TS and VS were measured for all the digester influent and effluent sludges, three times per week. The reduction in solids content in the effluent was then plotted as shown in Figure 5-4 and 5-5.
As expected, both the TS and VS reduction for the TH system was approximately 10% greater than that for the control. This indicated the better performance of the TH digested sludge as compared to the conventionally digested sludge. An increase of 8-10% was expected based on prior studies for DC WATER [Wilson et al., 2008]. The increase in VS reduction was 11% for the TH system operated at 37oC. When the temperature of the TH digester increased to 42oC, a slight reduction in the TS and VS reduction was observed which could be due to changes in the sludge characteristics. However, the increased VS reduction at 42oC was 9% for the TH system as compared to the control system, indicating that the TH digester preformed about as well at 42oC as at 37oC. This was a very promising result because it is economical to operate at 42oC because less cooling is required.
During phase II, the TS and VS reductions were statistically the same for the control and the two TH digesters. For the 15 days SRT operation, there was no benefit to thermal hydrolysis. This can be attributed to the increased loading of the digesters with organic substrate by reducing the SRT to 15 days and also the increase in ammonia associated with phase II. The ammonia data will be presented and discussed later. This also suggests that the 20 day SRT conditions were optimum for the TRA sludge