Fixed-biofilm reactors applied to waste water treatment and aquacultural water recirculating systems

Fixed-biofilm waste water treatment may be regarded as one of the oldest engineered biological waste water treatment methods. With the recent introduction of modern packing materials, this type of reactor has received a renewed impuls for implementation in a wide field of water treatment.In this thesis the possibilities are presented for fixed-film post-treatment of anaerobically digested domestic sewage and water reconditioning in aquacultural water recirculation systems. Emphasis is put on the nitrification process and removal processes for organic matter, using the ½-order/0-order kinetic model for fixed-biofilm processes as a starting point for the research.With regard to waste water treatment biofilm COD removal kinetics for waste water, containing both suspended and dissolved organics, are discussed illustrating that the apparent kinetic order of the combined process and the reaction constant strongly depends on the ratio of suspended/dissolved COD. The overall conclusion was that a rotating biological contactor is especially suitable for this application, and that such reactor may be regarded as a reactor in which biochemical oxidation of dissolved organic substrate is combined with adsorption/flocculation processes of suspended organic matter.The suitability of fixed-film reactors for application in aquacultural recirculation systems is demonstrated by the implementation of a nitrifying trickling filter in a pilot-scale recirculation system for the culture of the African catfish. The corresponding design philosophy behind this system is based on combining the waste production dynamics in the fish tank with the waste removal kinetics in the trickling filter. Attention is paid in this design philosophy to a) hydraulic loading of the primary clarifier, b) dimensions of the fixed-film reactor, c) water recirculation rate, and d) water exchange rate.Refinements of the presented design philosophy can be found in anticipating the effects of simultaneous COD loading, dissolved oxygen levels, pH and salinity, which are discussed in separate chapters of this research.It is concluded that the specific information generated in this thesis may be regarded as a valuable contribution to a more rational approach in design and operation of aerobic fixed-film reactors in the field of water treatment, as compared to the conventional, largely "folklore-based" approaches.</TT