The present study aimed to investigate the methane yield from anaerobic digestion of a lignocellulosic substrate subjected to different pretreatments. The lignocellulosic forest residues materials were milled and then pretreated with the organic solvent NMMO (N-Methylmorpholine N-oxide) and/or the lignolytic enzymes laccase and versatile peroxidase at a dosage of 60 U g-1 total solids (TS) substrate. The amount of methane produced was studied in a biomethane potential assay with inocula from a thermophilic biogas reactor treating municipal waste. All samples were run in triplicates. Due to the large amount of samples, two biomethane potential assays were conducted: series 10 & 20 and series 30 & 40. The gas production results show that NMMO-treated forest residues yielded 130 NmL CH4 g-1 volatile solids (VS) substrate and the untreated forest residues yielded 95 NmL CH4 g-1 VS substrate for series 10 & 20. For series 30 & 40, both untreated and NMMO-treated forest residues yielded 140 NmL CH4 g-1 VS substrate. NMMO-treatment appears to be favourable and no advantages from the enzyme pretreatment could be seen in terms of gas yield. An analysis of the reaction fluid after the enzymatic treatment showed presence of phenols, an indication of successful lignin hydrolysis. / Studien avsåg att undersöka metanutbytet från anaerob nedbrytning med förbehandlad lignocellulosa som substrat. Lignocellulosamaterialet, i form av skogsavfall, maldes och förbehandlades därefter med det organiska lösningsmedlet NMMO (N-metylmorfolin-N-oxid) och/eller de lignolytiska enzymerna laccase och versatile peroxidas med dosen 60 U g-1 torrsubstanshalt (TS). Mängden producerad metan undersöktes i en biometanpotentialanalys med inocula från en termofil biogasreaktor, som behandlade hushållsavfall. Triplikat av varje prov användes för att öka den statistiska stabiliteten. På grund av det stora antalet prover genomfördes studien i två omgångar: Serie 10 & 20 samt serie 30 & 40. Resultaten visade att det NMMO-behandlade skogsavfallet gav 130 NmL CH4 g-1 organisk substans (VS) och det obehandlade skogsavfallet gav 95 NmL CH4 g-1 VS i serie 10 & 20. Både obehandlat och NMMO- behandlat skogsavfall gav 140 NmL CH4 g-1 VS i serie 30 & 40. Förbehandling med NMMO verkar vara fördelaktig medan enzymbehandling endast resulterade i en smärre ökning av gasproduktionen. En analys av vätskan efter enzymbehandlingen visade förekomst av fenoler, vilket visar på en lyckad ligninnedbrytning.

Modern society depends on fossil fuels to fulfill the increasing energy demand, which could cause further damages in the environment. Therefore, it is mandatory to develop technologies for the production of efficient alternative renewable energy sources, like biofuels. Agricultural waste streams, such as wheat straw, produced in larger amount can be utilized for these purposes, and can be used as raw materials for both ethanol and biogas production. However, the compact structure of lignocelluloses present in these materials makes their biological degradation difficult.In order to enhance the biogas production, wheat straw milled to 2mm size was pretreated with N-methylmorpholine-N-oxide (NMMO) at 90°C for 7-30 hours in this study. 90°C was applied as treatment temperature for the treatment to be able to investigate if the district heating system could be utilized in the treatment process in the future. The effects of the different pretreatment conditions were then evaluated by running batch anaerobic digestion assays for 45 days at 55°C.The best result was achieved after 7h treatment, leading to 0.47 Nm3/kg VS of straw methane production, corresponding to an increase by 47% compared to methane production obtained for the untreated straw.Furthermore, it was possible to recover up to 91.33% of the straw after the NMMO pretreatment. There were no significant changes in the chemical composition of the straw caused by the treatment, however structural analyses, like FTIR for the determination of crystallinity and and Simon Staining for the determination of porosity of the material showed that the crytallinity decreased, while the porosity increased as results of the treatment.Soaking in water for 72h prior to NMMO treatment was also applied to see whether it can improve the diffusion of NMMO into the material, but without success, due to the dilution of the treatment chemical caused by the soaking. The findings made during the experimental stage indicated that it is possible to run the NMMO pretreatment at an industrial temperature, further evaluation for the economical feasibility of this treatment method is however needed in the future. / Program: MSc in Resource Recovery - Industrial Biotechnology

