Influence of ammonia and other abiotic factors on microbial activity and pathogen inactivation during processing of high-solid residues

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Bujoczek, Grzegorz
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In this research the objective was to achieve a better understanding of the nature of ammonia action that leads to enhancement or inhibition of anaerobic digestion process, and to optimization of alkaline disinfection. These processes are commonly used to treat organic residues. The improvement of anaerobic digestion of substrates with high Carbon-to-Nitrogen (C/N) ratio by means o supplementation of other organics rich in nitrogen can be achieved. Whether in the case with high-solid anaerobic digestion of residues like chicken manure or the organic fraction of municipal solid waste (OF MSW) or with alkaline disinfection of dewatered sludge, microbial injury or death, is the result of combination of the factors, including high free or un-ionized (UAN) ammonia nitrogen concentration. It was attempted to determine if it is ammonia alone, or a combination of factors including free ammonia, that is responsible for the aforementioned outcomes. This work led to the following major advancements: (1) Identification of practical process limitations due to free ammonia inhibition or toxicity during high-solid anaerobic digestion on the examples of (a) chicken manure and of (b) the OF MSW, as substrates for the digestion. The conditions responsible for system upset and technical requirements have been disclosed. (2) Development of a new, low-dose alkaline disinfection process to treat digested-dewatered sludge or other high-solid (e.g. OF MSW) anaerobic digestion residues. This process utilizes alkaline agents to raise the pH and activate free ammonia disinfection in a closed-system operation. A new bacterial indicator of alkaline disinfection efficiency, the spores of the pathogenic 'Clostridium perfringens', was characterized. (3) Determination of contribution of free ammonia concentration to the overall pathogen inactivation in alkaline treatment using ' Clostridium perfringens' spores and eggs of 'Ascaris suum' as model organisms. (Abstract shortened by UMI.)