Atmospheric parameters play an important role in driving hydrogen sulphide concentrations in ambient air near waste management centres.

Emissions of odorous compounds are major contributors to public opposition when siting waste management facilities. Thus, it is essential to understand how to minimise the concentration of odour-causing chemicals in ambient air surrounding such facilities. Although the concentration of pollutants in the atmosphere is a function of meteorology, there is limited data on the atmospheric parameters that drive ambient air concentrations of odour-causing substances in settlements near waste management facilities. Here, we analysed how temperature, wind direction, wind speed, atmospheric pressure and humidity impact the concentrations of hydrogen sulphide (H2S) in the ambient air, a potentially toxic chemical and a chief contributor to noxious odours. The relative contribution of each variable was assessed using multivariate statistical analysis applied to an extensive data set of over 7,000 data points collected during 2021. Our results show that all tested atmospheric parameters significantly affected H2S concentrations in ambient air. Wind direction had the greatest impact on H2S concentrations, followed by temperature, humidity, atmospheric pressure and wind speed. Specifically, the concentration of H2S was positively correlated with humidity and atmospheric pressure and had a U-shaped correlation with temperature. Atmospheric variables were able to explain 15% of variation in H2S concentrations (R2 = 15%), indicating the presence of other factors affecting H2S ambient air concentrations. Our study shows that proper consideration of atmospheric parameters, especially wind direction and temperatures, is of uttermost importance when siting waste management facilities. The conclusions are broadly applicable to odorous compounds near waste management facilities, so adverse effects to human health and the environment can be minimised.

A mini review on the main challenges of implementing mechanical biological treatment plants for municipal solid waste in the Latin America region: Learning from the experiences of developed countries.

Most of the municipal solid waste (MSW) generated in the Latin America (LATAM) region is currently disposed of in landfills and dumpsites, which results in many negative environmental impacts. Mechanical biological treatment (MBT) is a strategy that combines the mechanical separation of recoverable materials with the biological stabilization of organic matter. MBT plants have proven to be a good alternative for the management of MSW and have been successfully implemented in developed countries for more than 30 years. However, the efficient introduction of these facilities in developing countries, such as those in the LATAM region, requires further feasibility studies. Therefore, this mini review seeks to offer significant insights into the main challenges that must be overcome to facilitate the implementation and operation of MBT plants, considering the unique technological, sociocultural, economic and political context of the LATAM region, through a comparison of the reported experiences of MBT plants in more developed countries with those in the LATAM region. The analysis herein indicates that key actions for the successful operation of MBT plants in the LATAM region include both the implementation of source separation as well as selective collection practices. Moreover, this work shows that other factors, like the establishment of valorization markets with safe working conditions for informal collectors, the development of intermunicipal cooperation schemes and the enforcement of strong regulatory frameworks for waste disposal specifications, are important contextual factors that have allowed the efficient operation of MBT plants in developed countries. Although the implementation of many of these practices will be challenging, such measures are necessary to increase the sustainability of MSW treatment practices in the LATAM region.

Improvement of energy recovery potential of wet-refuse-derived fuel through bio-drying process.

This paper proposes novel wet-refuse-derived fuel (Wet-RDF) bio-drying process with the variation of initial organic substrate and moisture content. The bio-drying was carried out using 0.3 m3 lysimeter aerated continuously at different rates. Two conditions of Wet-RDF feedstock tested included: Experiment A ‒ 37% organic substrate and 58% moisture content with an initial heating value of 2,889 kcal/kg; and Experiment B ‒ 28% organic substrate and 35% moisture content with an initial heating value of 4,174 kcal/kg. The bio-drying was performed in both experiments under negative ventilation mode and non-ventilation mode, the ventilation mode was set at the aeration rates of 0.2 m3/kg/day and 0.4 m3/kg/day. The results suggest that the optimum aeration rate was 0.4 m3/kg/day, achieving a 30% moisture reduction and a 60% heating value increase from their initial values. As a result, the improved wet-RDF qualified for the local cement industry's standard in terms of heating value.

Mechanical-biological treatment of municipal solid waste: Case study of 100 TPD Goa plant, India.

