Application of flocculation combined with vacuum preloading to reduce river-dredged sludge

Abstract

To achieve the rapid dewatering of dredged sludge, the flocculation–vacuum-preloading method was tested indoors. In this study, the optimal mixing ratio of six flocculants was determined through the settling column test, and then the proposed method was tested. The water drainage and settlement were monitored during the test, while the soil moisture content and shear strength were measured after the test. The results show that all the flocculants had an optimal mixing ratio, and the addition of 0.8% FeCl₃ or 0.08% anionic polyacrylamide (APAM) in the sludge can better accelerate solid–liquid separation of the sludge. After the test, the water content in the sludge decreased from 140% to 60%. Compared with general vacuum preloading, the use of the proposed method increased the water drainage by 46.5% and 56.8% and decreased the soil volumes by 60.5% and 82.4% for FeCl₃ and APAM, respectively. Moreover, the corresponding shear strength was increased from 10 to 14 and 17 kPa. In addition, the use of APAM increased the solidification rate of heavy metals in the sludge to more than 80%, effectively inhibiting the migration of heavy metals.

Keywords:

• Flocculation
• vacuum preloading
• dredged sludge
• optimal mixing ratio

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the National Key R&D Program of China (2016YFC0800200), National Natural Science Foundation of China (Grant Nos. 51878402, 51878512, 51778501, 51622810, 51778500, 51478255, and 51678352), Zhejiang Province Natural Foundation Projects of China (Grant Nos. LR18E080001 and LY17E080010), Key Research and Development Program of Zhejiang Province (Grant No. 2018C03038), and Programs of Science and Technology of Wenzhou (Grant No. S20160001). All financial support is gratefully acknowledged.