Stabilization of dredged sludge using bio-carbonation of reactive magnesia cement method

Bio-carbonation of reactive magnesia cement (RMC) method was proposed for dredged sludge stabilization. A series of RMC bio-carbonation experiments, micro-penetration and direct shear tests were conducted to investigate the feasibility and stabilization performance of the method. The effects of curing agent components, bacteria concentration, urea content and curing age on the mechanical behavior of the stabilized dredged sludge samples were analyzed. Experimental and testing results showed that the proposed method was effective for the stabilization of the dredged sludge with 40% of high initial water content. The maximum penetration resistance of the bio-carbonized sample with 10% of RMC content and 2 M of urea content was up to 39.2 N after 48 h of curing, which was 130.7 times that of the raw dredged sludge sample and 1.7 times that of the Portland cement stabilized dredged sludge sample. Every curing agent component was essential to the effective RMC bio-carbonation process and stabilization effect. Moreover, the stabilization performance was influenced by bacteria concentration and urea content. The optimal formula in this study was the high bacteria concentration (OD 600 = 10.89) and medium urea content (2 M), while too high urea content such as above 2 M adversely affected the stabilization effect. The microstructure characteristics analysis revealed that the combined effect of cementation, filling and skeleton support from the mixture of brucite (hydration product of RMC) and HMCs (bio-carbonation products of RMC) was the primary contribution to the improvement of the physico-mechanical properties of the dredged sludge. This study is expected to provide informative insights into the application of new bio-mediated technologies for the efficient disposal of dredged sludge.