Five different combinations of Hydraulic Retention Times (HRT) and temperatures were used in a two stage (feed and test reactor) Autothermal Thermophilic Aerobic Digestion System to assess the impact of these parameters on the production of odorous gases. The gases monitored were hydrogen
sulphide, dimethyl sulphide, methyl mercaptan, ammonia, and amines. In order to assess the character of the wastewater solids and understand the digestion process the carbohydrate, fat, and protein content were also measured in the inputs and in the test reactor. It was found that all of
the odorous compounds measured were affected by stage of digestion and temperature and not by HRT. Most notably the gas concentrations measured in the feed and test reactor head spaces were often a degree of magnitude apart. The reduced sulphur compounds (hydrogen sulphide, methyl mercaptan,
and dimethyl sulphide) were found in higher concentrations in the feed reactor than in the subsequent test reactor, whereas ammonia and amines were found in much higher concentrations in the test reactor than in the feed reactor. Also, ammonia concentrations were significantly higher in both
reactors when the temperature was higher; and amine concentration was higher in the test reactor when the temperature was higher. The carbohydrate, protein, and fat analysis revealed that breakdown of the carbohydrates and fats occurred throughout the process. Also, it is clear that proteins
were broken down into their amino acids, releasing reduced sulphur compounds in the feed reactor, and then deaminated, releasing ammonia and amines, in the test reactor.
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