Toxicity in anaerobic digestion : with emphasis on the effect of ammonia, sulfide and long-chain fatty acids on methanogenesis

The dissertation concerns the problem of toxicity in anaerobic digestion, which to a large extent is the problem of inhibition of methanogenic conversions by chemical compounds. The dissertation begins with an extensive literature review in which the microbiology of anaerobic digestion and the chemical and physical requirements of the bacteria involved are discussed. A literature review concerning the general aspects of toxicity in anaerobic digestion is also included. The general aspects that are discussed include: synergism and antagonism, concentration dependency, influence of environmental factors (e.g. temperature and pH) on the effective concentration of toxicants, acclimatization of methanogenic populations to the presence of toxicants in the wastewater to be treated. The impact of modern reactor design on the ability of anaerobic wastewater treatment systems to deal with toxicant containing wastewater is also discussed, as is the fact that biofilms increase the toxicant tolerance of methanogenic populations.Many of the general aspects of toxicity in anaerobic digestion that are discussed in the literature review are illustrated in the chapters concerning research projects. In the chapter concerning long-chain fatty acids toxicity the phenomena of synergism and lowering the effective toxicant concentration by means of formation of insoluble molecules are shown. The influence of pH on toxicity is shown in the chapter on sulfide toxicity and the chapter on ammonia inhibited growth rate. The latter chapter also deals with the influence of temperature. The chapter on ammonia inhibition of methanogenic activity illustrates the concentration dependency and the acclimatization potential of methanogenic biomass. The extreme tolerance of methanogenic populations for toxicants is illustrated in the chapter on amminia inhibition of methanogenic inhibition and in the chapter on manure digestion.