Mechanical-biological Treatment Plants Research Articles

Soil restoration using compost-like-outputs and digestates from non-source-separated urban waste as organic amendments: Limitations and opportunities

Soil rehabilitation in the context of the restoration of quarries, dumping sites, or road slopes often requires the prior addition of organic amendments to improve the substrates used for Technosol construction. Bio-wastes coming from advanced Mechanical-Biological Treatment Plants, mainly compost-like-outputs (CLO) and digestates (DGT), are new and suitable sources of organic matter potentially useful as organic amendments for this purpose, in an approach clearly fulfilling the principles of circular economy. In order to assess the suitability of these materials, a complete physicochemical and biological evaluation was carried out, including an ecotoxicological evaluation to discard hazardous effects on key soil fauna groups. Field experiments were also carried out on several road slopes and a dumping site. The stability degree of organic matter and the impurities content could be restricting parameters for the use of CLO in soils. Low stability degree decreased plant development in the initial stages of restoration. Moreover, the high heterogeneity in terms of physicochemical parameters of the different CLOs assessed is a serious constraint to making generalizations about its use. In contrast, composition of DGTs was more stable between plants and batches, and presented low impurities and high N contents that make them more suitable for applying to soil and promoting plant development. Regarding the application rates, DGT application at 20 g kg−1 clearly improved plant growth after sowing, without compromising recruitment. However, application at 80 g kg−1 did not ameliorate seed germination and plant growth, in either CLO or DGT treatments, and increased N-leaching and toxicity risk to soil mesofauna in DGT amended Technosols.

Assessment of the Effects of Wastewater Treatment Plant Modernization by Means of the Field Olfactometry Method

Methodological aspects of odor studies in ex-post analyses for Polish wastewater management facilities were analyzed based on the example of a modernized and enlarged wastewater treatment plant (WWTP) in Mazovia, in the vicinity of the Warsaw agglomeration. It is a mechanical–biological treatment plant with increased efficiency of biogen removal, using activated sludge in the treatment process, with a maximum hydraulic capacity of 60,000 m3/day. Olfactometric research was carried out by means of a method based on identification and characterization of the odor plume emitted from the examined source. This paper presents the results of odor intensity assessment (in sensory examinations according to a 6-stage scale) and odor concentration measurement (using portable field olfactometers) after the completion of the project, and compares them with similar studies conducted before the commencement of the investment. A total of 10 measurement series were carried out before modernization, and 12 after modernization of the WWTP. Odor concentration and intensity were determined, and the current meteorological situation was assessed at the measurement and observation points (receptors) located within the premises (in total 462 points) and around the WWTP (342 points). In each series of measurements on the windward side of the treatment plant, the background of air pollution with odorous substances was marked. The research showed that air flowing into the area of the sewage treatment plant is clean in terms of odor. During the research, basic sources of odor nuisance were identified, and their impact before and after modernization was characterized. The results presented in radar diagrams show changes in the percentage distribution of frequency of occurrence of individual intensity values at receptor points within and outside the area of the treatment plant. After modernization, a significant decrease in the concentration of odor emitted from the sludge dewatering building and sludge containers was determined. The air-tightness of the sewage channel (covered with concrete slabs and sealed) resulted in a significant decrease in the concentration of odor emitted from this source. Waste (in particular, sewage sludge) collected in the emergency waste storage yard was identified as the main source of odor nuisance. The waste, even after modernization, was an emitter of odorous compounds spreading outside the area of the WWTP. Nevertheless, as a result of the investment, the desired effect of reduction of the degree of odor nuisance was achieved.

Particle Size Distribution in Municipal Solid Waste Pre-Treated for Bioprocessing

