A 35-year monitoring of an Italian landfill: Effect of recirculation of reverse osmosis concentrate on leachate characteristics

"Fossetto" landfill (Monsummano Terme - Tuscany, Italy) started operation in 1988 as a controlled landfill accepting mixed municipal solid waste collected without any attempt of recycling. Then, progressively, following the evolution of the state-of-the-art, it adopted biogas extraction and valorisation systems and mechanical-biological treatment for incoming waste (both since 2003). Finally, since 2006, in the plant is performed on-site reverse osmosis leachate treatment with the concentrated leachate being recirculated back into the landfill body. Recently a new landfill cell, separate from the others, was put in operation adding a capacity of 200,000 m3 to the already available 1,095,000 m3. This plant can provide long term leachate composition data to study the evolution and impact of changing landfill technology and waste composition on various parameters. The rise in leachate production (+84 % in 2018-2022 respect to the period before recirculation) cannot be totally attributable to recirculation but could be also linked to the increase in the amount of landfilled waste. The concentration of certain parameters (NH4+, Cl- and to a less extent of COD) increased (+60 %, +58 %, +17 % respectively in the last five years with respect to the period before recirculation); however, this increase did not influence the performance of the treatment plant. Nevertheless, the overall leachate management would benefit from an optimized reinjection system.

Anaerobic co-digestion of coffee waste with other organic substrates: A mixture experimental design

The viability of the anaerobic co-digestion of coffee waste (CFW) with other organic waste (cow manure-CM, food waste-FW, anaerobic sludge-AS) was investigated through measurements of biogas generation of various mixtures of the above substrates. The experiments were designed following the principles of mixture experimental design. Four different mixtures were tested anaerobically at 37 °C in 500 mL and 1 L anaerobic vessels. AS was used in some mixtures as an inoculum. The results were fitted to two empirical models in which biogas generation was the dependent variable and the fractions of the components in the mixture were the independent variables. According to the empirical models, the co-digestion of CFW with AS appeared to have a positive (synergistic) effect, generating 201 mL g^-1 VS_mixture, which was 12% higher than the amount generated from the mono-digestion of AS (179 mL g^-1 VS). On the other hand, the co-digestion of CFW with CM and of CFW with FW had a negative (antagonistic) effect on biogas generation indicating that CFW inhibits biogas generation when mixed with CM and FW. Although the mono-digestion of CM resulted in an average of 149 mL g^-1 VS of biogas, when CM was combined with CFW in a mixture, biogas generation was highly reduced by 43.8%-85.1%, depending on the CFW content of the mixtures, which was 25% and 50%, respectively. When co-digesting CFW with FW, the biogas generated was 7.02 mL g^-1 VS that was obtained only from the FW in the mixture.

A modeling methodology to predict the generation of wasted plastic pesticide containers: An application to Greece

Plant protection products (pesticides) are used throughout the world in the form of various types, such as insecticides, fungicides, herbicides etc. High Density Polyethylene is the principal material that those containers are made of. The aim of the study was to determine the factors that statistically affect the generation of the resulting wasted plastic pesticide containers after pesticide application. The objective was to develop a mathematical model to describe the generation rate of wasted plastic pesticide containers as a function of certain parameters. 603 data series were recorded based on information from 106 farmers in Greece and nineteen (19) parameters were initially included as potential predictors. Each farmer filled up questionnaires and provided data for more than one type of crops. Data were obtained from six Greek prefectures. Empirical models were developed for all pesticides through linear regression. The cultivated area (m²), the type of crop (perennial/annual, irrigated/dry) and the type of pesticide application (on soil, on foliage) were the statistically significant parameters to affect generation rates. Eighteen (18) farmers provided 56 (new) observations to validate the models. Two of the four models are reliable due to their low validation errors and should be ideally used for crop areas above 58,000 m². The total wasted plastic pesticide containers generation rate in Greece was estimated to be 0.028 kg farmer^-1 y^-1 1000 m^-2. Modeling results can aid to predict the generation rate of wasted pesticide plastic containers at a regional and national level so that to properly design their management systems.

Characterisation and composition identification of waste-derived fuels obtained from municipal solid waste using thermogravimetry: A review

Thermogravimetric analysis (TGA) is the most widespread thermal analytical technique applied to waste materials. By way of critical review, we establish a theoretical framework for the use of TGA under non-isothermal conditions for compositional analysis of waste-derived fuels from municipal solid waste (MSW) (solid recovered fuel (SRF), or refuse-derived fuel (RDF)). Thermal behaviour of SRF/RDF is described as a complex mixture of several components at multiple levels (including an assembly of prevalent waste items, materials, and chemical compounds); and, operating conditions applied to TGA experiments of SRF/RDF are summarised. SRF/RDF mainly contains cellulose, hemicellulose, lignin, polyethylene, polypropylene, and polyethylene terephthalate. Polyvinyl chloride is also used in simulated samples, for its high chlorine content. We discuss the main limitations for TGA-based compositional analysis of SRF/RDF, due to inherently heterogeneous composition of MSW at multiple levels, overlapping degradation areas, and potential interaction effects among waste components and cross-contamination. Optimal generic TGA settings are highlighted (inert atmosphere and low heating rate (⩽10°C), sufficient temperature range for material degradation (⩾750°C), and representative amount of test portion). There is high potential to develop TGA-based composition identification and wider quality assurance and control methods using advanced thermo-analytical techniques (e.g. TGA with evolved gas analysis), coupled with statistical data analytics.

Establishing a sub-sampling plan for waste-derived solid recovered fuels (SRF): Effects of shredding on representative sample preparation based on theory of sampling (ToS)

The uncertainty arising from laboratory sampling (sub-sampling) can compromise the accuracy of analytical results in highly inherent heterogeneous materials, such as solid waste. Here, we aim at advancing our fundamental understanding on the possibility for relatively unbiased, yet affordable and practicable sub-sampling, benefiting from state of the art equipment, theoretical calculations by the theory of sampling (ToS) and implementation of best sub-sampling practices. Solid recovered fuel (SRF) was selected as a case of a solid waste sample with intermediate heterogeneity and chlorine (Cl) as an analyte with intermediate variability amongst waste properties. ToS nomographs were constructed for different sample preparation scenarios presenting the trend of uncertainty during sub-sampling. Nomographs showed that primary shredding (final d₉₀ ≤ 0.4 cm) can reduce the uncertainty 11 times compared to an unshredded final sub-sample (d ≈ 3 cm), whereas cryogenic shredding in the final sub-sample can decrease the uncertainty more than three times compared to primary shredding (final d₉₀ ≤ 0.015 cm). Practices that can introduce bias during sub-sampling, such as mass loss, moisture loss and insufficient Cl recovery were negligible. Experimental results indicated a substantial possibility to obtain a representative final sub-sample (uncertainty ≤ 15%) with the established sub-sampling plan (57-93%, with 95% confidence), although this possibility can be considerably improved by drawing two final sub-samples instead (91-98%, with 95% confidence). The applicability of ToS formula in waste-derived materials has to be investigated: theoretical ToS calculations assume a poorer performance of the sub-sampling plan than evidenced by the experimental results.

