Large Municipal Wastewater Treatment Plant Research Articles

Microparticles in Wild and Caged Biota, Sediments, and Water Relative to Large Municipal Wastewater Treatment Plant Discharges.

Anthropogenically modified microparticles including microplastics are present in municipal wastewater treatment plant (WWTP) effluents; however, it is unclear whether biotic exposures are elevated downstream of these outfalls. In the fall of 2019, the present study examined whether microparticle levels in resident fish, environmental samples, and caged organisms were elevated near the Waterloo and Kitchener WWTP outfalls along the Grand River, Ontario, Canada. Wild rainbow darters (Etheostoma caeruleum) were collected from a total of 10 sites upstream and downstream of both WWTPs, along with surface water and sediment samples to assess spatial patterns over an approximately 70-km river stretch. Amphipods (Hyalella azteca), fluted-shell mussels (Lasmigona costata), and rainbow trout (Oncorhynchus mykiss) were also caged upstream and downstream of one WWTP for 14 or 28 days. Whole amphipods, fish digestive tracts, and mussel tissues (hemolymph, digestive glands, gills) were digested with potassium hydroxide, whereas environmental samples were processed using filtration and density separation. Visual identification, measurement, and chemical confirmation (subset only) of microparticles were completed. Elevated abiotic microparticles were found at several upstream reference sites as well as at one or both wastewater-impacted sites. Microparticles in amphipods, all mussel tissues, and wild fish did not show patterns indicative of increased exposures downstream of effluent discharges. In contrast, elevated microparticle counts were found in trout caged directly downstream of the outfall. Across all samples, cellulose fibers (mainly blue and clear colors) were the most common. Overall, results suggest little influence of WWTP effluents on microparticles in biota but rather a ubiquitous presence across most sites that indicates the importance of other point and nonpoint sources to this system. Environ Toxicol Chem 2024;43:1047-1061. © 2024 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Nitrous Oxide Generation, Influencing Factors and Emission Reduction in Anaerobic-Anoxic-Oxic Process Wastewater Treatment Plant

To achieve the reduction of emissions and control of non-CO2 greenhouse gases in municipal wastewater treatment plants, this study conducted a one-year monitoring of N2O in the A2O process of a large municipal wastewater treatment plant in Beijing. N2O released from the water surface of the A2O process was collected by using a gas flux chamber, and the key influencing factors affecting N2O were analysed using statistics. The results showed that N2O was not easy to be released under non-aerated conditions, and the aerobic zone was its main emission area. Temperature leads to high N2O emissions in winter and low in summer. Correlation analyses showed that NO2-N is one of the most critical factors affecting N2O production, and its accumulation level directly affects the amount of N2O produced in the system. DO also has a great influence on the production of N2O, and the amount of N2O produced decreases with the increase of the DO concentration, and the effect on the enzyme activity also makes the pH have a significant effect on the production of N2O.

The occurrence of heavy metals and antimicrobials in sewage sludge and their predicted risk to soil — Is there anything to fear?

The study assessed the occurrence of legally-monitored heavy metals and unmonitored antimicrobials in sludge from small, medium, large and very large municipal wastewater treatment plants (WWTPs), and the predicted environmental risk and risk of resistance selection associated with sludge administration to soil. The temporal variations of the studied compounds in sludge and associated risks to soil were determined by sampling over a year.Although the highest concentrations of heavy metals were noted in sludge from the largest WWTP, i.e. from 1.50 mg/kg (mean 1.61 mg/kg) for Cd to 2188 mg/kg (mean 1332 mg/kg) for Zn, the obtained values only reached a few percent of the legal limits. The same WWTP also demonstrated lower concentrations of antimicrobials compared to the smaller ones. The highest concentrations of antimicrobials, ranging from 24.04 μg/kg for trimethoprim to 900.24 μg/kg for tetracycline, were found in the small and medium WWTPs. However, due to lack of regulations at the national and EU levels, the results cannot be compared with legal limits. Principal Component Analysis (PCA), cluster and heatmap analysis separated samples according to WWTP size. Small WWTP demonstrated correlation with antimicrobials (tetracycline, trimethoprim, clindamycin, ciprofloxacin and ofloxacin), while the large and very large WWTP revealed correlations with heavy metals (Cu and Cr).The obtained environmental risk quotients confirmed that the heavy metals did not present a threat, measured either as individual risk quotients (RQenv), cumulative risk (RQcumulative) or risk of mixture of heavy metals (RQmix-metals). In the case of antimicrobials, only tetracycline demonstrated moderate RQenv, RQcumulative and RQmix-antimicrobials in the small WWTP sludge, with values of 0.1 to 1. Our findings highlight the importance of monitoring sewage sludge before soil application, especially from small WWTPs, to reduce the potential environmental impact of antimicrobials. They also confirm our previous data regarding the environmental risk associated with various toxic compounds, including emerging contaminants, in the sludge from small WWTPs.

