Pretreated Municipal Solid Waste Research Articles

Utilization of mechanochemically pretreated municipal solid waste incineration fly ash for supplementary cementitious material

With the rapid development of municipal solid waste (MSW) incineration, the effective disposal and recycling utilization of fly ash is attracting increasing attention. The mechanochemical (MC) treatment as a non-thermal method shows good stabilization of heavy metals and degradation of dioxins in fly ash. The inhibition effect and long-term safety of CaSO4, Ca3(PO4)2, NaH2PO4, and composite additives (50 %NaH2PO4 +50 %CaO) as additives for heavy metals stabilization were investigated. The composite additive showed the best inhibitory effect on heavy metals, and the leaching concentration of Cd, Cr, Cu, Ni, Pb, and Zn were decreased by 95.21 %, 46.84 %, 99.42 %, 49.91 %, 99.83 %, and 99.55 %, respectively. In addition, the modification by MC treatment reduced the particle size and increased the specific surface area of fly ash and improved the activity for resource utilization. Therefore, MC treated fly ash is used as supplementary cementitious material (SCM), which will produce a filling effect and pozzolanic effect improving the performance of fly ash concrete blocks. The compressive strength of the MC-treated fly ash concrete blocks curing for 28 days increased by 35.5 % and exceeded 40 MPa, close to OPC’s strength. The concrete block also had a secondary inhibition on potentially toxic elements, making the resource utilization of fly ash more stable and safer. In general, the MC treatment and the utilization of MC-treated fly ash as SCM effectively inhibit the leaching of heavy metals in fly ash, delivering a promising method for green fly ash disposal.

Statistical optimization of pretreatment of municipal solid waste by response surface methodology for fermentable sugar production

AbstractThis research aims to use low‐cost and easily available chemicals for chemical pretreatment to achieve a high yield of fermentable sugars using biodegradable municipal solid waste as a substrate. Biodegradable municipal solid waste was pretreated with locally available toilet cleaner (acidic in nature) and washing detergent (basic in nature) and to achieve maximum yield of reducing sugars, two variables; chemical concentration and time were selected for optimization using a central composite design. In Central composite design 13 runs for toilet cleaner (acidic in nature) and washing detergent (basic in nature) pretreatment models were created while ranges for two variables were selected as 1, 2, 3 days for time and 1%, 3%, 5% for chemical concentration. In the toilet cleaner (acidic in nature) pretreatment, optimum conditions were 5% (vol/vol) of toilet cleaner (acidic in nature) for 3 days. At optimal conditions, the model for toilet cleaner (acidic in nature) pretreatment released 167.755 g/L of reducing sugars and 2.684 MJ/L energy while the model for washing detergent (basic in nature) pretreatment released 159.141 g/L of reducing sugars and 2.546 MJ/L energy. An enzyme cocktail hydrolyzed the toilet cleaner (acidic in nature) pretreated sample, and the highest value of fermentable sugar was achieved at 36 h of 237.83 ± 11.028 g/L. Thus, the chemical pretreatment using toilet cleaner and washing detergent has a great potential for fermentable sugar production and effectively be used in industrial and household digesters for the conversion of waste into useful products.

Alkali-Activated Materials with Pre-Treated Municipal Solid Waste Incinerator Bottom Ash

This study presents the results of an experimental campaign on the use of municipal solid waste incinerator bottom ash (MIBA) and fly ash (FA) as precursors for the production of alkali-activated materials. MIBA was subjected to a pre-treatment stage in response to two issues: high metallic aluminum content, which reacts in a high pH solution, releasing hydrogen; and low amorphous content of silica-, aluminum- and calcium-bearing phases, which translates into a limited formation of reaction products. The proposed pre-treatment stage oxidizes most of the metallic aluminum fraction and compensates for the low reactivity of the material via the formation of additional reactants. Different combinations of MIBA and FA were tried—mass-based ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 for MIBA/FA. Two mix designs of the alkaline activator with sodium hydroxide and sodium silicate were evaluated by varying the Na2O/binder and SiO2/Na2O ratios. These mortars were tested in the fresh and hardened state. The results showed that the pre-treatment stage was effective at stabilizing the dimensional variation of MIBA. Despite the lower reactivity of MIBA, mortars with 50/50 of MIBA/FA presented a maximum 28-day compressive strength of 25.2 MPa, higher than the 5.7 MPa of mortars made with MIBA only.