Preliminary evaluation of the anaerobic biodegradability of three biobased materials used for the production of disposable plastics

Biodegradable plastics have been introduced to the market to substitute "traditional", non-biodegradable, petro-based plastics to alleviate plastic pollution. Biochemical methane potential tests were carried out on compostable bags made of MaterBi®, biodegradable bottle wine corks and cellulosic plates to examine the anaerobic biodegradability of those materials. The impact of four factors: type of pretreatment (predigestion, mechanical, alkaline, predigestion and alkaline), digestion duration, type of inoculum and temperature were statistically evaluated through regression modeling. Anaerobic tests on compostable and polyethylene bags (control) were carried out in mesophilic (35 °C) and thermophilic (55 °C) conditions, while tests on bottle wine corks and cellulosic plates were carried out in mesophilic conditions only. After 15 days of digestion, a dry mass reduction of 22.8 ± 6.2 % and 27.6 ± 14.0 % for mesophilic and thermophilic tests respectively was recorded for MaterBi®. Chemical pretreatment with NaOH led to a mass reduction of 78.2 ± 7.2 % and was the only statistically significant factor to affect both methane yields and dry mass loss. A higher digestion temperature led to an increased mass loss without a concurrent increase in methane production. The cellulosic plates were completely degraded (99.9 ± 0.03 % mass reduction), while the wine bottle corks weight did not change.

Statistical quantification of sub-sampling representativeness and uncertainty for waste-derived solid recovered fuel (SRF): Comparison with theory of sampling (ToS)

The level of uncertainty during quantification of hazardous elements/properties of waste-derived products is affected by sub-sampling. Understanding sources of variability in sub-sampling can lead to more accurate risk quantification and effective compliance statistics. Here, we investigate a sub-sampling scheme for the characterisation of solid recovered fuel (SRF) - an example of an inherently heterogeneous mixture containing hazardous properties. We used statistically designed experiments (DoE) (nested balanced ANOVA) to quantify uncertainty arising from material properties, sub-sampling plan and analysis. This was compared with the theoretically estimated uncertainty via theory of sampling (ToS). The sub-sampling scheme derives representative analytical results for relatively uniformly dispersed properties (moisture, ash, and calorific content: RSD ≤ 6.1 %). Much higher uncertainty was recorded for the less uniformly dispersed chlorine (Cl) (RSD: 18.2 %), but not considerably affecting SRF classification. The ToS formula overestimates the uncertainty from sub-sampling stages without shredding, possibly due to considering uncertainty being proportional to the cube of particle size (FE ∝ d³), which may not always apply e.g. for flat waste fragments. The relative contribution of sub-sampling stages to the overall uncertainty differs by property, contrary to what ToS stipulates. Therefore, the ToS approach needs adaptation for quantitative application in sub-sampling of waste-derived materials.

A new liquid-phase method and its comparison to two solid-phase microbial respiration activity methods to assess organic waste stability

Goal of the work was to compare the respiration activities, as measured via oxygen consumption with three different organic waste stability methods so that to propose the optimal one. The novelty of the work is that there exists no comparison of solid-phase with liquid-phase stability assessment techniques in the literature. The respiration activities were assessed using two solid-phase methods and a manometric liquid-phase method (MANLIQ) performed on twenty-seven organic substrates. The methods rely on measuring oxygen consumption (uptake) via pressure drops (liquid-phase test, static solid-phase test) or via direct O₂ measurements on the gaseous phases at the inlet and outlet of the respirometer (solid-phase dynamic test). A positive statistically significant correlation was calculated between the MANLIQ and the static solid-phase indices. The maximum rate MANLIQ index for the raw substrates was 2900 mg O₂ kg^-1 VS h^-1, while most of the processed substrates had cumulative MANLIQ indices below 160 g O₂ kg^-1 VS. The ratio of the liquid indices to the static solid-phase indices ranged from 1.6 to 2.7 and the ratio of the liquid indices to the dynamic solid-phase indices ranged from 0.2 to 0.4. The MANLIQ method failed to result in a good correlation of the processing time with the respiration indices. On the other hand, a correlation was more visible in the two solid-phase tests, despite the large variability of the types and sources of the substrates. Therefore, the solid-phase methods should be preferred over the liquid-phase method to assess stability for various organic substrates.

A standardized inspection methodology to evaluate municipal solid waste collection performance

The success of separate collection of municipal solid waste, the efficiency of the other connected services and the justification of a large cost assumed by an authority, depends on the level of service provided to customers as well as the citizens' attitude towards waste management. In this paper, a semi-qualitative inspection method to evaluate both the door-to-door collection system and the conventional curbside system is proposed. The method is based on the combined evaluation of waste collection using a set of indicators and the assessment of the perception of the citizens towards collection and street cleaning services using behavioural questionnaires. The ultimate goal was to assess potential differences between door-to-door and curbside collection systems. The standardized inspection evaluation method was applied to the city of Reggio, Calabria (Italy), since both collection systems are used there. The standardized inspection evaluation proved to be simple to implement and was effective to accurately evaluate the quality of the service delivered to the citizens. The results of the behavioural survey revealed that citizens that practised door-to-door separation had a higher recycling conscience and were more satisfied with the city waste management system than the ones that practised curbside separation. According to the results of the study, there was a qualitative agreement between the results of the standardized inspection evaluation and the behavioural survey. The door to door collection system is suggested to replace the curbside collection system.

Influence of four socioeconomic indices and the impact of economic crisis on solid waste generation in Europe

The standard of living and certain socioeconomic and development indices can influence solid waste generation. This potential association can aid to focus on, and to establish, appropriate policies to reduce waste generation, with waste prevention being the cornerstone of those policies so that to eventually decouple waste generation from economic growth. Although, several studies have been performed at a regional or municipal level to study the impact of socioeconomic factors on waste generation, this impact on a European scale using data of several individual special solid waste streams from the years of the economic crisis has not been studied. The goal of the work was to investigate the impact of the Gross Domestic Product (GDP), the Human Development Index (HDI), the Unemployment Rate (UR), and the CO₂ emissions on the generation rates of thirteen solid waste streams using data from ten European countries. Annual data ranged from years 2008/2009 to 2015. Regression modeling between the waste generation rates and each of the four indices was developed and significant correlations were calculated. Results revealed that nine solid waste streams were positively correlated to the GDP, with waste electronic and electric equipment (WEEE) having the strongest positive correlation. With the aid of a novel graphical methodology, the countries were grouped into "normally behaving", "affected", "preventive" and "wasteful". Greece and Portugal were the countries that belonged to the "affected" countries for most waste streams, whilst Germany and the United Kingdom belonged most frequently to the preventive countries.

