Critical review of the recovery rates of construction and demolition waste in the European Union - An analysis of influencing factors in selected EU countries.

Due to its intense use of resources, the construction sector was identified as a priority sector in the European Green Deal. Construction and demolition waste (CDW) is one of the largest waste streams of the European Union. As it shows a high potential for recycling, the European Commission set a recovery target of 70% under the Waste Framework Directive. To control the performance and achievements of the member states, annual national reports to the EU are required. However, there exist different ways to specify and report these rates. Recovery rates published by EUROSTAT are calculated on the basis of waste treatment data of non-hazardous mineral CDW, generated according to the EU Waste Statistics Regulation. Limiting factors like non-unified methods of data collection, different waste coding systems and misinterpretations of the term 'backfilling' impede a cross-country comparison of the published EU recovery rates. In this study, factors that may have a misleading impact on reporting EUROSTAT CDW recovery rates were compiled and a detailed analysis using national quality reports of twelve selected EU countries as a data base were performed. The development of the reported recycling rates over five years was examined and the influence of the various factors was determined. The findings may enhance a more purposeful (scientific) discussion of CDW data and for evidence-based reporting of national recovery rates, and may assist the development towards an improved, uniform EU-wide data set. Finally, this will provide support to decision makers for future policy and governmental requirements.

The dynamics of macro- and microplastic quantity and size changes during the composting process.

The quantity and type of macro- and microplastics was investigated in rotting material during the composting process of two state-of-the-art composting plants in Austria. Microplastics >0.2 mm, were found already after the first turning event in both facilities. The generation of microplastics was more extensive in the plant that used shorter turning intervals during the first four weeks and generated approx. 21 particles per week and kg-1 DM. After 4 weeks of operation less microplastic particles were detected, which suggested that particles were fractionated to smaller sizes during processing. In addition, a total of nine composts from three different facilities that were operated in various settlement structures were compared. 7 to 232 macro- and microplastic particles per kg DM were found, whereas the highest plastic burden was observed in the composts made from biowaste that originated from the most densely populated area.

Methane losses from different biogas plant technologies.

Biogas and biomethane production can play an important role in a fossil-fuel-free energy supply, provided that process-related methane (CH4) losses are minimized. Addressing the lack of representative emission data, this study aims to provide component specific CH4 emission factors (EFs) for various biogas plant technologies, enabling more accurate emission estimates for the biogas sector and supporting the identification of low emission technologies. Four measurement teams investigated 33 biogas plants in Austria, Germany, Sweden and Switzerland including mainly agricultural and biowaste treating facilities. For the first time, a harmonized measurement procedure was used to systematically survey individual on-site emission sources and leakages. Measurements revealed a large variability in technology specific emissions, especially for biogas utilization and upgrading. Median loss from combined heat and power (CHP) plants was 1.6 % for gas engines (n = 21), and 3.0 % for pilot injection units (n = 3) of the input CH4. Biogas upgrading units showed median CH4 slips of < 0.1 % (chemical scrubbers, n = 4), 0.1 % (after exhaust gas treatment, n = 3) and 2.9 % (water scrubbers, n = 2). Not-gastight digestate storage (n = 8) was identified as a major emission source with maximum 5.6 % of the produced CH4 emitted. Individual leakages (n = 37) released between 0.0 and 2.1 % (median 0.1 %) relative to the CH4 production. All measurement and secondary data are provided in a harmonized dataset (294 datapoints). A review of IPCC default EFs indicate an underestimation of emissions from biogas utilization (reported in the energy sector) while the impact of leakages on overall plant emissions (waste sector) may be overestimated for European biogas plants.

Formal and informal solid waste management in Kutaisi, Georgia: A status quo report based on material flow analysis.

