An effective strategy adopted in recent years for municipal solid waste management is the source-separation of solid waste, most commonly into organics, recyclables such as glass, plastics and papers, and refuse. It has been proposed that source-separated organic waste (SSO) is an excellent lignocellulosic biomass of fermentable carbohydrates, and has the potential to serve as a low-cost feedstock for bioconversion into energy products such as ethanol and hydrogen. To evaluate the feasibility of converting SSO to energy products, a better understanding on the energy contents and highly-variable composition of SSO is needed. This paper is based on the results obtained from a ten-month analysis on the SSO collected from the City of Toronto, Ontario, Canada. Detailed analyses on the composition in terms of the VOC, cellulose, hemicellulose, and lignin contents, as well the amounts of carbohydrates, glucose, xylose and other fermentable sugars are carried out. The experimental results show that the average values of moisture content, at 55%, and VOC, from 65% to 96% per dry mass, was sufficiently high to support microbial growth, making it an acceptable feedstock for anaerobic digestion. The results of SSO are compared to other traditional cellulosic feedstock, such as hardwood, agricultural products, food and herbaceous crops, and it was demonstrated that comparable amount of fermentable sugars are contained in SSO.
Ethanol production from organic fraction of municipal solid waste with inclusion of construction/demolition waste can be an effective waste management strategy to overcome the growing problems with landfill space and dependency on conventional fuels. The main challenge in ethanol conversion is the high cost of processing in which pre-treatment, enzymatic hydrolysis and fermentation are the major steps. This study investigates impact of several key parameters, namely: pH, temperature, adsorption capacity, cellulose hydrolysis rate, cell mass, enzyme and substrate loading doses on ethanol yield. The pre-treatment incorporates pre-processing and enzymatic hydrolysis steps through the use of a thermal screw press (TSP) and cellulose-organic-solvent based lignocellulosic fractionation (COSLIF) on the source-separated organic (SSO) waste to liberate fermentable sugars. Enzymatic hydrolysis experiments were featured with the addition of a commercially available enzyme complex, Accellerase 1500, to mediate the process and increase sugar yields. A kinetic model that uses a semi-mechanistic rate equation for cellulose hydrolysis was adapted and modified to accommodate batch simultaneous saccharification and co-fermentation (SSCF) process on pre-treated SSO waste by yeast, Saccharomyces cerevisiae DA2416. New experimentally defined SSO parameters have been fitted into a kinetic model to evaluate the sugar and ethanol yields. It was found that the model was capable of predicting ethanol productions with diminutive variance from experiments with substrate concentrations between 10 g/L and 50 g/L. Model predictions from experimental data deviated significantly with substrate loading rate from 60 g/L and higher. Fermentation results demonstrated that S. cerevisiae DA2416 produced ethanol in the range of 35 -50 g/L, with ethanol yield of 0.48 -0.50 g of ethanol/g sugar, in 5 days with 96% cellulose conversion. This study provides important insights for investigation on the use of SSO waste for ethanol production by S. cerevisiae DA2416. Furthermore, the model was proven to be a useful tool to facilitate future process optimization for up-scale bioreactors.
Production of biofuel such as ethanol from lignocellulosic biomass is a beneficial way to meet sustainability, energy security, and environmental goals. Lignocellulosic biomass such as source-separated organic (SSO) waste is particularly attractive since it is widely available, often at a negative cost, reduce the land depletion from using food-based biomass for ethanol production and reduce the amount of generated waste. Therefore, in order to meet the future fuel demands and cope with increasing volume of municipal waste this study was a first attempt to use SSO as a feedstock for ethanol production. The main objectives of the study were: a) to compare standard and modified celluloseorganic- solvent-based lignocellulosic fractionation (COSLIF) pretreatment of SSO waste for ethanol production in terms of enzyme savings, sugar formation and ethanol yields; b) to produce ethanol from SSO by using modified COSLIF pretreatment and fermentation with two different recombinant strains: Z. mobilis 8b and S. cerevisiae DA2416; and c) to develop experimental kinetic model capable of predicting behavior of batch SSCF on SSO waste with different SSO substrate concentrations using Berkeley Madonna program. Based on the obtained results, it was found that SSO is an excellent feedstock material for ethanol conversion. The efficiency of modified COSLIF pretreatment was improved by 20% compared to standard method using ethanol washing of pretreated SSO samples during the experimental procedures instead of acetone. On average, glucose yield from SSO samples pretreated by modified COSLIF was about 90% compared to 10% for untreated samples. S. cerevisiae DA2416 outperformed Z. mobilis 8b on ethanol yields during the fermentation process, with 0.50 g ethanol/g potential sugar fed on SSO in less than 5 days, with a 96% cellulose conversion, totalling in 150 g/L ethanol produced. A kinetic model with newly integrated values of experimentally defined SSO feedstock constants was proven to predict the ethanol yield accurately with substrate concentration ranges of 20 g/L - 50 g/L. Model prediction at higher substrate concentration (e.g. 100 g/L) deviated from the experimental values, suggesting that ethanol inhibition is a major factor in bioethanol conversion.
The extraction and purification technologies of landfill gas (LFG) from municipal waste continue to generate strong environmental concerns. Historically, the focus of these concerns was an odour in the immediate region of the landfill and the risk of explosions in structures caused by the movement of LFG through soil. While these are still important environmental issues, health risks associated with volatile organic compounds in LFG and damage to the atmosphere through the emission of greenhouse and ozone depleting gases, have also become prominent issues. The primary objective of this project is to study and examine LFG generation, extraction and purification technologies. Composition of LFG and gas extraction processes is analyzed. Comprehensive literature review of different models for LFG generation rate is provided. The study of LFG extraction and collection systems including design considerations and gas capture schemes are examined. Complete analysis of current purification processes of LFG along with upgrading techniques of methane to bio-methane are carried out. Discussion and recommendation on gas purification methods are conducted relevantly with certain type of LFG composition, level treatment required, quality of LFG anticipated, and its final application. Accurate portrayals of prior and current LFG extraction and purification technologies will advance the knowledge used to select appropriate waste management and reduction strategies in future.
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