Environmental and economic assessment of the use of biodrying before thermal treatment of municipal solid waste

Mass-burn incineration is a thermal treatment process for municipal solid waste (MSW) that is commonly applied worldwide. MSW can be sometimes pretreated prior to incineration to increase its calorific value. Biodrying is lately widely applied to MSW as a pretreatment process prior to incineration to produce a RDF of higher calorific value compared to raw commingled MSW. However, no information exists on the assessment of the overall environmental emissions and energy consumption of the combined biodrying-incineration process. Therefore, the goal of this work was to estimate the overall viability of biodrying prior to incineration by accounting for the greenhouse gas emissions, net energy balance and total cost. These parameters were compared to the corresponding parameters of the direct mass-incineration of MSW without any pretreatment. The study developed four scenarios that included mass-incineration alone and incineration of biodried waste. Additional scenarios were developed to include transport of waste to a distance of 100 km. Results revealed that direct mass-incineration led to slightly lower overall greenhouse gas emissions compared to incineration of biodried MSW, primarily due to the consumption of electricity during the preceding biodrying stage (because of the required aeration) and the direct emissions of biodrying. In addition, a 5% less overall energy consumption was calculated during mass-incineration, compared to incineration of biodried RDF, while the net cost was also lower in the case of the mass-incineration compared to the RDF based incineration.

Performance of semi-continuous anaerobic co-digestion of poultry manure with fruit and vegetable waste and analysis of digestate quality: A bench scale study

Poultry manure (PM) can contain ammonium and ammonia nitrogen, which may inhibit the anaerobic process. The aim of this work was to evaluate the performance of anaerobic digestion of PM co-digested with fruit and vegetable waste. Two semi-continuous bench scale (19L) stirred tank reactors were used. The operating conditions were: 34.5 °C, 2 gVS/L.d (organic load rate), 28 d of hydraulic retention time and 100 revolutions per m (1 h × 3 times by day) for the agitation. The reactors were fed PM and a mixture of PM and fruit and vegetable waste (FVW) at equal proportions (based on wet weight). The performance of the anaerobic process was assessed through biogas and methane yields, reduction of organic matter, release of nitrogen compounds and the monitoring of stability indicators (pH, volatile fatty acids (VFA), total (TA) and partial (PA) alkalinity). Moreover, the digestate quality was evaluated to determine potential risk and benefits from its application as biofertilizer. Toxicity was assessed using Daphnia magna immobilization tests. Results showed that biogas and methane yields from PM-FVW were 31% and 32% higher than PM alone, respectively. Values of organic matter, pH, alpha (PA/TA) and VFA revealed that stability was approached in PM and PM-FVW. The co-digestion of PM with FVW led to the highest methane and biogas yields, lower FAN and TAN concentrations, and a better digestate quality compared to mono-digestion of this manure.

Door-to-door recyclables collection programmes: Willingness to participate and influential factors with a case study in the city of Xanthi (Greece)

The implementation of a recyclable waste management system is a serious challenge for a society that aims to contribute to sustainability. The first operational step of such system is waste collection. In a number of European countries, the solid waste collection system has changed from the conventional kerbside system to a door-to-door collection. However, this type of waste collection system has not yet been introduced in Greece and its public acceptance prior to potential full implementation needs to be considered. This study aims to investigate the willingness of the residents of a Greek city (Xanthi, Thrace) to change from the existing kerbside collection system and initiate and participate in a door-to-door recyclable waste collection system instead. A questionnaire was designed and distributed randomly to 150 residents of Xanthi and a statistical analysis was then performed to assess the influence of a number of explanatory variables on recycling behaviour and the willingness to participate in a door-to-door collection system. The findings of this study indicate that most of the respondents (72.7%) were willing to participate in a future door-to-door recyclables collection programme in Xanthi. The factors that influenced the respondents' attitude with regard to such a programme were associated with level of education, their beliefs about the effectiveness of the current recycling system and also their attitudes towards recycling issues in general. Age and religion significantly affected recycling frequency. The survey and statistics presented in this article can be used as a model to assess the behaviour of citizens towards recyclable waste management systems worldwide.

Generation and composition of waste from medical histopathology laboratories

The aim of this work was to record the quantities and composition of medical waste (MW) generated by public and private medical histopathology laboratories (HISTOLB) and to provide pertinent waste generation design coefficients (e.g. g/examinee) for those laboratories. This can be a useful coefficient when designing medical waste treatment facilities. The study was conducted on three public and four private HISTOLBs in the city of Thessaloniki (Greece) for a period of 5 months. One sampling week was selected randomly per month. During the study period, the examinees per week were 108 and 90 in the public and private HISTOLBs, respectively. According to the results, 57% of the total MW generated in both the public and private laboratories were toxic waste (TXW), namely the liquid formaldehyde that is used to preserve the tissue. The mixed hazardous waste (MHW) comprised 28% and 24%, respectively, of the total MW, in the public and private facilities, respectively. The infectious waste constituted around 15% of the total MW generated in both types of facilities. Urban type waste was always less than 4% by weight. The total mean MW generated in the public and private laboratories were 208 ± 543 (n = 1614) and 195 ± 512 (n = 1789) g/examinee, respectively. A large variance among the mean MW generation rates of the participating individual laboratories that belonged to the same category was observed. The dominant fraction of the infectious waste was the plastic containers that contained the tissue samples, being around 75% of the total infectious waste, followed by the latex gloves (being around 17% of the infectious waste).

A review of research trends in the enhancement of biomass-to-hydrogen conversion

Different types of biomass are being examined for their optimum hydrogen production potentials and actual hydrogen yields in different experimental set-ups and through different chemical synthetic routes. In this review, the observations emanating from research findings on the assessment of hydrogen synthesis kinetics during fermentation and gasification of different types of biomass substrates have been concisely surveyed from selected publications. This review revisits the recent progress reported in biomass-based hydrogen synthesis in the associated disciplines of microbial cell immobilization, bioreactor design and analysis, ultrasound-assisted, microwave-assisted and ionic liquid-assisted biomass pretreatments, development of new microbial strains, integrated production schemes, applications of nanocatalysis, subcritical and supercritical water processing, use of algae-based substrates and lastly inhibitor detoxification. The main observations from this review are that cell immobilization assists in optimizing the biomass fermentation performance by enhancing bead size, providing for adequate cell loading and improving mass transfer; there are novel and more potent bacterial and fungal strains which improve the fermentation process and impact on hydrogen yields positively; application of microwave irradiation and sonication and the use of ionic liquids in biomass pretreatment bring about enhanced delignification, and that supercritical water biomass processing and dosing with metal-based nanoparticles also assist in enhancing the kinetics of hydrogen synthesis. The research areas discussed in this work and their respective impacts on hydrogen synthesis from biomass are arguably standalone. Thence, further work is still required to explore the possibilities and techno-economic implications of combining these areas for developing robust and integrated biomass-to-hydrogen synthetic schemes.

