Solidification/stabilization of organic matter and ammonium in high-salinity landfill leachate concentrate using one-part fly ash-based geopolymers

Landfill leachate concentrate (LLC) is a high-salinity organic wastewater produced in the process of membrane separation and has become an urgent problem because of its complex composition and high biological toxicity. Solidification/stabilization (S/S) technology using geopolymers provides a feasible and economical zerodischarge LLC treatment method. This study developed one-part fly ash-based geopolymers using LLC as the only solvent. The results showed that the solid alkali activator significantly increased the LLC treatment capacity with a high liquid-solid ratio of 0.55. The high-salinity LLC significantly promoted the substitution of Al for Si and improved the compressive strength of the geopolymers. Three leaching experiments showed that the prepared geopolymers had excellent stability, high S/S rates for organic matter (92.9%) and NH3-N (91.4%), and a high contaminant removal rate to reduce acute biological toxicity. Microscopy tests showed that sodium aluminosilicate hydrate (N-A-S-H) gel was the main component of the fly ash-based geopolymers after the addition of LLC. Cl- attached to the surface of the geopolymer gels through exchange with OH-, while SO(4)(2-)was bound within the geopolymer structure in the form of Na2SO4 crystals. There was no evidence that organic matter and NH3-N were chemically combined with the geopolymer material, rather, they were physically encapsulated within the geopolymer structure. This study proposes a technical strategy for LLC S/S using fly ashbased geopolymer. The geopolymer can be used as a new building material, which provides a new perspective for the treatment of LLC and the utilization of fly ash resources.

Automated summary

This study developed one-part fly ash-based geopolymers using landfill leachate concentrate (LLC) as the only solvent. The results showed that the addition of solid alkali activator significantly increased the LLC treatment capacity and the high-salinity LLC promoted the substitution of Al for Si, improving the compressive strength of the geopolymers. Leaching experiments demonstrated the excellent stability and high S/S rates of the prepared geopolymers for organic matter and NH3-N, reducing acute biological toxicity. Microscopy tests revealed the main component of the fly ash-based geopolymers after the addition of LLC was sodium aluminosilicate hydrate (N-A-S-H) gel.