Valorizing Waste Derived Fuels for Climate Change Mitigation: Techno-Economic Comparison of CCS and CCU Approaches based on the Carbonate Looping Process

It is common understanding that a reduction of anthropogenic CO2 emissions is undispensible. Furthermore, already emitted CO2 has to be removed from the atmosphere. To meet these objectives, novel processes must be developed and applied. Besides the utilization of renewable energy sources and a reduction of energy intensity, the application of carbon capture and storage/utilization (CCS/U) technologies is required. In a waste-to-energy (WtE) plant, the carbon contained in the waste is largely converted to CO2 and released to the environment. Thereby, heat and power are produced as valuable by-products of waste treatment. The carbon is partly of biogenic origin (e.g. wood and food waste) and of fossil origin (e.g. plastics derived from mineral oil). By separation, storage or utilization of the CO2 contained in the WtE plant flue gas, municipal solid waste (MSW) is utilized as a resource for clean energy and net negative CO2 emissions. The carbonate looping (CaL) process represents an efficient option for post-combustion CO2 capture from WtE plants. In this process, the heat for sorbent regeneration can be supplied by solid recovered fuels (SRF), which are sourced of pretreated MSW. Based on the results of experimental investigations in an SRF-fueled CaL pilot plant at 1 MWth scale, this study focuses on the techno-economic assessment and comparison of two valorization pathways for captured CO2, namely i) long term storage and ii) utilization to produce methanol. Key performance indicators (KPI) of the process chain, such as production costs of methanol and levelized costs of electricity (LCOE) are calculated and compared. Based on a steady-state process model for the CaL process, investment costs are determined according to a bottom-up approach for each component. Operational costs are derived from relevant material and product streams. The economic analysis takes various investment and operation scenarios into account to assess techno-economic characteristics in light of the future energy market. Factors such as negative emissions credits, low electricity cost, increased gate fees or plant size are considered.

Effects of Municipal Solid Waste Torrefaction and Classification Pretreatment on Hydrogen Chloride Release

The incineration treatment of municipal solid waste is widely used, but gas-phase hydrogen chloride (HCl) generated during the incineration seriously threatens the heating surface of boiler tail, and even causes serious harm to environment. Through incineration experiments, this paper found that many factors (temperature, oxygen concentration, residence time and moisture content) affect the HCl emission characteristics in the process of municipal solid waste incineration treatment. In order to effectively cut back the HCl emission in incineration treatment of municipal solid waste, this paper proposes torrefaction and classification pretreatment of municipal solid waste. Torrefaction pretreatment has a significant inhibitory effect on HCl emission during the incineration of mixed municipal solid waste. At the same time, compared with the incineration treatment of mixed municipal solid waste, sawdust and plastic municipal solid waste of the same quality after classification pretreatment can effectively curb HCl emissions within the entire temperature range. In particular, HCl emissions are reduced by 35% during sawdust incineration treatment at 400°C. Furthermore, by studying the reaction mechanics of HCl generation during combustion at different temperatures, and the reaction rate of HCl generation is: mixed municipal solid waste >plastic >sawdust. Therefore, this paper believes that torrefaction and classification pretreatment of mixed municipal solid waste is beneficial to inhibit the precipitation of chlorine during the incineration process and promotes the resource utilization of municipal solid waste, which is of significant significance for energy conservation and emission reduction.

