## 3 Results and Discussion
As reported, the organic matters could be effectively extracted with assistance of the cationic exchange resin [22]. In this work, we also introduced the inorganic salts into the reaction to promote the dissolution of protein, such as sodium sulfate, magnesium chloride, and calcium hydroxide, which were regarded as the microwave activators. They can not only adjust the acid-base balance of the sludge, but also improve the water removal [23]. Thus, we mixed sodium sulfate, magnesium chloride, and calcium hydroxide with the municipal dewatered sludge in the presence of ZnO and TiO\({}_{2}\) nanoparticles. Figure 5a-c presents the effects of added MgCl\({}_{2}\), Na\({}_{2}\)SO\({}_{4}\), and Ca(OH)\({}_{2}\) with different mass ratios on the mass losses of sludge and organic matter content. Figure 5a displays that the quality loss of the mixture is initially increased and then decreased as the content of MgCl\({}_{2}\) gradually increased. The largest mass loss is achieved when the added amount of MgCl\({}_{2}\) is 0.5 wt%. The content of the organic matters decreased from 42.17% to 26.98% as the MgCl\({}_{2}\) content increased from 0 to 1.5 wt%. Figure 5b shows that the mass loss rate of the mixture and reduction of the organic matters achieved the highest values when the content of Na\({}_{2}\)SO\({}_{4}\) was 6 wt%. Figure 5c shows that the sludge mass loss is firstly increased and then remains at a relative stable value as the content of Ca(OH)\({}_{2}\) increased from 0 to 15 wt%. The highest reduction rate of the sludge reached 72.86%, while the content of the organic matters decreased from 42.17% to 24.68%, with Ca(OH)\({}_{2}\) content of 5 wt%. To further optimize the added amount of MgCl\({}_{2}\), Na\({}_{2}\)SO\({}_{4}\), and Ca(OH)\({}_{2}\) in the process of the microwave treatment, we designed an orthogonal experiment to analyze the influence of each factor, and the orthogonal experiments determined the most suitable contents for Ca(OH)\({}_{2}\) of 7.5 wt%, MgCl\({}_{2}\) of 0.5 wt%, and Na\({}_{2}\)SO\({}_{4}\) of 6 wt%. The experimental results are listed in Table 1. The effects of MgCl\({}_{2}\), Na\({}_{2}\)SO\({}_{4}\), and Ca(OH)\({}_{2}\) on the mass loss of sludge and degradation of organic matters are crossed. It is necessary to elucidated the most suitable adding content of the microwave activators. In the orthogonal  
Figure 4: Effect of the sludge-based microwave absorber on mass losses and extraction of organic matter. Figure 5: Effect of the MgCl\({}_{2}\) (**a**), Na\({}_{2}\)SO\({}_{4}\) (**b**), and Ca(OH)\({}_{2}\) (**c**) added amounts on the mass losses and extraction of organic matter. experiment, we mixed into the 20 g of sludge TiO\({}_{2}\) nanoparticles of 0.02 g, ZnO nanoparticles of 0.02 g, dimethyl carbonate of 0.4 g, and sludge-based biological carbon after this microwave treatment of 1 g together. Finally, in order to further solidify the residual organic matters, we introduced liquid water glass into the mixture to conduct a curing process using the waste heat. In the experiment, 0.1 wt% ZnO nanoparticles, 0.1 wt% TiO\({}_{2}\) nanoparticles, 2 wt% dimethyl carbonate, 10 wt% sludge-based biological carbon, 0.5 wt% MgCl\({}_{2}\), 7.5 wt% Ca(OH)\({}_{2}\), 6 wt% Na\({}_{2}\)SO\({}_{4}\), and liquid water glass, with added amount ratios of 0 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, and 5 wt%, were introduced into 20g of sludge. Figure 6 reveals that the mass loss rate of the mixture and content of the organic matters maintain relative stable values when the content of liquid water glass was elevated, indicating that the liquid water glass cannot play a significant role in promoting the degradation, but it can solidify the residual organic matters and sodium silicate in the sludge mixture to produce lightweight construction materials using one-step microwave irradiation. The compressive strength is remarkably enhanced over 2 MPa.