Describing health care waste generation rates using regression modeling and principal component analysis

This work examined the dependence of the health care waste generation rates (HCWGR) from economic factors (gross domestic product per capita, health expenditure per capita), social and health-related factors (human development index, life expectancy at birth, mean years of schooling, deaths due to tuberculosis, under-five mortality rate, hospital beds, improved sanitation facilities, physicians, nurses and midwives, diabetes prevalence, deaths due to cancer, deaths due to asthma, deaths due to influenza and pneumonia), and one environmental sustainability factor (carbon dioxide emissions) from 41 countries using multiple linear regression modeling and principal component analysis (PCA). In addition, the Pearson correlation coefficients were calculated for all pairwise comparisons and a geographical grouping of the HCWGR was performed. The examined HCWGR included both the hazardous and the municipal fraction of health care waste (HCW). Results showed that the CO₂ emissions and the life expectancy at birth positively correlated to the HCWGR (kg/bed/d) and can be used as adequate statistical predictors. The resulting best reduced model explained 84.7% of the variability. The hospital beds and the deaths due to cancer were not correlated to any principal component due to their low loadings. Only the diabetes prevalence was correlated to the F2 principal component. The other fourteen variables were correlated to the F1, which was the most significant principal component. Thus, the HCWGR and the other thirteen variables that were grouped to the F1 component have strong autocorrelation and can be treated as one variable.

A systematic review on the composting of green waste: Feedstock quality and optimization strategies

Green waste (GW) is an important fraction of municipal solid waste (MSW). The composting of lignocellulosic GW is challenging due to its low decomposition rate. Recently, an increasing number of studies that include strategies to optimize GW composting appeared in the literature. This literature review focuses on the physicochemical quality of GW and on the effect of strategies used to improve the process and product quality. A systematic search was carried out, using keywords, and 447 papers published between 2002 and 2018 were identified. After a screening process, 41 papers addressing feedstock quality and 32 papers on optimization strategies were selected to be reviewed and analyzed in detail. The GW composition is highly variable due to the diversity of the source materials, the type of vegetation, and climatic conditions. This variability limits a strict categorization of the GW physicochemical characteristics. However, this research established that the predominant features of GW are a C/N ratio higher than 25, a deficit in important nutrients, namely nitrogen (0.5-1.5% db), phosphorous (0.1-0.2% db) and potassium (0.4-0.8% db) and a high content of recalcitrant organic compounds (e.g. lignin). The promising strategies to improve composting of GW were: i) GW particle size reduction (e.g. shredding and separation of GW fractions); ii) addition of energy amendments (e.g. non-refined sugar, phosphate rock, food waste, volatile ashes), bulking materials (e.g. biocarbon, wood chips), or microbial inoculum (e.g. fungal consortia); and iii) variations in operating parameters (aeration, temperature, and two-phase composting). These alternatives have successfully led to the reduction of process length and have managed to transform recalcitrant substances to a high-quality end-product.

Effect of the recirculation of a reverse osmosis concentrate on leachate generation: A case study in an Italian landfill

"Fossetto" landfill has been operating in the municipality of Monsummano Terme (Pistoia Province, Italy) since 1988; the authorized volume for landfilling is about 1,000,000 m³; at the moment the plant is being mainly used to dispose of mechanically and biologically treated residual municipal solid waste. Since September 2006, an in-situ reverse osmosis leachate treatment plant has been operating to treat leachate. The treated water is being discharged into a small nearby stream while the concentrated leachate is being recirculated back into the landfill body following Italian Regulations and an authorization from the local authority (Pistoia Province). This paper presents monitoring results on leachate generation rates and composition for the past fifteen years. A moderate increase of the concentration of some of the monitored parameters occurred (e.g. ammonium, chlorides) and a decrease for most heavy metals. The increase of concentrations for Cl^- and NH₄⁺ was more evident in the leachate coming from the wells closer to reinjection area. However, the change in leachate composition did not affect the quality of the effluent from the leachate treatment plant. The annual volume of the generated leachate increased significantly right after the recirculation started.

Strategies for the sustainable management of orange peel waste through anaerobic digestion

The processing of oranges is a major industry worldwide and leads to the production of large amounts of orange peel waste (OPW). Energy production through anaerobic digestion of OPW is a promising option; however, the high content of essential oil, mainly composed of d-limonene, a well-known antioxidant, can cause the inhibition of the biological activity. In this paper, different pretreatment methods were tested (e.g. ensiling, aeration, thermal and alkaline treatments) to optimize the anaerobic digestion of OPW focusing on d-limonene removal. The raw and pretreated substrates were characterized and their biochemical methane production was measured. The results demonstrated the ability of some of the treatments to reduce d-limonene content up to 80%. A relatively high biomethane potential production of OPW (up to about 500 NmL CH₄ g^-1VS) was measured. The importance of the acclimation of inoculum and the risk connected to the accumulation of inhibiting substances in the reactor is discussed.

Effect of three pretreatment techniques on the chemical composition and on the methane yields of Opuntia ficus-indica (prickly pear) biomass

Opuntia ficus-indica (OFI) is an emerging biomass that has the potential to be used as substrate in anaerobic digestion. The goal of this work was to investigate the effect of three pretreatment techniques (thermal, alkaline, acidic) on the chemical composition and the methane yield of OFI biomass. A composite experimental design with three factors and two to three levels was implemented, and regression modelling was employed using a total of 10 biochemical methane potential (BMP) tests. The measured methane yields ranged from 289 to 604 NmL/gVS_added; according to the results, only the acidic pretreatment (HCl) was found to significantly increase methane generation. However, as the experimental values were quite high with regards to the theoretical methane yield of the substrate, this effect still needs to be confirmed via further research. The alkaline pretreatment (NaOH) did not noticeably affect methane yields (an average reduction of 8% was recorded), despite the fact that it did significantly reduce the lignin content. Thermal pretreatment had no effect on the methane yields or the chemical composition. Scanning electron microscopy images revealed changes in the chemical structure after the addition of NaOH and HCl. Modelling of the cumulated methane production by the Gompertz modified equation was successful and aided in understanding kinetic advantages linked to some of the pretreatments. For example, the alkaline treatment (at the 20% dosage) at room temperature resulted to a μ_max (maximum specific methane production rate [NmLCH₄/(gVS_added·d)]) equal to 36.3 against 18.6 for the control.

Critical review of existing nanomaterial adsorbents to capture carbon dioxide and methane

Innovative gas capture technologies with the objective to mitigate CO₂ and CH₄ emissions are discussed in this review. Emphasis is given on the use of nanoparticles (NP) as sorbents of CO₂ and CH₄, which are the two most important global warming gases. The existing NP sorption processes must overcome certain challenges before their implementation to the industrial scale. These are: i) the utilization of the concentrated gas stream generated by the capture and gas purification technologies, ii) the reduction of the effects of impurities on the operating system, iii) the scale up of the relevant materials, and iv) the retrofitting of technologies in existing facilities. Thus, an innovative design of adsorbents could possibly address those issues. Biogas purification and CH₄ storage would become a new motivation for the development of new sorbent materials, such as nanomaterials. This review discusses the current state of the art on the use of novel nanomaterials as adsorbents for CO₂ and CH₄. The review shows that materials based on porous supports that are modified with amine or metals are currently providing the most promising results. The Fe₃O₄-graphene and the MOF-117 based NPs show the greatest CO₂ sorption capacities, due to their high thermal stability and high porosity. Conclusively, one of the main challenges would be to decrease the cost of capture and to scale-up the technologies to minimize large-scale power plant CO₂ emissions.

