Treating wastewater for microplastics to a level on par with nearby marine waters.

Retention of microplastics (MPs) at the third largest wastewater treatment plant (WWTP) in Sweden was investigated. The plant is one of the most modern and advanced of its kind, with rapid sand filter for tertiary treatment in combination with mechanical, biological, and chemical treatment. It achieved a significantly high treatment efficiency, which brought the MP concentration in its discharge on par with concentrations measured in marine waters of the same region. This novel data shows that properly designed modern WWTPs can reduce the MP content of sewage down to background levels measured in the receiving aquatic environment. Opposite to current understanding of the retention of MP by WWTPs, a modern and well-designed WWTP does not have to be a significant point source for MP. MPs were quantified at all major treatment steps, including digester inlet and outlet sludge. MPs sized 10-500 µm were analyzed by a focal plane array based micro-Fourier transform infrared (FPA-µFTIR) microscopy, a hyperspectral imaging technique, while MPs above 500 µm were analyzed by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Mass was estimated from the hyperspectral images for MPs <500 µm and from microscope images >500 µm. The overall treatment efficiency was in terms of MP counts 99.98 %, with a daily input of 6.42 × 1010 and output of 1.04 × 107 particles. The mass removal efficiency was 99.99 %. The mechanical part of the treatment, the pre-treatment, and primary stages, reduced both the MP counts and mass by approximately 71 %. The combined biological treatment, secondary settling, and final polishing with rapid sand filtration removed nearly all the remaining 29 %. MPs became successively smaller as they passed the different treatment steps. The digester inlet received 1.04 × 1011 MPs daily, while it discharged 9.96 × 1010 MPs, causing a small but not significant decrease in MP counts, with a corresponding MP mass reduction of 9.56 %.

Zeolite Imidazolate Frameworks-8@SiO2-ZrO2 Crystal-Amorphous Hybrid Core-Shell Structure as a Building Block for Water Purification Membranes.

Metal-organic frameworks (MOFs) are emerging as promising materials for water purification membranes, owing to their uniform microporous structures and chemical functionalities. Here, we report a simple procedure for depositing MOF-based nanofiltration membranes on commercial TiO2 ceramic tubular supports, completely avoiding the use of dispersants or binders. Zeolite imidazolate frameworks-8 (ZIF-8) nanocrystals were synthesized in methanol at room temperature and subsequently coated with an amorphous SiO2-ZrO2 gel to generate a dispersion of ZIF-8@SiO2-ZrO2 core-shell nanoparticles. The amorphous SiO2-ZrO2 gel served as a binding agent for the ZIF-8 nanocrystals, thus forming a defect-free continuous membrane layer. After repeating the coating twice, the active layer had a thickness of 0.96 µm, presenting a rejection rate >90% for the total organic carbon in an aquaculture effluent and in a wastewater treatment plant, while reducing the concentration of trimethoprim, here used as a target pollutant. Moreover, the oxide gel provided the MOF-based active layer with good adhesion to the support and enhanced its hydrophilicity, resulting in a membrane with excellent mechanical stability and resistance to fouling during the crossflow filtration of the real wastewater samples. These results implied the high potential of the MOF-based nanocomposite membrane for effective treatment of actual wastewater streams.

What is hiding below the surface - MPs including TWP in an urban lake.

