Start-Up Characteristics of Packed Bed Methane Fermentors

Start-up behavior of a packed bed methane fermentor was investigated using acetic acid as substrate to explain what kind of particle is desirable as bio-film support. Two types of packing particles with different surface and porous characteristics, i. e. unglazed kieselguhr particles of an average diameter of 6.4mm having hollows with diameters less than 0.5mm and porous ceramic particles of an average diameter of 5.4mm having macro-pores with diameters of about 0.41-0.82mm were tested as bio-film support particles. In the reactor packed with kieselguhr particles it took about 20 weeks for the methane yield to reach a value of about 50% which is the maximum value of theoretically attainable, while in the reactor packed with porous ceramic particles it took only 5 weeks for the methane yield to reach the same value. After a long term trained culture, both reactor showed a similar performance as expressed by values of the methane yield of 50% and values of the COD removal of greater than about 95%. The reason why the porous ceramic particles showed a good start-up performance for methane fermentation relative to the kieselguhr particles is that large amount of the initial seeding sludge was entrapped within the macro-pores of the particles and escaped from outflow accompanied by withdrawal of the culture medium. Both packed reactors showed a good performance for methane fermentation with a COD removal of more than 95% and a methane yield of about 50% for the substrate loading of up to 3.4 g⋅l-1⋅d-1 provided that the bed is cultured for a long period and sufficient amount of microorganism is attached to the packed support particles.