Vegetation Evolution with Dynamic Maturity Strategy and Diverse Mutation Strategy for Solving Optimization Problems.

We introduce two new search strategies to further improve the performance of vegetation evolution (VEGE) for solving continuous optimization problems. Specifically, the first strategy, named the dynamic maturity strategy, allows individuals with better fitness to have a higher probability of generating more seed individuals. Here, all individuals will first become allocated to generate a fixed number of seeds, and then the remaining number of allocatable seeds will be distributed competitively according to their fitness. Since VEGE performs poorly in getting rid of local optima, we propose the diverse mutation strategy as the second search operator with several different mutation methods to increase the diversity of seed individuals. In other words, each generated seed individual will randomly choose one of the methods to mutate with a lower probability. To evaluate the performances of the two proposed strategies, we run our proposal (VEGE + two strategies), VEGE, and another seven advanced evolutionary algorithms (EAs) on the CEC2013 benchmark functions and seven popular engineering problems. Finally, we analyze the respective contributions of these two strategies to VEGE. The experimental and statistical results confirmed that our proposal can significantly accelerate convergence and improve the convergence accuracy of the conventional VEGE in most optimization problems.

Tea saponin enhanced bioleaching of Fusarium solani to remove hexavalent chromium from soil.

Hexavalent chromium pollution is one of the most serious types of site pollution. In this study, a microorganism was screened to remove most hexavalent chromium from soil by leaching in 24 h. After ITS sequencing, the microorganism was identified as belonging to the genus Fusarium solani. The optimization experiment of leaching conditions determined that the removal rate reached the maximum 80% when the rotation speed was 200 rpm, the liquid-soil ratio was 15:1, the temperature was 35℃, and the pH was 7. The study has also shown that tea saponin can effectively strengthen the leaching of Fusarium solani to remove hexavalent chromium from the soil. Compared with tea saponin, the strengthening effect of glucose and rhamnolipid was relatively small. The removal rate of hexavalent chromium reached 85% when the added amount of tea saponin was 0.02 g/mL. The leaching solution destroyed part of the iron-manganese nodule structure of the soil, and its hydroxyl, carboxyl, and other groups complexed metal ions into the solution to achieve the purpose of removing hexavalent chromium. However, since the main crystal of the soil was SiO2, there was no obvious change in the XRD of the soil. Toxicity test showed that after leaching, the content of hexavalent chromium leached was 0.28 mg/L (< 1.5 mg/L), which meet the entry standard of the landfill site.