N-methylmorpholine-N-oxide has shown a positive effect for the pretreatmentof lignocelluloses. Pretreatment by NMMO was developed to enhance thedigestibility of lignocellulosic biomass.Barely straw and forest residue were pretreated by N-methylmorpholine-Noxide(NMMO) prior to anaerobic digestion. The effectiveness of NMMOtreatmenton straw and forest residue was examined as well as the recycling andreuse of NMMO for the next pretreatment process. During the first experimentalseries pretreatments were performed at 90 °C for 3h and 30h, followed bydigestion of the pretreated material for 41 days. Low methane yield was found inthese experiments due to high organic loading rate. In the second series therecycling and reuse of NMMO was investigated on straw. The pretreatmentswere carried out at 90 °C for 30 hr and the recycling and reuse were performedin three times. After treatments with fresh, as well as 1, 2, 3 times recycledNMMO methane yield of 0.45, 0.42, 0.38 and 0.4 Nm3/kg VS were obtained. / Program: Masterutbildning i energi- och materialåtervinning - industriell bioteknik

The application of anaerobic digestion technology is growing worldwide, mainly because of its environmental benefits. Nevertheless, anaerobic degradation is a rather slow and sensitive process. One of the reasons is the recalcitrance nature of certain fractions of the substrate (e.g., lignocelluloses) used for microbial degradation; thus, the hydrolysis becomes the rate-limiting step. The other reason is that the degradation of organic matter is based on a highly dynamic, multi-step process of physicochemical and biochemical reactions. The reactions take place in a sequential and parallel way under symbiotic interrelation of a variety of anaerobic microorganisms, which all together make the process sensitive. The first stage of the decomposition of the organic matter is performed by fast growing (hydrolytic and acid forming) microorganisms, while in the second stage the organic acids produced are metabolized by the slow growing methanogens, which are more sensitive than the acidogens; thus, methanogenesis becomes the rate-limiting step. The first part of this work evaluates the effects of a pretreatment using an organic solvent, N-methylmorpholine-N-oxide (NMMO), on cellulose-based materials in order to overcome the challenge of biomass recalcitrance and to increase the rate of the hydrolysis. NMMO-pretreatment of straw separated from the cattle and horse manure resulted in increased methane yields, by 53% and 51%, respectively, in batch digestion tests. The same kind of pretreatment of the forest residues led to an increase by 141% in the methane production during the following batch digestion assays. The second part of this work evaluates the efficacy of a two-stage process to overcome the second challenge with methanogenesis as the rate-limiting step, by using CSTR (continuous stirred tank reactors) and UASB (up flow anaerobic sludge blanket) on a wide variety of different waste fractions in order to decrease the time needed for the digestion process. In the two-stage semi-continuous process, the NMMO-pretreatment of jeans increased the biogas yield due to a more efficient hydrolysis compared to that of the untreated jeans. The results indicated that a higher organic loading rate (OLR) and a lower retention time could be achieved if the material was easily degradable. Comparing the two-stage and the single-stage process, treating the municipal solid waste (MSW) and waste from several food processing industries (FPW), showed that the OLR could be increased from 2 gVS/l/d to 10 gVS/l /d, and at the same time the HRT could be decreased from 10 to 3 days, which is a significant improvement that could be beneficial from an industrial point of view. The conventional single stage, on the other hand, could only handle an OLR of 3 gVS/l/d and HRT of 7 days.

Textile is a global product used by all people in the world. These textiles after the use are thrown into the trash for incineration or land filling. However an efficient way that can be used to produce more energy, in an environmentally friendly process is anaerobic digestion. Waste textiles which contain cellulosic fibers (e.g. Cotton and viscose) can be converted to biogas. In this study, the performance of a two-stage anaerobic digestion process for biogas production from four different materials, including untreated jeans, treated jeans, cotton, and starch was studied. Starch was used as an easy-to-digest material to compare its digestion with that of cellulosic materials.The two-stage processes were composed of a CSTR (for hydrolysis) and a UASB (for methanogenisis) which were investigated in two different configurations, namely (closed and open systems). In the closed system, the outlet of UASB was completely returned back to the CSTR, while in the open system the UASB outlet was sent to sewage. In a stepwise progress, the OLR was aimed to increase from 2 to 20 g Vs per L per day along with reduction in hydraulic retention time from 10 days to 1 day.The results showed that the closed system was more stable when compared to the open system. The pre-treatment of jeans by NMMO helped to produce methane as that of cotton. The hydraulic retention time was decreased to less than 9 days for treated jeans and less than 5 days for starch. The overall methane yield at OLR of 4 gVS per L per day for starch and treated jeans was 98.5% and 97.4% in the closed system, whereas in the open system the yield was 77.0% and 35.5%, respectively.Another experiment was conducted to compare the performance of two-stage process with that of a single stage process of anaerobic digestion of textiles containing polyester and cotton or viscose. Viscose textiles produced more gas compared to the cotton textile; it may be due to the higher crystalline of cotton which makes it hard to be degraded by the microorganisms. Furthermore, two-stage process could able to produce more methane than the single stage process.The parameters like total solids, volatile solids, pH, gas production, gas composition, concentration of nutrients, and COD were also analyzed for both of the experiments.