Estimating biogas production of biologically treated municipal solid waste

Response of food waste anaerobic digestion to the dimensions of micron-biochar under 30 g VS/L organic loading rate: Focus on gas production and microbial community structure

Biochar modification is an effective approach to enhance its ability to promote anaerobic digestion (AD). Focusing on the physical properties of biochar, the impact of different particle sizes of biochar on AD of food waste (FW) at high organic loading rate (OLR) was investigated. Four biochar with different sizes (40-200 mesh) were prepared and used in AD systems at OLR 30 g VS/L. The research results found that biochar with a volume particle size of 102 μm (RBC-P140) had top-performance in promoting cumulative methane production, increasing by 13.20% compared to the control group. The analysis results of the variety in volatile acids and alkalinity in the system did not show a correlation with the size of biochar, but small size has the potential to improve the environmental tolerance of the system to high acidity. Microbial community analysis showed that the abundance of aceticlastic methanogen and the composition of zoogloea were optimized through relatively small-sized biochar. Through revealing the effect of biochar particle size on AD system at high OLR, this work provided theoretical guidance for regulating fermentation systems using biochar.

The importance of particularising the model to estimate landfill GHG emissions

Methane generation in landfills can be estimated using mathematical models. One of the most widespread estimation models is that developed by the Intergovernmental Panel on Climate Change (IPCC). Despite its popularity, the simplicity that characterises this model markedly limits the possibility of representing operation alternatives, which can strongly impact surface emissions and hinder the introduction of local data that are sometimes available. In this study, the IPCC model was applied to a case study from which field data on gas emissions were available. To fit the model to the studied landfill conditions, a series of modifications were made, including changes in Degradable Organic Carbon (DOC) and methane generation rate constant (k) values, and degradation times for some waste fractions, and by considering leachate carbon and the inclusion of gas lateral migration phenomena or changes in the methane oxidation factor. The model's Final Version improved the fit of its Initial Version to the experimentally estimated values in the case study by more than 65%. Some modifications, such as considering the carbon dragged by leachate or the contour migration of gas, have a minor impact on the model's fit. However, changes in the degradation time of some fractions according to their particular pretreatment or the modification of parameter k in accordance with the moisture conditions in each landfill phase, strongly influence the model's results. This highlights the importance of particularising estimation models to achieve more accurate results, which allow better estimates of the efficiency of mitigation measures for landfill gas emissions in each facility.

Dry anaerobic digestion of the fine particle fraction of mechanically-sorted organic fraction of municipal solid waste in laboratory and pilot reactor

High-solid anaerobic digestion of the very small particle fraction of mechanically-sorted organic fraction of municipal solid waste (OFMSW) was examined in mesophilic digestion tests in a conventional laboratory (0.013 m³) and a pilot (0.300 m³) reactor. The non-biodegradable and recalcitrant molecules together with the low protein and starch contents of the small-particles of OFMSW limited the methane generation potential of substrate. In the conventional AD system, methane yields remained low at 0.139 m³kg_VS^-1 due to formation of a non-reacting layer on digestate surface, which restricted utilization of the available in OFMSW digestible organics. The absence of surface solid crust in the pilot unit favoured consumption of a greater proportion of volatile solids of the OFMSW. Dry AD was remarkably stable over the entire period and negligibly effected by the toxic H₂S yields. Methane generation (0.167 m³kg_VS^-1) was increased 1.2-fold compared to the conventional system due to a better mixing of substrate and microorganisms achieved inside the pilot reactor, which led to an increase of the digested volatile organics. Digestate presented low stability and high heavy metal content, both of which restrain its implementation as soil conditioner or fertilizer in agriculture. A secondary co-digestion treatment may be required for the neutralization of digestate.

Optimization of biochemical sulfide potential (BSP) assay for anaerobic biodegradability assessment

The anaerobic biodegradability assessment (biodegradation extent and kinetics) of organic wastes is critical for optimum design and evaluating treatment efficiencies for anaerobic treatment technologies. The biochemical sulfide potential (BSP) assay has previously demonstrated the advantages of its time efficiency and measurement accuracy for biologically assessing substrate degradability, while its application is limited by undefined operational parameters. In this study, the BSP assay was further optimized through a systematic investigation of a critical parameter, inoculum-to-substrate ratio (ISR), and the applicable kinetic model to unravel the potential use of BSP assays for anaerobic waste treatment. Under two series of experimental scenarios, the common ISR ranges of 0.5-4.0 (based on the traditional BMP assay) and extreme ISRs (as low as 0.1) were studied, in which the advantage of a BSP assay on extreme ISRs was highlighted. Meanwhile, the underlying cause and mechanism for biodegradability discrepancies under different ISRs (0.1-6.0) were further investigated. The extracellular polymeric substance (EPS) characterization of residual organics and the two-substrate first-order hydrolysis model analyses revealed that the hydrolysis process of slowly-biodegradable organics fraction was hindered under improper ISR conditions. Furthermore, the Cone model was evaluated as more appropriate for biodegradation kinetics analysis in BSP assays among the five common kinetic models (i.e., Exponential, Fitzhugh, Cone, Transference, and modified Gompertz models). Overall, the results provide fundamental guidance on designing consistent BSP assays and put a step forward in standardizing the BSP assay for anaerobic biodegradability assessments.