Production of gasoline from municipal solid waste via steam gasification, methanol synthesis, and Methanol-to-Gasoline technologies: A techno-economic assessment

A techno-economic analysis of the process of producing gasoline via steam gasification of municipal solid waste (MSW) using dolomite catalysts, followed by a methanol synthesis and a methanol-to-gasoline process (SGMG) was conducted using an Aspen Plus model and an economic assessment. The process includes six steps: MSW pretreatment, steam gasification of MSW to produce syngas, gas purification through CO₂ and acid gas removal, methanol synthesis using syngas, conversion of methanol to gasoline, and gasoline separation. The Aspen Plus model used to estimate the energy and mass balance for sizing the equipment assumed that 2000 dry metric tonnes of MSW per day would be processed. Capital investment required and operating costs of gasoline production were estimated based on the Aspen Plus model's mass and energy balance and an nth plant. The minimum selling price (MSP) of gasoline was calculated using the capital investment and operating costs of the process. The total capital investment of the process was estimated to be ＄148 million, with an annual operational cost of ＄56 million. The minimum selling price was determined at ＄2.40/gal for a 20-year project life. The sensitivity analysis showed that the cost of feedstock has a direct impact on the MSP of gasoline, and MSP could decrease to ＄1.55/gal if the owners of the plant received disposal fees. Increasing the gasoline yield to 0.125 kg of gasoline/kg of MSW decreased the MSP to ＄1.86/gal. The ash content in MSW played a vital role in estimating the MSP. If the ash content in the feedstock increased, the MSP increased owing to a decrease in the gasoline yield and an increase in the cost of operations.

Environmental and exergetic life cycle assessment of incineration- and gasification-based waste to energy systems in China

The clean and efficient energy production from municipal solid waste (MSW) is highly desirable due to increasing energy demand and environmental concerns. In this study, four incineration- (S1) and gasification-based (S2 with combustion boiler, S3 with gas turbine/combined cycle and S4 with internal combustion engine) MSW treatments were compared using methods of environmental life cycle assessment (LCA) and exergetic life cycle assessment (ELCA). LCA was applied to measure the environmental performances and ELCA was supplemented to reflect the thermodynamics efficiencies. Afterwards, cumulative degree of perfection (CDP) and abatement exergy (AbatCExC) efficiency of the considered systems were also calculated to determine the imperfection and environmental sustainability of the processes. Results showed that gasification-based systems were effective to mitigate the environmental impacts of acidification, nutrient enrichment, and photochemical ozone formation potential, but caused higher global warming impacts. The S3 system exhibited the best performance from both environmental and exergetic perspective, due to its high net efficiency of electricity generation and low exhaust emission into air. Results from ELCA indicated that the rest two gasification-based systems (S2 and S4) were inefficient as compared to MSW direct incineration, mainly due to auxiliary energy consumption for MSW pretreatment and more conversion steps. The CDP and AbatCExC of the systems in descending order was expressed as S3 system > S1 system > S2 system > S4 system.

The valorisation of residual waste bales by urban mining.

In the last decade, the approach to waste management has undergone severe changes. The urgent need to face the sustainable demand for energy and materials while limiting the burdens associated to traditional waste handling practices have figured out the concept of waste as a resource. New strategies boosting the extensive recovery and diverting waste from disposal activities have been promoted and framed in the wider context of the urban mining, promoting the full exploitation of waste as resource for either new materials or energy production. Such approach has been recently proposed to handle over 5 million tons of pretreated municipal solid waste produced and stored in the form of bales in Campania Region, in southern Italy, between 2000 and 2009. However, since the feasibility of this approach is related to the waste composition as well as to the selection process, an experimental study was performed at an industrial mechanical treatment plant to assess the potential for valorisation of this waste. Results showed that the overall sustainability of the urban mining strategies for the management of Campania waste bales is tightly linked to the flexibility of the selection process scheme to be adopted, which should make the waste recovery fit the market demand of either material or energy.