The effect of airflow rates and aeration mode on the respiration activity of four organic wastes: Implications on the composting process

The aim of this study was to assess the effect of the airflow and of the aeration mode on the composting process of non-urban organic wastes that are found in large quantities worldwide, namely: (i) a fresh, non-digested, sewage sludge (FSS), (ii) an anaerobically digested sewage sludge (ADSS), (iii) cow manure (CM) and (iv) pig sludge (PS). This assessment was done using respirometric indices. Two aeration modes were tested, namely: (a) a constant air flowrate set at three different initial fixed airflow rates, and (b) an oxygen uptake rate (OUR)-controlled airflow rate. The four wastes displayed the same behaviour namely a limited biological activity at low aeration, while, beyond a threshold value, the increase of the airflow did not significantly increase the dynamic respiration indices (DRI_{1 max}, DRI_{24 max} and AT₄). The threshold airflow rate varied among wastes and ranged from 42NL air kg^-1DMh^-1 for CM and from 67 to 77NL air kg^-1DMh^-1 for FSS, ADSS and PS. Comparing the two aeration modes tested (constant air flow, OUR controlled air flow), no statistically significant differences were calculated between the respiration activity indices obtained at those two aeration modes. The results can be considered representative for urban and non-urban organic wastes and establish a general procedure to measure the respiration activity without limitations by airflow. This will permit other researchers to provide consistent results during the measurement of the respiration activity. Results indicate that high airflows are not required to establish the maximum respiration activity. This can result in energy savings and the prevention of off-gas treatment problems due to the excessive aeration rate in full scale composting plants.

Solid-state fermentation and composting as alternatives to treat hair waste: A life-cycle assessment comparative approach

One of the wastes associated with leather production in tannery industries is the hair residue generated during the dehairing process. Hair wastes are mainly dumped or managed through composting but recent studies propose the treatment of hair wastes through solid-state fermentation (SSF) to obtain proteases and compost. These enzymes are suitable for its use in an enzymatic dehairing process, as an alternative to the current chemical dehairing process. In the present work, two different scenarios for the valorization of the hair waste are proposed and assessed by means of life-cycle assessment: composting and SSF for protease production. Detailed data on hair waste composting and on SSF protease production are gathered from previous studies performed by our research group and from a literature survey. Background inventory data are mainly based on Ecoinvent version 3 from software SimaPro® 8. The main aim of this study was to identify which process results in the highest environmental impact. The SSF process was found to have lower environmental impacts than composting, due to the fact that the enzyme use in the dehairing process prevents the use of chemicals traditionally used in the dehairing process. This permits to reformulate an industrial process from the classical approach of waste management to a novel alternative based on circular economy.

A systematic approach to evaluate parameter consistency in the inlet stream of source separated biowaste composting facilities: A case study in Colombia

Biowaste is commonly the largest fraction of municipal solid waste (MSW) in developing countries. Although composting is an effective method to treat source separated biowaste (SSB), there are certain limitations in terms of operation, partly due to insufficient control to the variability of SSB quality, which affects process kinetics and product quality. This study assesses the variability of the SSB physicochemical quality in a composting facility located in a small town of Colombia, in which SSB collection was performed twice a week. Likewise, the influence of the SSB physicochemical variability on the variability of compost parameters was assessed. Parametric and non-parametric tests (i.e. Student's t-test and the Mann-Whitney test) showed no significant differences in the quality parameters of SSB among collection days, and therefore, it was unnecessary to establish specific operation and maintenance regulations for each collection day. Significant variability was found in eight of the twelve quality parameters analyzed in the inlet stream, with corresponding coefficients of variation (CV) higher than 23%. The CVs for the eight parameters analyzed in the final compost (i.e. pH, moisture, total organic carbon, total nitrogen, C/N ratio, total phosphorus, total potassium and ash) ranged from 9.6% to 49.4%, with significant variations in five of those parameters (CV>20%). The above indicate that variability in the inlet stream can affect the variability of the end-product. Results suggest the need to consider variability of the inlet stream in the performance of composting facilities to achieve a compost of consistent quality.

Generation and composition of medical wastes from private medical microbiology laboratories

A study on the generation rate and the composition of solid medical wastes (MW) produced by private medical microbiology laboratories (PMML) was conducted in Greece. The novelty of the work is that no such information exists in the literature for this type of laboratories worldwide. Seven laboratories were selected with capacities that ranged from 8 to 88 examinees per day. The study lasted 6months and daily recording of MW weights was done over 30days during that period. The rates were correlated to the number of examinees, examinations and personnel. Results indicated that on average 35% of the total MW was hazardous (infectious) medical wastes (IFMW). The IFMW generation rates ranged from 11.5 to 32.5g examinee^-1 d^-1 while an average value from all 7 labs was 19.6±9.6g examinee^-1 d^-1 or 2.27±1.11g examination^-1 d^-1. The average urban type medical waste generation rate was 44.2±32.5g examinee^-1 d^-1. Using basic regression modeling, it was shown that the number of examinees and examinations can be predictors of the IFMW generation, but not of the urban type MW generation. The number of examinations was a better predictor of the MW amounts than the number of examinees. Statistical comparison of the means of the 7PMML was done with standard ANOVA techniques after checking the normality of the data and after doing the appropriate transformations. Based on the results of this work, it is approximated that 580 tonnes of infectious MW are generated annually by the PMML in Greece.

Effect of air flowrate on the dynamic respiration activity of the raw organic fraction of municipal solid wastes

Scope of this work was to study the effect of the aeration rate on the respiration activity of the fresh organic fraction of MSW and to compare the resulting dynamic respiration indices with those of MSW derived compost. Thus, a categorization of the dynamic respiration activity of MSW throughout a composting facility is provided. A simulated organic fraction of MSW was used as a substrate and four experimental runs were performed to achieve unit airflow rates (UAF) from around 6 to 30Lairkg^-1VSh^-1. Six dynamic respiration activity indices were calculated and compared to the corresponding indices of stable MSW compost from a previous work. Findings indicate that the increase of the UAF results in a corresponding increase of the dynamic stability indices. Dynamic respiration activity indices above 1500 and below 520mgO₂kg^-1VSh^-1 indicate fresh and very stable MSW materials, respectively.

Development of phytotoxicity indexes and their correlation with ecotoxicological, stability and physicochemical parameters during passive composting of poultry manure

Both raw and composted poultry manure is applied as soil amendment. The aims of this study were: (1) to develop phytotoxicity indexes for organic wastes and composts, and (2) to assess the correlation among phytotoxicity indexes, ecotoxicological endpoints and stability and physicochemical parameters during passive composting of poultry manure. Six 2-m(3) composting piles were constructed and four parameter groups (physicochemical and microbiological parameters, ecotoxicological endpoints, and biological activity) were determined at four sampling times during 92days. Extracts were used to carry out acute toxicity tests on Daphnia magna, Lactuca sativa and Raphanus sativus. Composting decreased average toxicity 22.8% for the 3 species and D. magna was the most sensitive species. The static respiration index decreased from 1.12 to 0.46mgO2gOMh(-1) whilst organic matter reduced by 64.1% at the end of the process. Escherichia coli colonies remained higher than values recommended by international guidelines. The D. magna immobilization test allowed the assessment of possible leachate or run-off toxicity. The new phytotoxicity indexes (RGIC0.8 and GIC80%), proposed in this study, as well as salinity, proved to be good maturity indicators. Hence, these phytotoxicity indexes could be implemented in monitoring strategies as useful ecotoxicological tools. Multivariate analyses demonstrated positive correlations between ecotoxicological endpoints (low toxicity) and biological activity (stability). These two parameter groups were associated at the final sampling time and showed negative correlations with several physicochemical parameters (organic and inorganic contents). The final poultry manure compost was rendered stable, but immature and, thus, unsuitable for soil amending.