Inland lakes play an important role as habitats for local species and are often essential drinking water reservoirs. However, there is limited information about the presence of microplastics (MPs) in these water bodies. Thirteen sediment samples were collected across a Danish urban lake to map MPs, including tyre wear particles (TWP). The lower size detection limit was 10 µm. MPs were quantified as counts, size, and polymer type by Fourier-transform infrared microspectroscopy (µFTIR) and mass estimated from the 2D projections of the MPs. As TWP cannot be determined by µFTIR, counts and sizes could not be quantified by this technique. Instead, TWP mass was determined by pyrolysis gas chromatography mass spectrometry (Py-GC/MS). The average MP abundance was 279 mg kg-1 (µFTIR), of which 19 mg kg-1 (Py-GC/MS) were TWP. For MPs other than tyre wear, the average MP count concentration was 11,312 counts kg-1. Urban runoff from combined sewer overflows and separate stormwater outlets combined with outflow from a wastewater treatment plant were potential point sources. The spatial variation was substantial, with concentrations varying several orders of magnitude. There was no pattern in concentration across the lake, and the distribution of high and low values seemed random. This indicates that large sampling campaigns encompassing the entire lake are key to an accurate quantification. No preferential spatial trend in polymer characteristics was identified. For MPs other than TWP, the size of buoyant and non-buoyant polymers showed no significant difference across the lake, suggesting that the same processes brought them to the sediment, regardless of their density. Moreover, MP abundance was not correlated to sediment properties, further indicating a random occurrence of MPs in the lake sediments. These findings shed light on the occurrence and distribution of MPs, including TWP, in an inland lake, improving the basis for making mitigation decisions.

Exploration of occurrence and sources of microplastics (>10 µm) in Danish marine waters.

Microplastics (MPs) were quantified in Danish marine waters of the Kattegat and the southernmost part of Skagerrak bordering to it. Kattegat is a waterbody between Denmark and Sweden that receives inflow from the Baltic Sea and direct urban runoff from the metropolitan area of Copenhagen and Malmö. MPs were measured in 14 continuous transects while steaming between monitoring stations. MP levels tended to be highest close to the Copenhagen-Malmö area, albeit this was more obvious from the abundance of particles rather than mass. The outcome of the measurements allowed a rough MP budget in the Danish Straits region, suggesting that urban waste- and stormwater discharges could not be neglected as potential MP source in these waters. The marine samples were collected by pumping and filtering water over 10 µm steel filters, hereby sampling a total of 19.3 m3. They were prepared and analyzed by FPA-µFTIR imaging, and the scans interpreted to yield MP size, shape, polymer type, and estimated mass. The average concentration was 103 ± 86 items m-3, corresponding to 23.3 ± 28.3 µg m-3 (17-286 items m-3; 0.6-84.1 µg m-3). Most MPs were smaller than 100 µm and fragments dominated the samples. The carbonyl index was assessed for polyolefins, showing that oxidation increased with decreasing MP size, but did not correlate with distance to urban areas. A rough budget of MP in the Danish Straits region suggested that MPs discharged from urban waste- and stormwaters were an import source of MPs.

In vivo calibration of the T2* cardiovascular magnetic resonance method at 1.5 T for estimation of cardiac iron in a minipig model of transfusional iron overload.

BACKGROUND: Non-invasive estimation of the cardiac iron concentration (CIC) by T2* cardiovascular magnetic resonance (CMR) has been validated repeatedly and is in widespread clinical use. However, calibration data are limited, and mostly from post-mortem studies. In the present study, we performed an in vivo calibration in a dextran-iron loaded minipig model. METHODS: R2* (= 1/T2*) was assessed in vivo by 1.5 T CMR in the cardiac septum. Chemical CIC was assessed by inductively coupled plasma-optical emission spectroscopy in endomyocardial catheter biopsies (EMBs) from cardiac septum taken during follow up of 11 minipigs on dextran-iron loading, and also in full-wall biopsies from cardiac septum, taken post-mortem in another 16  minipigs, after completed iron loading. RESULTS: A strong correlation could be demonstrated between chemical CIC in 55 EMBs and parallel cardiac T2* (Spearman rank correlation coefficient 0.72, P < 0.001). Regression analysis led to [CIC] = (R2* - 17.16)/41.12 for the calibration equation with CIC in mg/g dry weight and R2* in Hz. An even stronger correlation was found, when chemical CIC was measured by full-wall biopsies from cardiac septum, taken immediately after euthanasia, in connection with the last CMR session after finished iron loading (Spearman rank correlation coefficient 0.95 (P < 0.001). Regression analysis led to the calibration equation [CIC] = (R2* - 17.2)/31.8. CONCLUSIONS: Calibration of cardiac T2* by EMBs is possible in the minipig model but is less accurate than by full-wall biopsies. Likely explanations are sampling error, variable content of non-iron containing tissue and smaller biopsies, when using catheter biopsies. The results further validate the CMR T2* technique for estimation of cardiac iron in conditions with iron overload and add to the limited calibration data published earlier.