Utilization of pretreated municipal solid waste incineration fly ash for cement-stabilized soil

In this study, the feasibility of using municipal solid waste incineration fly ash (MSWIFA) as additive for the strengthening of pretreated cement-stabilized soil was evaluated. Results indicated that the leaching concentrations of chromium and lead in MSWIFA after the water washing process and addition of 4% ferrous sulphate were reduced by 67% and 89%, respectively, which was lower than the limit value of Identification standard for hazardous waste (GB 5085.3-2007). After pretreatment, MSWIFA samples with ratios of 5% and 10% were blended into cement-stabilized soil with ordinary Portland cement (OPC) content of 10%, 15% and 20%. The unconfined compressive strength (UCS), internal friction angle and cohesion of the cement-stabilized soil increased with OPC and pretreated MSWIFA (PFA) content. The same effect was observed on UCS after the addition of 10% PFA as replacement of 5% OPC. In the subsequent X-ray powder diffraction test, scanning electron microscopy and leaching tests, the leaching concentrations of heavy metals in cement-stabilized soil became far lower than the limit value under the synergistic effects of the physical encapsulation of hydration products and stabilization of chemical agents. The incorporation of PFA as a supplementary material can effectively accelerate the formation of hydration products and can thus provide cleaner options for foundation reinforcement.

Assessing pretreated municipal solid waste degradation by BMP and fibre analysis

Landfill continues to be the major method of Municipal solid waste (MSW) disposal in the UK and many other countries despite considerable efforts to limit its use. The EU Landfill Directive requires, amongst other things, that waste is treated to reduce its biodegradability prior to disposal to landfill. This pre-treatment is often achieved through what is generically termed mechanical-biological treatment. Predicting the biodegradability or degradation potential of these pre-treated wastes is important for the long term management and aftercare of landfill sites. To address this, a series of biochemical methane potential (BMP) tests have been undertaken to characterize the anaerobic biodegradation potential of two mechanically biologically treated (MBT) waste samples in terms of biogas yield, solids composition (loss on ignition, total carbon, cellulose, hemicellulose and lignin contents), and assessment of leachate characteristics during the biodegradation process. Experimental results from a long term study of MBT wastes treated to different standards are analyzed and compared. The relationship between biogas potential and solids composition was investigated, and carbon and nitrogen mass balances are discussed. The biogas potential was shown to correlate well with the ratio of cellulose plus hemicellulose to lignin, loss on ignition and total carbon content of the waste indicating a clear link between these parameters. The results indicate that solids composition of MBT wastes may provide a useful indication of the biodegradation potential. The mass balance indicates that a large proportion of carbon and nitrogen remain locked up in the waste material and is not released.

Low-temperature pre-treatment of municipal solid waste for efficient application in combustion systems

Municipal solid waste (MSW) is considered a valuable energy source that can be applied as a secondary (co-combustion) or even primary fuel in a power plant. Unfortunately, due to some formal (legislative) and technological barriers, MSW is not widely applied in the Polish energy sector. Especially, a crucial problem is the utilization of part of MSW called the over-sieve fraction (OSF). This fraction, which accounts for 30%–40% of MSW, is a by-product from the mechanical separation of MSW. Crude OSF can generate problems because it includes moisture and organic matter. Thus, it is not a stable material and can generate some technological and hygienic problems due to suppuration, unpleasant odor, and parameter changes during storage. These problems can be solved by the application of low-temperature pre-treatment of solid waste. During this process, some physical and chemical properties of crude OSF can be improved, such as calorific value, energy demand for fragmentation and milling, and property stability. The aim of this paper is to investigate the physical and chemical properties of OSF after low-temperature (150–250 °C) treatment. Proximate and ultimate analysis of waste after thermal pre-treatment are presented and discussed in terms of waste application as an alternative fuel in the energy sector.