Monitoring the performances of a real scale municipal solid waste composting and a biodrying facility using respiration activity indices

Objective of the work was to monitor two full-scale commingled municipal solid waste (MSW) mechanical and biological pretreatment (MBT) facilities in Greece, namely a biodrying and a composting facility. Monitoring data from a 1.5-year sampling period is presented, whilst microbial respiration indices were used to monitor the decomposition process and the stability status of the wastes in both facilities during the process. Results showed that in the composting facility, the organic matter reduced by 35 % after 8 weeks of combined composting/curing. Material exiting the biocells had a moisture content of less than 30 % (wb) indicating a moisture limitation during the active composting process. The static respiration indexes indicated that some stabilization occurred during the process, but the final material could not be characterized as stable compost. In the biodrying facility, the initial and final moisture contents were 50 % and less than 20 % wb, respectively, and the biodrying index was equal to 4.1 indicating effective biodrying. Lower heating values at the inlet and outlet were approximately 5.5 and 10 MJ/wet kg, respectively. The organic matter was reduced by 20 % during the process and specifically from a range of 63-77 % dw (inlet) to a range of 61-70 % dw. A significant respiration activity reduction was observed for some of the biodrying samples. A statistically significant correlation among all three respiration activity indices was recorded, with the two oxygen related activity indices (CRI7 and SRI24) observing the highest correlation.

Biocompatible polydopamine-like particles for the removal of heavy metals at extremely low concentrations

A family of catechol-based submicron particles, with sizes between 200 and 300 nm, was tested for the removal of Cd(ii), Pb(ii) and Cr(vi) in water.

The importance of aeration mode and flowrate in the determination of the biological activity and stability of organic wastes by respiration indices

The aim of this study was to assess the effect of different air flowrates and different aeration modes on the respiration activity of three organic substrates of different stability degree: (i) a constant flowrate and (ii) a continuously adjusted air flowrate that optimized the oxygen uptake rate (OUR). Above 20L air kg(-1)DMh(-1), at the constant flow regime, the resulting dynamic respiration index at 24h (DRI24) and the cumulative respiration at four days (AT4) were statistically similar. At the OUR based aeration regime, the DRI24 and AT4 were statistically similar at all initial flowrates tested. Above a minimum threshold, cumulative air flow of around 3000Lairkg(-1) DM during a 5day period, the respiration activity was similar, particularly for the two less active substrates. This study highlights the importance of selecting the aeration to obtain reliable measures of biological activity and stability in organic wastes.

Anaerobic digestion of tomato processing waste: Effect of alkaline pretreatment

The objective of the work was to assess the effect of mild alkaline pretreatment on the anaerobic biodegradability of tomato processing waste (TPW). Experiments were carried out in duplicate BMP bottles using a pretreatment contact time of 4 and 24 h and a 1% and 5% NaOH dosage. The cumulative methane production during a 30 d period was recorded and modelled. The alkaline pretreatment did not significantly affect methane production in any of the treatments in comparison to the control. The average methane production for all runs was 320 NmL/gVS. Based on first order kinetic modelling, the alkaline pretreatment was found to slow down the rate of methanogenesis, mainly in the two reactors with the highest NaOH dosage. The biodegradability of the substrates ranged from 0.75 to 0.82 and from 0.66 to 0.72 based on two different approaches.

Stability and maturity of biowaste composts derived by small municipalities: Correlation among physical, chemical and biological indices

Stability and maturity are important criteria to guarantee the quality of a compost that is applied to agriculture or used as amendment in degraded soils. Although different techniques exist to evaluate stability and maturity, the application of laboratory tests in municipalities in developing countries can be limited due to cost and application complexities. In the composting facilities of such places, some classical low cost on-site tests to monitor the composting process are usually implemented; however, such tests do not necessarily clearly identify conditions of stability and maturity. In this article, we have applied and compared results of stability and maturity tests that can be easily employed on site (i.e. temperature, pH, moisture, electrical conductivity [EC], odor and color), and of tests that require more complex laboratory techniques (volatile solids, C/N ratio, self-heating, respirometric index, germination index [GI]). The evaluation of the above was performed in the field scale using 2 piles of biowaste applied compost. The monitoring period was from day 70 to day 190 of the process. Results showed that the low-cost tests traditionally employed to monitor the composting process on-site, such as temperature, color and moisture, do not provide consistent determinations with the more complex laboratory tests used to assess stability (e.g. respiration index, self-heating, volatile solids). In the case of maturity tests (GI, pH, EC), both the on-site tests (pH, EC) and the laboratory test (GI) provided consistent results. Although, stability was indicated for most of the samples, the maturity tests indicated that products were consistently immature. Thus, a stable product is not necessarily mature. Conclusively, the decision on the quality of the compost in the installations located in developing countries requires the simultaneous use of a combination of tests that are performed both in the laboratory and on-site.

Assessing the leaching of hazardous metals from pharmaceutical wastes and their ashes

The purpose of this research was the determination of the leaching potential of eight hazardous metals from expired pharmaceutical wastes and their ashes obtained after simulated incineration. A standardized leaching test (EN 14429) was used to assess leaching over a range of pH and comparison with the limits included in Decision 2003/33/EC was done at liquid/solid ratio 10. The goal was to assess the environmental impacts of pharmaceutical wastes after different disposal techniques (direct landfilling, incineration). A 3-year old composite sample of expired pharmaceutical wastes (drugs) was obtained and was separated into solid and liquid drugs. The packaging from each type of drug was also removed and tested separately, whilst the solid drugs and their packaging were incinerated at 900°C. Leaching tests on all solid substrates (solid drugs, packaging, ashed drugs, ashed packaging) were performed over a wide range of pH. The experiments showed that ashed drugs leached the highest amounts of all metals, except iron, and should be disposed of to a hazardous waste landfill, since Cd, Ni, and Pb exceeded the corresponding limits. Raw expired drugs, raw and ashed packaging did not exceed the pertinent limit values and could be, thus, disposed of directly to a non-hazardous waste landfill. In all experiments, the highest leaching potential (>90% of the total metal content) was measured at acidic pHs (<4). The leachable concentration of all metals increased as pH decreased, whilst Zn observed a small re-dissolution in the alkaline range.

