Effects of Temperature Variations on Activated Sludge Performance Treating Pulp and Paper Mill Effluent, 2002 Environmental Conference Proceedings

F. Morgan-Sagastume and D. Allen

The effects of temperature variations on activated sludge were evaluated with respect to treatment efficiency, solids discharges, sludge physicochemical properties, and system microbiology. The effects of controlled temperature shifts (35-45ºC, 45-35ºC) and periodic temperature oscillations (31.5-40°C, 6-day period, for 30 days) were assessed in 4 parallel, lab-scale sequencing batch reactors (SBRs) that treated real pulp and paper mill effluent.

Overall, the temperature shifts caused higher effluent suspended solids (ESS) levels and a decrease (up to 17%) in the removal efficiencies of soluble chemical oxygen demand (SCOD). Lower ESS levels were triggered by a slow (2ºC/day) versus a fast (10ºC/12 h) temperature shift from 35º to 45ºC, but the SCOD removal efficiency decreased similarly in both cases. Temperature oscillations caused an increased deterioration of the sludge settleability [high sludge volume index (SVI), low zone settling velocity (ZSV)], and high ESS levels.

The temperature transients were associated with an increase in filament abundance, poor sludge settleability, and more negatively charged sludge. The controlled, periodic temperature oscillations did not seem to select for microorganisms that handled temperature variations more robustly, although they did not impact SCOD removal. Sludge deflocculation seemed to have been the origin of higher ESS levels due to temperature transient conditions. Filament proliferation may have also promoted high ESS concentrations.