MICROAEROPHILIC DIGESTION OF EXCESS MBR SLUDGE

摘要

Microaerophilic sludge digestion is better suited to excess MBR sludge digestion becausernthe long SRTs already in place during operation of MBRs. A comparison of the designrnparameters of aerobic and micro-aerophilic sludge digestion of MBRs is presented. Whenrnusing option 4 of 503 rule for reduction of vector attraction, SOUR less than 1.5 mg O2 /rng TS d, the criteria is met consistently within two days of digestion for all conditionsrntested in this project. For initial SOUR rates of 3 mg O2/g TS h the required digestionrntime is only 5 days. This is in contrast to over 35 days required for obtaining 38%rnreduction in VS. No significant differences were observed in the rate of SOUR reductionrnor the time required for achieving the target SOUR when digesting MBR sludge underrnaerobic or anoxic conditions. No significant effect of the initial TSS concentration wasrnobserved either. This is effect is consistent with theory. It is advantageous to control thernORP of the digestion process to a level over – 200mV when using anoxic digestion. ORPrnvalues lower than this would induce significant accumulation of ammonia in the system.rnAmmonia has a strong effect on the determination of SOUR. Concentrations as low as 1rnmg/L induce saturation of the kinetics of oxygen uptake creating a confounding factor inrnthe SOUR determinations. It is recommended to aerate the sludge for a short aerationrnperiod of 30 minutes in order to remove trace ammonia levels and to obtain consistentrnresults for comparison with aerobic digestion. The aerobic process exhibited higherrnpathogen reduction rate than the microaerophilic process. It is likely that pathogenrnreduction criteria might control the overall sizing of the digester if Class B sludge isrndesired. Combination of SOUR and pathogen reduction criteria could be optimized forrndifferent disposal scenarios.