A Review of Rotating Biological Contactors for Wastewater Treatment

A rotating biological contactor (RBC) is a type of attached-growth biological wastewater treatment system and a widely used biological wastewater treatment technology. It employs a series of rotating discs to support microbial growth and promote the removal of pollutants from wastewater. RBC is widely recognized for its simplicity of design, high reliability, and low energy consumption. It has been used in various applications, from small-scale decentralized systems to large municipal wastewater treatment plants. The current review provides an overview of RBC bioreactors, design parameters, and the factors that influence biological performance, such as hydraulic retention time, sludge retention time, organic loading rate, disc rotational speed, and temperature. The review also highlights the advantages and disadvantages of RBCs compared with other wastewater treatment technologies and discusses their role in sustainable environmental performance. The future prospects of RBC are also discussed, including integration with other technologies, such as membrane filtration and potential use in resource recovery. The review explores the application of RBC in decentralized wastewater treatment and the potential to provide sustainable solutions for wastewater management in rural and remote areas. Overall, RBC remains a promising option for effective and efficient wastewater treatment, particularly in situations where simplicity, reliability, and low energy consumption are desired.

Occurrence and Characteristics of Microplastics in Leachate at a Large Municipal Wastewater Treatment Plant

Abstract Due to the widespread occurrence and the potential threat to the environment, plastic materials are currently a growing problem of environmental protection in the world. Plastics whit dimensions not exceeding 5 mm are called microplastics. One of the main sources of microplastics in the aquatic environment are municipal wastewater treatment plants. The paper presents the results of research on the presence of microplastics in leachate from sludge processing at a large municipal wastewater treatment plant. The leachate was divided into the leachate produced in the processes of sludge thickening and dewatering. The analysis of the isolated microplastics included a physical analysis, which focuses on determining size, shape, and color of the isolated material. The next step was the chemical identification of the microplastic, where the type of polymer of the tested material was confirmed by means of Attenuated Total Reflection Fourier Transform Infrared. Among the isolated microplastic particles, almost a half was identified as fragments, and a smaller amount was confirmed for the presence of foil, fibers, foams and granules. The identified particles were plastic materials, including polypropylene, polyethylene, polystyrene or poly(terephthalate). Based on the results of the conducted research, the mass of microplastics in leachate was characterized and determined.

The performance of a Multi-Stage Hybrid Reactor to treat real wastewater: Benzophenone and Diethyl Phthalate removal