While it is well known that particle size reduction impacts the performance of bioprocessing such as anaerobic digestion or composting, there is a relative lack of knowledge about particle size distribution (PSD) in pre-treated organic material, i.e., the distribution of particles across different size ranges. PSD in municipal solid waste (MSW) pre-treated for bioprocessing in mechanical–biological treatment (MBT) was researched. In the first part of this study, the PSD in pre-treated waste at two full-scale MBT plants in the UK was determined. The main part of the study consisted of experimental trials to reduce particle sizes in MSW destined for bioprocessing and to explore the obtained PSD patterns. Shredders and a macerating grinder were used. For shear shredders, a jaw opening of 20 mm was found favourable for effective reduction of particle sizes, while a smaller jaw opening rather compressed the wet organic waste into balls. Setting the shredder jaw opening to 20 mm does not mean that in the output all particles will be 20 mm or below. PSD profiles revealed that different particle sizes were present in each trial. Using different types of equipment in series was effective in reducing the presence of larger particles. Maceration yielded a PSD dominated by very fine particles, which is unsuitable for composting and potentially also for anaerobic digestion. It was concluded that shredding, where equipment is well selected, is effective in delivering a material well suited for anaerobic digestion or composting.

Performance assessment of landfill in-situ aeration – A case study

The assessment of landfill in-situ aeration eludes standardization as its application highly depends on varying local conditions. The prevailing work tries to assess the procedure performance by using typically available data.In the here presented case study the aeration pipes were applied horizontally. To evaluate the air-distribution and its effect on the landfill solid body, two monitoring fields with 10 × 10 m were created. From there in total 60 solid and 336 gaseous samples were taken over five years. As the material from the landfill was rather old and characterized by comparatively low reactivity, “new” material from a mechanical biological treatment (MBT) plant was introduced in the landfill. Additionally online gas data from eight technically separated landfill sections were analyzed during in-situ aeration.In total, about 46 Mm3 (0.27 m3/kg waste) air was introduced into the landfill body. The eight sections showed differences in reactivity (overall C-discharge was 8 g C kg−1 dry weight, ranging from 4.5 to 11). With solid sampling we could not show a significant decrease in landfill TOC but for the introduced MBT-material. Ammonium in solid samples was significantly reduced (to 14.7% initial) and NO3 significantly increased (2.1% initial). The reduction of the initial TOC (4.58%) was on average 11%.The application of horizontal landfill aeration led to a widespread air-distribution in a rather shallow landfill. Monitoring fields allowed for a screening of the impact of the measures on the solid body with reduced sampling costs.

Life cycle costing of energy recovery from solid recovered fuel produced in MBT plants in Italy

The Environmental Life Cycle Costing (LCC) methodology was applied to assess the costs of the processing in Italy of municipal Residual Waste (RW) in Mechanical-Biological Treatment (MBT) plants aimed at the production of Solid Recovered Fuels (SRFs), delivered to dedicated waste-to-energy (WTE) plants or to co-combustion. Two different functional units were defined to consider two different perspectives: 1 tonne of residual waste in input of the MBT plant, and 1 MWh of exergy produced by the energy valorisation of the streams delivered by the MBT plant. Four strategies were analysed that differ for the type of MBT (single stream or separated streams) and the destiny of the SRF (dedicated WTE plant or cement kiln). The results appear to strongly recommend the treatment of the RW in a single stream MBT plant and the production of a SRF with characteristics suitable to meet the technological, economic and environmental needs for co-combustion, substituting fossil fuels.

Location of mixed municipal waste treatment facilities: Cost of reducing greenhouse gas emissions

Abstract Municipal solid waste treatment leads to the production of a considerable amount of mixed municipal waste, in case of which material recovery is difficult. Its treatment represents a worldwide challenge since landfilling is still a major treatment method and the respective emissions of greenhouse gases are significant. Approximately 126 Mt of municipal solid waste were landfilled or incinerated within the EU-28 in 2017, while the waste management sector produced 3% of the overall greenhouse gases emissions. Regarding mixed municipal waste, Waste-to-Energy plants seem to be a suitable disposal option as they substitute both landfills and energy production from fossil fuels in combined heat and power plants. However, new treatment facilities of this type need to take into account also the heat and electricity demands in their vicinity to ensure economic stability. This paper therefore analyses the relationship between greenhouse gases emissions and the cost of mixed municipal waste treatment, while considering environmental impact of different treatment options. A reverse logistic (mixed integer programming) model has been developed to optimise future strategies of mixed municipal waste treatment in a large geographical area. The model is nonlinear because of the nonlinear nature of the cost of mixed municipal waste treatment as well as the economic incentive associated with the avoided greenhouse gases emissions. These, in turn, are influenced by plant capacities, locations, and other location-specific parameters (such as the yearly heat demand profile) that must be considered during the integration of a future plant into the existing district heating systems. The results are presented through a case study for the Czech Republic, with 206 micro-regions (waste producers), 148 landfills, 113 potential mechanical-biological treatment plants, 24 potential locations for plants utilising refuse-derived fuels, 4 existing Waste-to-Energy plants, and 32 candidate locations for new Waste-to-Energy plants have been considered. The proposed future concepts involving various processing chains (small Waste-to-Energy plant, large Waste-to-Energy plant with the necessary complex logistics, mechanical biological treatment prior to incineration), are compared with the current (2016) waste treatment strategy, in which 73% of mixed municipal waste is landfilled. The trade-off between economically viable and environmentally acceptable solution is also targeted. The obtained data suggest a possible reduction in greenhouse gases emissions by almost 150% with the cost of waste treatment being increased only by approx. 2.5 EUR/t.

