Application of kernel extreme learning machine and Kriging model in prediction of heavy metals removal by biochar

Kernel extreme learning machine (KELM) and Kriging models are proposed to predict biochar adsorption efficiency of heavy metals. Both six popular ions (Pb²⁺, Cd²⁺, Zn²⁺, Cu²⁺, Ni²⁺, As³⁺) and single ion are considered to test the accuracy of KELM and Kriging models. Two ways (data selection and fix output value) are attempted to improve the model fitting accuracy and the best R² can reach 0.919 (KELM) and 0.980 (Kriging). In addition, stepwise regression and local sensitivity analysis show that adsorption efficiency has strong relationship with pH_solute and T. Moreover, the most sensitive parameters are T, pH_H2O, r, C and pH_solute. The accurate KELM and Kriging models identify the most important controlling factors on metal adsorption, and ultimately provide some sort of predictive framework that will be useful in selecting appropriate biochar for particular treatment scenarios. This, in turn, will reduce the number of metal-biochar adsorption experiments needed going forward.