One of the consequences of the increasing diversity of new chemical compounds used in industrialized products is the release of these compounds as micropollutants (MPs) in the environment around the world, particularly in aqueous matrices. Benzophenone (BP) and Diethyl Phthalate (DEP), two MPs of environmental concern due to their potential toxicity are widely used and found with considerable concentrations mostly in wastewaters. Information about the efficiency of biological treatment in removing DEP from the wastewater is scarce and until recently, there was no information on the removal of BP. Due to the risks these substances pose to the human and environmental health there is a worldwide demand for the improvement of biological treatment plants with focus on the removal of these and other MPs, since conventional Wastewater Treatment Plants (WWTP) have very limited capacity to remove them and advanced treatment steps (e.g.: ozonation, photocatalysis, ultrafiltration.) increases substantially the treatment costs. A promising biological treatment approach for the removal of MPs combines fixed and suspended biomasses in the same reactor (hybrid reactors) and includes multiple compartments with different redox conditions. The objective of this study was to assess the performance of a new Multi-Stage Hybrid Reactor, focusing on the removal of Benzophenone (BP) and Diethylphthalate (DEP). The pilot system has seven units (anaerobic, anoxic 1, aerobic, anoxic 2, re-aeration and 2 sedimentation tanks) and it was installed at a large Municipal WWTP in Rio to treat real domestic wastewater. The total volume was 400 L and 50% of the aerobic tank (120 L) was filled with carriers (support media). The reactor’s efficiency was evaluated during two periods: (a) one with predominantly suspended biomass and (b) another one with predominantly fixed biomass in the aerobic tank. The highly variable composition of the affluent, affecting the organic load, caused fluctuations in the treatment performance. Even though, multi-stage hybrid bioreactor was able to remove up to 69.6% of BP and up to 74.5% of DEP, being the highest removal efficiencies achieved during the period when the aerobic tank had predominantly fixed biomass.

The efficiency of microalgae-based remediation as a green process for industrial wastewater treatment

Wastewater treatment including microalgae is an economically promising and environmentally friendly alternative to conventional wastewater treatment due to the concurrent nutrient removal and production of high-value biomass. This work aimed to choose the most suitable type of wastewater and its appropriate dilution for sustaining microalgal growth by testing unialgal versus mixed microalgae cultures and raw versus autoclaved wastewater. Based on pilot experiments including microplate screening, unialgal cultures of Chlorella emersonii grown in 1:5 diluted, non-autoclaved wastewater were selected as the optimum scenario for further testing. In the main experiments, Chlorella emersonii was cultivated in Erlenmeyer flasks and bubble column reactors. Additionally, a photoautotrophic biofilm was grown in flumes. We studied three types of wastewater originating from a large municipal wastewater treatment plant, a brewery, and a dairy. Dairy wastewater performed best in all cultivation systems and resulted in a maximum biomass per irradiated area of around 145 μg cm−2 chlorophyll-a of Chlorella cultures in bubble columns, followed by 105 μg cm−2 in flumes run by a photoautotrophic biofilm. Furthermore, phosphorus reduction of 96 % for dairy, 40 % for the brewery, and 43 % for municipal wastewater were achieved in the flumes. Due to the easy harvest of algae biomass, low construction and operation costs, flumes represent a recommendable cultivation system for dairy wastewater treatment on a larger scale.

Unwanted mainstream nitritation-denitritation causing massive N2O emissions in a continuous activated sludge process.

Nitrous oxide emissions can contribute significantly to the carbon footprint of municipal wastewater treatment plants even though emissions from conventional nitrogen removal processes are assumed to be moderate. An increased risk for high emissions can occur in connection with process disturbances and nitrite (NO2-) accumulation. This work describes the findings at a large municipal wastewater treatment plant where the levels of NO2- in the activated sludge process effluent were spontaneously and strongly increased on several activated sludge lines which was suspected to be due to shortcut nitrogen removal that stabilized for several months. The high NO2- levels were linked to a dramatic increase in nitrous oxide (N2O) emissions. As much as over 20% of the daily influent nitrogen load was emitted as N2O. These observations indicate that highly increased NO2- levels can occur in conventional activated sludge processes and result in high nitrous oxide emissions. They also raise questions concerning the risk of increased greenhouse gas (GHG) emissions of the nitritation-denitritation processes - although the uncontrolled nature of the event described here must be taken into consideration - and underline the importance of continuous monitoring and control of N2O emissions.