Volatile fatty acid production from mesophilic acidogenic fermentation of organic fraction of municipal solid waste and food waste under acidic and alkaline pH

This study is focused on the effects of pH on the production of volatile fatty acids (VFAs) and their distribution through the acidogenic fermentation of source-sorted organic fraction of municipal solid waste (OFMSW) from a mechanical-biological treatment (MBT) plant, and food waste (FW) from a university canteen. In semi-continuous lab-scale digesters using OFMSW at a hydraulic retention time (HRT) of 3.5 days under acidic conditions (pH 6.0), the VFA concentration in the effluent increased to 9.8–11.5 g L−1 (VS content of the feedstock between 4.2 and 5.2% w/w), while its individual VFA profiling was similar to the influent which was already pre-fermented (namely, C2 35–41%, C3 18–22%, C4 17–21%, and C5 9–12%). When working with the same conditions but using FW as feedstock, an effluent with a VFA concentration up to 11.5 g VFA L−1 (FW with a VS content of 5.5% w/w) and a stable distribution of C2 and C4 acids (up to 60.3% and 12.9%, respectively) but with very low quantities of C3 and C5 acids (lower than 1.8 and 2.7%, respectively) was obtained. Anaerobic batch tests using FW revealed that alkaline pH near 9 could lead to higher VFA production with high acetic acid content when compared to pH 6. In the semi-continuous fermenters working at alkaline conditions (pH 9.5–10) using OFMSW and FW, an enhanced solubilization of organic matter was registered with respect to the fermenters working under acidic conditions. This fact was not reflected in a higher VFA production when using OFMSW as feedstock, probably due to free ammonia inhibition, since OFMSW was mixed in the MBT plant with supernatant from anaerobic digestion of this biowaste. However, when using FW, alkaline conditions lead to an enhanced VFA production with respect to the reactor working under acidic conditions, being acetic acid the predominant product, which represented up to 91% of the VFA spectrum obtained.

Sustainable Transition Models for Municipal Solid Waste Management: A Case Study of Saraburi Provincial Administration Organization, Thailand

Municipal solid waste (MSW) generation exceeding the capacity of mechanical biological treatment (MBT) plants is a major problem for most municipalities in Thailand. The problem is serious for the Saraburi Provincial Administration Organization (SPAO) as the high daily volumes of MSW sent to the SPAO greatly exceeds the MBT plant capacity of 20 ton d-1. This results in accumulation and ultimately, open-dumping of MSW. Transition from a small (< 50 ton d-1) to a medium-sized cluster (50 - 300 ton d-1) is under consideration to address this problem. Therefore, this study evaluated pre-feasibility information, comparing two possible transition models. Model 1 proposes modification of the existing MBT plant to enlarge its capacity to 50 ton d-1, while Model 2 would require establishing a new medium-sized MBT plant (50 - 70 ton d-1). Results from field data collection as well as mass balance calculation and financial modelling indicate that without additional income from tipping or MSW management fee as well as sale of recyclable materials and scrap metals, both models exhibit negative net present value (NPV) or are not economically feasible due to high initial investment in machinery. However, sensitivity analysis based on an expected fall in future machinery prices indicates that the NPV for both models become positive if prices fall by a minimum 20 %. Due to the much higher initial investment, but the higher capacity with higher separation technology and the higher environmental benefits as well as higher ratings for sustainable development indicators, Model 2 is recommended for a long-term transition. Model 1 can still be recommended for a short - to medium-term transition. Results from in-depth interviews also confirm that Model 1, which offers additional local employment and incomes from selling recyclable materials and scrap metals would be the more feasible option owing to familiarity with the process and its lower initial investment requirement.

