Experimental Design and Optimization of Hydrolysis of Paper for Biogas Production

The waste production in Sweden and Europe is increasing each year. Swedish households throw away 2.7 million tonnes material annually and because of though waste legislations, most of this is recycled as material or energy. The Swedish goal to increase the amount of biologically treated food waste and also to increase the biogas production requires not only investments but research in this area. Increased biogas yield from anaerobically treated waste materials will be beneficial to reach the goals. About 45 % of the biological waste consists of lignocellulosic material. Lignocellulose is also the most abundant renewable material in the world which makes it very interesting for biogas production. Sweden is also a country were over 10 % of its total export value is generated from the forest industry. An industry which produces large amounts of waste streams. In this thesis work the author investigates how hydrolysis can increase the digestibility of industrial waste paper. The scope was to find an efficient pretreatment method of paper and determine which affecting factors levels are the most successful ones. A literature study was followed by a series of experiments in order to find the optimal parameters for pretreatment of an industrial waste paper with the goal to increase its digestibility for anaerobic biogas production. From the study three pretreatment methods for hydrolysis of paper were chosen and an experimental design was conducted. The methods were hot water, alkali and wet oxidation. The result of the treatment was evaluated by measuring the soluble chemical oxygen demand (sCOD) in the supernatant of each treated samples and then analyse the results using a statistical software program. The highest levels of dissolved organic materials was found in samples treated at 250 °C for 30 minutes and with 2 % additive concentration of NaOH. The result was 42 g/l from a suspension of dry milled paper tubes of 50 g/l. By using the results in an analysis of variance it was possible to determine that sodium hydroxide was the most significant factor for hydrolysation of paper, followed by temperature and then addition of hydrogen peroxide. The results also revealed that there are no interaction effects between the examined factors in any of the tested methods