A long-term feasibility analysis of a 100 ton per day mechanical biological treatment (MBT) plant for municipal solid waste (MSW) valorization and material and energy recovery was carried out. It involves the material recovery and segregation stage (MRSS), organic extraction (pulping), thermophilic anaerobic digestion (AD), composting, effluent treatment plant (ETP), and biogas genset stages producing: 11.90% recyclables, 33% refused derived fuel (RDF), 5% compost of total waste received, 70 m3/day recyclable water and 0.435 MWh/day electricity. The biogas and methane yield were 0.535 and 0.350 m3/kg VSadded (avg.), respectively, with 40% VS removal (avg total solids (TS) 10%). Less than 3% (inert) of total waste received was subjected to landfill disposal. The MBT plant's revenue generation is 995 US$ per day/148 tons ($ 6.72/ton) waste processed. The gross OPEX is 24 US$/ton making the net OPEX of 17 US$/ton (minus revenue), which could be considered as the excellent OPEX for MSW based MBT plants as per global benchmarks. Further, local usage of RDF can significantly reduce the OPEX to 14 US$/ton, as almost 16% of the OPEX goes towards RDF disposal to cement companies located at a distance of 200-500 km from the MBT plant site. As per LCA study, the total GHG emissions have been calculated to be -25.68 tons CO2 eq./100 tons MSW. The negative emissions result from the export of electricity, compost, and RDF as well as recycling of paper and plastic products. Our study presents a cutting-edge scenario of all-inclusive recycling, recovery, and reuse loop of MSW direly required for accomplishing a circular economy.

The organic output from mechanical-biological treatment plants as a source of microplastics: Mini-review on current knowledge, research methodology and future study perspectives.

Plastic pollution is one of the biggest environmental problems facing the world. In recent years, microplastics, polymer particles from 1 µm to 5 mm, have been getting much attention. The presence of microplastics has already been confirmed in aquatic and marine ecosystems, soil, atmosphere, biota, and others. The organic output from mechanical-biological treatment (MBT) plants was added to the list of microplastics sources only recently. However, according to preliminary estimates, it may be the second-largest source of microplastics. This article presents an overview of already published investigations on this microplastics source and explains the supposed pathway of microplastics in the MBT plants. The main waste treatment processes that can affect the amount of microplastics in the organic output have been identified as shredding, sieving and, to a lesser extent, aerobic or anaerobic processing. This mini-review also includes methods used in the scientific literature for microplastics extraction, purification, and identification in organic-rich samples, their advantages and limitations. Particular attention is paid to the methods of identifying the small microplastics, less than 1 mm, since the methods for particles 1-5 mm have been more extensively studied. Furthermore, future research needs are highlighted.

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.

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.

Characterization of selected municipal solid waste components to estimate their biodegradability.

Biological treatments of Residual Municipal Solid Waste (RMSW) allow to divert biodegradable materials from landfilling and recover valuable alternative resources. The biodegradability of the waste components needs however to be assessed in order to design the bioprocesses properly. The present study investigated complementary approaches to aerobic and anaerobic biotests for a more rapid evaluation. A representative sample of residual MSW was collected from a Mechanical Biological Treatment (MBT) plant and sorted out into 13 fractions according to the French standard procedure MODECOM™. The different fractions were analyzed for organic matter content, leaching behavior, contents in biochemical constituents (determined by Van Soest's acid detergent fiber method), Biochemical Oxygen Demand (BOD) and Bio-Methane Potential (BMP). Experimental data were statistically treated by Principal Components Analysis (PCA). Cumulative oxygen consumption from BOD tests and cumulative methane production from BMP tests were found to be positively correlated in all waste fractions. No correlation was observed between the results from BOD or BMP bioassays and the contents in cellulose-like, hemicelluloses-like or labile organic compounds. No correlation was observed either with the results from leaching tests (Soluble COD). The contents in lignin-like compounds, evaluated as the non-extracted RES fraction in Van Soest's method, was found however to impact negatively the biodegradability assessed by BOD or BMP tests. Since cellulose, hemicelluloses and lignin are the polymers responsible for the structuration of lignocellulosic complexes, it was concluded that the structural organization of the organic matter in the different waste fractions was more determinant on biodegradability than the respective contents in individual biopolymers.

Sampling, characterisation and processing of solid recovered fuel production from municipal solid waste: An Italian plant case study.

This article presents the classification of solid recovered fuel from the Massafra municipal solid waste treatment plant in Southern Italy in compliancy with the EN 15359 standard. In order to ensure the reproducibility of this study, the characterisation methods of waste input and output flow, the mechanical biological treatment line scheme and its main parameters for each stage of the processing chain are presented in details, together with the research results in terms of mass balance and derived fuel properties. Under this study, only 31% of refused municipal solid waste input stream from mechanical biological line was recovered as solid recovered fuel with a net heating value (NC=HV) average of 15.77 MJ kg-1; chlorine content average of 0.06% on a dry basis; median of mercury <0.0064 mg MJ-1 and 80th percentile <0.0068 mg MJ-1. The solid recovered fuel produced meets the European Union standard requirements and can be classified with the class code: Net heating value (3); chlorine (1); mercury (1).