Effect of a Further Maturation Phase on the Chemical and Environmental Properties of a Bio-stabilised Waste from a Mechanical–Biological Treatment Plant

This work aimed at investigate the effects of a maturation treatment on the chemical and environmental properties of a bio-stabilised waste (BSW) produced from a Mechanical Biological Treatment (MBT) plant. Whilst several studies assessed the effects of maturation on compost properties, only a few works focused on BSW subjected to prolonged stabilisation processes. To this aim, the BSW produced from a MBT plant was subjected to a further pilot-scale prolonged curing, monitoring volatile solids and carbon content. Furthermore, a detailed characterization was performed on three BSW samples collected at different treatment duration, evaluating the biological stability, the total metal content, the metal speciation and their release in water. The obtained results confirmed that the adoption of a prolonged maturation process could improve the characteristics of the BSW produced in the MBT plant. After 28 days of treatment, the BSW presented a dynamic respiration index (DRI) value proper of a biologically unstable matrix. However, a higher stability degree was observed after at least 118 days (as shown by the DRI, the C/N ratio and the humification indices). The adopted treatment entailed also an improvement of the environmental behaviour of the material due to the decrease in the release of metal and organic carbon, as also shown by the reduction in the mobile fraction of metals observed in the metal speciation analysis. This study also showed that a preliminary assessment of the biological stability of a matrix could be already obtained analysing several parameter such as DOC, volatile solids and carbon content.

Viability of the Use of Leachates from a Mechanical Biological Municipal Solid Waste Treatment Plant as Fertilizers

The main environmental issue associated with compost production is the production of a liquid leachate. Leachate from municipal wastes contains carbon, nitrogen, phosphorus, potassium and trace elements that can be used as nutrients by plants. The advantages of the use of organic wastes such as compost leachate as fertilizers are evident. Their use would reduce the consumption of commercial fertilizers, which need, with their production, high cost and energy. This work aims to determine the physical and chemical properties of a specific leachate with a variable composition, collected from the composting line of a mechanical and biological treatment facility. The goal is to assess if the leachates can be used as a potential source for fertilizers, and thus develop and design a sequence of processes which could effectively convert the leachates to commercial fertilizers according to the requirements of the proposal of regulation of the European Parliament of 2016 for fertilizers. Preliminary results show that the leachate samples qualitatively meet the requirements established for the composition of commercial fertilizers, especially organo-mineral fertilizers. Furthermore, there is no production cost of leachate as a raw material. The results show that the leachate is characterized by manageable concentrations of heavy metals which can be removed by adsorption processes, and it presents suitable amounts of organic carbon after a water removal procedure. However, the establishment of the conditions for suitable conversion processes are still under investigation considering the high composition variability due to factors like storage and environmental conditions.

Effect of meteorological conditions on odour emission at biogas plants processing municipal waste – pilot research

Biogas plants processing municipal waste on the one hand represent a trend in waste management, and on the other hand constitute an alternative energy source. Next to their unquestionable benefits, due to the character of the provided activity, they can be a potential source of odours. Municipal waste, largely containing biodegradable fractions, is often subject to decomposition processes in uncontrolled conditions still before it is supplied to the mechanical biological treatment plant. One of the effects of the processes, both controlled and uncontrolled conditions, is emission of odorants. Their spread depends on the applied technologies and adherence to the technological regime during operation. One of the factors determining the types and concentrations of emitted odorants are also meteorological conditions in which waste is stored and processed. The paper presents results of two series of pilot research conducted at four plants, involving a preliminary analysis of the effect of meteorological conditions on the emission of odorants at biogas plants processing municipal waste.

