1 performance of AnFBR treating Adelaide WWTP Primary sludge
Table 2 sunnarizes the steady-state Performance of the AnFBR treating PS over the five testing Phases. PS feeding to the AnFBR was started at an OLR of 4.2kg COD/m3 –d and increased gradually to 19kg COD/m3 –d to 39kgCOD/m3 –d in Phase IV, Prior to reduction to 28 kg COD/m3 –d in Phase V. During the first three Phases, both COD and VSS removal efficiencies decreased gradually with increasing the OLRs. The VSS removal efficiencies of 88%, 79% and 70% were achieved at OLRs of 4.2, 9.5 and 19kg COD/m3 –d, respectively. Increasing the OLR to 39kg/m3 –d in Phase IV resulted in sharp deterioration in Performanace as evidedenced by COD remoal efficiency of 30% and VSS destruction efficiency of 31% ( Table 3 ) to sudden doubling of OLRs. Reducing the OLR to 28kg COD/m3 –d in Phase V resulted in slight improvrment in the system Performance, with both COD and VSS removal efficiencies increased to 42%. The VFA – to - alkalinity ratio (x) is a widely accepted measure of anaerobic digestion stadility ( chen et al….2007 ). The steady – state VFA (as acetate) – to – alkalinity ratio (x) were consistetently below 0.2 in Phases I – IV, although during the tranasition from one Phase to another x increased due to sudden doubling of OLRs. However. In Phases IV and V, an increase in x value to 0.5 was observed due to the accumulation of the VFA. The widely variation of x value between 0.29 and 0.41 clearly suggesting that digestion stability at OLR of 28 – 39 kg/m3-d was compromised.