Improvement of Activated Sludge Dewaterability by Humus Soil Induced Bioflocculation

Abstract

Effects of humus soil particles on the dewaterability of activated sludge were investigated. Cations leaching increased proportionally with the dosage of humus soil, and the leaching was not significant after 2 h. Divalent cations, Ca²⁺ and Mg²⁺, leaching from the humus soil played an important role in improving dewaterability of the biological sludge. On the contrary, dewaterability was not affected or slightly deteriorated by the monovalent cations, K⁺ and Na⁺ leached from the humus soil. Improvement in dewaterability of the sludge by addition of humus soil was higher than that of equivalent cations mixture. It seemed that the decrease of supracolloidal bio-particles (1 to 100 µm in diameter) resulted in diminishing of the blinding effect on cake and filter medium. SRF (specific resistance to filtration) of the humus soil added sludge varied in parallel with the M/D (monovalent to divalent cation) ratio, and the M/D ratio could be utilized as a useful tool for evaluation of the sludge dewatering characteristics. Long-term effects of humus soil on the improvement of activated sludge dewaterability were clearly identified by continuous operation results of a bench-scale MLE (Modified Ludzack Ettinger) system combined with a humus soil contactor. On the other hand, dewaterability of the control sludge was only slightly improved by a decrease in M/D ratio of the wastewater influent.

Keywords:

• Biosolids
• Cation
• Dewaterability
• Humus soil
• M/D ratio
• Supracolloids

Acknowledgment

This work was supported by Brain Korea 21 (BK21) and Korea Science and Engineering Foundation (KOSEF, Project No. 1999-2-309-004-3).