Upgrading a large and centralised municipal wastewater treatment plant with sequencing batch reactor technology for integrated nutrient removal and phosphorus recovery: Environmental and economic life cycle performance

Although nutrient removal and recovery from municipal wastewater are desirable to protect phosphorus resource and water-bodies from eutrophication, it is unclear how much environmental and economic benefits and burdens it might cause. This study evaluated the environmental and economic life cycle performance of three different upgraded Processes A, B and C with commercially available technologies for nutrient removal and phosphorus recovery based on an existing Malaysian wastewater treatment plant with a sequencing batch reactor technology and diluted municipal wastewater. It is found that the integration of nutrient removal, phosphorus recovery and electricity generation in all upgraded processes reduced eutrophication potential by 62–76%, and global warming potential by 7–22%, which, however, were gained at the cost of increases in human toxicity, acidification, abiotic depletion (fossil fuel) and freshwater ecotoxicity potentials by an average of 23%. New technologies for nutrient removal and phosphorus recovery are thus needed to achieve holistic rather than some environmental benefits at the expense of others. In addition, the study on two different functional units (FU), i.e. per m3 treated wastewater and per kg struvite recovered, shows that FU affected environmental assessment results, but the upgraded Process C had the least overall environmental burden with either of FUs, suggesting the necessity to use different functional units when comparing and selecting different technologies with two functions such as wastewater treatment and struvite production to confirm the best process configuration. The total life cycle costs of Processes A, B and C were 10.7%, 29.8% and 28.1%, respectively, higher than the existing process due to increased capital and operating costs. Therefore, a trade-off between environmental benefits and cost has to be balanced for technology selection or new integrated technologies have to be developed to achieve environmentally sustainable wastewater treatment economically.

Engineered silver nanoparticle (Ag-NP) behaviour in domestic on-site wastewater treatment plants and in sewage sludge amended-soils

Untreated sludge from small-scale on-site domestic wastewater treatment systems (septic tanks) was spiked with 20, 60 and 100 nm silver nanoparticles (Ag-NPs) to investigate Ag-NP behaviour in these systems that are widely distributed in rural areas. In addition, the release of Ag-NPs from a previously spiked clay-rich loam reference soil (LUFA 2.4) was evaluated, in the presence and absence of untreated sludge, to simulate the common practice of sludge disposal by spreading on agricultural land. Single particle ICP-MS was used to determine Ag-NP size distribution and the results were compared with total Ag (Ag-NP and ionic) measured in acid digested samples. As documented previously for large municipal scale wastewater treatment plants, Ag-NPs are found to be overwhelmingly (~98%) retained in the sludge in these small-scale systems. The Ag-NP retention efficiency on the LUFA reference soil amended with sludge is approximately 10 times greater than that of LUFA soil alone (in the absence of sludge). For soil spiked with 60 nm Ag-NPs, the calculated average diameter of Ag-NPs in the supernatant, after 24 h was 45 ± 3 nm (dissolution rate 7.2E−06 mol/m2·h for 60 nm Ag-NP), smaller than that of supernatant from the combined sludge/soil system (52 ± 2 nm), indicating lower Ag-NP dissolution rates in the sludge-amended soil. This study provides new information about the leachability of Ag-NPs from septic tank sludge and suggests that the effluent and sludge from septic tanks are potential sources of both nano- and dissolved ionic-Ag to environmental waters.

Sustainable design of large wastewater treatment plants considering multi-criteria decision analysis and stakeholders’ involvement

The typical treatment scheme of a large municipal wastewater treatment plant (LWWTP) is almost always the result of design based on technical and economic criteria. Once a threshold in terms of population equivalent (PE) is reached, it is possible that additional sludge thermal treatment might be required. Aspects such as greenhouse gas (GHG) emissions and land use for the construction of the WWTP or the service landfill are considered marginal in current design practice; in a world that requires increasingly attention to the environment, these criteria cannot be ignored when defining the treatment scheme of a LWWTP. With the intent of providing a sustainable approach to design, this study aims to identify the best treatment scheme for a LWWTP with a 720,000 PE size. Methodologically, the study involves the development of an approach based on multi-criteria decision analysis (MCDA). Six alternative treatment schemes were considered; two simplified schemes, without primary sedimentation, with extended aeration activated sludge processes and aerobic sludge stabilization; four full schemes, with primary sedimentation and anaerobic sludge digestion. Some schemes differ for the organic loading rate applied; others for the use of sludge incineration. Subsequently, six evaluation criteria (ECs) such as GHG emissions, electricity consumption, running costs, WWTP planimetric area, surface for the service landfill, as well as WWTP as biorefinery have been considered. The weighting of the ECs involved the participation of the main stakeholders in such a decision-making process, following a bottom-up approach. The resolution of the MCDA problem allowed the identification of the full scheme based on primary sedimentation, biological activated sludge at low organic load (0.210 kgBOD5/kgVSS/d) and anaerobic sludge digestion as the best solution. The sensitivity analysis, able to indirectly take into account the multitude of decision makers involved, allowed corroborating the results. The obtained treatment scheme was different from that generally adopted in current design practice for LWWTPs.