Automated monitoring system for events detection in sewer network by distribution temperature sensing data measurement.

This study is related to distribution temperature sensing (DTS) in sewers for tracing illicit or unintended inflows to foul sewers. A DTS measurement is performed with a fiber optic cable that is installed at the invert of a sewer pipe in combination with a standalone laser/computer instrument. This set-up generates in-sewer temperature measurements with high resolutions in time (every minute) and space (every metre) along the cable over long periods of time (weeks on end). The prolonged monitoring period in combination with the high level of detail in the dataset allows the study of anomalies (i.e., unexpected temperatures and/or temperature variations at certain locations), even if these only occur very infrequently. The objective of this paper is to develop an automated tool to analyze the large data masses and identify anomalies caused by illicit or unintended inflows. In this study, an algorithm for detecting the temperature changes that are caused by both wastewater discharge and inflow of stormwater are developed. A comparison of the results of the automated procedure to the results of a manual assessment of the datasets (Elmehaven, Denmark) shows that the automated procedure performs very well.

Liquid-Gas Mass Transfer of Volatile Substances in an Energy Dissipating Structure.

Mass transfer of a range of volatile substances was studied under highly turbulent conditions. The applied setup mimicked drop structures, where the release of volatile organic carbons likely occurs at a high rate. The experiments covered several substances in a range of resistances from residing entirely in the liquid film to being fully in the gas film. The two-film theory yielded a good prediction of the whole measured range. This allowed the experimental validation of a method where two reference substances are applied, to determine the transfer of any other substance - independently of where its resistance to mass transfer resides. One finding was that the range of dimensionless Henry's constants, where both films contributed by more than 5%, was 0.0027 to 1.05, which is over five times higher than the accepted rule of thumb (0.0005-0.18). Another finding was that the ratio between the liquid and the gas film mass transfer coefficients of the reference substances was similar for the two drop configurations studied. If this holds true over a wider range of configurations, such a ratio constitutes a valuable shortcut to the current practice of ignoring gas film resistance in the estimation of mass transfer rates.

Liquid-gas mass transfer at drop structures.

Over the last decades, considerable progress has been made in the understanding of the sulfur cycle in sewer systems. In spite of a wealth of experimental and field studies that have addressed the release of hydrogen sulfide from free surface flows in gravity sewers and the corresponding air-water mass transfer, little is known about hydrogen sulfide emission under highly turbulent conditions (e.g., drop structures, hydraulic jumps). In this study, experimental work was carried out to analyze the influence of characteristics of drops on reaeration. Physical models were built, mimicking typical sewer drop structures and allowing different types of drops, drop heights, tailwater depths and flow rates. In total, 125 tests were performed. Based on their results, empirical expressions translating the relationship between the mass transfer of oxygen and physical parameters of drop structures were established. Then, by applying the two-film theory with two-reference substances, the relation to hydrogen sulfide release was defined. The experiments confirmed that the choice of the type of drop structure is critical to determine the uptake/emission rates. By quantifying the air-water mass transfer rates between free-fall and backdrop types of drop, the latter resulted in considerably lower oxygen uptake rates.

Unified understanding of physico-chemical properties of activated sludge and fouling propensity.

