Modification of a Moving Bed Biofilm Reactor(MBBR) due to radically changed process conditions : A case study of Kvarnsveden paper mill

Abstract: Papermaking process require large amounts of energy and water; therefore, pulp and paper mills can be potentially very polluting. The wastewater resulting from the papermaking process must be carefully managed as it is very rich in dissolved organic matter and contain compounds that make it difficult to treat. MBBR technology emerged as a possibility to increase the treatment capacity and to make more compact treatment systems designed to remove high organic loads, since in addition to having biomass in suspension as the activated sludge process, also has biomass adhered to plastic supports. This research was commissioned by Stora Enso Kvarnsveden and emerged in need of a bioreactor modification due to reduction of the wastewater load after the closure of PM11 in 2013 and PM8 in 2017. An evaluation of the performance of bioreactors is necessary with possible results to only run one bioreactor in the future and save energy. For performance analysis, two weeks of measurements were performed, one with the two bioreactors running at the same time and one with only K150 reactor running, trying to simulate what happens if one of them is stopped. Analysis of the main operating parameters of the MBBR system were evaluated during this research. As result, it was recommended an action to remove the excess of adhered biomass and an increase of the filling rating to 50%, in order to optimize TOC reduction.