Application of stability indicators for the assessment of the degradation of residual household waste before landfilling.

In France, domestic waste production is estimated at c 350 kg year-1 per person and landfilling still represents a predominant way of municipal solid waste management, with 39% of waste dumped in 2007. Waste characterization campaigns were conducted at different stages of a mechanical-biological treatment process in order to evaluate its efficiency. Waste samples were sorted by size (>100 mm, <100-20 mm and <20 mm) in order to assess the opportunity for mechanical and aerobic degradation and to reduce the volume of waste landfilled. The monitoring of parameter characteristics of waste stabilization highlighted a decrease in both organic matter and oxidizable organic matter, and an increase in fine particles <20 mm. The respirometric index after 4 days performed on waste samples from the pre-treatment stage showed a decrease in the biological activity compared with the samples taken upstream in the process. The biochemical methane potential of the waste is above the German limit of acceptance in landfills. This intermediate phase of stabilization is confirmed by the results of the leaching tests and hydrophobic fractionation.

Formaldehyde: a chemical of concern in the vicinity of MBT plants of municipal solid waste.

The mechanical-biological treatment (MBT) of municipal solid waste (MSW) has a number of advantages in comparison to other MSW management possibilities. However, adverse health effects related to this practice are not well known yet, as a varied typology of microbiological and chemical agents may be generated and released. In 2010, we initiated an environmental monitoring program to control air levels of volatile organic compounds (VOCs) and microbiological pollutants near an MBT plant in Montcada i Reixac (Catalonia, Spain). In order to assess any temporal and seasonal trends, four 6-monthly campaigns were performed. Important fluctuations were observed in the levels of different biological indicators (total and Gram-negative bacteria, fungi grown at 25 °C and 37 °C, and more specifically, Aspergillus fumigatus). Although overall bioaerosols concentrations were rather low, a certain increase in the mean values of bacteria and fungi was observed in summer. In contrast, higher concentrations of VOCs were found in winter, with the only exception of formaldehyde. Interestingly, although this compound was not detected in one of the sampling campaigns, current airborne levels of formaldehyde were higher than those previously reported in urban areas across Europe. Furthermore, the non-carcinogenic risks (Hazard Quotient), particularly in winter, as well as the cancer risks associated with the inhalation of VOCs, exceeded the threshold values (1 and 10(-5), respectively), reaffirming the need of continuing with the monitoring program, with special emphasis on formaldehyde, a carcinogenic/mutagenic substance.

Removal of nitrogen from MBT residues by leachate recirculation in combination with intermittent aeration.

Mechanical-biological treatment (MBT) techniques have been used to reduce the emission potential of waste before placement in landfills for a couple of years, especially in Europe. The main focus of MBT is on the reduction of native organic substances and not on nitrogen compounds. As a result, the concentrations of organic substances in leachate from MBT landfills are considerably reduced in comparison to leachates from municipal solid waste landfills, while the ammonia nitrogen concentrations remain at a high level. From the stabilization of old landfills it is well known that recirculation of leachate and supplementary aeration can reduce emissions to an acceptable level in a comparatively short time. In a series of laboratory-scale tests the efficiency of this technique for MBT residues was investigated under different boundary conditions. While the effect of leachate recirculation is also well known for MBT residues, the additional aeration has so far not been investigated. The results show that this technique has only a limited influence on the reduction of organic carbon compounds. In view of nitrogen compounds, only the additional aeration during recirculation shows a strong effect on the quality of leachate, in which the concentrations of ammonium and total nitrogen are reduced by more than 90%. The results indicate that by using simple techniques the long-term emission behavior of MBT residues can be quickly reduced to an acceptable level.

Critical analysis of the integration of residual municipal solid waste incineration and selective collection in two Italian tourist areas.

Municipal solid waste management is not only a contemporary problem, but also an issue at world level. In detail, the tourist areas are more difficult to be managed. The dynamics of municipal solid waste production in tourist areas is affected by the addition of a significant amount of population equivalent during a few months. Consequences are seen in terms of the amount of municipal solid waste to be managed, but also on the quality of selective collection. In this article two case studies are analyzed in order to point out some strategies useful for a correct management of this problem, also taking into account the interactions with the sector of waste-to-energy. The case studies concern a tourist area in the north of Italy and another area in the south. Peak production is clearly visible during the year. Selective collection variations demonstrate that the tourists' behavior is not adequate to get the same results as with the resident population.