The goal of this study is a qualitative and quantitative evaluation of processes and flows within the solid waste management (WM) system in Kutaisi, Georgia, and the wider Imereti region. The applied methodology based upon data collected through customized questionnaires enabled both the formal and informal sectors (IS) to be characterized. Moreover, waste composition studies in the region's rural and semi-urban areas revealed that the share of recyclables is higher in urban areas and commercial centres. A material flow analysis was used to transparently consolidate the collected data, showing that dumping and landfilling still play a major role within the Georgian WM system. The total amount of waste landfilled on 'Nikea' landfill in 2019 equals 58,000 tonnes year-1, from where around 55,500 tonnes year-1 is formally collected municipal solid waste, and 2,503 tonnes year-1 is commercial and industrial waste. According to the findings, the size of the IS in Kutaisi is 0.07-0.15% of the city's population, whose supposed cumulative income is estimated GEL 0.57-1.13 million (EUR 180-360 thousand) in 2019. Informally collected recyclables are estimated 870-1,750 tonnes year-1, comprising 6-11% of recyclables landfilled in Kutaisi in 2019. The study provides a basis for decision-makers. Replicating the applied methodologies and approaches to create this sound database could support the WM system across whole Georgia. The study further reveals the importance of the need to stop neglecting the IS and recognizes the importance of its role in the WM system of Kutaisi and the wider Imereti region, respectively.

The use and detection of quantum dots as nanotracers in environmental fate studies of engineered nanoparticles.

Investigations of the behavior and effects of engineered nanoparticles (ENPs) on human health and the environment need detailed knowledge of their fate and transport in environmental compartments. Such studies are highly challenging due to low environmental concentrations, varying size distribution of the particles and the interference with the natural background. A strategy to overcome these limits is to use mimics of ENPs with unique detectable properties that match the properties of the ENPs as nanotracers. A special class of ENPs that can be tracked are quantum dots (QDs). QDs are composed of different metals, metalloids, or more recently also carbon (e.g., graphene), that result in unique optical properties. This allows the tracking of such particles by fluorescence microscopic and photometric techniques. Many types of QDs consist of heavy elements, allowing to track and visualize these particles also by electron microscopy and to quantitate the particles indirectly based on these elements. QDs can also be surface modified in various ways which enable them to be used as a label or as traceable mimics for ENPs. This review reflects a broad range of methods to synthesize and modify QDs based on metals, metalloids, and graphene for studying the environmental fate of nanoparticles and discusses and compares analytical methods that can be used for tracking and quantifying QDs. In addition, we review applications of QDs as ENP mimics in environmental studies of surface waters, soils, microorganisms, and plants with respect to the applied analytical techniques.

Estimation of dump and landfill waste volumes using unmanned aerial systems.

The paper discusses how the choice of software and hardware components used in unmanned aerial systems (UAS) affects the accuracy of estimating volume on landfills and dumpsites, and the amount of ground work needed to create a high-altitude justification of reference geodetic network. A non-specialized low-cost unmanned aerial vehicle (UAV) and a specialized UAV of a geodetic class were compared in scenarios with different numbers of ground control points. In addition, the use of desktop and cloud software for photogrammetric data-processing was assessed. Both specialized geodetic and non-specialized low-cost UAVs made it possible to obtain fairly accurate estimates of waste volume. The differences in the UAV results compared to data obtained by ground surveys were about 1.0%, even with a minimum number of ground control points (GCP). With complete abandonment of GCP and processing aerial data in cloud services, these differences increased to 5.0%. Low-cost UAV and cloud services can be used for operational monitoring of waste volume changes at landfills and dumpsites. A geodesic-class UAV allows researchers to build a more accurate digital terrain model of the landfill surface, but it does not give any advantages in waste volume estimation.

Drone technology in municipal solid waste management and landfilling: A comprehensive review.

The paper discusses the experience of using unmanned aerial vehicles (UAV) in the management of municipal solid waste landfills and dumpsites. Although the use of drones at waste disposal sites (WDS) has a more than ten-year history, the active application of these technologies has increased in the last 3-4 years. The paper analyzes scientific publications of 2010-2021 (July) and identifies the main WDS management task groups for which the solution of UAV can be used. It illustrates that most of the research is devoted to studying spatial and volumetric characteristics of landfills, which is connected with the practical needs. About a quarter of the publications focus on monitoring the emissions of landfill gas or its individual components, mainly methane. Issues of a comprehensive assessment of the technological and environmental safety of landfills and dumps are covered in the scientific literature fragmentarily and insufficiently. At the same time, the current level of technologies for collecting and processing remote sensing air data (UAV, sensors for aerial imagery, software for photogrammetric processing of aerial imagery data, geographic information systems (GIS)) makes it possible to identify and assess many environmental effects of landfills and dumps and to monitor compliance with the standards for the landfills operation, which could bring management of these facilities to a fundamentally different level. Promising areas of further research in the field of UAV application at WDS are indicated: development of processes for automatic interpretation of aerial imagery materials; product analysis of photogrammetric data processing in a GIS environment, etc.

