## 3 Results and Discussion
Through calculating the organic matter content, the result shows that it is decreased from 42.17% to 37.87% after microwave treatment, and the degradation rate of the organic matters in the sludge is 10.23%, suggesting an effective treatment by using a small amount of ZnO. It was also found that the TiO\({}_{2}\) nanomaterial is another kind of effective additive to assist in the degradation of organic matter. We conducted the microwave treatment using 0.1-0.5 wt% TiO\({}_{2}\) nanoparticles and 2 wt% dimethyl carbonate. Figure 3b depicts the change of mass losses and organic matter content with the added content of TiO\({}_{2}\), demonstrating a similar variation tendency with the case of ZnO. Therefore, the added amount of TiO\({}_{2}\) powder is set as 0.1 wt%, and the content of organic matter is decreased from 42.17% to 24.68%. The improvement in degradation efficiency of the organic matters by ZnO and TiO\({}_{2}\) powders is mainly because the nanomaterials could be suspended on the surface of organic matters, and the friction between the nanomaterial and organic matter occur under  
Figure 2: Mass loss of the sludge and content of the organic matters with respect to the content of the dimethyl carbonate during the process of the microwave treatment. the microwave with high frequency, leading to the requirement of a large amount of energy to improve the degradation efficiency of the organic matters. Before microwave treatment, ZnO and TiO\({}_{2}\) nanomaterials should undergo a surface modification process to reduce nanoparticle aggregation and improve the surface free energy of the nanomaterials. Thus, we put the nanomaterials into the microwave oven to facilitate short-term activation before mixing them with the sludge for the microwave treatment. When the microwave activation time is set below 10 s, the degradation efficiency of the organic matters increased with the extension of activation time. However, if the time is set as 10-20 s, the degradation efficiency would gradually decrease. Thus, 10 s is an optimized pretreatment time, making the organic matter content decrease from 42.17% to 26.91%. ZnO and TiO\({}_{2}\) nanomaterials have been confirmed to effectively assist in degrading organic matter. Furthermore, to further improve the degradation efficiency, microwave-absorbing agents are also applied in the experiment. There have been many investigations that report their effects during the process of microwave treatment [20]. Sludge-activated carbon powder, due to its decontamination performance, was used as the microwave-absorbing agent in this work, which has been proven to exhibit high removal efficiency of some organic materials and heavy metals [21]. Thus, 2 wt% dimethyl carbonates, 0.1 wt% TiO\({}_{2}\), and 0.1 wt% ZnO nanoparticles, as well as the sludge-activated carbon powder with content of 5 wt%, 10 wt%, and 15 wt% were introduced into the sludge for the microwave treatment. The mixture without sludge-activated carbon powder is also carried out for comparison. It should be mentioned that the temperature of the mixture is increased when the amount of the sludge-activated carbon enhanced. The highest temperature reached 212 \({}^{\circ}\)C, when the content of sludge-activated carbon is 15 wt%. The mass reduction rate of the mixture exceeded 10%, and the content of the organic matters was remarkably decreased from 42.19% to 26.25%, as displayed in Figure 4. The effective degradation of the organic matters is ascribed to the elevation of the temperature, and consequently resulted in the promotion of reactive activity. Furthermore, after microwave treatment, the sludge-based biological carbon changed to residual dry sludge consisting of carbonaceous materials, ZnO and TiO\({}_{2}\) nanoparticles, and others. Thus, the dewatered sludge can be further used as raw material of the microwave absorber. Figure 3: Relationship of mass losses and organic matter content with the content of ZnO (**a**) and TiO\({}_{2}\) powder (**b**).