Anaerobic co-digestion of paper sludge: Feasibility of additional methane generation in mechanical-biological treatment plants.

In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical-biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH4 kg-1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates.

Estimation of long-term methane emissions from Mechanical-Biological Treatment waste through biomethane potential test.

Mechanical-Biological Treatment (MBT) is a technology applied to reduce the environmental impacts of urban waste based on stabilizing the organic matter content. As the process is not entirely efficient, the residue can generate methane when it is landfilled. Long-term methane emissions estimation based on models is usually over or underestimated because the actual waste composition after stabilization is generally unknown. This work proposes a single tool to improve the emission estimations of the landfilled MBT waste based on the determination of the biomethane potential test (BMP). Experimental BMP of the crude and stabilized organic fractions of municipal solid waste obtained from an MBT plant were carried out, and the results were used to predict the methane emission from two models, LandGEM (2005) and IPCC (2006). In the LandGEM model, the experimental value of BMP represents the methane potential L0 while in the IPCC model it allowed to obtain the ultimate organic carbon anaerobically degraded (DOCf), based on a linear correlation (R2 = 0.944, p-value < .05) that can be used to obtain the DOCf in a waste of any composition. The results of the long-term (40 years) methane emissions of the stabilized waste disposed on land showed overestimations of up 56.0% (IPCC model) and 259.5% (Landgem model) when default data, instead the actual DOCf were applied in stabilized waste; similar behaviour was observed for the crude waste (23.3% and 241.3% overestimations). Moreover, the impact of the stabilization process revealed methane emission reductions of 5.1% and 20.9% based on LandGEM and IPCC models, respectively.

Total organic carbon as a proxy for metal release from biostabilized wastes.

In this study, we introduce a simple screening method to predict the metal release from biostabilized wastes as a function of the total organic carbon (TOC) content of the sample. The method relies on a model that simulates the release of dissolved organic carbon (DOC) as a function of the applied liquid to solid (L/S) ratio. The metal release is then estimated using generic empirical DOC to metal correlation coefficients (KDOC,Me) extrapolated from the literature. Specifically, the results of leaching tests carried out on different types of biowastes and biostabilized wastes were used to calculate the upper and lower KDOC,Me values that can be expected for common metals of concern (Al, Ba, Cr, Cu, Mo, Ni, Pb, V, and Zn). The statistical analysis of the estimated empirical coefficients highlighted that for most of the investigated metals, the adoption of generic DOC to metal correlation coefficients introduces relatively low uncertainties. The quartiles ratio (QR calculated as the ratio of third and first quartile) of the KDOC,Me coefficients extrapolated from the literature was indeed below 3 for Cu, Ni, and Zn and below 5 for Al, Ba, Cr, Pb, and V. Only for Mo, the QR was around 10 indicating that for this element, DOC can be a poor indicator of the release expected as a function of the applied L/S. Furthermore, by performing a sensitivity analysis, we found that the experimental conditions only slightly influence the metals release predicted by the model. Based on this evidence, simple nomograms that estimate the cumulative metal release in percolation column tests as a function of the applied L/S are provided. Furthermore, a simple equation that predicts the cumulative metal release expected at L/S of 10 L/kg is presented. The application of the latter to the results of percolation column tests carried out on 8 mechanical biological treatment (MBT) waste samples highlighted that the predicted metals release was close to the measured values with deviations within a factor of 5 for all the investigated metals.

Impact of digestate addition on the biostabilization of undersized fraction from municipal solid waste.

Biostabilization is a commonly applied method in mechanical-biological treatment (MBT) plants to process municipal solid waste. In many ways, e.g. by applying additives to waste, MBT plant operators strive to enhance the effectiveness of biostabilization, which leads to reducing the time and energy outlays necessary for the process, as well as to minimizing the amount of final stabilized waste directed to landfills. This paper deals with the impact of digestate waste from agricultural biogas plants used as additive to the biostabilization process of undersized fraction from municipal solid waste (UFMSW) on the intensive phase of the process and properties of stabilized waste. The aim of this study was to assess whether, and if so to what extent, the application of digestate waste affects the process. Five different input compositions were tested (without digestate and with the addition of digestate at: 2.5; 5; 7.5 and 10 wt%). Waste treatment time was 2 weeks. Changes in moisture content, organic matter (OM), respiration activity (AT4), bulk density, air-filled porosity, heavy metal content, pH, carbon to nitrogen ratio, as well as composition of process gases emitted were evaluated. Additionally, microorganisms (including pathogens) inhabiting the processed waste in the aspect of waste sanitation were analyzed. It was found that the addition of digestate at 2.5, 5 and 7.5 wt% extended the duration of the thermophilic phase and decreased the CO2 content in process gases. The addition of digestate at 2.5 wt% and 5 wt%, decreased also OM by approx. 25% of the initial value and AT4 by approx. 30%. It was also proved that the addition of digestate favors the limited sanitation of UFMSW. As a result of the research, it was found that the addition of digestate at 2.5 wt% and 5 wt% is sufficient to accelerate the aerobic biological degradation of UFMSW.