Recirculation of Process Water in a Wet Fermentation of Organic Fraction of Municipal Solid Waste

The mechanical biological treatment plant of Freienhufen is used to stabilize residual waste. Since the rural districts Elbe - Elster and Oberspreewald - Lausitz match their waste management with federal law, organic fraction of municipal solid waste (OFMSW) will be collected separately in future. Hence the anaerobic digestion process has to be converted. The accomplishment has to refer to the existing operating regime to reduce investment costs. This contains a wet fermentation. In order to facilitate the conversion of the operating process, suitable particle sizes and volumetric loads have to be examined. In addition, the liquid phase of the digestate shall be recirculated maximal to save both fresh water and waste water disposal costs. The one year lasting investigations were performed in lab-scale with a various number of reactors. Before feeding the bio-waste was pre-treated. In order to do that, the bio-waste was milled to particle sizes of 2, 4, 8, and 10 mm. In addition, the digestate was dewatered to gain process water. While using the process water fresh water was substituted in varying proportions. The feeding of the reactors was adjusted to the standards of the operating plant. For that reason, the dry matter content in the reactor was adjusted at 10.5 %. Depending on the delivered raw material, this restriction led both to unsteady water requirements and volumetric loading. As a result of investigations an optimal particle size as well as optimal proportion of recirculated process water were defined. For that reason, comprehensive analyses were conducted weekly to characterize the delivered raw material as well as the solid and liquid phase of the digestate in order to determine critical moments due to recirculation of process water. In conclusion, liquid and solid phase of the digestate should be evaluated with regards to application as fertilizer.

Catalytic gasification of refuse-derived fuel in a two-stage laboratory scale pyrolysis/gasification unit with catalyst based on clay minerals

Municipal solid waste (MSW) disposal is a serious environmental issue requiring immediate solution and good waste management strategy. Mechanical-biological treatment (MBT) plants offer the opportunity to reduce the amount of MSW that is, otherwise, disposed of in landfills. Up to 40% of MSW is converted to waste fuel, also called refuse-derived fuel (RDF). Gasification is a promising alternative of RDF processing. It can be defined as high temperature treatment of the feedstock with lower than stoichiometric amount of oxygen resulting mainly in a gaseous product (syngas). High hydrogen content, specific ratio of H2/CO, and low tar content are important parameters of syngas for its application in both energy production and chemical synthesis. Reduction of tar content in syngas can be achieved by catalytic tar cracking. In this work, a catalyst prepared from natural clay was characterised by thermogravimetric, specific surface area, X-ray diffraction, X-ray fluorescence and scanning electron microscopy (SEM) analyses. Catalyst activity was tested in two reactions, namely in decomposition of model tar constituent, p-xylene, and in cracking of tar produced in RDF gasification experiments. Influence of the reaction temperature and the amount of catalyst on the p-xylene conversion and products’ distribution was studied. The results proved high catalytic activity of the prepared catalyst in the decomposition of p-xylene. Coupled RDF pyrolysis and the produced volatiles gasification experiments were carried out in a two-stage laboratory scale reactor using a bed of tar cracking catalyst in the second stage. Tar decomposition experiments were carried out at the reactor temperatures of 700–850 °C applying different amounts of catalyst (0.75 g, 1 g, 1.25 g, 1.5 g, 2 g and 4 g) per 1 g of pyrolised RDF. Results indicate that the presence of catalyst had significant effect on both tar cracking efficiency and gas composition. Loss of the catalyst specific surface area was observed when the experiments were carried out at temperatures exceeding 800 °C.

A comparison of methods for early prediction of anaerobic biogas potential on biologically treated municipal solid waste

Anaerobic gas production tests, generically Biochemical Methane Potential (BMP) or Biogas Potential (BP) tests, are often used to assess biodegradability, though long duration limits their utility. This research investigated whether simple modelling approaches could provide a reliable earlier prediction of total biogas production. Data were assessed from a non-automated biogas test on a large number of both fresh and processed municipal solid waste (MSW) samples, sourced from a mechanical biological treatment (MBT) plant. Non-linear models of biogas production curves were useful in identifying a suitable test endpoint, supporting a test duration of 50 days. Biogas production at 50 days (B50) was predicted using the first 14 days of test data, using (a) linear correlation, (b) a new linearisation process, and (c) non-linear kinetic models. Prediction errors were quantified as relative root mean squared error of prediction (rRMSEP), and bias. Predictions from most models were improved by removing the initial exponential increase phase. Linear correlation gave the most precise and accurate predictions at 14 days (rRMSEP = 2.8%, bias under 0.05%) and allowed acceptable prediction (rRMSEP <10%) both at 8 days, and at 6 days using separate correlations for each sample type. Of the other predictions, the new linearisation process gave the lowest rRMSEP (10.6%) at 14 days. More complex non-linear models conferred no advantage in prediction of B50. These results demonstrate that early prediction of anaerobic gas production is possible for a well-optimised test, using only basic equipment and without recourse to external data sources or complex mathematical modelling.