A water budget model for operating landfills: an application in Greece

The goal of the work was to develop and verify a one-dimensional monthly water budget model (MWBM) to predict leachate generation rates from operating landfills. Although there has been a considerable modelling work on the hydraulic behaviour of landfills after they reach closure, less attention has been given on such modelling for operating landfills that have a continuously changing geometry. A MWBM was developed here that accounted for landfill cell development, precipitation and evaporation, the change of the water holding capacity of a waste cell and waste decomposition. The MWBM was verified using a two-year leachate generation rate database from a new operating sanitary landfill in Greece. The MWBM results showed a very good agreement with field data whilst it was observed that peak precipitation rates followed a parallel trend with peak leachate generation rates. A distinct two-month lag phase between the model results and actual values was observed during a certain period, which is a likely indication of the presence of channelling within the waste mass. A sensitivity analysis performed in the MWBM showed that the leachate is affected by the initial municipal solid waste moisture content as well as by the precipitation rates. A linear regression empirical model showed that precipitation can still be an adequate predictor of leachate generation rates in operating landfills.

Effect of organic matter and moisture on the calorific value of solid wastes: an update of the Tanner diagram

Objective of the work was to experimentally determine the effect of the organic matter and moisture contents on the calorific value of organic solid wastes. Nine substrates (i.e. newsprint, biodried municipal solid wastes, municipal solid waste derived composts, wastewater sludges, and sea weed derived compost), with organic matter contents that ranged from 12% to 91% (dry weight) were used in the experiments. All substrates were dried and ground and deionized water was artificially added in order to achieve certain target moisture contents per substrate. The higher heating value (HHV) was, then, determined experimentally for each sample using a bomb calorimeter. Best reduced models were developed to describe the higher and lower heating values as a function of organic matter, ash and moisture contents. A triangular plot was constructed and the self-combustion area was determined and compared to that of the Tanner diagram. Response surfaces were drawn to visually assess the effect of organic matter and moisture contents on the calorific value of the wastes.

Aerobic biological pretreatment of municipal solid waste with a high content of putrescibles: effect on landfill emissions

The objective of this work was to study the effect of aerobic biological pretreatment on the emissions of municipal solid waste (MSW) with a high content of putrescibles after landfilling. For this purpose, the organic fraction of MSW was simulated by a mixture of food waste and office paper at a 2.4:1 wet weight ratio. MSW was first pretreated aerobically for three different time periods (8, 45 and 90 days) resulting in organic matter reductions equal to 15%, 45% and 81% respectively. MSW were then placed in 160-L air-tight anaerobic bioreactors. The control anaerobic bioreactors contained untreated MSW. Anaerobic experiments lasted from 300 to 550 days. Results showed that the biogas production from untreated MSW was 372 NL dry kg(-1) (average of two replications) after 530 days. The MSW that was pretreated aerobically for 45 days and 90 days yielded 130 and 62 NL dry kg(-1) of biogas after 310 days and 230 days respectively. However, the 8-day (very short-term) pretreatment period led to an increase of the biogas yield (550 NL dry kg(-1) after 340 days) compared with that of raw refuse. All three runs with aerobically pretreated MSW reached the steady methanogenic phase faster than raw MSW. Leachate emissions were significantly lower in the aerobically-pretreated MSWthan the untreated ones. The leachate ammonium concentrations had an increasing trend in all anaerobic reactors and reached a plateau of between 2 and 3.5 g L(-1) at the end of the process.

Use of municipal solid waste compost as a growth media for an energy plant (rapeseed)

Objective of this work was to study the effect of mixtures of municipal solid waste (MSW) compost with a peat based growth media on the yields of rapeseed. The MSW compost and the peat were respectively mixed at ratios equal to 10%:90%, 20%:80% and 50%:50% (wet weight basis). A randomized block design was adopted with 5 treatments and 3 blocks per treatment. The 50%:50% mixture achieved a statistically higher yield (dry weight and average leaf area) compared to all other treatments, whilst compost alone led to the lowest shoot growth. Negative correlations were calculated between the total contents of Pb, Ni and Cd of the plant tissues and the corresponding dry weights of the shoots. Regression equations were developed that described shoot yields as a function of the water holding capacity, pH, electrical conductivity, C/N ratio and the total and leachable contents of certain metals in the growth media.

A fractional factorial field experiment to study the decomposition of municipal solid wastes stored in wrapped bales

Wrapped bales can be temporarily used to store municipal solid wastes (MSW) prior to treatment or final disposal. The degree of transformation of wastes within the bales can determine the method to treat MSW after their storage. Goal of the research described in this paper was to monitor the decomposition of the organic fraction of MSW stored in wrapped bales. The monitoring was based on the momentary volumetric concentrations of O(2), CO(2) and CH(4) that were regularly measured in the centre of 23 low density polyethylene (LDPE) wrapped bales over a 617-day period. The field experiment was designed at two levels and four factors, based on the principles of fractional factorial designs. The factors that were studied were: shredding, waste particle size and waste density, thickness of wrapping layers, and type of wrapping film. Two bales were randomly chosen and opened after one year of storage and their solid contents were analysed. Results indicate that carbon dioxide was the prevalent decomposition gaseous product that started from around 80% (v/v) and gradually diminished to around 20%. A non-steady methanogenic phase was established after 150 days from initial wrapping and lasted for approximately 150 days. Methane concentration never exceeded 17%, on average, in the interior of the bales. A 40% dry mass reduction was measured after one year of storage in two bales that contained 74% organics. The factorial analysis revealed that particle size/density and film type were the two main factors that significantly affected methane and carbon dioxide generation.

Static respiration indices to investigate compost stability: effect of sample weight and temperature and comparison with dynamic respiration indices

Goal of this work was to study the effect of sample weight and temperature on the microbial respiration indices of a static microbial respiration test used to quantify compost stability. The static respiration tests (SRT) were performed at two different temperatures (20°C and 35°C) using five different sample weights (19, 38, 56, 75 and 94 dry g). Results showed that at 35°C, as sample weight increased, the magnitude of the respiration indices reduced. In addition, the 35°C temperature resulted in higher static respiration activity indices compared to that at the 20°C for two sample weights. The static respiration tests led to 2-2.5 times lower oxygen-related indices compared to those calculated in dynamic respiration tests (DRT); the 7-day CO(2) cumulative generations were, however, almost similar for both types of tests. Respiratory quotients (RQs) were constantly between 0.8 to 1.2 during the SRT.

A modified dynamic respiration test to assess compost stability: effect of sample size and air flowrate

Goal of this work was to study the effect of the unit air flowrate on dynamic respiration activity indexes during the assessment of compost stability. A MSW compost was used and six experimental runs were performed with variable compost masses and variable air flowrates, so that to achieve six unit air flowrates (6, 9, 16, 17, 23 and 30 L air kg(-1) organic matter h(-1)). Six respiration activity indexes were quantified, namely a dynamic respiration index (DRI24), the cumulative O2 consumption at 4 and 7 days (DCRI4, DCRI7), a CO2 index, the cumulative CO2 generation after 7 days (Total CO2) and the respiratory quotient. Results indicate that the CO2 related indexes and the respiratory quotients had a strong negative correlation with the unit air flowrate, whilst the DRI24 and both DCRIs slightly increased with increasing unit air flowrates.

