillage could be considered a management system that is effective at reducing water contamination by bentazon in Mediterranean rice-growing agroecosystems. © 2017 Society of Chemical Industry.

Degradation and enantiomeric fractionation of mecoprop in soil previously exposed to phenoxy acid herbicides - New insights for bioremediation

Phenoxy acid-contaminated subsoils are common as a result of irregular disposal of residues and production wastes in the past. For enhancing in situ biodegradation at reducing conditions, biostimulation may be an effective option. Some phenoxy acids were marketed in racemic mixtures, and biodegradation rates may differ between enantiomers. Therefore, enantio-preferred degradation of mecoprop (MCPP) in soil was measured to get in-depth information on whether amendment with glucose (BOD equivalents as substrate for microbial growth) and nitrate (redox equivalents for oxidation) can stimulate bioremediation. The degradation processes were studied in soil sampled at different depths (3, 4.5 and 6m) at a Danish urban site with a history of phenoxy acid contamination. We observed preferential degradation of the R-enantiomer only under aerobic conditions in the soil samples from 3- and 6-m depth at environmentally relevant (nM) MCPP concentrations: enantiomer fraction (EF)<0.5. On the other hand, we observed preferential degradation of the S-enantiomer in all samples and treatments at elevated (μM) MCPP concentrations: EF>0.5. Three different microbial communities were discriminated by enantioselective degradation of MCPP: 1) aerobic microorganisms with little enantioselectivity, 2) aerobic microorganisms with R-selectivity and 3) anaerobic denitrifying organisms with S-selectivity. Glucose-amendment did not enhance MCPP degradation, while nitrate amendment enhanced the degradation of high concentrations of the herbicide.

Establishment of Bacterial Herbicide Degraders in a Rapid Sand Filter for Bioremediation of Phenoxypropionate-Polluted Groundwater

In this study, we investigated the establishment of natural bacterial degraders in a sand filter treating groundwater contaminated with the phenoxypropionate herbicides (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and (RS)-2-(2,4-dichlorophenoxy)propanoic acid (DCPP) and the associated impurity/catabolite 4-chlorophenoxypropanoic acid (4-CPP). A pilot facility was set up in a contaminated landfill site. Anaerobic groundwater was pumped up and passed through an aeration basin and subsequently through a rapid sand filter, which is characterized by a short residence time of the water in the filter. For 3 months, the degradation of DCPP, MCPP, and 4-CPP in the sand filter increased to 15 to 30% of the inlet concentration. A significant selection for natural bacterial herbicide degraders also occurred in the sand filter. Using a most-probable-number (MPN) method, we found a steady increase in the number of culturable phenoxypropionate degraders, reaching approximately 5 × 10(5) degraders per g sand by the end of the study. Using a quantitative PCR targeting the two phenoxypropionate degradation genes, rdpA and sdpA, encoding stereospecific dioxygenases, a parallel increase was observed, but with the gene copy numbers being about 2 to 3 log units higher than the MPN. In general, the sdpA gene was more abundant than the rdpA gene, and the establishment of a significant population of bacteria harboring sdpA occurred faster than the establishment of an rdpA gene-carrying population. The identities of the specific herbicide degraders in the sand filter were assessed by Illumina MiSeq sequencing of 16S rRNA genes from sand filter samples and from selected MPN plate wells. We propose a list of potential degrader bacteria involved in herbicide degradation, including representatives belonging to the Comamonadaceae and Sphingomonadales.

Establishment of Bacterial Herbicide Degraders in a Rapid Sand Filter for Bioremediation of Phenoxypropionate-Polluted Groundwater