Life Cycle Assessment of Advanced Circulating Fluidized Bed Municipal Solid Waste Incineration System from an Environmental and Exergetic Perspective.

The production of clean and efficient energy from municipal solid waste (MSW) is extremely urgent matter due to an increasing energy demand and environmental concerns. In this study, a high steam parameter (520 °C, 7.9 MPa) circulating fluidized bed (CFB) MSW incineration system, equipped with a mechanical, biological treatment and external heat exchanger systems, was introduced and a comparative study with a typical mechanical grate (450 °C, 5.3 MPa) incineration system and conventional CFB (485 °C, 5.3 MPa) incineration system was carried out from a life-cycle, environmental and exergetic perspective which could assess different energy and material outputs based on real operating data. Moreover, the potential system optimization of this advanced CFB system was proposed. The results showed that the advanced CFB system was more environmentally friendly and resource-efficient than conventional MSW incineration systems. The recovery of material should be given priority over energy recovery. According to the assessment of the environment, and energy and material recovery, a process improvement with an incinerated refuse-derived fuel and a semi-compost produced by MBT as a soil conditioner was highly recommended.

Life Cycle Assessment of electricity production from refuse derived fuel: A case study in Italy.

Biomasses and bio-waste have an important role in decarbonizing the European energy mix, the latter contributing to the transition towards a circular economy. In particular, Refuse Derived Fuel (RFD) - a biofuel obtained from dry residue of waste - appears a really interesting energy option. In this framework this study aims at assessing the environmental profile of electricity generation from RDF in Italy, comparing two different kinds of RDF production and combustion plants. The functional unit is 1 kWh of net electricity from RDF delivered to the grid. Two Italian plants are examined: one located in Ravenna (RDF is produced in a direct flow treatment plant) and the other one in Bergamo (RDF is produced in a unique flow treatment plant and electricity is generated in a cogenerator). Results show that, comparing the plants, it is not possible to identify an option for RDF production or electricity generation characterized by lowest impacts for all the examined impact categories. However, cogeneration process and the avoided burdens due to the valorisation of ferrous metals and dry fractions during RDF production can reduce most of the environmental impacts. A dominance analysis reveals that chimney direct emissions generated during RDF combustion significantly contribute to some impact categories, as well as electricity consumption during RDF production. Furthermore, disposal of incineration wastes is a relevant contributor to human toxicity and freshwater eutrophication. The eco-profile of electricity from RDF is compared with electricity from the Italian grid and from multi-Si PV. The comparison highlights that electricity from RDF performs worse for relevant environmental impact categories such as climate change, human toxicity and photochemical oxidant formation. On the other hand, electricity from RDF performs better than electricity from the grid and from photovoltaic for resource depletion, an impact category of growing importance in the framework of circular economy.

Volatile fatty acids production from biowaste at mechanical-biological treatment plants: Focusing on fermentation temperature.

The impact of temperature (20, 35, 45, 55, 70 °C) on volatile fatty acid (VFA) production from biowaste collected at a mechanical-biological treatment plant was analysed. Additionally, relevant streams of the treatment plant were characterised to assess seasonality effects and conceive the integration of a fermentation unit. Batch fermentation tests at 35 °C showed the highest VFA yields (0.49-0.59 gCODVFA/gVS). The VFA yield at 35 °C was 2%, 6%, 10% and 14% higher than at 55, 45, 20 and 70 °C, respectively. The VFA profile was not affected by the fermentation temperature nor seasonality and was dominated by acetic, propionic and butyric acid (75-86% CODVFA). The concentration of non-VFA soluble COD and ammoniacal nitrogen in the fermentation liquor increased with temperature. The fermentation unit in the treatment plant was conceived after the pulper and hydrocyclones and before the anaerobic digester, while the fermenter temperature depends on the VFA application.