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

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

Emission and Neutralization of Methane from a Municipal Landfill-Parametric Analysis

An attempt was made to estimate the annual production of CH4 at a municipal waste landfill site in Poland. As a matter of fact, the extent of the unorganized emission of CH4 from the landfill surface was approached based on the adopted mathematical model. The Ward agglomeration method for cluster analysis and the Pearson coefficient were employed to evaluate the distance-based similarity measure and to optimize methods for estimating methane emissions from a landfill as well as to verify the input parameters for the model. In order to calculate the content of biodegradable organic parts in the waste, morphological tests of the landfilled waste were performed. Physical quantities, measurements and the actual amount of the landfilled waste as well as the volume of CH4 neutralized in a collective flare were implemented in the model, respectively. The model-based findings and experimental outcome demonstrated stable gas production in the landfill with a high CH4 content. On the other hand, a rather low efficiency of the landfill passive degassing installation indicated the necessity to design and develop its active counterpart with the prospective application of the generated biogas for energy production in a cogeneration system.

Scaling up laboratory column testing results to predict coupled methane generation and biological settlement in full-scale municipal solid waste landfills

Prediction of methane (CH₄) generation and settlement of biodegrading municipal solid waste (MSW) is of primary interest to landfills aiming at biogas recovery for energy generation and MSW stabilization. We investigate these two concurring processes using datasets from 35 laboratory column tests and 8 pilot- and full-scale landfill cells available in the literature. We fit the datasets using three CH₄ generation models, i.e., conventional first-order decay (FOD) model, coupled FOD model, and coupled Gompertz model. The latter two models are proposed in this study which couple CH₄ generation with biological settlement strain (ε_B) instead of elapsed time. Each model requires only four to five input parameters which can be reasonably estimated a priori based on the initial conditions of the MSW and landfills. The performances of the models are compared using jackknife resampling approach and normalized root-mean-square error (NRMSE) values. The coupled Gompertz model results in on average 50% lower NRMSE when predicting the time-dependent CH₄ generation in all the datasets compared to the other two models. Thus, we demonstrate that CH₄ generation from biodegrading MSW in landfills can be better predicted using the corresponding ε_B than the elapsed time.

Evaluation of the biochemical methane potential of residual organic fraction and mechanically-biologically treated organic outputs intended for landfilling

Mechanical biological treatment (MBT) approaches are being adopted to manage residual municipal waste (RMW) to promote the prevention or reduction of potential environmental impacts of landfilling. From this perspective, the present study aimed to increase the knowledge of the biological (anaerobic) stability of different MBT organic outputs and, conversely, initial methane generation from residual organic waste. Biochemical methane potential (BMP) tests, along with initial and final characterisations of substrates and digestates, were conducted on: a mechanically separated organic fraction from RMW (ms-OFRMW); a first MBT organic output represented by a biostabilised organic fraction from RMW (bios-OFRMW); and a different MBT organic output represented by a biodried fine fraction from RMW (biod-FFRMW). The ms-OFRMW had a BMP of 445.6 Nml CH₄ g VS^-1, which was comparable or even higher than those from separately collected and source-sorted organic fractions. The fibre and liquor fractions of the digestate from ms-OFRMW with inoculum showed potential profiles of P-rich amendment and N-rich fluid phase, respectively, even satisfying environmental limits (with the exclusion only of Cu and Zn contents in fibre fraction that, however, remained within typical ranges for agricultural digestates). The BMPs for bios-OFRMW and biod-FFRMW were 143.4 and 261.0 Nml CH₄ g VS^-1, respectively, indicating that these streams may still contribute to landfill methane generation. The BMPs for bios-OFRMW, biod-FFRMW, and ms-OFRMW were positively associated with the degrees of conversion of the substrates (17, 32, and 55%, respectively) and the potential dynamic respiration indexes (955, 3126, and 6062 mg O₂ kg VS^-1 h^-1, respectively).

BIOLEACH: A New Decision Support Model for the Real-Time Management of Municipal Solid Waste Bioreactor Landfills

This paper introduces BIOLEACH, a new decision support model for the real-time management of municipal solid waste bioreactor landfills that allows estimating the leachate and biogas production. Leachate production is estimated using an adaptation of the water balance equation which considers every hydrological component and the water consumed by anaerobic organic matter degradation to create biogas and the leachate recirculation flows pumped from the landfill pond under a bioreactor management scheme. Landfill gas production is estimated considering the leachate formation process as a coupled effect through the production or consumption of water. BIOLEACH uses waste production and climate data at monthly scale and computes leachate production accounting for the actual conditions inside the waste mass. Biogas production is computed simultaneously, considering the available water to adjust the chemical organic matter biodegradation. BIOLEACH is a valuable bioreactor managing tool as it allows calculating the recirculation volume of leachate that ensures optimal moisture conditions inside the waste mass and therefore maximizing biogas production. As an illustrative example of a BIOLEACH application, the model has been applied to a real landfill located in Murcia Region (Spain) showing the economic and environmental benefits derived from leachate superficial recirculation.

