## 3 Results
### Analysis of the Effects of Various Factors on the Indicators  
To analyze the effects of the rotation speed of the trommel screen, the rotation speed of the spike teeth, and the inclination angle of the trommel screen on the impurity content and the insect rate more intuitively, a response surface diagram of the relationship between the test index and each factor was created according to the quadratic regression model. The shape of the response surface reflects the effects of the interaction factors, as shown in Figure 12.  
As depicted in Figure 12a, when the trommel rotation speed was fixed at a certain level, and the spike tooth rotation speed increased from 10 r/min to 40 r/min, the impurity content first decreased and then increased. The main reason for this phenomenon is that when the speed of the spike teeth is slow, part of the wet BSF sand has a low contact frequency with the spike teeth and is not sufficiently broken by the spike teeth. The ratio is relatively high, such that the impurity content is relatively high. When the speed of the spikes increased to 25 r/min, the sticky and wet agglomerated particles in the BSF sand mixture were effectively broken by the spikes, and the separation effect was the best. However, with the increase in the speed of the spike teeth, some of the sticky and wet BSF sand was impacted by the spike teeth, but it did not have enough time to slide down to \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Source**} & \multicolumn{4}{c}{**Impurity Content in BSF Larvae**} & \multicolumn{4}{c}{**Insect Impurity Rate**} \\ \cline{2-9}  & _df_ & **Mean Square** & \(F_{1}\) & \(P_{1}\) & _df_ & **Mean Square** & \(F_{2}\) & \(P_{2}\) \\ \hline Model & 9 & 4.70 & 58.32 & \textless{}0.0001 & 9 & 0.92 & 39.42 & \textless{}0.0001 \\ \(X_{1}\) & 1 & 1.71 & 21.22 & 0.0025 & 1 & 0.66 & 28.48 & 0.0011 \\ \(X_{2}\) & 1 & 0.61 & 7.50 & 0.0290 & 1 & 0.45 & 19.44 & 0.0031 \\ \(X_{3}\) & 1 & 0.36 & 4.48 & 0.0721 & 1 & 0.41 & 17.45 & 0.0042 \\ \(X_{1}X_{2}\) & 1 & 1.32 & 16.40 & 0.0049 & 1 & 0.000 & 0.000 & 1.0000 \\ \(X_{1}X_{3}\) & 1 & \(\times\) 10\({}^{-2}\) & 0.12 & 0.7351 & 1 & 0.30 & 13.03 & 0.0086 \\ \(X_{2}X_{3}\) & 1 & 0.022 & 0.28 & 0.6137 & 1 & 0.12 & 5.28 & 0.0552 \\ \(X_{1}{}^{2}\) & 1 & 5.38 & 66.67 & \textless{}0.0001 & 1 & 6.06 & 261.18 & \textless{}0.0001 \\ \(X_{2}{}^{2}\) & 1 & 30.81 & 382.04 & \textless{}0.0001 & 1 & 0.095 & 4.08 & 0.0831 \\ \(X_{3}{}^{2}\) & 1 & 0.14 & 1.69 & 0.2346 & 1 & 0.32 & 13.72 & 0.0076 \\ Residual & 7 & 0.081 & & & 7 & 0.023 & & \\ Lack of fit & 3 & 0.077 & 0.93 & 0.5025 & 3 & 0.021 & 0.83 & 0.5413 \\ Pure error & 4 & 0.083 & & & 4 & 0.025 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Significance test of model. the trommel screener and be rolled up by the rotating spike teeth, resulting in the higher impurity content in the insects. When the rotation speed of the spike teeth was fixed, the impurity content in the insects first decreased and then increased sharply with the increase in the rotation speed of the trommel. The main reason for this is that the BSF sand mixture is constantly turned with the increase in the rotation speed of the trommel, and there is a large drop in the trommel screener, and the screening effect is better. At the trommel speed of 48 r/min, the screening effect was the best. With the increase in the rotation speed of the trommel screener, part of the BSF sand mixture easily attached to the wall of the trommel screen due to the centrifugal force. Furthermore, the internal relative movement was diminished, and most of the fine materials were difficult to screen out, resulting in the increase in the impurity content in the insects. The shape and contour density of the response surface, shown in Figure 12b, indicated that the interaction between the trommel screener speed and the trommel screener inclination angle did not significantly affect the impurity content.