Insight into the synergistic effect and products distribution during co-pyrolysis of phytoremediation residue and municipal sewage sludge through experiment and reaction force field simulation

We co-pyrolyzed municipal sewage sludge (MS) and Sedum Alfredii L. (SA, a heavy metal hyperaccumulator plant) for the first time to solve their disposal issue. Experimental and simulation results show that synergistic effects exist during the co-pyrolysis process. The thermal decomposition mechanism, kinetics, and product distribution of MS and SA at different mixing ratios (1:0, 3:1, 1:1, 1:3, 0:1) were investigated by thermogravimetric analysis and co-pyrolysis experiments. According to thermogravimetric results, the decomposition of all feedstocks can be divided into three stages. FWO method and Master plot method were used to calculate the activation energy and determine the reaction mechanism. When the addition ratio of SA was 75 %, the difference between theoretical and practical activation energies was greatest, indicating that the best synergy could be achieved at this mixing ratio. Co-pyrolysis experiment shows that more bio-oil and gas were produced. The synergistic effect between MS and different fractions of SA was studied using Reaction Force Field simulation, revealing that the free radicals generated by MS and SA advance the MS decomposition time while increasing the decomposition degree of SA. In addition, we built an artificial neural network with a 3 x 21 x 1 structure to predict the degradation process of various mixtures, which exhibits a high agreement with the experimental results. This study can provide a new idea for the disposal of SA and MS, i.e., co-pyrolysis, by solving their disposal issue while obtaining valuable products.