The Evaluation of Indicators Used to Assess the Suitability of Agricultural Waste for Fermentation

To ensure high fermentation efficiency, it is necessary to assess the biodegradability of a substrate. These parameters are most often determined on the basis of the amount of loss on ignition and total organic carbon. We are more and more often using chemical indices. However, these indices do not provide information on how much an organic substance is susceptible to biodegradation. The actual assessment of the content of easily biodegradable matter in substrates that are used for fermentation should be performed on the basis of aerobic (AT4) and anaerobic tests (BMP), which require specialised equipment and are time consuming. The AT4 index is being more and more frequently adopted for the analysis of substrates that are used in the fermentation process, because AT4 takes a much shorter time than BMP and provides information on the biodegradability of substrates. The aim of the article is to answer the question of whether the AT4 parameter can be used to assess the suitability of the substrate from the agricultural sector for the fermentation process. The results show that the AT4 index could be used instead of the BMP parameter.

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

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

Introduction of the circular economy within developing regions: A comparative analysis of advantages and opportunities for waste valorization

The introduction of effective solid waste management strategies in developing countries should be considered for improving sustainability at global level. Many barriers should be overcome, concerning the introduction of environmental policies, effective investments, social inclusion and public awareness, which are significant issues in low-middle income countries. The Circular Economy could represent the answer for improving current solid waste management activities worldwide, since denote the principle of waste valorization and recycling for boosting developing economies. This paper is focused on this theme, analyzing main opportunities for improving the current state of solid waste management in developing big cities. The solid waste management of two countries are reviewed: Romania is the emerging country where Circular Economy is becoming a future objective due to economic aids and strength regulations which the European Union (EU) established for the nations forming parts the alliance; as a comparison, Bolivia is reported for evaluating main differences founded for developing recycling systems in a no-EU country. These two case studies could be of interest for highlighting main pros and cons of the participation into a wide organization like the EU for introducing in short terms Circular Economy principles. Moreover, a theoretical Circular Economy model for developing big cities in low-middle income countries is described within the study for effectively comparing which chances can spread for these countries as regard municipal solid waste exploitation. Despite the economic level, Romania and Bolivia are both facing with many solid waste management issues although in different magnitude. For the Romanian case study, it is visible how it cannot achieve the European goals for 2020 due the need of change in public recycling behavior. Bolivia, instead, represents the case where international aids and new investments are required, considering the informal sector into the formal management system as a real opportunity for improving local recycling rate. In conclusion, the comparison suggests how external supports led to implement the principles of the Circular Economy within a developing region. The model of Circular Economy proposed is recommended for developing big cities in order to advance a new form of safe employment, encouraging the activities that are still in action (i.e. informal sector) and boosting the principles of sustainable development.

A Comparison of Waste Stability Indices for Mechanical⁻Biological Waste Treatment and Composting Plants

Achieving high efficiency of biological waste treatment in mechanical–biological treatment (MBT) plants requires reliable methods for measuring the degree of biodegradation of organic substances. For this purpose, several physical, chemical, and biological indices are used. This paper presents respirometric activity (AT4), biogas potential (GB21), total and dissolved organic carbon (TOC and DOC, respectively), and loss on ignition (LOI) values, as well as the correlations between the indices selected for stabilized waste produced in 18 MBT plants in Poland, which use various technologies for biological processing of the organic fraction of municipal solid waste. The study confirms that there is a linear relationship between AT4 and GB21 for stabilized waste produced in MBT plants, regardless of the waste treatment technology used. It has also been found that there is a linear relationship between AT4 and the concentration of dissolved carbon in water extract from stabilized waste. This indicates that DOC can be used for monitoring the organic matter stabilization process in mechanical–biological waste treatment plants. Its advantage is a shorter time needed for measurements in comparison to AT4 and GB21 tests.

Characterization of selected municipal solid waste components to estimate their biodegradability

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

Characterisation of the biodegradability of post-treated digestates via the chemical accessibility and complexity of organic matter

The stability of digestate organic matter is a key parameter for its use in agriculture. Here, the organic matter stability was compared between 14 post-treated digestates and the relationship between organic matter complexity and biodegradability was highlighted. Respirometric activity and CH₄ yields in batch tests showed a positive linear correlation between both types of biodegradability (R²=0.8). The accessibility and complexity of organic matter were assessed using chemical extractions combined with fluorescence spectroscopy, and biodegradability was mostly anti-correlated with complexity of organic matter. Post-treatments presented a significant effect on the biodegradability and complexity of organic matter. Biodegradability was low for composted digestates which comprised slowly accessible complex molecules. Inversely, solid fractions obtained after phase separation contained a substantial part of remaining biodegradable organic matter with a significant easily accessible fraction comprising simpler molecules. Understanding the effect of post-treatment on the biodegradability of digestates should help to optimize their valorization.

