Affiliation:
1. College of Civil Engineering, Liaoning Petrochemical University, Fushun 113001, China
Abstract
As a solid waste, the amount of residual sludge produced by the municipal wastewater treatment process is escalating. How to dispose it properly is attracting much attention in society. Herein, solidifying residual sludge using magnesium oxychloride cement (MOC) is promising for converting it into building materials. Various factors of mass ratio (RW/S) of liquid to solid, molar ratio (Rn) of MgO to MgCl2 in MOC, mass ratio (Rm) of residual sludge to MOC, the mass concentration of Na2SiO3 (DNa2SiO3), and dosage of fly ash (DF) influenced the unconfined compression strength (RC) of the as–obtained MOC–solidified residual sludge, and it was characterized using SEM and XRD analysis. The results show that the value of RC for MOC–residual sludge solidified blocks increased initially and then decreased as Rn and Rm increased, respectively, for 60–day curing. At 10–day curing, equilibrium RC was reached at all RW/S values except 1.38, and at 60–day curing, RC decreased with RW/S increasing. The maximum RC of 60 days of 20.90 MPa was obtained at RW/S = 0.90, Rn = 5.0, and Rm = 1.00. Furthermore, adding Na2SiO3 or fly ash in the solidifying process could improve RC. The water resistance test showed that SM13 and NF5 samples exhibited good alkaline resistance after immersion for 7 and 14 days in an aqueous solution with pH = 7.0–11.0. The water resistance of MOC–residual sludge solidified blocks decreased with increase in immersion duration in aqueous solutions. The fly ash could also help improve water resistance of MOC–solidified residual sludge in neutral and basic aqueous solutions. This work provides an important theoretical basis and possibility for the efficient disposal and comprehensive utilization of residual sludge through solidification/stabilization technology using MOC from the perspective of mechanics and water resistance.
Funder
China College Students Innovation and Entrepreneurship Fund
Talent Scientific Research Fund of Liaoning Petrochemical University
Subject
Process Chemistry and Technology,Chemical Engineering (miscellaneous),Bioengineering
Reference82 articles.
1. Recycling of raw water treatment sludge in cementitious composites: Effects on heat evolution, compressive strength and microstructure;Gomes;Resour. Conserv. Recycl.,2020
2. Comparative life cycle assessment of water treatment plants;Bonton;Desalination,2012
3. Processed wastewater sludge for improvement of mechanical properties of concretes;Gencel;J. Hazard. Mater.,2011
4. Sewage sludge land application program in West Virginia;Skousen;J. Soil Water Conserv.,1996
5. Valorization of sewage sludge in the fabrication of construction and building materials: A review;Chang;Resour. Conserv. Recycl.,2020