A range of parameters affecting floc characteristics, sludge composition and filtration properties was investigated by analyzing 29 sludge samples from municipal and industrial conventional activated sludge systems and municipal membrane bioreactors (MBR). Samples were characterized by physico-chemical parameters, composition of ions and EPS, degree of flocculation, settling properties, dewatering properties, and filtration properties. By analyzing the interplay between various metrics instead of single parameters, a unified understanding of the influence of sludge composition and characteristics was developed. From this, a conceptual model was proposed to describe the interplay between sludge composition, characteristics, and filtration properties. The article shows three major results contributing to describe the interplay between sludge characteristics and fouling propensity: First, the degree of flocculation could be quantified by the ratio between floc size and residual turbidity and was a key parameter to assess fouling propensity. Second, extracted EPS to polyvalent cations ratio was used as an indicator of the flocculation. A high ratio combined with a high concentration of EPS resulted in large, loosely bound, and weak flocs that were easily deformed, hence giving compressible fouling layers. Finally, high amounts of carbohydrates in both total and extracted EPS resulted in more pronounced fouling, which may be explained by carbohydrates forming poorer flocs than humic substances and proteins. Accordingly, samples with high humic content showed lower specific resistance to filtration due to better floc structure. The amount of carbohydrates in EPS correlated positively to the influent COD/N ratio, which may explain why systems with high influent COD/N ratio demonstrated higher fouling propensity.

Spatial Variability of Anaerobic Processes and Wastewater pH in Force Mains.

The present study focuses on anaerobic organic matter transformation processes in force mains for the purpose of improving existing sewer process models. Wastewater samples were obtained at 100 m intervals from a 1 km long pilot scale force main and measured for several wastewater parameters. Transformation rates for selected parameters were calculated and their spatial variability analyzed. In terms of electron transfer, fermentation was the most significant process, resulting in a net volatile fatty acid formation of 0.83 mmol/L. Sulfate reduction resulted in a production of 0.73 mmol/L of inorganic sulfide. Methanogenesis was negligable in all experiments despite an anaerobic residence time of more than 30 hours. As a result of the anaerobic processes, the wastewater pH decreased by approximately one pH unit, resulting in a corresponding increase in the fraction of molecular hydrogen sulfide. A significant spatial variablilty was observed for the average transformation rates of all parameters.

Invertebrates in stormwater wet detention ponds - Sediment accumulation and bioaccumulation of heavy metals have no effect on biodiversity and community structure.

The invertebrate diversity in nine stormwater wet detention ponds (SWDP) was compared with the diversity in eleven small shallow lakes in the western part of Denmark. The SWDPs and lakes were chosen to reflect as large a gradient of pollutant loads and urbanization as possible. The invertebrates as well as the bottom sediments of the ponds and shallow lakes were analyzed for copper, iron, zinc, cadmium, chromium, lead, aluminum, nickel, arsenic and the potentially limiting nutrient, phosphorus. The Principal Component Analysis showed that invertebrates in SWDPs and lakes differed with respect to bioaccumulation of these elements, as did the sediments, albeit to a lesser degree. However, the Detrended Correspondence Analysis and the TWINSPAN showed that the invertebrate populations of the ponds and lakes could not be distinguished, with the possible exception of highway ponds presenting a distinct sub-group of wet detention ponds. The SWDPs and shallow lakes studied seemed to constitute aquatic ecosystems of similar taxon richness and composition as did the 11 small and shallow lakes. This indicates that SWDPs, originally constructed for treatment and flood protection purposes, become aquatic environments which play a local role for biodiversity similar to that of natural small and shallow lakes.

Airflow in Gravity Sewers - Determination of Wastewater Drag Coefficient.

Several experiments have been conducted in order to improve the understanding of the wastewater drag and the wall frictional force acting on the headspace air in gravity sewers. The aim of the study is to improve the data basis for a numerical model of natural sewer ventilation. The results of the study shows that by integrating the top/side wall shear stresses the log-law models for the air velocity distribution along the unwetted perimeter resulted in a good agreement with the friction forces calculated by use of the Colebrook-White formula for hydraulic smooth pipes. Secondly, the water surface drags were found by log-law models of the velocity distribution in turbulent flows to fit velocity profiles measured from the water surface and by integrating the water surface drags along the wetted perimeter, mean water surface drags were found and a measure of the water surface drag coefficient was found.

Modeling Sulfides, pH and Hydrogen Sulfide Gas in the Sewers of San Francisco.