Thermophilic Co-Digestion of the Organic Fraction of Municipal Solid Wastes-The Influence of Food Industry Wastes Addition on Biogas Production in Full-Scale Operation.

Anaerobic digestion (AD) has been used widely as a form of energy recovery by biogas production from the organic fraction of municipal solid wastes (OFMSW). The aim of this study was to evaluate the effect of the introduction of co-substrates (restaurant wastes, corn whole stillage, effluents from the cleaning of chocolate transportation tanks) on the thermophilic anaerobic digestion process of the mechanically separated organic fraction of municipal solid wastes in a full-scale mechanical-biological treatment (MBT) plant. Based on the results, it can be seen that co-digestion might bring benefits and process efficiency improvement, compared to mono-substrate digestion. The 15% addition of effluents from the cleaning of chocolate transportation tanks resulted in an increase in biogas yield by 31.6%, followed by a 68.5 kWh electricity production possibility. The introduction of 10% corn stillage as the feedstock resulted in a biogas yield increase by 27.0%. The 5% addition of restaurant wastes contributed to a biogas yield increase by 21.8%. The introduction of additional raw materials, in fixed proportions in relation to the basic substrate, increases biogas yield compared to substrates with a lower content of organic matter. In regard to substrates with high organic loads, such as restaurant waste, it allows them to be digested. Therefore, determining the proportion of different feedstocks to achieve the highest efficiency with stability is necessary.

Ecological risk assessment of sewage sludge from municipal wastewater treatment plants: a case study

The aim of this study was to characterize sewage sludge from mechanical-biological wastewater treatment plants (WWTPs) in terms of total concentrations of heavy metals (HMs) and their distribution. Moreover, HM mobility, stability and ecological risk were assessed by calculating the mobility factor (MF), the reduced partition index (Ir) and the ecological risk index (ERI). Hierarchical cluster analysis (CA) was used to group the HMs in the sludges on the basis of their MF, Ir and ERI. The concentration of HMs decreased in the following order: Zn > Cu > Ni > Pb > Cd. HM mobility, as indicated by the MF values, was as follows: 18.7%–30.6% (Zn), 8.1%–36.4% (Ni), 6.8%–11.1% (Cu), 3.2%–32.2% (Pb) and 0% (Cd). Based on the average Ir values, the stability of the metals in the sludge increased in this order: Zn (0.23)=Pb (0.23)<Cd (0.45)=Cu (0.45)<Ni (0.69). Despite the high mobility of some metals, each sewage sludge had low environmental risk, as indicated by the ERI (ERI ≪ 150). The HMs were more similar in terms of their mobility (two clusters) than in terms of their ecological risk (three clusters).

Optimizing municipal biodegradable waste management system to increase biogas output and nutrient recovery: a case study in Lithuania

Despite large investments to modern centralised mixed municipal waste (MMW) management plants (mechanical biological treatment (MBT)), environmental impact has been decreased less than was expected due to several determined reasons in Lithuania. Energy consumption for MMW management exceeds production volume of alternative energy in municipal biodegradable waste (BDW) fermentation equipment. Produced “technical compost” does not correspond to the requirements for contamination and quality of compost to be used in agriculture and can be used only as a stabilate for overlay of landfill layer and landfill restoration. This article presents the results of optimization possibilities of municipal BDW management in one of the Lithuanian regions. A few alternatives were suggested, but the source separation of municipal BDW from individual household was selected for implementation as the best available alternative for the target region from a technical, environmental, and economic point of view. The results of the carried out experiment with the source separation of municipal BDW and processing in the tunnel of the existing MBT plant have shown that biogas output can increase up to 114 m3 per tonne of the municipal BDW. This approach would allow increasing alternative energy production in MBT plant by 4.9 times and producing compost instead of the stabilate. In case of the target region, overall alternative energy production would exceed energy demand (including for BDW transportation), by over 7 thousand GJ per year. Thus GHGs (without biogenic CO2) would decrease by approximately 600 tonnes per year.

