The activated sludge process has been widely used in biological wastewater treatment with which sludge bulking has been a key operational problem. To overcome the problem, most studies focused on the control of filamentous growth. This study however investigates whether carrier docking is a viable method. A novel light-beam settling column with computer monitoring was developed in this study for settling test of mixed liquid suspended solid (MLSS) on pulping wastewater. The carrier was made of fine sand (d = 0.07 ~ 0.2 mm) and the spike dosage was 8 ~ 52 % to the solids by weight. Results of the batch study show that initial settling velocity increases by 68~127 % relative to the velocity of 0.41 cm/min (MLSS = 2,740 mg/L) for the control (0 % carrier). When taking into account of the dilution effect associated with the addition of carrier solution, the net contribution by the carrier addition remained as high as 77 ~ 93 % with lower contribution for higher dosage. This indicates that velocity increase approached a margin as carrier dosage increased. Comparing with the graduated cylinder test in last year, the settling column developed in this study can significantly eliminate the wall effect of graduated cylinder. Accordingly the new design of the settling column can better evaluate the effect of carrier docking. A dosage of 10 % is suggested, provided that a continuous test is conducted for further confirmation.