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

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

Treatment of mechanically sorted organic waste by bioreactor landfill: Experimental results and preliminary comparative impact assessment with biostabilization and conventional landfill

Treatment and disposal of the mechanically sorted organic fraction (MSOF) of municipal solid waste using a full-scale hybrid bioreactor landfill was experimentally analyzed. A preliminary life cycle assessment was used to compare the hybrid bioreactor landfill with the conventional scheme based on aerobic biostabilization plus landfill. The main findings showed that hybrid bioreactor landfill was able to achieve a dynamic respiration index (DRI)<1000 mgO2/(kgVSh) in 20weeks, on average. Landfill gas (LFG) generation with CH4 concentration >55% v/v started within 140days from MSOF disposal, allowing prompt energy recovery and higher collection efficiency. With the exception of fresh water eutrophication with the bioreactor scenario there was a reduction of the impact categories by about 30% compared to the conventional scheme. Such environmental improvement was mainly a consequence of the reduction of direct and indirect emissions from conventional aerobic biostabilization and of the lower amount of gaseous loses from the bioreactor landfill.

Targeted modification of organic components of municipal solid waste by short-term pre-aeration and its enhancement on anaerobic degradation in simulated landfill bioreactors

Pre-aeration is effective on regulating subsequent anaerobic degradation of municipal solid waste (MSW) with high organic fractions during landfilling. The strength of pre-aeration should be optimized to intentionally remove some easily biodegradable fractions while conserve bio-methane potential as much as possible. This study investigates the evolution of organic components in MSW during 2-14days pre-aeration process and its impacts on subsequent anaerobic degradation in simulated landfill bioreactors. Results showed that a 6-day pre-aeration enabled to develop a thermophilic stage, which significantly accelerated biodegradation of organics except lignocelluloses, with removal rates of 42.8%, 76.7% and 25.1% for proteins, carbohydrates and lipids, respectively. Particularly, ammonia from accelerated ammonification in the thermophilic stage neutralized VFAs generated from anaerobic landfilling. As a result, the MSW with 6-day pre-aeration obtained the highest methane yield 123.4NL/kg dry matter. Therefore, it is recommended to interrupt pre-aeration before its cooling stage to switch to anaerobic landfilling.

Organic fraction of municipal solid waste from mechanical selection: biological stabilization and recovery options

Although current trends address towards prevention strategies, the organic fraction of municipal solid waste is greatly produced, especially in high-income contexts. Its recovery-oriented collection is a common practice, but a relevant portion of the biodegradable waste is not source selected. Mechanical and biological treatments (MBT) are the most common option to sort and stabilize the biodegradable matter ending in residual waste stream. Following the changes of the framework around waste management, this paper aimed at analyzing the quality of the mechanically selected organic waste produced in MBT plants, in order to discuss its recovery options. The material performance was obtained by its composition as well as by its main chemical and physical parameters; biological stability was also assessed by both aerobic and anaerobic methods. On this basis, the effectiveness of an aerobic biostabilization process was assessed at pilot scale. After 21 days of treatment, results proved that the biomass had reached an acceptable biostabilization level, with a potential Dynamic Respirometric Index (DRIP) value lower than the limit required for its use as daily or final landfill cover material. However, the final stabilization level was seen to be influenced by scaling factors and the 21 days of treatment turned to be not so adequate when applied in the existing full-scale facility.

Assessment of biogas production from MBT waste under different operating conditions

In this work, the influence of different operating conditions on the biogas production from mechanically-biologically treated (MBT) wastes is investigated. Specifically, different lab-scale anaerobic tests varying the water content (26-43% w/w up to 75% w/w), the temperature (from 20 to 25°C up to 55°C) and the amount of inoculum have been performed on waste samples collected from a full-scale Italian MBT plant. For each test, the gas generation yield and, where applicable, the first-order gas generation rates were determined. Nearly all tests were characterised by a quite long lag-phase. This result was mainly ascribed to the inhibition effects resulting from the high concentrations of volatile fatty acids (VFAs) and ammonia detected in the different stages of the experiments. Furthermore, water content was found as one of the key factor limiting the anaerobic biological process. Indeed, the experimental results showed that when the moisture was lower than 32% w/w, the methanogenic microbial activity was completely inhibited. For the higher water content tested (75% w/w), high values of accumulated gas volume (up to 150Nl/kgTS) and a relatively short time period to deplete the MBT waste gas generation capacity were observed. At these test conditions, the effect of temperature became evident, leading to gas generation rates of 0.007d(-1) at room temperature that increased to 0.03-0.05d(-1) at 37°C and to 0.04-0.11d(-1) at 55°C. Overall, the obtained results highlighted that the operative conditions can drastically affect the gas production from MBT wastes. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of disposed waste, the presence and type of temporary and final cover systems.