Removal of Microplastics by Different Treatment Processes in Shanghai Large Municipal Wastewater Treatment Plants

Wastewater treatment plants are important sources of microplastics (MPs) in aquatic environments. The present study was conducted to investigate the number concentration, removal rate, and fate of MPs in two large municipal treatment plants in Shanghai. The MPs number concentration in the influent water of WWTP1 and WWTP2 were (226.27±83.00) piece·L-1 and (171.89±62.98) piece·L-1, respectively. WWTP1 had a MPs removal efficiency of 63.25%, which is slightly higher than that of WWTP2, at 59.84%. The removal efficiency during the primary treatment process of the two sewage treatment plants on MPs accounted for 70%-80% of the whole treatment process. The primary treatment process and secondary treatment process transferred (48.10%±1.62%) and (12.97%±0.05%) of MPs in the sewage to the sludge, respectively. As a whole, (38.82%±1.55%) of MPs in the sewage treatment plants were finally discharged into natural waters, and the remaining (61.18%±1.55%) entered the sludge. This study shows that the removal rate of MPs in Shanghai's municipal treatment plants is low and that after treatment, large amounts still enter the natural waters with the final effluent, which causes significant ecological risks. This study provides basic data of MPs removal and trends of large urban sewage treatment plants in a plain river network area, which can provide reference for further design of MPs removal processes.

Dissemination prevention of antibiotic resistant and facultative pathogenic bacteria by ultrafiltration and ozone treatment at an urban wastewater treatment plant

Conventional wastewater treatment is not sufficient for the removal of hygienically relevant bacteria and achieves only limited reductions. This study focuses on the reduction efficiencies of two semi-industrial ultrafiltration units operating at a large scale municipal wastewater treatment plant. In total, 7 clinically relevant antibiotic resistance genes, together with 3 taxonomic gene markers targeting specific facultative pathogenic bacteria were analysed via qPCR analyses before and after advanced treatment. In parallel with membrane technologies, an ozone treatment (1 g ozone/g DOC) was performed for comparison of the different reduction efficiencies. Both ultrafiltration units showed increased reduction efficiencies for facultative pathogenic bacteria and antibiotic resistance genes of up to 6 log units, resulting mostly in a strong reduction of the bacterial targets. In comparison, the ozone treatment showed some reduction efficiency, but was less effective compared with ultrafiltration due to low ozone dosages frequently used for micro-pollutant removal at municipal wastewater treatment plants. Additionally, metagenome analyses demonstrated the accumulation of facultative pathogenic bacteria, antibiotic resistance genes, virulence factor genes, and metabolic gene targets in the back flush retentate of the membranes, which opens further questions about retentate fluid material handling at urban wastewater treatment plants.

Disinfection and nutrient removal in laboratory‐scale photobioreactors for wastewater tertiary treatment

AbstractBACKGROUNDSecondary effluent wastewaters still contain resources including water and nutrients that must be safely reused and recovered. In this study, the combined role of microalgae as disinfectant and nutrient removal agent was evaluated for the potential application of a microalgae‐based process as a cost‐effective tertiary treatment. Nutrient removal, biomass productivity and disinfection performances were monitored in laboratory‐scale photobioreactors (batch and continuous) fed on a secondary effluent mixed with a 10% on influent collected at a large municipal wastewater treatment plant where tertiary disinfection is performed by UV treatment.RESULTSIn microalgae‐based batch disinfection tests, Escherichia coli counts (0.5 ± 0.7 log CFU 100 mL−1) were comparable to those after traditional UV process (0.7 ± 0.84 log CFU 100 mL−1) and lower than in tests where light was applied without microalgae. In the following continuous test, E. coli counts were reduced by one order of magnitude and the pathogenic strain of E. coli O157:H7/H−, Salmonella spp. and indicators such as Bacteroides spp. and Enterococcus spp. were never detectable in the effluents by molecular tools. Total nitrogen and phosphorus removals reached 93 and 100%, respectively, while the algal biomass productivity of the system averaged 50 ± 30 mg TSS L−1 day−1.CONCLUSIONSThe effluents of the photobioreactors reached quality standards appropriate for water reuse. Moreover, nutrients could be recovered through the generation of algal biomass suitable for further valorization. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Fate of triclosan, triclocarban, and their transformation products in wastewater under nitrifying conditions

