Recycling of sewage sludge incineration ashes as construction material

Sewage sludges that are originating from the municipal wastewater treatment plants of Bursa city have been incinerated with a fluidized bed reactor of 400 tons/day capacity since 2017. Each month, on an average, 615 tons of ash is generated as a waste of the incineration process, which needs disposal. The purpose of this study was to investigate if the sludge incinerator ash can be recycled as a construction material. Heavy metal content, chemical composition and amorphous-crystal properties of sludge ash obtained from two different flue gas treatment systems as bag filter and multicyclone were analyzed with this aim. Stabilization/solidification (S/S) and geopolymerization technologies were applied to sludge ashes. The efficiency of S/S and geopolymerization technologies was observed in paste and mortar samples. S/S and geopolymer samples were prepared in dimensions of 50×50×50 mm. S/S paste samples were prepared by using cement, geopolymer paste samples were prepared by using cement and without cement. NaSilNaOH and 8M NaOH solutions were used as activators in geopolymer paste samples. S/S mortar samples were prepared in accordance with ASTM standards using geopolymer mortar samples were prepared with Ms=1,6 (Si2O/Na2O), %8 Na2O solution. The compressive strength, water absorption, porosity, freeze-thaw tests were performed to evaluate the sludge ash as a construction material. As a result of the analysis, it was determined that the ash did not show heavy metal properties and had an amorphous structure. The highest compressive strength of S/S paste samples containing sludge ash was 30,69 MPa (multicyclone unit sludge ash + cement + water), the highest compressive strength of geopolymer and cement paste samples was 50 MPa (bag filter unit sludge ash + cement + NaSilNaOH), geopolymer and without cement paste samples with the highest compressive strength of 40,56 MPa (multicyclone unit sludge ash + marble sludge + fly ash + NaSilNaOH) was mesured. The highest compressive strength of S/S mortar samples containing sludge ash was 50,53 MPa (15% multicyclone unit sludge ash), the highest compressive strength of geopolymer mortar samples was 11,88 MPa (20% bag filter unit treatment sludge ash + 40% fly ash + 40% marble sludge) was mesured. As a result of the experiments, showed that sludge ash has the potential to be considered as a construction material.