Early prediction of Biochemical Methane Potential through statistical and kinetic modelling of initial gas production

A major drawback of Biochemical Methane Potential (BMP) tests is their long test duration, which could be reduced substantially if the final gas production could be predicted at an earlier stage. For this purpose, this study evaluates 61 different algorithms for their capability to predict the final BMP and required degradation time based on data from 138 BMP tests of various substrate types. By combining the best algorithms it was possible to predict the BMP with a relative root mean squared error (rRMSE) of less than 10% just 6days after initiation of the experiment. The results from this study indicate that there is a possibility to shorten the test length substantially by combining laboratory tests and intelligent prediction algorithms. Shorter test duration may widen the possible applications for BMP tests in full-scale biogas plants, allowing for a better selection and proper pricing of biomass.

What is the acceptable margin of error for the oxygen uptake method in evaluating the reactivity of organic waste?

The acceptable margin of error for the organic waste reactivity measured by the oxygen uptake method was assessed. Oxygen uptake was determined by the Dynamic Respiration Index (DRI) (mgO2/kgVS h). The composed uncertainty (uC) of the experimental set up used for the DRI test was evaluated and the uncertainty (u) of all the components of the apparatus was evaluated. A procedure for calculating the uC of the apparatus is proposed. The components affecting the uC of the DRI to a more significant extent were the one of the oxygen mass rate and the u of the amount of VS in the sample analyzed. For a confidence level of 99.73%, the extended uC (UC) interval for a DRI = 1024 mgO2/kgVS h was ± 440 mgO2/kgVS h, whereas for a DRI = 3,489 mgO2/kgVS h, the UC interval was ± 1288 mgO2/kgVS h. When oxygen consumption and VS content become lower than 600 mgO2/h and 0.9 kg, respectively, the UC interval is similar to the measured DRI.

Sulfide emissions from different areas of a municipal solid waste landfill in China

Degradation of municipal solid waste in landfills generates sulfide compounds, which are considered one of the main sources of odor emissions. Field sampling was conducted at surfaces of operating, inoperative, and soil-covered areas of a landfill site in northern China to characterize the sulfide compounds. The results showed that dimethyl disulfide dominated the sulfide compounds, accounting for up to 73.6% of the total detected sulfide. With the biggest odor concentration of 365, diethyl sulfide was the most significant sulfide compound. The estimated sulfide emission rates at surfaces of operating and soil-covered areas were similar, and the emission rate of dimethyl disulfide at Surface of Operating Area was up to 345.9 μg/m(3) h. Dimethyl disulfide could be released from the fresh waste, and its normalized concentration at 0.2 m beneath operating surface was 10.4 times that at 0.4 m.

Prediction of anaerobic biodegradability and bioaccessibility of municipal sludge by coupling sequential extractions with fluorescence spectroscopy: towards ADM1 variables characterization

Advanced dynamic anaerobic digestion models, such as ADM1, require both detailed organic matter characterisation and intimate knowledge of the involved metabolic pathways. In the current study, a methodology for municipal sludge characterization is investigated to describe two key parameters: biodegradability and bioaccessibility of organic matter. The methodology is based on coupling sequential chemical extractions with 3D fluorescence spectroscopy. The use of increasingly strong solvents reveals different levels of organic matter accessibility and the spectroscopy measurement leads to a detailed characterisation of the organic matter. The results obtained from testing 52 municipal sludge samples (primary, secondary, digested and thermally treated) showed a successful correlation with sludge biodegradability and bioaccessibility. The two parameters, traditionally obtained through the biochemical methane potential (BMP) lab tests, are now obtain in only 5 days compared to the 30-60 days usually required. Experimental data, obtained from two different laboratory scale reactors, were used to validate the ADM1 model. The proposed approach showed a strong application potential for reactor design and advanced control of anaerobic digestion processes.

Experimental and life cycle assessment analysis of gas emission from mechanically-biologically pretreated waste in a landfill with energy recovery

The global gaseous emissions produced by landfilling the Mechanically Sorted Organic Fraction (MSOF) with different weeks of Mechanical Biological Treatment (MBT) was evaluated for an existing waste management system. One MBT facility and a landfill with internal combustion engines fuelled by the landfill gas for electrical energy production operate in the waste management system considered. An experimental apparatus was used to simulate 0, 4, 8 and 16weeks of aerobic stabilization and the consequent biogas potential (Nl/kg) of a large sample of MSOF withdrawn from the full-scale MBT. Stabilization achieved by the waste was evaluated by dynamic oxygen uptake and fermentation tests. Good correlation coefficients (R(2)), ranging from 0.7668 to 0.9772, were found between oxygen uptake, fermentation and anaerobic test values. On the basis of the results of several anaerobic tests, the methane production rate k (year(-1)) was evaluated. k ranged from 0.436 to 0.308year(-1) and the bio-methane potential from 37 to 12Nm(3)/tonne, respectively, for the MSOF with 0 and 16weeks of treatment. Energy recovery from landfill gas ranged from about 11 to 90kWh per tonne of disposed MSOF depending on the different scenario investigated. Life cycle analysis showed that the scenario with 0weeks of pre-treatment has the highest weighted global impact even if opposite results were obtained with respect to the single impact criteria. MSOF pre-treatment periods longer than 4weeks showed rather negligible variation in the global impact of system emissions.