The nitrification process was simulated using benchtop bioreactors to gain insight into the fate of the antimicrobials triclosan (TCS) and triclocarban (TCC), as well their transformation products, during wastewater treatment. Currently, little information exists on the impact of nitrification treatment on concentrations of TCC, TCC degradation products, and TCS degradation products. Reactors were run using samples collected from a large municipal wastewater treatment plant at two pH ranges (6.5–7.5 and 8.5–9.5) for 171 h to simulate an extended hydraulic retention time (HRT). TCS was degraded under both pH conditions, with a 28.5% overall reduction in solids samples when the pH range was 6.5–7.5 and an overall reduction of 83.2% in solids samples when the pH ranged 8.5–9.5. Methyltriclosan (MeTCS) was formed in solids samples during both treatment conditions. MeTCS formed the most rapidly during the first 25 h of treatment at pH 8.5–9.5. Levels of 2,4-dichlorophenol, a TCS photolysis product, and TCC did not change over the 171 h treatment period, indicating that nitrification is not an effective treatment for reduction of these compounds. Three TCC dechlorination products and triclosan-O-sulfate were not observed at or above the limit of quantitation in any bioreactor samples.

On the accuracy of three dimensional flow measurements at low velocity ranges in municipal wastewater treatment reactors

The paper shows investigations about the accuracy of three dimensional flow measurements at low velocity ranges in wastewater treatment reactors. The investigations were carried out at a conventional rectangular primary clarifier, and a pre-anoxic tank. Both structures are very frequently used at large municipal wastewater treatment plants, but operated for different aims (sedimentation, denitrification, respectively). Therefore the analysis of the measurement and data recorded by Acoustic Doppler Velocimetry (ADV) is useful for operators, co-workers and researchers, who would like to investigate existing, unified treatment units with various flow patterns. Moreover, the paper provides general constructive recommendations for the preparation of such in situ measurement campaigns, data evaluation and the determination of uncertainties often considerably deteriorating the interpretation of the results.

Dealing with a cluster of large centralized municipal wastewater treatment plants: A case study

The article deals with a cluster of large centralized municipal wastewater treatment plants (LCMWWTPs) assessing the main economic, energy, environmental and management aspects. With reference to the case study of the Regi Lagni system (Southern Italy), composed of five WWTPs for an overall effective population of 2,235,800 inhabitants the study focused first on the multi-disciplinary characterization of the system investigated and then on potential future upgrading options, identifying the best suitable solution. For the scope, several indicators such as running costs, energy consumptions, Greenhouse Gas Emissions (GHG), waste for landfilling and two scenarios were defined. The first scenario focused on the role of anaerobic digestion while the dewatered sludge was sent to landfill. The second scenario implemented the same operations of the previous one although the construction of a thermal treatment plant for the dewatered sludge was also planned. Results showed how LCMWWTPs could be characterised by low resilience; the upgrading of plants to comply with the increasingly stringent legal limits was difficult, especially where works were carried out to ensure continuity of operation. Multi-criteria analysis allowed the cluster system based on anaerobic digestion to be the best solution from an economic, energy and environmental point of view.

Distribution of polychlorinated biphenyls in effluent from a large municipal wastewater treatment plant: Potential for bioremediation?

