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

Aerobic biodegradation of micropollutants by nitrifiers and heterotrophs: Changes in biodegradation rate constant depending on levels of growth substrates and microbial activities

This study investigated how the biodegradation rate constant (kbio) of 11 micropollutants (MPs) responded to changes in the concentrations of growth substrates and microbial activities while considering the predominant microbial degraders of MPs. Metformin, losartan, valsartan, and cimetidine (group A) were biodegraded predominantly by nitrifiers. MPs of group A showed a positive correlation with kbio and nitrifying activity, while a negative correlation was observed with the initial concentration of ammonium, possibly due to competitive inhibition. Atenolol, caffeine, and naproxen (group B) were biodegraded predominantly by heterotrophs, with kbio remaining stable despite changes in organic matter concentration or heterotrophic activity. Olmesartan, candesartan, diclofenac, and sulfamethoxazole (group C) showed low kbio regardless of growth substrate concentration and microbial activity, which could be attributed to their chemical structures. These findings suggest that the kbio of MPs in WWTPs could respond differently to growth substrate concentration and microbial activity depending on their predominant degraders.

Re-evaluation of acesulfame K (E 950) as food additive

The present opinion deals with the re-evaluation of acesulfame K (E 950) as a food additive. Acesulfame K (E 950) is the chemically manufactured compound 6-methyl-1,2,3-oxathiazin-4(3H)-one-2,2-dioxide potassium salt. It is authorised for use in the European Union (EU) in accordance with Regulation (EC) No 1333/2008. The assessment involved a comprehensive review of existing authorisations, evaluations and new scientific data. Acesulfame K (E 950) was found to be stable under various conditions; at pH lower than 3 with increasing temperatures, it is degraded to a certain amount. Based on the available data, no safety concerns arise for genotoxicity of acesulfame K (E 950) and its degradation products. For the potential impurities, based on in silico data, a concern for genotoxicity was identified for 5-chloro-acesulfame; a maximum limit of 0.1 mg/kg, or alternatively, a request for appropriate genotoxicity data was recommended. Based on the synthesis of systematically appraised evidence of human and animal studies, the Panel concluded that there are no new studies suitable for identification of a reference point (RP) on adverse effects. Consequently, the Panel established an acceptable daily intake (ADI) of 15 mg/kg body weight (bw) per day based on the highest dose tested without adverse effects in a chronic toxicity and carcinogenicity study in rats; a study considered of moderate risk of bias and one of two key studies from the previous evaluations by the Scientific Committee on Food (SCF) and the Joint FAO/WHO Expert Committee on Food Additives (JECFA). This revised ADI replaces the ADI of 9 mg/kg bw per day established by the SCF. The Panel noted that the highest estimate of exposure to acesulfame K (E 950) was generally below the ADI in all population groups. The Panel recommended the European Commission to consider the revision of the EU specifications of acesulfame K (E 950).

Fate of wastewater trace organic chemicals in vegetated biofiltration systems

Vegetated biofiltration system (VBS) is an effective green technology for urban stormwater and greywater treatment. However, VBS is yet to be optimised for effective treatment of wastewater, particularly if it contains trace organic chemicals (TrOCs). The effect of plant species has not been addressed under TrOC wastewater loading. This study tested and evaluated the effectiveness of VBS over a one-year period in removing six TrOCs commonly found in wastewater, namely Caffeine (CAF), Paracetamol (PCM), Sulfamethoxazole (SMX), N diethyl‑meta-toluamide (DEET), Bisphenol A (BPA) and Ibuprofen (IBU). Eleven VBS configurations were tested in a year-long laboratory column study to explore the role of seven different plant species (with differing characteristic), varied soil media depths, and soil characteristics, on the fate of TrOCs in the systems. The effect of different operational conditions (e.g., dosing volume and regime) on removal efficiency was investigated. The results indicated VBS was able to maintain a high removal rate (>95 %) of CAF, BPA, and IBU throughout the experiment, followed by PCM (>79 %), SMX (50 %-80 %), and DEET (<12 %). Plant species significantly impacted the removal of SMX and DEET (p<0.05), with C. indica as the best performer. Reducing hydraulic loading rate and decreasing daily dosing volume and frequency contributed positively to the PCM, SMX, and DEET removal rates. Noticeable accumulations of SMX, DEET, and BPA (8.2, 43.1, and 54.5 ng·g-1, respectively) were detected in the filter media, particularly within the saturated zone. Higher chemical concentrations (i.e., CAF and DEET) were found in plant root tissue than in plant shoot tissue. This study offers valuable insights into VBS's design and operational aspects for removing TrOCs.