Static modelling of the material flows of micro- and nanoplastic particles caused by the use of vehicle tyres.

The emissions of tyre wear particles (TWPs) into the environment are increasing and have negative impacts on the environment and human health. The aim of this study was therefore to establish a mass balance for vehicle tyres und TWP emissions in Austria using static material flow analysis, which enabled a quantification of mass flows of rubber including carbon black as the most mass-relevant tyre filler. Vehicle-specific and mileage-dependent emission factors were used to calculate the TWP emissions. The results for the year 2018 indicate that 80% of the tyre rubber remained in use, while 14% was re-treaded, recycled, incinerated or exported as end-of-life tyres and 6% was emitted as TWPs to air, soil or surface water. Of these 21,200 t/y released and dissipative lost TWPs, 6% were microscale, with a possible size between 0.1 and 10 µm, and 0.3% were nanoscale below 0.1 µm. The mass balance on the substance level shows that the TWPs contained 5,500 t/y of carbon black emitted in the form of airborne TWPs (6%) or entering in the soil or surface waters (47% each). Regarding air pollution from road vehicles, about 3,600 t/y were non-exhaust emissions, including tyre, brake and road-surface wear, which contributed to 9% of total dust emissions across Austria. Scenario analysis for 2050 with regard to e-mobility and the European Green Deal reveals that non-exhaust emissions can only be significantly reduced by a general reduction of the mileage or an environmentally friendly tyre design. This modelling approach provides a solid basis for decision makers in traffic planning as well as for chemical risk assessment. However, dynamic models with higher temporal and spatial resolution are needed to predict future mass flows of TWPs and their environmental fate, including their degradation products and possible accumulation effects.

A European nano-registry as a reliable database for quantitative risk assessment of nanomaterials? A comparison of national approaches.

Despite the fact that nanomaterials have been in use for decades and chemicals legislation is largely harmonised within the EU, quantitative and safety-relevant information on nanomaterials is still scarce. In particular, information about production volumes, their unique physicochemical properties (size, specific surface area, etc.) and nanomaterial exposure, which may lead to adverse effects on human health and the environment, is still lacking. While the latest amendments of the REACH Annexes have led to certain improvements, a harmonised EU-wide nano-registry would provide additional quantitative data for risk assessment but is not foreseeable for the near future. Since the European Commission, the European Parliament and some member states take contrasting approaches to the regulation of nanomaterials, France, Belgium, Denmark, Sweden and Norway (as a country of the European Economic Area), launched national mandatory reporting systems to collect quantitative information, thus fostering early risk assessment of nanomaterials. In this study, we compare national registries - based on a literature review and expert interviews - and show differences between the regulations under the respective national laws and REACH regulation. These include, for instance, thresholds for notification and level of detail on the specification of the nanomaterial, mixture and/or product, the definition of exceptions for the requirement to register and the timing of registration. As this heterogenous regulatory framework hinders comparability and potentially creates trade barriers, we argue that a harmonised EU-wide nano-registry would substantially improve the current situation by promoting the safe and sustainable handling of nanomaterials, increasing transparency and trust, and consequently nurturing innovation. Such an EU-wide nano-registry should both cover nanomaterials as substances or mixtures, such as in REACH registration, and the semi-/finished products they will be used in, since the exposure, and thus the hazardous potential of released nanomaterials during their life cycle, depends largely on the scope of application.

Mobility and fate of ligand stabilized semiconductor nanoparticles in landfill leachates.

Semiconductor quantum dots (QDs) are nanocrystals used in diverse optoelectronics. At the end of their useful life they are likely to end up in landfills, where they could be mobilzed by infiltrating rain water. In this work, spectroscopic and light scattering techniques were employed to investigate the environmental fate of QDs exposed to leachates from Austrian landfill sites containing municipal solid and bulky wastes. Brij-58-coated CdSe QDs, a model for surfactant stabilized hydrophobic nanoparticles, primarily sedimented before being degraded on a slower timescale in the course of 6 months. In contrast, N-acetyl-l-cystein-coated CdTe QDs, which represent electrostatically stabilized nanoparticles with a small covalently linked stabilizing molecule, mainly underwent a degradation mechanism that was accelerated by temperature. 71-95 % of this QD type was still dispersed in all leachates after 6 months at low temperature. Leachate temperature and composition, such as the DOC, as well as the used particle coating determined the mechanistic route of clearance of sedimentation versus degradation. Our study shows, that mechanistic investigations are necessary to determine the persistence of nanoparticles depending on their coatings in waste matrices which can be further used to assess hazardous risks of such nanowastes.