In this study, we investigated the establishment of natural bacterial degraders in a sand filter treating groundwater contaminated with the phenoxypropionate herbicides (RS)-2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP) and (RS)-2-(2,4-dichlorophenoxy)propanoic acid (DCPP) and the associated impurity/catabolite 4-chlorophenoxypropanoic acid (4-CPP). A pilot facility was set up in a contaminated landfill site. Anaerobic groundwater was pumped up and passed through an aeration basin and subsequently through a rapid sand filter, which is characterized by a short residence time of the water in the filter. For 3 months, the degradation of DCPP, MCPP, and 4-CPP in the sand filter increased to 15 to 30% of the inlet concentration. A significant selection for natural bacterial herbicide degraders also occurred in the sand filter. Using a most-probable-number (MPN) method, we found a steady increase in the number of culturable phenoxypropionate degraders, reaching approximately 5 × 10(5) degraders per g sand by the end of the study. Using a quantitative PCR targeting the two phenoxypropionate degradation genes, rdpA and sdpA, encoding stereospecific dioxygenases, a parallel increase was observed, but with the gene copy numbers being about 2 to 3 log units higher than the MPN. In general, the sdpA gene was more abundant than the rdpA gene, and the establishment of a significant population of bacteria harboring sdpA occurred faster than the establishment of an rdpA gene-carrying population. The identities of the specific herbicide degraders in the sand filter were assessed by Illumina MiSeq sequencing of 16S rRNA genes from sand filter samples and from selected MPN plate wells. We propose a list of potential degrader bacteria involved in herbicide degradation, including representatives belonging to the Comamonadaceae and Sphingomonadales.

Modeling the Factors Impacting Pesticide Concentrations in Groundwater Wells

This study examines the effect of pumping, hydrogeology, and pesticide characteristics on pesticide concentrations in production wells using a reactive transport model in two conceptual hydrogeologic systems; a layered aquifer with and without a stream present. The pumping rate can significantly affect the pesticide breakthrough time and maximum concentration at the well. The effect of the pumping rate on the pesticide concentration depends on the hydrogeology of the aquifer; in a layered aquifer, a high pumping rate resulted in a considerably different breakthrough than a low pumping rate, while in an aquifer with a stream the effect of the pumping rate was insignificant. Pesticide application history and properties have also a great impact on the effect of the pumping rate on the concentration at the well. The findings of the study show that variable pumping rates can generate temporal variability in the concentration at the well, which helps understanding the results of groundwater monitoring programs. The results are used to provide guidance on the design of pumping and regulatory changes for the long-term supply of safe groundwater. The fate of selected pesticides is examined, for example, if the application of bentazone in a region with a layered aquifer stops today, the concentration at the well can continue to increase for 20 years if a low pumping rate is applied. This study concludes that because of the rapid response of the pesticide concentration at the drinking water well due to changes in pumping, wellhead management is important for managing pesticide concentrations.

Sources, occurrence and predicted aquatic impact of legacy and contemporary pesticides in streams

We couple current findings of pesticides in surface and groundwater to the history of pesticide usage, focusing on the potential contribution of legacy pesticides to the predicted ecotoxicological impact on benthic macroinvertebrates in headwater streams. Results suggest that groundwater, in addition to precipitation and surface runoff, is an important source of pesticides (particularly legacy herbicides) entering surface water. In addition to current-use active ingredients, legacy pesticides, metabolites and impurities are important for explaining the estimated total toxicity attributable to pesticides. Sediment-bound insecticides were identified as the primary source for predicted ecotoxicity. Our results support recent studies indicating that highly sorbing chemicals contribute and even drive impacts on aquatic ecosystems. They further indicate that groundwater contaminated by legacy and contemporary pesticides may impact adjoining streams. Stream observations of soluble and sediment-bound pesticides are valuable for understanding the long-term fate of pesticides in aquifers, and should be included in stream monitoring programs.

Bioremediation of pesticide-contaminated water resources: the challenge of low concentrations

The use of pesticides in agricultural and urban environments has improved quality of life around the world. However, the resulting accumulation of pesticide residues in fresh water resources has negative effects on aquatic ecosystem and human health. Bioremediation has been proposed as an environmentally sound alternative for the remediation of pesticide-contaminated water resources, though full-scale implementation has thus far been limited. One major challenge that has impeded progress is the occurrence of pesticides at low concentrations. Recent research has improved our fundamental understanding of pesticide biodegradation processes occurring at low concentrations under a variety of environmental scenarios and is expected to contribute to the development of applied bioremediation strategies for pesticide-contaminated water resources.