Arvimicrobium flavum gen. nov., sp. nov., A Novel Genus in the Family Phyllobacteriaceae Isolated From Forest Soil

During the study of microbial diversity of forest soil in the Republic of Korea, a yellow pigment-producing, Gram-stain-negative, rod-shaped, motile bacterium was isolated and designated as strain 1W2T. This strain grew at temperature of 10-37 °C, at pH of 5.0-9.0, and at NaCl concentration of 0-3.0% (w/v). The 16S rRNA gene sequencing and genome sequencing revealed that strain 1W2T is a member of the family Phyllobacteriaceae but exhibits low similarity with known genera, suggesting that this strain is a new genus within the family. This strain showed the closest similarity to the genera Mesorhizobium (96.6-96.9%), Aminobacter (96.4 -96.6%), Aquamicrobium (96.5-96.7%), and Pseudaminobacter (96.6-96.7%). The nearest relative of 1W2T was Mesorhizobium shangrilense CCBAU 65327 T with the 16S rRNA gene sequence similarity of 96.9%. The genome size was 5,545,526 bp with DNA G + C content of 64.7%. The values of overall genomic relatedness indices between strain 1W2T and the reference members were 20.4-21.3% for digital DNA-DNA hybridization, 74.0-76.6% for average nucleotide identity, and 68.1-61.2% for amino acids identity. Chemotaxonomic profiling revealed that Q-10 was the sole ubiquinone; summed feature 8 (C18:1ω7c and/or C18:1ω6c), iso-C13:0, and C19:0 cyclo ω8c were the predominant fatty acids; and diphosphatidylglycerol, phosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylcholine, and phosphatidylethanolamine were the major polar lipids. Based on these data, strain 1W2T represents a novel species of a new genus in the family Phyllobacteriaceae. Accordingly, we proposed the name Arvimicrobium flavum gen. nov., sp. nov., with the type strain 1W2T (= KCTC 92441 T = NBRC 116019 T).

Real time control of stormwater biofilters improves the removal of organic chemicals

Biofilters are among the most popular nature-based systems for treating stormwater and delivering multiple environmental benefits. However, as a passive system, their performance tends to be inconsistent in removing emerging organic contaminants produced by anthropogenic activities that can be persistent, mobile, and toxic. Thus, in this study, real time control (RTC) of stormwater biofilters is introduced to enhance the removal of a diverse range of organic chemicals. Laboratory columns were employed to investigate the performance of five RTC strategies, i.e., dynamic soil moisture control (RTC-Moisture), infiltration rate control (RTC-IR), pre-drain (RTC-PreDrain), fully unsaturated (RTC-UnSat), and fully saturated (RTC-FulSat). These RTC strategies were tested under varying rainfall sizes, as well as dry and wet conditions. Additionally, the study examined the accumulation of organic chemicals in the media. The results revealed that RTC-Moisture, RTC-IR, and RTC-PreDrain were the top three performing strategies, which achieved a significantly higher removal rate than Non-RTC biofilters for the majority of tested organic chemicals (p-value < 0.05). The best RTC strategy, RTC-Moisture, not only had the highest overall performance (average removal rate of 76.1 %) but was also least affected by various rainfall events. Despite a better chemical removal found in RTC-Moisture and RTC-PreDrain, there was no significant overall increase in the accumulation of organic chemicals within the media (p-value > 0.05) when compared to Non-RTC biofilters. This may indicate that the biodegradation process could be promoted in the well-performing RTC biofilters. This study confirms the possibility of using RTC strategies to enhance organic chemical removal in stormwater biofilters.

Exploring long-term retention and reactivation of micropollutant biodegradation capacity

The factors limiting micropollutant biodegradation in the environment and how to stimulate this process have often been investigated. However, little information is available on the capacity of microbial communities to retain micropollutant biodegradation capacity in the absence of micropollutants or to reactivate micropollutant biodegradation in systems with fluctuating micropollutant concentrations. This study investigated how a period of 2 months without the addition of micropollutants and other organic carbon affected micropollutant biodegradation by a micropollutant-degrading microbial community. Stimulation of micropollutant biodegradation was performed by adding different types of dissolved organic carbon (DOC)-extracted from natural sources and acetate-increasing 10 × the micropollutant concentration, and inoculating with activated sludge. The results show that the capacity to biodegrade 3 micropollutants was permanently lost. However, the biodegradation activity of 2,4-D, antipyrine, chloridazon, and its metabolites restarted when these micropollutants were re-added to the community. Threshold concentrations similar to those obtained before the period of no substrate addition were achieved, but biodegradation rates were lower for some compounds. Through the addition of high acetate concentrations (108 mg-C/L), gabapentin biodegradation activity was regained, but 2,4-D biodegradation capacity was lost. An increase of bentazon concentration from 50 to 500 µg/L was necessary for biodegradation to be reactivated. These results provide initial insights into the longevity of micropollutant biodegradation capacity in the absence of the substance and strategies for reactivating micropollutant biodegrading communities.

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.