A review of the fate of engineered nanomaterials in municipal solid waste streams.

Significant knowledge and data gaps associated with the fate of product-embedded engineered nanomaterials (ENMs) in waste management processes exist that limit our current ability to develop appropriate end-of-life management strategies. This review paper was developed as part of the activities of the IWWG ENMs in Waste Task Group. The specific objectives of this review paper are to assess the current knowledge associated with the fate of ENMs in commonly used waste management processes, including key processes and mechanisms associated with ENM fate and transport in each waste management process, and to use that information to identify the data gaps and research needs in this area. Literature associated with the fate of ENMs in wastes was reviewed and summarized. Overall, results from this literature review indicate a need for continued research in this area. No work has been conducted to quantify ENMs present in discarded materials and an understanding of ENM release from consumer products under conditions representative of those found in relevant waste management process is needed. Results also indicate that significant knowledge gaps associated with ENM behaviour exist for each waste management process investigated. There is a need for additional research investigating the fate of different types of ENMs at larger concentration ranges with different surface chemistries. Understanding how changes in treatment process operation may influence ENM fate is also needed. A series of specific research questions associated with the fate of ENMs during the management of ENM-containing wastes have been identified and used to direct future research in this area.

Modeling the fate and end-of-life phase of engineered nanomaterials in the Japanese construction sector.

To date construction materials that contain engineered nanomaterials (ENMs) are available at the markets, but at the same time very little is known about their environmental fate. Therefore, this study aimed at modeling the potential fate of ENMs by using the example of the Japanese construction sector and by conducting a dynamic material flow analysis. Expert interviews and national reports revealed that about 3920-4660 tons of ENMs are annually used for construction materials in Japan. Nanoscale TiO2, SiO2, Al2O3 and carbon black have already been applied for decades to wall paints, road markings or concrete. The dynamic material flow model indicates that in 2016 about 95% of ENMs, which have been used since their year of market penetration, remained in buildings, whereas only 5% ended up in the Japanese waste management system or were diffusely released into the environment. Considering the current Japanese waste management system, ENMs were predicted to end up in recycled materials (40-47%) or in landfills (36-41%). It was estimated that only a small proportion was used in agriculture (5-7%, as ENM-containing sewage sludges) or was diffusely released into soils, surface waters or the atmosphere (5-19%). The results indicate that ENM release predominantly depend on their specific applications and characteristics. The model also highlights the importance of adequate collection and treatment of ENM-containing wastes. In future, similar dynamic flow models for other countries should consider, inasmuch as available, historical data on ENM production (e.g. like declaration reports that are annually published by relevant public authorities or associations), as such input data is very important regarding data reliability in order to decrease uncertainties and to continuously improve model accuracy. In addition, more environmental monitoring studies that aim at the quantification of ENM release and inadvertent transfer, particularly triggered by waste treatment processes, would be needed in order to validate such models.

Performance and completion assessment of an in-situ aerated municipal solid waste landfill - Final scientific documentation of an Austrian case study.

By converting anaerobic landfills into a biologically stabilized state through accelerating aerobic organic matter degradation, the effort and duration necessary for post-closure procedures can be shortened. In Austria, the first full-scale application of in-situ landfill aeration by means of low pressure air injection with simultaneous off-gas collection and treatment was implemented on an old MSW-landfill and operated between 2007 and 2013. Besides complementary laboratory investigations, which included waste sampling from the landfill site prior to aeration start, a comprehensive field monitoring program was conducted to assess the influence of the aeration measure on the emission behavior of the landfilled waste during the aeration period as well as after aeration completion. Although the initial waste material was described as rather stable, the lab-scale aeration tests indicated a significant improvement of the leachate quality and even the biological solid waste stability. However, the aeration success was less pronounced for the application at the landfill site, mainly due to technical limitations in the full-scale operation. In this paper main performance data of the field investigation are compared to four other scientifically documented case studies along with stability indicators for solid waste and leachate characteristics in order to evaluate the success of aeration as well as the progress of a landfill towards completion and end of post-closure care. A number of quantitative benchmarks and relevant context information for the performance assessment of the five hitherto conducted international aeration projects are proposed aiming to support the systematization and harmonization of available results from diverse field studies and full-scale applications in future.

