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 VSmixture, 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.

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.

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 ±â€¯543 (n = 1614) and 195 ±â€¯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.

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.

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.

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.

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 (DRI1 max, DRI24 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.

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.