An extensive measuring campaign targeted on sewer odor problems was undertaken in San Francisco. It was assessed whether a conceptual sewer process model could reproduce the measured concentrations of total sulfide in the wastewater and H2S gas in the sewer atmosphere, and to which degree such simulations have potential for further improving odor and sulfide management. The campaign covered measurement of wastewater sulfide by grab sampling and diurnal sampling, and H2S gas in the sewer atmosphere was logged. The tested model was based on the Wastewater Aerobic/Anaerobic Transformations in Sewers (WATS) sewer process concept, which never had been calibrated to such an extensive dataset. The study showed that the model was capable of reproducing the general levels of wastewater sulfide, wastewater pH, and sewer H2S gas. It could also reproduce the general variability of these parameters, albeit with some uncertainty. It was concluded that the model could be applied for the purpose in mind.

Retainment of the antimicrobial agent triclosan in a septic tank.

Laboratory experiments were conducted to investigate the fate of the antimicrobial agent triclosan (TCS) in a conventional septic tank. The main mechanism of TCS removal from wastewater was identified to be rapid TCS sorption to suspended particles followed by settling of these particles to the bottom of the septic tank. Sorption to particles was completed within minutes while the settling took several days. Therefore, in a septic tank the removal of TCS from wastewater is mainly determined by the removal of suspended particles by sedimentation. Over 5 days of hydraulic residence time the initial dissolved TCS concentration of 100 µg L(-1) was reduced by 87 ± 8%. During the first 24 hours, 66-86% of all removed TCS was retained, whereas during the remainder of the experiment a slight but steady decrease in TCS concentration was observed. This was most likely caused by TCS diffusion and its subsequent sorption onto the septic sludge.

Modeling anaerobic organic matter transformations in the wastewater phase of sewer networks.

A conceptual model to simulate transformations of organic matter and sulfur compounds in the wastewater phase of sewer networks under anaerobic conditions was developed. For calibration and validation of the model, a series of laboratory experiments on generation of readily biodegradable organic matter and sulfide under anaerobic conditions in samples of wastewater was conducted. Compared with previous studies, the proposed model includes sulfate reduction in the bulk water as well as a revised description of fermentation processes. Substrate affinity for fermentative bacteria was found to be significantly higher than what has been proposed in the activated sludge model, resulting in higher fermentation rates at low substrate concentrations. The findings of the study are important to understand formation of volatile organic compounds and odorous substances in sewers.

Effect of sewer headspace air-flow on hydrogen sulfide removal by corroding concrete surfaces.

Hydrogen sulfide adsorption and oxidation by corroding concrete surfaces at different air-flows were quantified using a pilot-scale sewer reactor. The setup was installed in an underground sewer research station with direct access to wastewater. Hydrogen sulfide gas was injected into the headspace of the sewer reactor once per hour in peak concentrations of approximately 500 ppmv. The investigated range of sewer air-flows was representative for natural ventilated sewer systems, and covered both laminar and turbulent conditions. The experiments demonstrated a significant effect of sewer air-flow on the kinetics of hydrogen sulfide removal from the sewer headspace. From the lowest to the highest air-flow investigated, the rate of adsorption and oxidation increased more than threefold. At all air-flows, the reaction kinetics followed a simple n-th order rate equation with a reaction order of 0.8. The effect of air-flow on hydrogen sulfide adsorption and oxidation kinetics was quantified by a simple empirical equation.

Anaerobic transformations of organic matter in collection systems.

Anaerobic transformations of wastewater organic matter in the bulk water phase of collection system networks were investigated in laboratory-scale experiments. The wastewater was collected from three locations, which provided samples with different characteristics, ranging from young to mature. Hydrolysis, fermentation, and sulfate reduction were identified as the most important anaerobic processes. Significant quantities of readily biodegradable substrate were produced by hydrolysis of complex organic substrates. The readily biodegradable substrate was further fermented into volatile fatty acids (VFA). The rate of fermentation was found to be limited by the hydrolysis process. The readily biodegradable substrate generated was almost entirely composed of VFA, primarily acetic and propionic acids. A production of sulfide was observed in all experiments, demonstrating that part of the readily biodegradable substrate was consumed by sulfate respiration. The sulfide production was most pronounced in mature wastewater that had previously undergone extended anaerobic transport.