Effect of alkali and alkaline earth metals on co-pyrolysis characteristics of municipal solid waste and biomass briquettes

To investigate the influence of alkali and alkaline earth metals (AAEMs: K, Na, Ca, and Mg) on the co-pyrolysis of municipal solid waste (MSW) and biomass briquettes (CSBs), the pyrolysis properties and products distribution for the blends of pretreated CSBs and MSW were studied by thermogravimetric analysis with Fourier-transform infrared spectroscopy under N2 and CO2 atmospheres. Results showed that the AAEM salts were effective at reducing the initial temperature during pyrolysis process. The presence of AAEM salts inhibited the volatile release rate of the first pyrolysis stage of the blend, while the alkali and alkaline earth salts separately enhanced the volatile release rates of the second and third pyrolysis stages under both atmospheres. Replacement of N2 with CO2 caused lower residual masses of the blend, which were further reduced by the catalytic effect of the AAEM salts. The CO2 yields were enhanced by adding AAEM salts under the N2 atmosphere. Ca had the most obvious catalytic effect on the CO production in the third pyrolysis stage. Different AAEM salts added to the samples displayed different effects on the emissions of alkyl and carbonyl groups.

Innovative system of organization, accounting treatment of solid municipal and bulky waste, economic incentives for their separate collection and processing

Introduction. The approach to the creation and development of the system of separate collection and pre-treatment of municipal solid waste (MSW) and bulky waste. At present, Russia is lagging behind in the level of waste disposal, the expedient use of secondary resources. One of the main reasons is the lack of a cost-effective system for managing waste and secondary resources. Despite the deteriorating environmental situation, the closure of landfills for municipal solid waste, the growth of unauthorized landfills, there has been a trend of growth in tariffs for removal and disposal of municipal solid waste (MSW) and bulky waste affecting the entire population of Russia. This problem determines the need to find new scientific and methodological approaches and practical solutions for planning not only the placement of industrial waste disposal infrastructure, but also creating a system for separate collection and pretreatment of MSW and bulky waste in the sources of their formation, justification and optimization of the standards for the accumulation of this waste for citizens. Materials and methods. Materials for conducting a scientific research are: legal acts, standards, guidelines and recommendations, regulatory and technical documentation in the field of waste management, published materials of domestic and foreign scientific research. The methods of scientific research are based on the use of factor, comparative, expert types of analysis. Results. Optimization of the system for calculating the standard of accumulation of MSW and bulky waste is proposed; reducing the financial burden on citizens in terms of tariffs for garbage collection; economic incentives for the population to separate the collection of MSW with the pretreatment of the components of this waste to the level of demanded secondary resources. Conclusions. The introduction of the proposed system will allow achieving socio-economic, environmental, natural resource, political effect, consolidating the society to solve the problem of resource conservation, the use of secondary resources.

Simultaneous organosolv pretreatment and detoxification of municipal solid waste for efficient biobutanol production

Municipal solid waste (MSW) was used as a source for biobutanol production via acetone, butanol, and ethanol (ABE) fermentation. Organosolv pretreatment was used for simultaneous extraction of inhibitors, particularly tannins, and pretreatment of lignocellulosic fraction prior to hydrolysis. The hydrolysates of the pretreated MSW contained appreciable amounts of sugars and soluble starch together with a tolerable amount of inhibitors for Clostridium acetobutylicum. The hydrolysate obtained from MSW pretreated with 85% ethanol at 120 °C for 30 min fermented to the highest ABE concentration of 13.06 g/L with the yield of 0.33 g/g carbon source. Through this process, 102.4 mg butanol, 40.16 mg acetone, and 13.14 mg ethanol were produced from each g of organic fraction of MSW (OFMSW). The pretreatment at mild conditions with higher ethanol concentration accompanied with the lowest glucose yield (0.145 g/g) and the highest starch recovery resulted in the uppermost ABE yield of 0.16 g/g OFMSW.

Effectiveness of aerobic pretreatment of municipal solid waste for accelerating biogas generation during simulated landfilling

