Granular biomasses for biological treatment of breeding wastewater

Abstract

Over the last few years, biogranulation has been regarded with increasing interest according to granules advantages over conventional activated sludge. This thesis focused on two specific granular consortia: the anammox bacteria, as a specific case of denitrifying anaerobic granules, and the aerobic granular sludge. Specifically, both solutions were evaluated for swine wastewater treatment. As swine wastewaters contain high concentrations of veterinary antibiotics, the potential negative effects of these compounds on microbial activities need to be studied carefully. In detail, the research activity focused on the evaluation of the most advantageous operating conditions for aerobic granules cultivation, and on the estimation of the toxicity of three veterinary antibiotics respectively on anammox granules, aerobic granules and conventional activated sludge. The short- and long-term toxicity of selected compounds on the anammox biomass was evaluated through batch tests designed to estimate the Specific Anammox Activity. Moreover, the short-term toxicity of combined concentrations of antibiotics was evaluated so to verify whether a synergistic effect could establish. Results demonstrated that at antibiotics concentrations expected for swine wastewaters, the application of the anammox process seems conceivable, as at those levels, the activity was just slightly reduced. Aerobic granulation of activated sludge was achieved in a Sequencing Batch Reactor fed with a mixture of synthetic medium and domestic sewage. The operating parameters, which were found to influence mostly granules stability and performances were the selection of slow, growing organisms, dissolved oxygen concentration, feeding strategy and temperature. The inhibitory effect of target compounds on aerobic granules was then assessed for ammonium oxidizing bacteria and phosphorus accumulating organisms, which demonstrated to be highly resistant to those compounds. Finally antibiotics toxicity was assessed for granular and flocculent microbial populations performing the same nitrifying and denitrifying activities. Results highlighted the higher resistance of the microbial guilds performing aerobic ammonium oxidation present in granules towards all the tested antibiotics compared to conventional activated sludge. Anammox bacteria susceptibility was instead depending on the specific antibiotic tested, leading to an overall inhibition nearly comparable to that of conventional flocculent denitrifiers.