It was a warm and sunny Monday, the last week of June, when we set out to visit Uppsala Vatten and their biogas facility at Kungsängen. We were met by Stina Bengtsson, who gave us a short introduction to the methane-producing bioreactors they have. In short, Uppsala Vatten collects organic waste from Uppsala municipality and several others, grinds and boils it to finally feed it to methane-producing bacteria. The natural gas is collected and methane is concentrated from it, while the remaining organic waste-slurry is used as fertiliser for local farmers. We were then given a tour of the facility and its machines, followed by a short lecture on plastic waste management. Stina gave us some names of people we could contact in order to get a better understanding of how these bioreactors were designed, so that we could use that knowledge in order to understand how our system could possibly be designed in the future if successful.</p>
<li>These bioreactors worked as a tiny eco-system. Based on bacteria from manure, different types of organic waste have been added and the bacterial flora has been formed over time. We wondered if they had a “starter culture”, or if they sometimes had to supplement with bacteria when production was slow, but the starter culture from the manure provided at the start and the constant adding of new “feed” meant that the bacterial flora was very stable.</li>
<li>We also asked about external factors, such as temperature, pH-levels, moisture, and oxygen levels. They do keep the reactors isolated so they have a very low oxygen level, which is crucial to the bacteria forming methane rather than carbon dioxide. However, besides this, they did not affect temperature (for example cooling in the summer heat or warming during winter), pH-levels nor moisture levels. It truly worked as an ecosystem achieving homeostasis.</li>
<li>We were also curious about possible contaminations. It is well known that organic waste can contain E. coli, Listeria and Salmonella, but the boiling of the organic waste in 70°C for an hour was done to prevent contamination. They have never had problems with unfavourable bacteria growing within their bioreactors. </li>
