Based on the whole experimental process, the reduction effect of TN in group D was the most significant, with an average net purification rate of 31.29%, followed by group C with 25.28%. By contrast, the reduction efficiency of TN was not more than 13% in groups A and D.
According to the TN content in Ottelia, groups A and B reached the peak on June 1, decreased on June 11, and remained basically stable. The difference is that the TN content in Ottelia of group A was low and volatile but always in a steady upward trend in group B. The TN content in Ottelia of group C showed a fluctuated upward trend. Even though the data were missing on June 1 in group D, the TN content in Ottelia stub still increased compared with the initial value.
3.2.2. Experimental results of ammonia nitrogen removal in Ottelia
In the simulated experiment system, the net purification rate of ammonia nitrogen in group A was the highest, with an average net purification rate of 32.4%, followed by group B with 24.84%. By contrast, the purification rate of ammonia nitrogen in groups C and D was extremely low at less than 4% (Fig. 3).