Prediction of biogas yield and its kinetics in reed canary grass using near infrared reflectance spectroscopy and chemometrics

A rapid method is needed to assess biogas and methane yield potential of various kinds of substrate prior to anaerobic digestion. This study reports near infrared reflectance spectroscopy (NIRS) as a rapid alternative method to the conventional batch methods for prediction of specific biogas yield (SBY), specific methane yield (SMY) and kinetics of biogas yield (k-SBY) of reed canary grass (RCG) biomass. Dried and powdered RCG biomass with different level of maturity was used for biochemical composition analysis, batch assays and NIRS analysis. Calibration models were developed using partial least square (PLS) regression from NIRS spectra. The calibration models for SBY (R(2)=0.68, RPD=1.83) and k-SBY (R(2)=0.71, RPD=1.75) were better than the model for SMY (R(2)=0.53, RPD=1.49). Although the PLS model for SMY was less successful, the model performance was better compared to the models based on chemical composition.

Short mechanical biological treatment of municipal solid waste allows landfill impact reduction saving waste energy content

The aim of this work was to evaluate the effects of full scale MBT process (28 d) in removing inhibition condition for successive biogas (ABP) production in landfill and in reducing total waste impact. For this purpose the organic fraction of MSW was treated in a full-scale MBT plant and successively incubated vs. untreated waste, in simulated landfills for one year. Results showed that untreated landfilled-waste gave a total ABP reduction that was null. On the contrary MBT process reduced ABP of 44%, but successive incubation for one year in landfill gave a total ABP reduction of 86%. This ABP reduction corresponded to a MBT process of 22 weeks length, according to the predictive regression developed for ABP reduction vs. MBT-time. Therefore short MBT allowed reducing landfill impact, preserving energy content (ABP) to be produced successively by bioreactor technology since pre-treatment avoided process inhibition because of partial waste biostabilization.

Mechanical biological treatment of organic fraction of MSW affected dissolved organic matter evolution in simulated landfill

The aim of this paper was to study the evolution of DOM during 1 year of observation in simulated landfill, of aerobically treated vs. untreated organic fraction of MSW. Results obtained indicated that aerobic treatment of organic fraction of MSW permitted getting good biological stability so that, successive incubation under anaerobic condition in landfill allowed biological process to continue getting a strong reduction of soluble organic matter (DOM) that showed, also, an aromatic character. Incubation of untreated waste gave similar trend, but in this case DOM decreasing was only apparent as inhibition of biological process in landfill did not allow replacing degraded/leached DOM with new material coming from hydrolysis of fresh OM.

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.

Large scale study on measurement of respiration activity (AT(4)) by Sapromat and OxiTop

In the run-up for amending the Austrian landfill ordinance, parameters were developed to assess the stability/reactivity of mechanically-biologically pretreated residual wastes. The Landfill Ordinance 2008 regulates limit values for Respiration Activity (="Atmungsaktivität") RA(4) (AT(4))<7mgO(2)*(g dry matter (DM))(-1), Gas Generation Sum GS(21)<20Nl*kgDM(-1) and alternatively Gas Evolution (="Gasbildung") GB(21)<20Nl*kgDM(-1). Methods for analysing these parameters were established by the Austrian Standards Institute (2004). As laboratory practice shows, these methods also are used for the assessment of other wastes (sewage sludge, commercial waste, material from abandoned sites, biowaste compost). For measurement of respiration activity in Austria mainly two methods are used: the Sapromat®-method and the OxiTop®-method. Whether respectively to what extent these two methods give same results, is discussed in this paper. Since 2009 at ABF-BOKU 169 respiration activity tests of samples taken from different stages of MBT - as well as biowaste composting processes, materials from landfills as well as abandoned sites and residues from anaerobic treatment plants were analysed parallel by Sapromat® and OxiTop®. The results manifest very strong correlation between the Sapromat® and OxiTop® method. The correlation coefficient is 0.993. As a very clear tendency OxiTop® gives lower amounts than Sapromat®. In average the lower values of OxiTop® are around 88%.

Stabilisation of biodried municipal solid waste fine fraction in landfill bioreactor

The biodrying process of solid waste is a pre-treatment for the bio-stabilisation of the municipal solid waste. This study aims to investigate the fate of the municipal solid waste fine fraction (MSWFF) resulting from a biodrying treatment when disposed in landfills that are operated as bioreactors. Biodried MSWFF was apparently stable due to its low moisture content that slows down the microbial activity. The lab-scale anaerobic bioreactors demonstrated that a proper moisture content leads to a complete biodegradation of the organic matter contained in the biodried MSWFF. Using a pilot-scale landfill bioreactor (LBR), MSWFF stabilisation was achieved, suggesting that the leachate recirculation could be an effective approach to accomplish the anaerobic biodegradation and biostabilisation of biodried MSWFF after landfilling. The biostabilisation of the material resulting from the LBR treatment was confirmed using anaerobic and aerobic stability indices. All anaerobic and aerobic indices showed a stability increase of approximately 80% of the MSWFF after treatment in the LBR. The similar values of OD7 and BMP stability indices well agree with the relationship between the aerobic and anaerobic indices reported in literature.