This study evaluates the effectiveness of aerobic pretreatment of municipal solid waste (MSW) on reducing lag phase and accelerating biogas generation. Aerobic pretreatment degree (APD) was determined on the basis of reduction in volatile solids (VS) on a wet weight basis. In this study, intermittent aeration (IA) was applied to three reactors as a main aeration mode; since a single reactor was operated under continuous aeration mode. However, the purpose of the experiment was to reduce VS content of waste, irrespective of the comparison between aeration modes. Fresh MSW was first pretreated aerobically with different aeration rates (10, 40, 60 and 85 L/min/m3) for the period of 30–50 days, resulting in VS-loss equivalent to 20%, 27%, 38% and 53% on w/w basis for the wastes A1, A2, A3 and A4, respectively. The cumulative biogas production, calculated based on the modified Gompertz model were 384, 195, 353, 215, and 114 L/kg VS for the wastes A0, A1, A2, A3 and A4, respectively. Untreated waste (A0) showed a long lag phase; whereas the lag phases of pretreated MSW were reduced by more than 90%. Aerobically pretreated wastes reached stable methanogenic phase within 41 days compared to 418 days for untreated waste. The waste mass decreased by about 8% to 27% compared to untreated MSW, indicative that even more MSW could be placed in the same landfill. The study confirmed the effectiveness of aerobic pretreatment of MSW prior to landfilling on reducing lag phase and accelerating biogas generation.

Torrefaction of Municipal Solid Waste in Malaysia

Municipal solid waste (MSW) disposal is one of the main issues towards sustainable development in Malaysia. Current practices for MSW disposal such as landfilling and incineration poses a serious problems on the environment and health. Therefore a significant efforts have been made to utilize MSW for energy source by employing gasification process. However, the MSW is characterized by its high moisture content and low high heating value (HHV) which lowering the energy efficiency. In order to overcome this problems, torrefaction can be used as pretreatment method to remove the moisture content and upgrading MSW properties. The objective of this work is to study the effects of torrefaction temperatures ranging from 240 to 330°C for residence time of 30 minutes on two types of MSW namely food waste and wood waste. The torrefied MSWs are characterized in terms of ultimate analysis, proximate analysis and HHV. The mass and energy yields are also performed for both MSW. Based on the torrefaction, it was found that both food waste and wood waste show an increment on the weight percentage of C contents and decrement on the weight percentage of H and O content which resulting into reduce O/C ratio as the temperature is increased. The HHV for both food waste and wood waste are also increased after torrefaction between 240 and 330°C. The mass yield and energy yield were found to decrease with an increase in the torrefaction temperature. This suggests that torrefaction can be used as an effective MSW pretreatment and the torrefied MSW is more suitable to be used as fuel in gasification process.

Evaluation of the rotary drum reactor process as pretreatment technology of municipal solid waste for thermophilic anaerobic digestion and biogas production

Municipal solid waste (MSW) contains a large fraction of biodegradable organic materials. When disposed in landfills, these materials can cause adverse environmental impact due to gaseous emissions and leachate generation. This study was performed with an aim of effectively separating the biodegradable materials from a Mechanical Biological Treatment (MBT) facility and treating them in well-controlled anaerobic digesters for biogas production. The rotary drum reactor (RDR) process (a sub-process of the MBT facilities studied in the present work) was evaluated as an MSW pretreatment technology for separating and preparing the biodegradable materials in MSW to be used as feedstock for anaerobic digestion. The RDR processes used in six commercial MSW treatment plants located in the USA were surveyed and sampled. The samples of the biodegradable materials produced by the RDR process were analyzed for chemical and physical characteristics as well as anaerobically digested in the laboratory using batch reactors under thermophilic conditions. The moisture content, TS, VS and C/N of the samples varied between 64.7 and 44.4%, 55.6 to 35.3%, 27.0 to 41.3% and 24.5 to 42.7, respectively. The biogas yield was measured to be between 533.0 and 675.6 mL g−1VS after 20 days of digestion. Approximately 90% of the biogas was produced during the first 13 days. The average methane content of the biogas was between 58.0 and 59.9%. The results indicated that the biodegradable materials separated from MSW using the RDR processes could be used as an excellent feedstock for anaerobic digestion. The digester residues may be further processed for compost production or further energy recovery by using thermal conversion processes such as combustion or gasification.

