Fig. 6

Pollutant concentrations in water with different biogas slurry concentrations; (A) represents COD content, (B) represents total nitrogen content, (C) represents ammonia nitrogen content, and D represents total phosphorus content. CK: No biogas slurry added; 2-10%: Biogas slurry added at the percentages indicated on the labels. The data are presented as the mean ± standard error of three replicates. Different lowercase letters indicate significant differences at the 0.05 level among the data at the same time point.