Traceability of fluorescent engineered nanomaterials and their fate in complex liquid waste matrices.

The number of products containing engineered nanomaterials (ENMs) has increased due to their high industrial relevance as well as their use in diverse consumer products. At the end of their life cycle ENMs might be released to the environment and therefore concerns arise regarding their environmental impact. In order to track their fate upon disposal, it is crucial to establish methods to trace ENMs in complex environmental samples and to differentiate them from naturally-occurring nanoparticles. The goal of this study was to distinctively trace ENMs by (non-invasive) detection methods. For this, fluorescent ENMs, namely quantum dots (QDs), were distinctively traced in complex aqueous matrices, and were still detectable after a period of two months using fluorescence spectroscopy. In particular, two water-dispersible QD-species, namely CdTe/CdS QDs with N-acetyl-l-cysteine as capping agent (NAC-QDs) and surfactant-stabilized CdSe/ZnS QDs (Brij(®)58-QDs), were synthesized to examine their environmental fate during disposal as well as their potential interaction with naturally-occurring substances present in landfill leachates. When QDs were spiked into a leachate from an old landfill site, alteration processes, such as sorption, aggregation, agglomeration, and interactions with dissolved organic carbon (DOC), led to modifications of the optical properties of QDs. The spectral signatures of NAC-QDs deteriorated depending on residence time and storage temperature, while Brij(®)58-QDs retained their photoluminescence fingerprints, indicating their high colloidal stability. The observed change in photoluminescence intensity was mainly caused by DOC-interaction and association with complexing agents, such as fulvic or humic acids, typically present in mature landfill leachates. For both QD-species, the results also indicated that pH of the leachate had no significant impact on their optical properties. As a result, the unique spectroscopic fingerprints of QDs, specifically surfactant-stabilized QDs, allowed distinctive tracing in complex aqueous waste matrices in order to study their long-term behavior and ultimate fate.

Determination of leachate compounds relevant for landfill aftercare using FT-IR spectroscopy.

Controlling and monitoring of emissions from municipal solid waste (MSW) landfills is important to reduce environmental damage and health risks. Therefore, simple and meaningful monitoring tools are required. This paper presents how Fourier Transform Infrared (FT-IR) Spectroscopy can be used to monitor leachate from various landfill sites. The composition of percolated leachate provides information about reactivity or stability of organic matter in landfills. Chemical compounds of investigated leachate are depicted by distinct spectral pattern. Partial least squares regression (PLS-R) models, a multivariate analysis tool, were developed based on infrared spectra to determine simultaneously conventional parameters such as ammonium, nitrate, sulfate, and dissolved organic carbon. The developed models are appropriate for application in waste management practice with respect to their excellent coefficients of determination, namely R(2)=0.99, 0.99, 0.98, and 0.98, their low errors of cross-validation and their high ratios of performance to deviation (RPD=9.3, 12.5, 6.5, 7.3). Thus, FT-IR spectroscopy turned out to be a reliable, time-saving tool to determine four parameters relevant for landfill aftercare monitoring by one single easy adaptable measurement.

Current limitations and challenges in nanowaste detection, characterisation and monitoring.

Engineered nanomaterials (ENMs) are already extensively used in diverse consumer products. Along the life cycle of a nano-enabled product, ENMs can be released and subsequently accumulate in the environment. Material flow models also indicate that a variety of ENMs may accumulate in waste streams. Therefore, a new type of waste, so-called nanowaste, is generated when end-of-life ENMs and nano-enabled products are disposed of. In terms of the precautionary principle, environmental monitoring of end-of-life ENMs is crucial to allow assessment of the potential impact of nanowaste on our ecosystem. Trace analysis and quantification of nanoparticulate species is very challenging because of the variety of ENM types that are used in products and low concentrations of nanowaste expected in complex environmental media. In the framework of this paper, challenges in nanowaste characterisation and appropriate analytical techniques which can be applied to nanowaste analysis are summarised. Recent case studies focussing on the characterisation of ENMs in waste streams are discussed. Most studies aim to investigate the fate of nanowaste during incineration, particularly considering aerosol measurements; whereas, detailed studies focusing on the potential release of nanowaste during waste recycling processes are currently not available. In terms of suitable analytical methods, separation techniques coupled to spectrometry-based methods are promising tools to detect nanowaste and determine particle size distribution in liquid waste samples. Standardised leaching protocols can be applied to generate soluble fractions stemming from solid wastes, while micro- and ultrafiltration can be used to enrich nanoparticulate species. Imaging techniques combined with X-ray-based methods are powerful tools for determining particle size, morphology and screening elemental composition. However, quantification of nanowaste is currently hampered due to the problem to differentiate engineered from naturally-occurring nanoparticles. A promising approach to face these challenges in nanowaste characterisation might be the application of nanotracers with unique optical properties, elemental or isotopic fingerprints. At present, there is also a need to develop and standardise analytical protocols regarding nanowaste sampling, separation and quantification. In general, more experimental studies are needed to examine the fate and transport of ENMs in waste streams and to deduce transfer coefficients, respectively to develop reliable material flow models.