Management of municipal solid waste in Croatia: Analysis of current practices with performance benchmarking against other European Union member states.

The European Commission has adopted a very ambitious circular economy package and has consequently revised many legislative proposals on waste. The new targets include achieving a recycling rate of 65% by 2030 and imposing a cap on landfilled waste to no more than 10% (as a percentage of weight). Using available European and national databases on municipal solid waste indicators, we have analysed municipal solid waste production trends for Croatia and have benchmarked the indicators against other EU member states and EU averages. Our analysis points out that the production of municipal solid waste has steadily risen over the last two decades. Although Croatia produces a relatively low amount of municipal solid waste compared with other EU countries and EU averages, gross domestic product adjusted waste production reveals that for every euro of gross domestic product Croatia produces substantial amounts of municipal solid waste. As a matter of fact, among all the EU member states, only Bulgaria had a worse performance than Croatia. Regarding recycling rates, Croatia recycles 15% of its municipal solid waste and incinerates approximately 3% (by weight). The rest (82% by weight) is currently being landfilled. Regarding the treatment of waste, Croatia has implemented mechanical-biological treatment technology, but our analysis reveals that the initial number of mechanical-biological treatment plants will likely have to be scaled down taking into consideration the new EU waste management targets.

Implementation of waste-to-energy options in landfill-dominated countries: Economic evaluation and GHG impact

The economic and environmental impact of several waste-to-energy (WtE) schemes to produce electricity from municipal solid waste (MSW) refuse is evaluated and compared with landfill disposal. Both incineration and gasification alternatives are considered. The gasification option includes three different configurations: (1) a fluidized bed gasifier (FBG) with internal combustion engine (ICE), (2) a FBG with organic Rankine cycle (ORC) and (3) a grate gasifier with steam Rankine cycle (SRC). The study is primarily applied to regions where the management system is based on Mechanical Biological Treatment (MBT) plants, generating a large share of refuse (>70%), which is currently landfilled. The specific case of Andalusia, a region in the south of Spain with 23 MBT plants distributed over a region of 87.000 km2, where about 80% of municipal solid waste (MSW) is currently landfilled, is taken as main reference; thereafter, the study is further extended to preliminary assess other regions of some European landfill-dominated countries with similar characteristics. The results show that both incineration and gasification improve landfill disposal, contributing favorably to greenhouse gas (GHG) reduction and fulfilling EU environmental regulations, although the three gasification options analyzed yield lower GHG emissions than incineration. In addition, gasification enables better integration of WtE into existing MBT plants, especially in the particular case of Andalusia, where MBT plants are widespread on the region, making it a more promising option than incineration, which is mainly based on large centralized plants, and less socially accepted. From the options analyzed, the WtE scheme based on FBG with ICE gives the highest profitability for a given gate fee, due to much higher electrical efficiency. However, FBG with ORC seems to be a better option in the short-term for landfill-dominated countries, due to its higher technical reliability and the low gate fee currently available in these countries.

Evaluation of the effects of bio stabilised waste on soil in terms of heavy metal accumulation and leaching

This work evaluated and compared potential impacts related to the accumulation and/or release of heavy metals resulting from the application of different types of stabilized waste to soil. Namely, the following three types of flows were considered: waste produced by aerobic bio-stabilization of municipal solid waste at a Mechanical Biological Treatment (MBT) plant, and compost produced either from aerobic composting or from a combination of anaerobic and aerobic biodegradation processes. After a preliminary characterization of the materials (organic matter content, volatile solid, and heavy metals content), heavy metal accumulation in soil caused by possible long-term application of these organic materials was evaluated by implementing a discretized mass balance based on the total content of the heavy metals in each type of solid matrix investigated. In addition, results of percolation leaching tests performed on each type of material were presented and discussed. Results highlight that although the total content of heavy metals of the three types of materials differed considerably, with the MBT waste presenting the highest concentrations, the results of the leaching percolation tests were quite similar.