The public defense of Linda Kanders´s doctoral thesis
Doctoral thesis and Licentiate seminars
The public defense of Linda kanders´s doctoral thesis in environmental and energy engineering will take place on MDH on June 10.
Title of the thesis: ”Start-up and operational strategies for deammonification plants - a study with one-stage moving bed biofilm reactors treating reject water”
Serial number: 290
Faculty examinor is Professor Susanne Lackner, TU Darmstadt. The examination committee consits of Kenneth M Persson, Lund University, associate Professor Åsa Davidsson, Lund University and Professor Britt-Marie Wilén, Chalmers university of Technology.
Nitrogen, a key element for all life, is found in proteins and makes it possible, for example, to build new cells in both plants and animals. Living things release nitrogen when they decay or as a waste product (for example, in the form of urine), which arrives at wastewater treatment plants. One of the main tasks of wastewater treatment plants is to remove nitrogen from the wastewater and release it back to the atmosphere and in this way, prevent excess nitrogen in water causing eutrophication in lakes and oceans. This is usually achieved using biological methods in which bacteria are encouraged to grow by aeration and sometimes addition of ethanol.
The recently discovered “anammox bacteria” has shown to be of great importance for the nitrogen cycle in nature. In wastewater treatment, these bacteria provide a potential short cut through the nitrogen cycle and can contribute to savings in energy and cost. However, anammox bacteria grow more slowly than other bacteria used in the wastewater process, and suitable conditions must be implemented in the plant for successful growth. These bacteria have been implemented successfully in warmer wastewater streams such as reject water from municipal biogas production, which is the subject of my research.
Start-up of an anammox process usually involves addition of inoculum, a small amount of bacteria from a different plant, as a seed to help the process start and shorten the start-up time. However, I have performed several start-ups without seeding, both in the laboratory and in full-scale plants, with good results. Further studies have shown that there is already enough anammox bacteria in the reject water for a start-up to occur within a reasonable time (<100 days), given the right conditions in the basin.
Treating reject water with the anammox process reduces energy consumption by 60% in comparison to conventional treatment, but there is a risk that other types of bacteria form nitrous oxide, a potent greenhouse gas, which can increase the carbon footprint. My measurements from a full-scale reject water treatment plant serving 200,000 person equivalents in a Swedish city show that switching from conventional nitrogen removal to a plant containing anammox, reduced nitrous oxide emissions by >97%. This reduction corresponds to 320 kg CO2 per hour, equivalent to the emissions of a large passenger aircraft during flight.
My research has demonstrated a valid methodology for quick start-up of the anammox process and shown the importance of measuring and minimizing the emissions of the gas nitrous oxide.