Removal of micropollutants and ecotoxicity during combined biological activated carbon and ozone (BO3) treatment.

Ozonation is a viable option to improve the removal of micropollutants (MPs) in wastewater treatment plants (WWTPs). Nevertheless, the application of ozonation is hindered by its high energy requirements and by the uncertainties regarding the formation of toxic transformation products in the process. Energy requirements of ozonation can be reduced with a pre-ozone treatment, such as a biological activated carbon (BAC) filter, that removes part of the effluent organic matter before ozonation. This study investigated a combination of BAC filtration followed by ozonation (the BO3 process) to remove MPs at low ozone doses and low energy input, and focused on the formation of toxic organic and inorganic products during ozonation. Effluent from a WWTP was collected, spiked with MPs (approximately 1 µg/L) and treated with the BO3 process. Different flowrates (0.25-4 L/h) and specific ozone doses (0.2-0.6 g O3/g TOC) were tested and MPs, ecotoxicity and bromate were analyzed. For ecotoxicity assessment, three in vivo (daphnia, algae and bacteria) and six in vitro CALUX assays (Era, GR, PAH, P53, PR, andNrf2 CALUX) were used. Results show that the combination of BAC filtration and ozonation has higher MP removal and higher ecotoxicity removal than only BAC filtration and only ozonation. The in vivo assays show a low ecotoxicity in the initial WWTP effluent samples and no clear trend with increasing ozone doses, while most of the in vitro assays show a decrease in ecotoxicity with increasing ozone dose. This suggests that for the tested bioassays, feed water and ozone doses, the overall ecotoxicity of the formed transformation products during ozonation was lower than the overall ecotoxicity of the parent compounds. In the experiments with bromide spiking, relevant formation of bromate was observed above specific ozone doses of approximately 0.4 O3/g TOC and more bromate was formed for the samples with BAC pre-treatment. This indirectly indicates the effectivity of the pre-treatment in removing organic matter and making ozone more available to react with other compounds (such as MPs, but also bromide), but also underlines the importance of controlling the ozone dose to be below the threshold to avoid formation of bromate. It was concluded that treatment of the tested WWTP effluent in the BO3 process at a specific ozone dose of 0.2 g O3/g TOC, results in high MP removal at limited energy input while no increase in ecotoxicity, nor formation of bromate was observed under this condition. This indicates that the hybrid BO3 process can be implemented to remove MPs and improve the ecological quality of this WWTP effluent with a lower energy demand than conventional MP removal processes such as standalone ozonation.

Microbial dynamics and bioreactor performance are interlinked with organic matter removal from wastewater treatment plant effluent.

Optimizing bioreactor performance for organic matter removal can achieve sustainable and energy-efficient micropollutant removal in subsequent tertiary treatment. Bioreactor performance heavily depends on its resident microbial community; hence, a deeper understanding of community dynamics is essential. The microbial communities of three different bioreactors (biological activated carbon, moving bed biofilm reactor, sand filter), used for organic matter removal from wastewater treatment effluent, were characterized by 16S rRNA gene amplicon sequence analysis. An interdependency between bioreactor performance and microbial community profile was observed. Overall, Proteobacteria was the most predominant phylum, and Comamonadaceae was the most predominant family in all bioreactors. The relative abundance of the genus Roseococcus was positively correlated with organic matter removal. A generalized Lotka-Volterra (gLV) model was established to understand the interactions in the microbial community. By identifying microbial dynamics and their role in bioreactors, a strategy can be developed to improve bioreactor performance.

The effect of organic matter fractions on micropollutant ozonation in wastewater effluents.

Organic matter (OM) is the most important factor influencing the effectivity and efficiency of micropollutant (MP) ozonation in wastewater effluents. The importance of the quantity of OM is known, because of this, total organic carbon (TOC) is generally used to determine the required ozone dose for any water sample. Still, the effect of OM type on MP ozonation is not well understood. In this study, effluents from five wastewater treatment plants were collected and the organic matter in these effluents was fractionated using membranes (F1-4) and resin (HI, HOA, HON and HOB). Fractions were diluted to the same TOC concentration, spiked with MPs and ozonated at three ozone doses. Our results show that all five effluents had comparable OM compositions and similar MP removal, confirming the suitability of OM quantity (TOC) to compare the ozone requirements for wastewater effluents. From the 19 analysed MPs, three groups were identified that showed similar removal behaviour. The strongest differences between the groups were observed around MP ozone reactivities of 102, 104 and 106 M-1 s-1. This indicates the presence of three OM groups in the samples that interfere with the removal of different MPs. MP removal in the resin fraction HON were higher for MPs with high and medium ozone reactivity, indicating a low interference of OM in this fraction with MP ozonation. OM in the resin fractions HOA and HI showed higher interference with MP ozonation. Therefore, removing the HOA and HI fractions prior to ozonation would result in a lower required ozone dose and a more efficient removal of the MPs. MP removal correlated with the OM characteristics A300, SR and fluorescence component comp 2. These characteristics can be used as inline tools to predict the required ozone dose in water treatment plants.

Performance of full scale constructed wetlands in removing antibiotics and antibiotic resistance genes.

