Evaluation of process parameters and treatments of different raw materials for biogas production

Abstract

The anaerobic digestion process results in the production of biogas from a large diversity of organic residues, which can be used as an alternate source of energy generation and for waste management. However, the biogas production technology is not exploited efficiently due to the characteristics of raw materials, poor methane yields, process instability, limited raw materials and lack of knowledge about the process. Effects of various parameters and different treatments on the performance and stability of the anaerobic digestion process were investigated in this thesis work. Arrays of substrates were subjected to the biochemical methane potential (BMP) batch assay to evaluate the impact of source of inoculum, inoculum to substrate ratio, characteristics of substrate and presence of toxic chemicals on the methane yield and kinetics of methane production during anaerobic digestion. Biogas production from sugarcane bagasse and pulp mill sludges was studied after different pretreatments. Biogas production from rectified methanol condensate from pulp and paper mill was investigated at different operating conditions.

Inoculum was found to be an important factor that affects the anaerobic digestion. Different parameters related to inoculum studied were: source of inoculum, inoculum to substrate ratio and adaptation of inoculum. It was found that inoculum to substrate ratio has impact on the reduction of volatile solids and the rate of methanogenesis during anaerobic digestion. Increasing the inoculum to substrate ratio enhanced the reduction in volatile solids and methane production rate during anaerobic digestion of sodium acetate. The source of inoculum significantly affected the methane production rate but had no marked influence on the ultimate methane yield.

Long term exposure of anaerobic consortia to methanol condensate from pulp mill in an upflow anaerobic sludge bed reactor caused adaptation of the microbial consortia to the feed and hence it became more tolerant to toxic material in methanol condensate. The adaptation resulted in an increase in the methane yield and reduced the recovery time after failure of the process.

The treatment with diluted acid of sugarcane bagasse followed by enzymatic hydrolysis resulted in the release of considerable amounts of monomeric sugars that afterwards were subjected to anaerobic digestion. These treatments led to significant improvements in yields as compared to when raw sugarcane bagasse was digested. Additionally, higher amount of methane was produced from anaerobic digestion of sugarcane bagasse treated with acid alone compared to when raw sugarcane was subjected to anaerobic digestion but the yields were lower than that of treatment with diluted acid followed by enzymatic hydrolysis.

Furaldehydes i.e. furfural and hydroxymethylfurfural at concentrations formed during the pretreatments of lignocellulosic biomass were found to be non-inhibitory and degradable during anaerobic digestion. However, high concentrations of furaldehydes affected the biogas production. The effect of the higher concentration of furaldehydes was evident on biogas production kinetics.

The amount and rate of biogas production from a substrate is highly dependent on the composition and characteristics of the substrate. To compare the extent of degradability among different substrates, the methane yield based on the COD basis provides a better option than the methane yield based on volatile solids.

Abstract (Swedish)

Popular Abstract in English

In the age where there is a great demand of energy, raise in the prices of fossil fuels and increase of environmental concerns because of the greenhouse gas emissions, biogas production through anaerobic digestion, of different organic materials, provides a full or partial solution. There is a large number of cheap substrates as organic waste materials that can be utilized for the production of biogas. Biogas production not only generates an energy rich compound ‘methane’ but also is the technology for waste management. These wastes can, if not handled properly, cause emission of greenhouse gases as in the case of manure. Even though anaerobic digestion has been known from long ago, several processes were started in 1970s but due to the lack of proper knowledge, most of the processes failed. In order to make the anaerobic digestion process efficient enough to compete with traditional sources of energy, there is need of research.

In this thesis we have studied the effect of different parameters on anaerobic digestion and evaluated the raw materials after different treatments to enhance the biogas production. For instance, sugarcane bagasse after different treatments was evaluated for production of biogas. Additional studies were carried out to evaluate the possible positive or negative effect of different substrate compositions and different sources of microorganisms (inoculum) on anaerobic digestion.

Biochemical methane potential test is the procedure used to know how much methane can be produced from a given organic material. In this study we have used automatic and real time measurement of methane production during anaerobic digestion of organic biomass, which can run fifteen lab scale digesters in parallel.



The effect of inoculum to substrate ratio was studied and the effect of this parameter was evaluated using different concentrations. In order to be able to produce biofuels from lignocellulosic materials (2nd generation biofuel), the lignocellulosic materials have to be pretreated. During different pretreatments toxic compounds are produced, which affect biotechnological processes like production of bioethanol using yeast. The effect of such toxic compounds at different concentrations and different combinations was studied on methane production. It was found that these compounds, at low concentrations, were not only non-inhibitory for the anaerobic digestion process but were also used as source for methane production.



Globally millions of tons of methanol condensates are produced in pulp and paper mill. The methanol condensate contains up to 80 % methanol and has strong pungent smell. Because of impurities present in methanol condensate from pulp mill, it cannot be used for industrial application. The methanol condensate was anaerobically treated at different operating conditions. Methanol condensate was efficiently treated with the benefit of biogas production. As a bonus effect of the treatment, much of the smell of the feed was also eliminated. Additionally, enhancement of biogas production from different sludges from a pulp and paper mill using enzymes was evaluated.

• author: Badshah, Malik
• supervisor: Bo Mattiasson
• opponent: Prof. Svensson, Bo, Department of Water and Environmental Studies, Linköping University, Sweden
• organization: Biotechnology
• publishing date: 2012
• type: Thesis
• publication status: published
• subject: Industrial Biotechnology
• keywords: Anaerobic digestion, biogas, lignocellulosics, inoculum to substrate ratio, feed composition, toxicity, furaldehydes, paper and pulp sludges.
• pages: 158 pages
• defense location: lecture hall A, at the Center for Chemistry and Chemical Engineering, Sölvegatan 39, Lund
• defense date: 2012-11-09 10:30:00
• ISBN: 978-91-89627-86-4
• language: English
• LU publication?: yes
• id: 2c0578d6-b975-48d4-b9a7-f0048635f156 (old id 3130472)
• date added to LUP: 2016-04-04 11:14:33
• date last changed: 2018-11-21 21:03:35