Effect of organic compositions of aerobically pretreated municipal solid waste on non-methane organic compound emissions during anaerobic degradation

Odor pollution caused by municipal solid waste (MSW) treatment plants has become a growing public concern. Although aerobic pretreatment of MSW has advantages in accelerating landfill stabilization, the property of non-methane organic compound (NMOC) emissions from aerobically pretreated MSW (APMSW) during landfilling is unknown. To investigate NMOC emissions from anaerobic degradation of APMSW and to study the impact of organic compositions of APMSW and their decomposition stages, five simulative anaerobic bioreactors (R1-R5) were filled up with APMSW of different original organic compositions in a laboratory. For NMOC analysis, samples were collected from the gas that accumulated separately during two successive independent stages of the whole experiment. The results showed that the cumulative quantities of NMOCs from R1 to R5 were 1.11, 0.30, 0.18, 0.28, and 0.31 mg/kg DM, respectively, when volatile solid was degraded by 34.8-47.2%. As the organic content of the original waste was lower, the proportion of NMOCs generated in the early stage of anaerobic degradation became higher. Multiple linear regression analyses of the relationship between the quantities of degraded organics and generated NMOCs showed that lipid and protein have a strong effect on NMOC amount. The effect of lipid on NMOC quantity lasts longer than that of protein. This observation suggests that controlling the lipid and protein contents in MSW can reduce the odor from landfills.

A complete mass balance of a complex combined anaerobic/aerobic municipal source-separated waste treatment plant

In this study a combined anaerobic/aerobic full-scale treatment plant designed for the treatment of the source-separated organic fraction of municipal solid waste (OFMSW) was monitored over a period of one year. During this period, full information was collected about the waste input material, the biogas production, the main rejects and the compost characteristics. The plant includes mechanical pre-treatment, dry thermophilic anaerobic digestion, tunnel composting system and a curing phase to produce compost. To perform the monitoring of the entire plant and the individual steps, traditional chemical methods were used but they present important limitations in determining the critical points and the efficiency of the stabilization of the organic matter. Respiration indices (dynamic and cumulative) allowed for the quantitative calculation of the efficiency of each treatment unit. The mass balance was calculated and expressed in terms of Mgy(-1) of wet (total) matter, carbon, nitrogen and phosphorus. Results show that during the pre-treatment step about 32% of the initial wet matter is rejected without any treatment. This also reduces the biodegradability of the organic matter that continues to the treatment process. About 50% of the initial nitrogen and 86.4% of the initial phosphorus are found in the final compost. The final compost also achieves a high level of stabilization with a dynamic respiration index of 0.3±0.1g O(2) per kg of total solids per hour, which implies a reduction of 93% from that of the raw OFMSW, without considering the losses of biodegradable organic matter in the refuse (32% of the total input). The anaerobic digestion process is the main contributor to this stabilization.

Modelling of biogas extraction at an Italian landfill accepting mechanically and biologically treated municipal solid waste

This paper presents the results of the modelling of the biogas extraction in a full-scale Italian landfill by the USEPA LandGEM model and the Andreottola-Cossu approach. The landfill chosen for this research ('Il Fossetto' plant, Monsummano Terme, Italy) had accepted mixed municipal raw waste for about 15 years. In the year 2003 a mechanical biological treatment (MBT) was implemented and starting from the end of the year 2006, the recirculation in the landfill of the concentrated leachate coming from the internal membrane leachate treatment plant was put into practice. The USEPA LandGEM model and the Andreottola-Cossu approach were chosen since they require only input data routinely acquired during landfill management (waste amount and composition) and allow a simplified calibration, therefore they are potentially useful for practical purposes such as landfill gas management. The results given by the models are compared with measured data and analysed in order to verify the impact of MBT on biogas production; moreover, the possible effects of the recirculation of the concentrated leachate are discussed. The results clearly show how both models can adequately fit measured data even after MBT implementation. Model performance was significantly reduced for the period after the beginning of recirculation of concentrated leachate when the probable inhibition of methane production, due to the competition between methanogens and sulfate-reducing bacteria, significantly influenced the biogas production and composition.

Effects of biodrying process on municipal solid waste properties

In this paper, the effect of biodrying process on municipal solid waste (MSW) properties was studied. The results obtained indicated that after 14d, biodrying reduced the water content of waste, allowing the production of biodried waste with a net heating value (NHV) of 16,779±2,074kJ kg(-1) wet weight, i.e. 41% higher than that of untreated waste. The low moisture content of the biodried material reduced, also, the potential impacts of the waste, i.e. potential self-ignition and potential odors production. Low waste impacts suggest to landfill the biodried material obtaining energy via biogas production by waste re-moistening, i.e. bioreactor. Nevertheless, results of this work indicate that biodrying process because of the partial degradation of the organic fraction contained in the waste (losses of 290g kg(-1) VS), reduced of about 28% the total producible biogas.