Additional treatment of wastewater, such as constructed wetlands (CWs), is a possible solution to reduce the discharge of antibiotics and antibiotic resistance genes (ARGs) from households and industry to the environment. This study aims to investigate the occurrence and removal of antibiotics and ARGs by two full scale CWs operated at different hydraulic retention times (HRT), namely 1 day and 3 days. Both CWs were receiving the same wastewater treatment plant (WWTP) effluent. Temporally and spatially distributed sampling of water and sediment was conducted for one year and samples were analyzed for antibiotics and ARGs by using LC-MS/MS and qPCR. Results showed that both CWs removed antibiotics significantly with a comparable overall removal of 28%-100%, depending on the type of antibiotics. However, some of the antibiotics showed higher concentration after the CW treatment. Five antibiotics (tiamulin, tylosin, oxytetracycline, sulfamethoxazole and trimethoprim) were the most abundant (>1500 ng/l on average) in winter. Meanwhile, ermB was the most abundant (average of 5.0 log) in winter compared to summer (average of 3.5 log). Other ARGs did not show a significant increase or decrease between winter and summer. ARGs were removed from the wastewater by 0.8 to 1.5 log. The HRT did not influence the removal of either the antibiotics or the ARGs. A strong correlation was found between sul genes and intI1. The results also revealed a positive and a negative relationship from sampling point 1 to sampling point 5: a positive relation between abundance of antibiotics, ARGs, and of NO3-N, NH4-N, TP, COD and a negative relation between antibiotics, ARGs and temperature. This relationship showed the effect between antibiotics and ARGs concentrations with physicochemical parameters and nutrients. The ability of CWs to reduce the input of micropollutants into the environment makes CWs a potential post treatment to WWTP.

Fate of antibiotics and antibiotic resistance genes during conventional and additional treatment technologies in wastewater treatment plants.

Information on the removal of antibiotics and ARGs in full-scale WWTPs (with or without additional treatment technology) is limited. However, it is important to understand the efficiency of full-scale treatment technologies in removing antibiotics and ARGs under a variety of conditions relevant for practice to reduce their environmental spreading. Therefore, this study was performed to evaluate the removal of antibiotics and ARGs in a conventional wastewater treatment plant (WWTP A) and two full-scale combined with additional treatment technologies. WWTP B, a conventional activated sludge treatment followed by an activated carbon filtration step (1-STEP® filter) as a final treatment step. WWTP C, a treatment plant using aerobic granular sludge (NEREDA®) as an alternative to activated sludge treatment. Water and sludge were collected and analysed for 52 antibiotics from four target antibiotic groups (macrolides, sulfonamides, quinolones, tetracyclines) and four target ARGs (ermB, sul 1, sul 2 and tetW) and integrase gene class 1 (intI1). Despite the high removal percentages (79-88%) of the total load of antibiotics in all WWTPs, some antibiotics were detected in the various effluents. Additional treatment technology (WWTP C) showed antibiotics removal up to 99% (tetracyclines). For ARGs, WWTP C reduced 2.3 log followed by WWTP A with 2.0 log, and WWTP B with 1.3 log. This shows that full-scale WWTP with an additional treatment technology are promising solutions for reducing emissions of antibiotics and ARGs from wastewater treatment plants. However, total removal of the antibiotics and ARGS cannot be achieved for all types of antibiotics and ARGs. In addition, the ARGs were more abundant in the sludge compared to the wastewater effluent suggesting that sludge is an important reservoir representing a source for later ARG emissions upon reuse, i.e. as fertilizer in agriculture or as resource for bioplastics or bioflocculants. These aspects require further research.

Enhancement of methane production from 1-hexadecene by additional electron donors.

1-Hexadecene-contaminated wastewater is produced in oil refineries and can be treated in methanogenic bioreactors, although generally at low conversion rates. In this study, a microbial culture able to degrade 1-hexadecene was enriched, and different stimulation strategies were tested for enhancing 1-hexadecene conversion to methane. Seven and three times faster methane production was obtained in cultures stimulated with yeast extract or lactate, respectively, while cultures amended with crotonate lost the ability to degrade 1-hexadecene. Methane production from 1-hexadecene was not enhanced by the addition of extra hydrogenotrophic methanogens. Bacteria closely related to Syntrophus and Smithella were detected in 1-hexadecene-degrading cultures, but not in the ones amended with crotonate, which suggests the involvement of these bacteria in 1-hexadecene degradation. Genes coding for alkylsuccinate synthase alpha-subunit were detected in cultures degrading 1-hexadecene, indicating that hydrocarbon activation may occur by fumarate addition. These findings are novel and show that methane production from 1-hexadecene is improved by the addition of yeast extract or lactate. These extra electron donors may be considered as a potential bioremediation strategy of oil-contaminated sites with bioenergy generation through methane production.

Benzene degradation coupled with chlorate reduction in a soil column study.

Perchlorate and chlorate are electron acceptors that during reduction result in the formation of molecular oxygen. The produced oxygen can be used for activation of anaerobic persistent pollutants, like benzene. In this study chlorate was tested as potential electron acceptor to stimulate benzene degradation in anoxic polluted soil column. A chlorate amended benzene polluted soil column was operated over a period of 500 days. Benzene was immediately degraded in the column after start up, and benzene removal recovered completely after omission of chlorate or a too high influent chlorate concentration (22 mM). Mass balance calculations showed that per mole of benzene five mole of chlorate were reduced. At the end of the experiment higher loading rates were applied to measure the maximal benzene degradation rate in this system; a breakthrough of benzene was not observed. The average benzene degradation rate over this period was 31 micromol l(-1) h(-1) with a maximal of 78 micromol l(-1) h(-1). The high degradation rate and the necessity of chlorate indicate that oxygen produced during chlorate reduction indeed is used for the activation of benzene. This is the first column study where benzene biodegradation at a high rate coupled with anaerobic chlorate reduction is observed.