Monitoring of Activated Sludge Systems Using a Combination of Specific Oxygen Uptake Rates and Specific Adenosine Triphosphate Measurements

Two five-litre activated sludge (AS) bioreactors were operated for several months to demonstrate potential mill applications of a four-assay set, which has been proposed as a tool for monitoring the health of the AS microbial population. The set consists of three specific oxygen uptake rate (SOUR) determinations at different substrate concentrations (SOURat, SOURnmax and SOURtox where at, nmax and tox are defined as aeration tank, near maximum, and toxic, respectively), and a specific adenosine triphosphate (SATP) assay. Two disturbances were applied at different times to an AS system treating kraft effluent. First, temperature was increased from 25 to 40°C, and second, a black liquor spill was simulated. The data before, during, and after these disturbances were statistically analyzed. From this analysis, we concluded that the four-assay set could be used as a microbial health characterization (MHC) tool. It allows an operator to correlate microbial changes with operating data over a mediumterm time scale. We compared the values obtained during periods of upset in the system treating the kraft effluent, to the baseline data set determined from stable operation periods. This demonstrated how the four-assay set could be used as a biological early warning (BEW) tool. It allows a treatment system operator to make appropriate adjustments immediately after detecting values that fall outside the baseline data range.

Anaerobic-Aerobic Lagoon Treatment of Kraft Mill Effluent for Enhanced Removal of AOX

A continuous-flow sequential anaerobic-aerobic lagoon treatment process was developed and evaluated for removal of adsorbable organic halide (AOX) from whole-mill kraft effluent at both laboratory and pilot-scale. The rationale underlying the development of the process was that the AOX removal efficiency of aerated lagoons currently in use might be significantly increased through relatively simple modification. Bench-scale studies showed that sequential anaerobic-aerobic treatment of whole-mill kraft effluent resulted in AOX-removal efficiencies of over 70% at hydraulic retention times (HRTs) of 10 days, 5 days and 2 days. In contrast, only 20%, 35% and 36% removal was obtained in a control aerobic lagoon. Pilot-scale studies showed that up to 65% removal of AOX from whole-mill kraft effluent was consistently obtained at HRTs ranging from 5 to 10 days. This compares with typical AOX removal efficiencies in conventional aerated lagoons of about 25%. Conversion of the anaerobic section in the pilot-scale lagoon from a simple sludge blanket to a combination of sludge blanket and submerged biofilm further increased AOX removal efficiencies to about 70%.