Hazardous medical waste generation rates of different categories of health-care facilities

Goal of this work was to calculate the hazardous medical waste unit generation rates (HMWUGR), in kg bed(-1)d(-1), using data from 132 health-care facilities in Greece. The calculations were based on the weights of the hazardous medical wastes that were regularly transferred to the sole medical waste incinerator in Athens over a 22-month period during years 2009 and 2010. The 132 health-care facilities were grouped into public and private ones, and, also, into seven sub-categories, namely: birth, cancer treatment, general, military, pediatric, psychiatric and university hospitals. Results showed that there is a large variability in the HMWUGR, even among hospitals of the same category. Average total HMWUGR varied from 0.012 kg bed(-1)d(-1), for the public psychiatric hospitals, to up to 0.72 kg bed(-1)d(-1), for the public university hospitals. Within the private hospitals, average HMWUGR ranged from 0.0012 kg bed(-1)d(-1), for the psychiatric clinics, to up to 0.49 kg bed(-1)d(-1), for the birth clinics. Based on non-parametric statistics, HMWUGR were statistically similar for the birth and general hospitals, in both the public and private sector. The private birth and general hospitals generated statistically more wastes compared to the corresponding public hospitals. The infectious/toxic and toxic medical wastes appear to be 10% and 50% of the total hazardous medical wastes generated by the public cancer treatment and university hospitals, respectively.

Revisiting the elemental composition and the calorific value of the organic fraction of municipal solid wastes

In this work, the elemental content (C, N, H, S, O), the organic matter content and the calorific value of various organic components that are commonly found in the municipal solid waste stream were measured. The objective of this work was to develop an empirical equation to describe the calorific value of the organic fraction of municipal solid waste as a function of its elemental composition. The MSW components were grouped into paper wastes, food wastes, yard wastes and plastics. Sample sizes ranged from 0.2 to 0.5 kg. In addition to the above individual components, commingled municipal solid wastes were sampled from a bio-drying facility located in Crete (sample sizes ranged from 8 to 15 kg) and were analyzed for the same parameters. Based on the results of this work, an improved empirical model was developed that revealed that carbon, hydrogen and oxygen were the only statistically significant predictors of calorific value. Total organic carbon was statistically similar to total carbon for most materials in this work. The carbon to organic matter ratio of 26 municipal solid waste substrates and of 18 organic composts varied from 0.40 to 0.99. An approximate chemical empirical formula calculated for the organic fraction of commingled municipal solid wastes was C(32)NH(55)O(16).

Monitoring and optimizing the co-composting of dewatered sludge: a mixture experimental design approach

The management of dewatered wastewater sludge is a major issue worldwide. Sludge disposal to landfills is not sustainable and thus alternative treatment techniques are being sought. The objective of this work was to determine optimal mixing ratios of dewatered sludge with other organic amendments in order to maximize the degradability of the mixtures during composting. This objective was achieved using mixture experimental design principles. An additional objective was to study the impact of the initial C/N ratio and moisture contents on the co-composting process of dewatered sludge. The composting process was monitored through measurements of O(2) uptake rates, CO(2) evolution, temperature profile and solids reduction. Eight (8) runs were performed in 100 L insulated air-tight bioreactors under a dynamic air flow regime. The initial mixtures were prepared using dewatered wastewater sludge, mixed paper wastes, food wastes, tree branches and sawdust at various initial C/N ratios and moisture contents. According to empirical modeling, mixtures of sludge and food waste mixtures at 1:1 ratio (ww, wet weight) maximize degradability. Structural amendments should be maintained below 30% to reach thermophilic temperatures. The initial C/N ratio and initial moisture content of the mixture were not found to influence the decomposition process. The bio C/bio N ratio started from around 10, for all runs, decreased during the middle of the process and increased to up to 20 at the end of the process. The solid carbon reduction of the mixtures without the branches ranged from 28% to 62%, whilst solid N reductions ranged from 30% to 63%. Respiratory quotients had a decreasing trend throughout the composting process.

Hazardous medical waste generation in Greece: case studies from medical facilities in Attica and from a small insular hospital

The accurate calculation of the unit generation rates and composition of medical waste generated from medical facilities is necessary in order to design medical waste treatment systems. In this work, the unit medical waste generation rates of 95 public and private medical facilities in the Attica region were calculated based on daily weight records from a central medical waste incineration facility. The calculated medical waste generation rates (in kg bed(-1) day( -1)) varied widely with average values at 0.27 ± 113% and 0.24 ± 121%, for public and private medical facilities, respectively. The hazardous medical waste generation was measured, at the source, in the 40 bed hospital of the island of Ikaria for a period of 42 days during a 6 month period. The average hazardous medical waste generation rate was 1.204 kg occupied bed(-1) day(-1) or 0.33 kg (official) bed( -1) day(-1). From the above amounts, 54% resulted from the patients' room (solid and liquid wastes combined), 24% from the emergency department (solid waste), 17% from the clinical pathology lab and 6% from the X-ray lab. In average, 17% of the total hazardous medical waste was solely infectious. Conclusively, no correlation among the number of beds and the unit medical waste generation rate could be established. Each hospital should be studied separately, since medical waste generation and composition depends on the number and type of departments/laboratories at each hospital, number of external patients and number of occupied beds.

The influence of spent household batteries to the organic fraction of municipal solid wastes during composting

The objective of this work was to investigate the potential transfer of 9 heavy metals from spent household batteries (zinc-carbon and alkaline-manganese batteries) to the organic fraction of municipal solid wastes during active composting. Six runs were performed including one control and 2 replications. Eleven types of alkaline and non-alkaline batteries were added at 3 different levels to the organic fraction of municipal solid wastes, namely at percentages equal to 0.98% w/w (low), 5.2% w/w (medium) and 10.6% w/w (high). Experiments were performed in 230 l insulated plastic aerobic bioreactors under a dynamic air flow regime for up to 60 days. Iron, copper and nickel masses contained in the organic fraction of the wastes were found significantly higher in the high level runs compared to the corresponding masses in the control. No metal transfer was obtained in the low and medium level runs. Metal mass balance closures ranged from 51% to 176%. Metals' concentrations in the leachates were below 10 mg l⁻¹ for most metals, except iron, while an increasing concentration trend versus time was measured in the leachates of the high level runs. In all cases, the contents of 5 regulated heavy metals in all end products were below the Hellenic limits.

A modified static respiration assay and its relationship with an enzymatic test to assess compost stability and maturity

Despite the numerous compost stability and maturity tests, no universally accepted compost stability or maturity index exists. The fluorescein di-acetate (FDA) enzymatic assay, originating from soil studies, is examined here as a potential new compost stability test, and is compared to microbial respiration and phytotoxicity indices. Thirteen composts were used in the study from different source materials. Static microbial respiration activity indices calculated were the cumulative O(2) consumptions, O(2) consumption rates, total C-CO(2) production, the respiratory quotient and the bio C/N ratio. Compost phytotoxicity was quantified via a 7-day tomato seed germination assay. Results showed that the net fluorescein release rates correlated with all stability indices. The germination index marginally correlated with the fluorescein release rates, but not with any of the other stability indices. New limits to classify composts regarding their stability were proposed.