The constant and progressive need to find new energy sources to cover the world necessities have made the study of this field a priority all over the globe. Not only are the existing energy supplies (mostly fossil fuel and natural gas) slowly being depleted, but, in the hurry to produce the energy that is so precious to the everyday life of people by other means (like combustion of coal), a huge impact has been taken by the environment, and not in a positive way. Greenhouse gases (GHG) emissions, ozone depletion among others are affecting the weather all around the world and other series of emissions like that of particulate matter (PM) are affecting human health at serious levels. As a result of the combination of these factors new ways to produce energy in a “green” friendly way are being evaluated every day. The production of methane via anaerobic digestion has taken a big role in this group of “green” energy producers. In several countries of Europe like Italy and the United Kingdom, where there are appropriate conditions to carry out this kind of practice the number of biogas farms keeps increasing day by day. As a result of the rapid growth of biogas farms new issues were introduced. For the scope of this study it is of particular importance the amount of digestate that is produced as a by-product of the anaerobic digestion process. Usually, the digestate is used as fertilizer due to its particular characteristics, like the readily amount of nitrogen it can deliver. However, with the increase in the number of biogas farms, the amount of digestate being produced surpasses by far the local requirements of fertilizer. Besides, in order to use it as a fertilizer the digestate must be stored in open tanks, where it emits significant quantities of CO2, NH3, N2O and CH4. To avoid these emissions, that are direct contributors to global warming, digestate is now being stored in covered tanks. To try and overcome the fact that there is now an enormous quantity of digestate being produced and taking into account the fact that it produces a residual amount of methane, attention is now on how the release of this residual methane can be enhanced through the pretreatment of the digestate and its successive anaerobic digestion. In the particular case of this study, digestate and solid separate by-products of a biogas farm in Lombardy, Italy were subjected to several pretreatments to analyze how they affect the rate of methane production. Thermal, chemical and enzymatic pretreatments were applied. In the case of the thermal pretreatment, specific amount of the substrate were heated at 80°C for one hour. Chemical pretreatment was performed applying NaOH and CaOH2, maintaining 1 g of the alkaline compound by every 100 g of TS of the substrates. This mixture was then allowed to react for 24 h at 40°C. For the enzymatic pretreatment the commercial enzyme Methaplus ®, designed to enhance the production of methane was applied on the substrates. The dosage used was 0.15 mL/g TS. Nitrogen was injected into the environment in order to guarantee anaerobic conditions and the substrate along with the enzyme was allowed to react for 24 h at 40°C. After the application of the pretreatments it was found that only the enzymatic pretreatment provided beneficial effects on the methane yield of the substrates. As a result of this pretreatment, the methane yield of digestate increased over 50% and the methane yield of the solid separate over 12%. No other pretreatment ended up improving the anaerobic digestion of the substrates. On the contrary, they produced a reduction on the methane production of both digestate and solid separate, although the effect was more pronounced on the digestate. In spite of these results both untreated digestate and solid separate produced significant amounts of methane, which leads to conclude that the exploitation of this residual methane is a good way of increasing the productivity of the biogas farms and reduce at the same time unwanted and damaging gaseous emissions.
L’esigenza costante e progressiva di trovare nuove fonti di energia per coprire le necessità del mondo hanno reso possibile lo studio di questo settore una priorità in tutto il mondo. Non solo le forniture energetiche esistenti (principalmente combustibili fossili e gas naturale) ci sono lentamente impoverito, ma, nella fretta di produrre l'energia che è così preziosa per la vita quotidiana delle persone con altri mezzi (come la combustione del carbone), un enorme impatto è stato adottato dall'ambiente, e non in modo positivo. I gas serra (GHG), l’impoverimento dello strato di ozono, tra gli altri stanno influenzando il tempo in tutto il mondo e altre serie di emissioni come quella di materiale particolato (PM) stanno interessando la salute umana a livelli gravi. Come risultato della combinazione di questi fattori, nuovi modi di produrre energia in modo amichevole "verde" sono stati valutati ogni giorno. La produzione di metano attraverso la digestione anaerobica ha assunto un ruolo importante in questo gruppo di produttori di energia "verde". In diversi paesi europei come l'Italia e il Regno Unito, dove ci sono le condizioni adeguate per svolgere questo tipo di pratica il numero di impianti di produzione di biogas continua ad aumentare ogni giorno. Come conseguenza della rapida crescita degli impianti di biogas ci sono state introdotte nuove emissioni. Per lo scopo di questo studio è di particolare importanza la quantità di digestato che viene prodotto come un sottoprodotto del processo di digestione anaerobica. Solitamente, il digestato viene utilizzato come fertilizzante per le sue particolari caratteristiche, come la quantità di azoto pronto in grado di fornire. Tuttavia, con l'aumento del numero di aziende agricole biogas, la quantità di digestato essere prodotta supera di gran lunga le esigenze locali di fertilizzante. Inoltre, al fine di utilizzarlo come fertilizzante il digestato deve essere conservato in vasche aperte, dove emette quantità significative di CO2, NH3, N2O e CH4. Per evitare queste emissioni che sono collaboratori diretti per il riscaldamento globale, il digestato viene ora conservato in vasche coperte. Per tentare di superare il fatto che vi è ora una enorme quantità di digestato prodotta e tenendo