| Summary: | 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. Other liquid parameters were also monitored in order to better
understand the impacts of temperature and HRT. These parameters are total solids
content, volatile solids content, volatile solids destruction, specific oxygen uptake rate,
alkalinity, ammonia concentration, and pH. In order to assess the character of the sludge
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 more than by HRT. Of the five compounds monitored, none
were affected by changes in the HRT of the test reactor. However, the concentrations
measured in the feed and test reactors 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 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. One set of tests for volatile fatty acid
concentration was also undertaken.
While breakdown of the carbohydrates and fats occurred throughout the process,
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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