Odours and volatile organic compounds emitted from municipal solid waste at different stage of decomposition and relationship with biological stability

Odours (OU(E)) and volatile organic compounds (VOC) emission during biological process used to treat MSW were studied under standardized conditions in order to detect potential risk for workers and population. Results obtained indicated that odours and VOCs emitted depend on the biological stability of waste measured by the dynamic respiration index (DRI) and a very good correlation were found between these parameters (OU(E) vs. DRI, r=0.96, p<0.001, n=6; VOC vs. DRI, r=0.97, p<0.001, n=6). GC-MS study of the VOCs indicated the presence of a group of molecules that were degraded during the process. On the other hand, a second group of molecules, i.e. aromatic and halogenated compounds, and furan persisted in the waste sample, although molecule concentrations were always lower than Threshold Limit Value-Time Weighted Average (TLV-TWA).

Intra- and inter-laboratory variability in Real Dynamic Respiration Index (RDRI) method used to evaluate the potential rate of microbial self heating of solid recovered fuel

Microbial activity acts as primer in the self combustion process of solid recovered fuels (SRF) during their storage or transport. Thus, EU gave mandate to the European Committee for Standardization (CEN) to develop biological methods, (i.e. respirometric method) able to assess the risk of potential self combustion of SRF. Real Dynamic Respiration Index (RDRI) was chosen as official method, and a validation procedure was requested, to assure the quality of the results, when the method is applied for official purpose, i.e. repeatability and reproducibility detection. Two SRF coming from full-scale plants were analyzed for RDRI by three laboratories in six replicates. Results indicated a good precision of the method proposed in agreement with other biological methods, i.e. relative standard deviations of repeatability ranged from 16.7% to 17.8%, and a relative standard deviations of reproducibility ranged from 17.5% to 23.9%.

First step towards a fast analytical method for the determination of Biochemical Methane Potential of solid wastes by near infrared spectroscopy

Methane can be produced by anaerobic digestion. The Biochemical Methane Potential (BMP) test is widely applied to determine the anaerobic biodegradability of wastes. It is based on a fermentation process, which is time consuming, about 30 days. This study investigates the use of near infrared spectroscopy to predict the Biochemical Methane Potential value of municipal solid waste. Near infrared spectroscopy has the advantage to be very fast and applicable to solid waste with a light sample preparation. Satisfying results were obtained: R(2)=0.76; Standard Error of Prediction=28 ml CH(4) g(-1) VS, that compare very favourably with reported results for other more expensive and more time-consuming methods. To our knowledge, it is the first time near infrared spectroscopy is used to predict the Biochemical Methane Potential value. Using near infrared spectroscopy for waste management would thus lead to a real benefit from an industrial point of view.

Precision determination for the dynamic respirometric index (DRI) method used for biological stability evaluation on municipal solid waste and derived products

Dynamic respiration index (DRI) is an effective respirometric method to measure the biological stability of municipal solid waste (MSW). It allows testing MSW biological stability under standardized conditions and is now used as a routine analytical method. However, the method needs to be studied for precision parameters to ensure the quality of results generated. This work reports on a DRI validation study, detecting repeatability (r) and reproducibility limits (R). To perform the study, 4-6 Italian laboratories took part in an interlaboratory test for the validation of the DRI method on four different municipal solid wastes from different mechanical-biological treatment full-scale plants. Precision values (r and R) of DRI, expressed as relative standard deviation, were in the range of 3.6% and 15.5%, and were acceptable when compared with previous data obtained in another respirometric test. On the other hand, no regressions were found between r and R, and DRI, and as a consequence prediction of precision values was not possible a priori for different DRI levels, unless the same typology of waste was considered.

Assessing amendment and fertilizing properties of digestates from anaerobic digestion through a comparative study with digested sludge and compost

Digestate, with biogas represents the final products of anaerobic digestion (AD). The methane-rich biogas is used to produce electricity and heat, whereas the digestate could be valorized in agriculture. Contrarily to well-recognized biomasses such as digested sludge and compost, the properties of the digestate are not well known and its agricultural use remains unexplored. In this work, a first attempt to study the agronomic properties of digestates was performed by comparing the chemical, spectroscopic, and biological characteristics of digestates with those of compost and digested sludge, used as reference organic matrices. A total of 23 organic matrices were studied, which include eight ingestates and relative digestates, three composts, and four digested sludges. The analytical data obtained was analyzed using principal component analysis to better show in detail similarities or differences between the organic matrices studied. The results showed that digestates differed from ingestates and also from compost, although the starting organic mix influenced the digestate final characteristics. With respect to amendment properties, it seems that biological parameters, more than chemical characteristics, were more important in describing these features. In this way, amendment properties could be ranked as follows: compost≅digestate>digested sludge≫ingestate. As to fertilizer properties, AD allowed getting a final product (digestate) with very good fertilizing properties because of the high nutrient content (N, P, K) in available form. In this way, the digestate appears to be a very good candidate to replace inorganic fertilizers, also contributing, to the short-term soil organic matter turnover.