A 2-PHASE ANAEROBIC-DIGESTION PROCESS (UASB-UASB) - INDUCED FAILURE AND SYSTEM RECOVERY USING A STEP LOADING REDUCTION APPROACH AND MODIFIED RECYCLE RATIO (RR)

This research demonstrated the feasibility of recovery of a UASB-UASB system treating simulated sewage sludge, after operating in a deliberate failure mode. The approach employed an application of step-loading reduction and a modification of the internal recycle ratio (RR). The system recovered exponentially (r(2) - 0.99) and logarithmically (r(2) = 0.81), with an increase in HRT (loading reduction), in so far as COD (sol) removal efficiency (92%) and CH4 gas production (100%), were concerned. The system appeared to return to its initial stage of operation, after 43 days of recovery period, by the application of a two-step increase in the HRT(M-UASB) at 1.5 and 5.5 times that of the failure HRT(M-UASB) (0.63 days); coincidentally, a dimensional time of 5.5 and 10 times the minimum HRT was employed for the overall system and the M-UASB, respectively.