This study involved an evaluation of the potential for bioremediation of polychlorinated biphenyls (PCBs) in the effluent from a large municipal wastewater treatment plant. It was focused on the presence of PCBs in two types of effluents: the continuous effluent present during dry weather conditions and the intermittently present effluent that was present during wet weather due to incoming stormwater. The annual discharge of PCBs for both types of effluent was calculated based on a five-year dataset (2011–2015). In addition, the toxicity and bioremediation potential of the PCBs in the effluent were also assessed. It was found that the continuous effluent was responsible for the majority of the discharged PCB into the receiving river (1821 g for five years), while the intermittent effluent contributed 260 g over the five years. The average number of chlorine per biphenyl for the detected PCB congeners showed a 19% difference between the two types of effluent, which indicated a potential for organohalide respiration of PCBs during the continuous treatment. This was further supported by a high level of tri-, tetra- and penta-chlorinated congeners accounting for 75% of the anaerobically respired PCBs. Potential for aerobic degradation and thus biomineralization of PCBs was identified for both effluents. Furthermore, toxicity of 12 dioxin-like PCBs showed that normal operation of the wastewater reduced the toxicity throughout the wastewater treatment plant.

Degradation of triclosan and triclocarban and formation of transformation products in activated sludge using benchtop bioreactors

Benchtop bioreactors were run aerobically with activated sludge samples collected from a large municipal wastewater treatment plant (WWTP) to understand how increased hydraulic retention time (HRT), sludge retention time (SRT), and varying treatment temperatures (21°C and 30°C) impact concentrations of the endocrine disrupting antimicrobials triclosan (TCS), triclocarban (TCC), and their transformation products. Samples from the reactors were collected periodically over a 122–196h period and the solid and liquid fraction were separately quantitated for TCS, TCC, and methyltriclosan (MeTCS) and scanned qualitatively for six other transformation products. Results indicated that TCS, TCC and MeTCS were predominately associated with the solids fraction of the activated sludge with only nominal concentrations in the liquids fraction. TCS was degraded in the solids fraction, with increased rates at 30°C (−0.0224 ± 0.007h−1) when compared to reactors run at 21°C (− 0.0170 ± 0.003h−1). Conversely, TCC concentrations did not significantly change in solids samples from reactors run at 21°C, while an increase in reactor temperature to 30°C resulted in TCC degradation at an average rate of − 0.0158 ± 0.012h−1. Additionally, MeTCS formation in the solids fraction was observed in three out of four reactors run - indicating a notable transformation of TCS. Qualitative appearance of 2,4-dichlorophenol and 4-chloroanaline was observed in the liquids fraction of all reactor samples. The remaining four qualitatively scanned compounds were not detected. These experiments demonstrate that increased HRT, SRT, and temperature result in enhanced removal of TCS and TCC from wastewater during the activated sludge process. Furthermore, a substantial formation of TCS into MeTCS was observed.

Cell-free DNA: A Neglected Source for Antibiotic Resistance Genes Spreading from WWTPs.

Cell-associated ARGs in wastewater treatment plants (WWTPs) has been concerned, however, cell-free ARGs in WWTPs was rarely studied. In this study, the abundances of four representative ARGs, sulII, tetC, blaPSE-1, and ermB, in a large municipal WWTP were investigated in both cell-associated and cell-free fractions. Cell-associated ARGs was the dominant ARGs fraction in the raw wastewater. After biological treatment, sludge settling, membrane filtration, and disinfection, cell-associated ARGs were substantially reduced, though the ratios of ARG/16S rRNA gene were increased with disinfection. Cell-free ARGs persisted in the WWTP with a removal of 0.36 log to 2.68 logs, which was much lower than the removal of cell-associated ARGs (3.21 logs to 4.14 logs). Therefore, the abundance ratio of cell-free ARGs to cell-associated ARGs increased from 0.04-1.59% to 2.00-1895.08% along the treatment processes. After 25-day-storage, cell-free ARGs in both biological effluent and disinfection effluent increased by 0.14 log to 1.99 logs and 0.12 log to 1.77 logs respectively, reflecting the persistence and low decay rate of cell-free ARGs in the discharge water. Therefore, cell-free ARGs might be a kind of important but previously neglected pollutant from WWTPs, which added potential risks to the effluent receiving environments.