Assuming that urea can be completely decomposed, 30 mL of a 1 mol/L urea solution contains 1.8018 g of urea, and complete decomposition will yield 3 × 10−2 mol ; thus, 3 × 10−2 mol Ca2+ or a 5.285 g calcium acetate test sample is required. Twelve test samples with this mass of calcium acetate were weighed and set aside. A 1 mol/L urea solution was prepared in 12 reaction bottles, each set to 30 mL, divided into two groups, A and B. Group A was set as the calcium addition first group by mixing the urea solution with calcium acetate thoroughly, then adding the bacterial solution, and then filtering, drying, and weighing after 48 h of resting. Group B was the later calcium addition group; the urea solution was mixed with the bacterial solution, followed by 24 h of rest, and then the calcium acetate was added to the solution. The solution was allowed to rest for 24 h and was then filtered, dried, and weighed. There were six bacteria-to-calcium ratios: 1/9, 2/9, 3/9, 4/9, 5/9, and 6/9, and the amount of bacterial solution added was 3.3 mL, 6.6 mL, 9.9 mL, 13.2 mL, 16.5 mL, and 19.8 mL, respectively. When the conductivity was measured in this study, the ratio of the bacterial solution to the 1 mol/L urea solution was 1/9, and for the purpose of the control test, the starting bacteria-to-calcium ratio was set to 1/9. Calcium-first and calcium-later addition modes are shown in Figure 1 .
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