Determining methane emissions from biogas plants--Operational and meteorological aspects.

A micrometeorological method, combining an inverse dispersion technique with path-integrated concentration measurements, was applied on an Austrian biogas plant over the period of more than one year to determine emissions of the whole plant. Measurement campaigns were conducted to characterize the emission response to operational activities (e.g. digestate management) and meteorological changes. When digestate storage tanks were filled, an average emission rate of 7.2 kg CH4/h (approx. 4% of the calculated CH4 production) was determined, while 5.4 kg CH4/h of emissions (approx. 3% of the calculated CH4 production) were quantified after the tanks had been emptied. It could be observed that besides the operation mode (e.g. filling level or agitation of the openly stored digestate, maintenance), the meteorological conditions such as wind speed and solar radiation (e.g. heat flux) can also affect the emission rate.

Quantification of methane emissions from full-scale open windrow composting of biowaste using an inverse dispersion technique.

An inverse dispersion technique in conjunction with Open-Path Tunable-Diode-Laser-Spectroscopy (OP-TDLS) and meteorological measurements was applied to characterise methane (CH4) emissions from an Austrian open-windrow composting plant treating source-separated biowaste. Within the measurement campaigns from July to September 2012 different operating conditions (e.g. before, during and after turning and/or sieving events) were considered to reflect the plant-specific process efficiency. In addition, the tracer technique using acetylene (C2H2) was applied during the measurement campaigns as a comparison to the dispersion model. Plant-specific methane emissions varied between 1.7 and 14.3 gCH4/m(3)d (1.3-10.7 kg CH4/h) under real-life management assuming a rotting volume of 18,000 m(3). In addition, emission measurements indicated that the turning frequency of the open windrows appears to be a crucial factor controlling CH4 emissions when composting biowaste. The lowest CH4 emission was measured at a passive state of the windrows without any turning event ("standstill" and "sieving of matured compost"). Not surprisingly, higher CH4 emissions occurred during turning events, which can be mainly attributed to the instant release of trapped CH4. Besides the operation mode, the meteorological conditions (e.g. wind speed, atmospheric stability) may be further factors that likely affect the release of CH4 emissions at an open windrow system. However, the maximum daily CH4 emissions of 1m(3) rotting material of the composting plant are only 0.7-6.5% of the potential daily methane emissions released from 1m(3) of mechanically-biologically treated (MBT) waste being landfilled according to the required limit values given in the Austrian landfill ordinance.

Multisource emission retrieval within a biogas plant based on inverse dispersion calculations--a real-life example.

Open digestate storage tanks were identified as one of the main methane (CH4) emitters of a biogas plant. The main purpose of this paper is to determine these emission rates using an inverse dispersion technique in conjunction with open-path tunable diode laser spectroscopy (OP-TDLS) concentration measurements for multisource reconstruction. Since the condition number, a measure of "ill-conditioned" matrices, strongly influences the accuracy of source reconstruction, it is used as a diagnostic of error sensitivity. The investigations demonstrate that the condition number for a given source-sensor configuration in the highly disturbed flow field within the plant significantly depends on the meteorological conditions (e.g., wind speed, stratification, wind direction, etc.). The CH4 emissions are retrieved by removing unrepresentative periods with high condition numbers, which indicate uncertainty in recovering the individual sources. In a final step, the CH4 emissions are compared with the maximum biological methane potential (BMP) in the digestate analyzed under laboratory conditions. The retrieved methane emission rates represent an average of 50% of the maximum BMP of the stored digestate in the winter months, while they comprised an average of 85% during the measurement campaigns in the summer months. The results indicate that the open tanks have the potential to represent a substantial emission source even during colder periods.