conto del fatto che produce una quantità residua di metano, l'attenzione è ora su come rilascio del metano residuo può essere migliorato attraverso il pretrattamento del digestato e la sua successiva digestione anaerobica. Nel caso particolare di questo studio, digestato e separato solido sottoprodotti di un impianto di biogas in Lombardia, Italia sono stati sottoposti a diversi pretrattamenti per analizzare come influenzano il tasso di produzione di metano. Sono stati applicati pretrattamenti termici, chimici ed enzimatici. Nel caso del pretrattamento termico, quantità specifica del substrato sono stati riscaldati a 80 °C per un'ora. Pretrattamento chimico è stato eseguito applicando NaOH e CaOH2, mantenendo 1 g del composto alcalino per ogni 100 g di TS dei substrati. Questa miscela è stata poi lasciata reagire per 24 ore a 40 °C. Per il pretrattamento enzimatico, l'enzima commerciale Methaplus®, progettata per migliorare la produzione di metano è stata applicata sui substrati. Il dosaggio utilizzato era 0,15 ml/g TS. L'azoto è stato iniettato nell'ambiente per garantire condizioni anaerobiche e il substrato con l'enzima viene fatta reagire per 24 ore a 40 °C. Dopo l’applicazione dei pretrattamenti è emerso che solo il pretrattamento enzimatico produce effetti benefici sulla resa metano dei substrati. Come risultato di questo pretrattamento, la resa di metano del digestato è aumentata oltre il 50% e la resa ni metano del separato solido è aumentata circa il 12%. Nessun altro pretrattamento ha potuto migliorare la digestione anaerobica dei substrati. Al contrario, hanno prodotto una riduzione sulla produzione di metano del digestato e il separato solido sebbene l’effetto e più pronunciato sul digestato. Nonostante questi risultati, sia digestato oppure separato solido hanno prodotto quantità significative di metano, che porta a concludere che lo sfruttamento del metano residuo è un buon modo di aumentare la produttività delle aziende agricole di biogas e di ridurre al stesso tempo emissioni gassose indesiderate e dannose.
Thermal, alkaline and enzymatic pretreatments to increase methane production of digestates
ALARCON GARZON, DIANA PATRICIA
2012/2013
Abstract
The constant and progressive need to find new energy sources to cover the world necessities have made the study of this field a priority all over the globe. Not only are the existing energy supplies (mostly fossil fuel and natural gas) slowly being depleted, but, in the hurry to produce the energy that is so precious to the everyday life of people by other means (like combustion of coal), a huge impact has been taken by the environment, and not in a positive way. Greenhouse gases (GHG) emissions, ozone depletion among others are affecting the weather all around the world and other series of emissions like that of particulate matter (PM) are affecting human health at serious levels. As a result of the combination of these factors new ways to produce energy in a “green” friendly way are being evaluated every day. The production of methane via anaerobic digestion has taken a big role in this group of “green” energy producers. In several countries of Europe like Italy and the United Kingdom, where there are appropriate conditions to carry out this kind of practice the number of biogas farms keeps increasing day by day. As a result of the rapid growth of biogas farms new issues were introduced. For the scope of this study it is of particular importance the amount of digestate that is produced as a by-product of the anaerobic digestion process. Usually, the digestate is used as fertilizer due to its particular characteristics, like the readily amount of nitrogen it can deliver. However, with the increase in the number of biogas farms, the amount of digestate being produced surpasses by far the local requirements of fertilizer. Besides, in order to use it as a fertilizer the digestate must be stored in open tanks, where it emits significant quantities of CO2, NH3, N2O and CH4. To avoid these emissions, that are direct contributors to global warming, digestate is now being stored in covered tanks. To try and overcome the fact that there is now an enormous quantity of digestate being produced and taking into account the fact that it produces a residual amount of methane, attention is now on how the release of this residual methane can be enhanced through the pretreatment of the digestate and its successive anaerobic digestion. In the particular case of this study, digestate and solid separate by-products of a biogas farm in Lombardy, Italy were subjected to several pretreatments to analyze how they affect the rate of methane production. Thermal, chemical and enzymatic pretreatments were applied. In the case of the thermal pretreatment, specific amount of the substrate were heated at 80°C for one hour. Chemical pretreatment was performed applying NaOH and CaOH2, maintaining 1 g of the alkaline compound by every 100 g of TS of the substrates. This mixture was then allowed to react for 24 h at 40°C. For the enzymatic pretreatment the commercial enzyme Methaplus ®, designed to enhance the production of methane was applied on the substrates. The dosage used was 0.15 mL/g TS. Nitrogen was injected into the environment in order to guarantee anaerobic conditions and the substrate along with the enzyme was allowed to react for 24 h at 40°C. After the application of the pretreatments it was found that only the enzymatic pretreatment provided beneficial effects on the methane yield of the substrates. As a result of this pretreatment, the methane yield of digestate increased over 50% and the methane yield of the solid separate over 12%. No other pretreatment ended up improving the anaerobic digestion of the substrates. On the contrary, they produced a reduction on the methane production of both digestate and solid separate, although the effect was more pronounced on the digestate. In spite of these results both untreated digestate and solid separate produced significant amounts of methane, which leads to conclude that the exploitation of this residual methane is a good way of increasing the productivity of the biogas farms and reduce at the same time unwanted and damaging gaseous emissions.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/86585