Mechanisms Of Activated Sludge Deflocculation Under Mesophilicthermophilic Temperature Transients

Recent research in our laboratory has been focused on assessing the impacts of temperature shifts from 30°C or 35°C to 45°C on the treatment performance of activated sludge.108 As part of this research, activated sludge deflocculation under such temperature shifts has been identified and studied.109 The impacts of these temperature transients with respect to deflocculation mechanisms are discussed in the following sections.

17.4.1 Sludge Floc Responses to the Temperature Shifts

The temperature shift stress from 30°C or 35°C to 45°C caused three major responses in activated sludge flocs, as assessed in continuous sequencing batch reactors (SBRs) treating pulp and paper mill effluent, and in batch experiments with fresh municipal sludge. The three responses were decreased or more negative sludge surface charge,108 increased maintenance respiration rates, and sublethal inhibition of metabolism or decreased substrate removal capacity. Figure 17.1 and Figure 17.2 show the effects of the temperature shift from 30°C to 45°C on increasing maintenance respiration rates and inhibiting metabolism of activated sludge in batch and continuous experiments, respectively.

Figure 17.1 and Figure 17.2 present measurements of three specific oxygen uptake rates (SOURs) conducted to assess the sludge substrate removal capacity: the mixed liquor standard SOUR, the SOUR of mixed liquor diluted by 10% with raw wastewater (SOURi0%), and the SOUR of mixed liquor diluted by 50% with raw wastewater (SOUR50%). The measurement of SOURs in samples that are diluted with raw wastewater (SOUR10% and SOUR50%) is comparable with traditional respirometric assays with substrate addition, and has been proposed by Archibald et al.46 (2001) and Archibald and Young36 (20 02) to monitor sludge activity under different stresses. These measurements allow for a comparative assessment of sludge oxygen consumption rates associated with the endogenous respiration phase and with substrate uptake rates under transients and stresses. Details of this are explained elsewhere.46,51

The decrease in the sludge substrate removal capacity is demonstrated by the significant decrease in the three sets of SOURs after the temperature shift. The

0 0

Post a comment