Utveckling av substratmixen vid Mosseruds biogasanläggning
Substratkartläggning och rötningsförsök i laboratorieskala
The world?s growing need for energy together with a desire to ward off the worst consequences of global climate change has resulted in a never seen desire to invest resources in renewable energy sources. Biogas production through anaerobic digestion is one of those growing energy sources. In Sweden there are over two hundred plants that uses this biological process to break down organic substances while producing carbon dioxide and the energy-rich gas methane.This master?s thesis has focused on development of the mixture of different organic substances that is treated at a specific plant, namely Mosserud biogas plant. Located a couple of kilometers west of the city of Karlskoga it has good possibilities to treat material from a big geographic area. Today the plant mainly treats organic fraction of municipality solid waste, cattle manure and ley crops. The study is based partly on a survey of what substrates are accessible in the region and if they are feasible to treat at the plant in both a practical and theoretical sense. This part of the study resulted in a new potential waste amount of 6 000 tonnes per year which is almost 10 % of what the plant is built to treat. Slaughterhouse waste from Na?rke slakteri is one of the most promising waste fractions as it has high methane potential while the cost for transportation is relatively low. Packaged food waste from supermarkets may contribute with additional waste amounts if not the competition from waste incineration plants is too big.The second part of the study consisted of a laboratory scale digestion experiment at Karlstad University whose goal was to evaluate what consequences an altered substrate mixture has on methane production and process stability. Due to neglible amounts of new kinds of waste in the mapping survey no single waste could change the overall substrate mixture. Therefore a change in the original substrate mixture was made so that more food waste and less ley crop and manure are digested. This may lead to process failure due to VFA accumulation because of a higher food waste/manure-ratio (from 2 to 5).No accumulation of organic acids could be detected which may have resulted in a pH- drop followed by a restricted methane production. This doesn?t necessarily mean that there won?t be any problem in the full-scale biogas plant, due to a higher organic loading applied there. The methane production was 0,385 Nm3/kgVS/day and 0,352 Nm3/kgVS/day in the two substrate mixtures and the difference could be explained by a higher amount of food waste, which is the substrate with the highest methane potential, in one of the mixtures.