Methane oxidation and attenuation of sulphur compounds in landfill top cover systems: Lab-scale tests

In this study, a top cover system is investigated as a control for emissions during the aftercare of new landfills and for old landfills where biogas energy production might not be profitable. Different materials were studied as landfill cover system in lab-scale columns: mechanical–biological pretreated municipal solid waste (MBP); mechanical–biological pretreated biowaste (PB); fine (PBSf) and coarse (PBSc) mechanical–biological pretreated mixtures of biowaste and sewage sludge, and natural soil (NS). The effectiveness of these materials in removing methane and sulphur compounds from a gas stream was tested, even coupled with activated carbon membranes. Concentrations of CO2, CH4, O2, N2, H2S and mercaptans were analysed at different depths along the columns. Methane degradation was assessed using mass balance and the results were expressed in terms of methane oxidation rate (MOR). The highest maximum and mean MOR were observed for MBP (17.2gCH4/m2/hr and 10.3gCH4/m2/hr, respectively). Similar values were obtained with PB and PBSc. The lowest values of MOR were obtained for NS (6.7gCH4/m2/hr) and PBSf (3.6gCH4/m2/hr), which may be due to their low organic content and void index, respectively. Activated membranes with high load capacity did not seem to have an influence on the methane oxidation process: MBP coupled with 220g/m2 and 360g/m2 membranes gave maximum MOR of 16.5gCH4/m2/hr and 17.4gCH4/m2/hr, respectively. Activated carbon membranes proved to be very effective on H2S adsorption. Furthermore, carbonyl sulphide, ethyl mercaptan and isopropyl mercaptan seemed to be easily absorbed by the filling materials.

Optimizing Cellulase Production from Municipal Solid Waste (MSW) using Solid State Fermentation (SSF)

This paper explores the possibility of using an industrially processed municipal solid waste (MSW) for cellulase enzyme production via solid state fermentation (SSF) by Trichoderma reesei and Aspergillus niger. Both fungi grew well on the MSW substrate and production of cellulase enzymes was optimized for temperature, moisture content, inoculation and period of incubation. The effect of additional minerals, and alternative carbon and nitrogen sources were also examined. Following optimization a cellulase activity of 26.10 ± 3.09 FPU/g could be produced using T. reesei at 30°C with a moisture content of 60% with an inoculums of 0.5 million spores/g and incubation for 168 hours. Addition of extra nitrogen and/or carbon did not improve cellulase accumulation. Acid or alkali pretreatment of MSW led to reduced cellulase production. Crude enzymes produced from MSW by T. reesei were evaluated for their ability to release glucose from MSW. A cellulose hydrolysis yield of 24.7% was achieved, which was close to that obtained using a commercial enzyme. Results demonstrated that MSW can be used as an inexpensive lignocellulosic material for the production of cellulase enzymes.

Life Cycle Assessment of mechanical biological pre-treatment of Municipal Solid Waste: A case study

The environmental performance of mechanical biological pre-treatment (MBT) of Municipal Solid Waste is quantified using Life Cycle Assessment (LCA), considering one of the 57 French plants currently in operation as a case study. The inventory is mostly based on plant-specific data, extrapolated from on-site measurements regarding mechanical and biological operations (including anaerobic digestion and composting of digestate). The combined treatment of 46,929 tonnes of residual Municipal Solid Waste and 12,158 tonnes of source-sorted biowaste (as treated in 2010 at the plant) generates 24,550 tonnes CO2-eq as an impact on climate change, 69,943kg SO2-eq on terrestrial acidification and 19,929kg NMVOC-eq on photochemical oxidant formation, in a life-cycle perspective. On the contrary MBT induces environmental benefits in terms of fossil resource depletion, human toxicity (carcinogenic) and ecotoxicity. The results firstly highlight the relatively large contribution of some pollutants, such as CH4, emitted at the plant and yet sometimes neglected in the LCA of waste MBT. Moreover this study identifies 4 plant-specific operation conditions which drive the environmental impact potentials induced by MBT: the conditions of degradation of the fermentable fraction, the collection of gaseous flows emitted from biological operations, the abatement of collected pollutants and NOx emissions from biogas combustion. Finally the results underline the relatively large influence of the operations downstream the plant (in particular residuals incineration) on the environmental performance of waste MBT.