Growth kinetics of hydrogen sulfide oxidizing bacteria in corroded concrete from sewers.

Hydrogen sulfide oxidation by microbes present on concrete surfaces of sewer pipes is a key process in sewer corrosion. The growth of aerobic sulfur oxidizing bacteria from corroded concrete surfaces was studied in a batch reactor. Samples of corrosion products, containing sulfur oxidizing bacteria, were suspended in aqueous solution at pH similar to that of corroded concrete. Hydrogen sulfide was supplied to the reactor to provide the source of reduced sulfur. The removal of hydrogen sulfide and oxygen was monitored. The utilization rates of both hydrogen sulfide and oxygen suggested exponential bacterial growth with median growth rates of 1.25 d(-1) and 1.33 d(-1) as determined from the utilization rates of hydrogen sulfide and oxygen, respectively. Elemental sulfur was found to be the immediate product of the hydrogen sulfide oxidation. When exponential growth had been achieved, the addition of hydrogen sulfide was terminated leading to elemental sulfur oxidation. The ratio of consumed sulfur to consumed oxygen suggested that sulfuric acid was the ultimate oxidation product. To the knowledge of the authors, this is the first study to determine the growth rate of bacteria involved in concrete corrosion with hydrogen sulfide as source of reduced sulfur.

Modeling of hydrogen sulfide oxidation in concrete corrosion products from sewer pipes.

Abiotic and biotic oxidation of hydrogen sulfide related to concrete corrosion was studied in corrosion products originating from a sewer manhole. The concrete corrosion products were suspended in an acidic solution, mimicking the conditions in the pore water of corroded concrete. The removal of hydrogen sulfide and dissolved oxygen was measured in parallel in the suspension, upon which the suspension was sterilized and the measurement repeated. The results revealed the biotic oxidation to be fast compared with the abiotic oxidation. The stoichiometry of the hydrogen sulfide oxidation was evaluated using the ratio between oxygen and hydrogen sulfide uptake. The ratio for the biotic oxidation pointed in the direction of elemental sulfur being formed as an intermediate in the oxidation of hydrogen sulfide to sulfuric acid. The experimental results were applied to suggest a hypothesis and a mathematical model describing the hydrogen sulfide oxidation pathway in a matrix of corroded concrete.

Influence of pipe material and surfaces on sulfide related odor and corrosion in sewers.

Hydrogen sulfide oxidation on sewer pipe surfaces was investigated in a pilot scale experimental setup. The experiments were aimed at replicating conditions in a gravity sewer located immediately downstream of a force main where sulfide related concrete corrosion and odor is often observed. During the experiments, hydrogen sulfide gas was injected intermittently into the headspace of partially filled concrete and plastic (PVC and HDPE) sewer pipes in concentrations of approximately 1,000 ppm(v). Between each injection, the hydrogen sulfide concentration was monitored while it decreased because of adsorption and subsequent oxidation on the pipe surfaces. The experiments showed that the rate of hydrogen sulfide oxidation was approximately two orders of magnitude faster on the concrete pipe surfaces than on the plastic pipe surfaces. Removal of the layer of reaction (corrosion) products from the concrete pipes was found to reduce the rate of hydrogen sulfide oxidation significantly. However, the rate of sulfide oxidation was restored to its background level within 10-20 days. A similar treatment had no observable effect on hydrogen sulfide removal in the plastic pipe reactors. The experimental results were used to model hydrogen sulfide oxidation under field conditions. This showed that the gas-phase hydrogen sulfide concentration in concrete sewers would typically amount to a few percent of the equilibrium concentration calculated from Henry's law. In the plastic pipe sewers, significantly higher concentrations were predicted because of the slower adsorption and oxidation kinetics on such surfaces.