## Results and Discussion  
### Composition of the Slurries  
The initial (0 days) and final (85 days) composition of the Control and amended treatments (Biochar, Clinoptiolite and Biochar + Clinoptiolite) are presented in Tables 1 and 2. The initial pH values did not differ significantly (\(p>0.05\)) among treatments Control and Clinoptiolite (pH = 8.5), being significantly higher (\(p<0.05\)) in treatments Biochar and Biochar + Clinoptiolite (pH = 9.0) (Table 1). Compared to the beginning of the experiment, the pH values of treatments Biochar and Biochar + Clinoptiolite increased significantly (\(p<0.05\)) in the end of experiment (Table 1). The initial dry matter content increased significantly (\(p<0.05\)) in amended treatments (Biochar, Clinoptiolite and Biochar + Clinoptiolite) when compared with treatment Control, with higher values for treatments Biochar and Biochar + Clinoptiolite (2.1% for Biochar against 2.7% for Clinoptiolite). However, the dry matter content did not differ significantly (\(p>0.05\)) between the beginning and the end of the experiment, although being observed a difference of about 30% (2.7 vs. 1.9) for treatment Biochar + Clinoptiolite (Table 1). At the beginning of the experiment, the treatments Biochar and Biochar + Clinoptiolite increased significantly (\(p<0.05\)) by about 100% the total C, as well as the C/N ratio when compared with the treatments Control and Clinoptiolite (C/N = 22 for Biochar treatments against C/N = 11 for non-Biochar treatments). In all treatments, the initial values of total C were reduced significantly (\(p<0.05\)) at the end of the experiment (Table 1). The initial values of total N, NH\({}_{4}\)+-N, NO\({}_{3}\)-N, NH\({}_{4}\)+/total N ratio, biological oxygen demand (BOD) and volume of slurry were not significantly different (\(p>0.05\)) among treatments (Tables 1 and 2). These same parameters decreased in the end of the experiment. However, the final values of total N were significantly higher (\(p<0.05\)) in treatments Clinoptiolite and Biochar + Clinoptiolite (1.5 g total N kg\({}^{-1}\) for Clinoptiolite-alone against \(<\)0.5 g total N kg\({}^{-1}\) for Biochar treatments) (Table 1). In addition, the final BOD values of amended treatments decreased significantly (\(p<0.05\)) by the following order: Biochar + Clinoptiolite + Biochar + Clinoptiolite (Table 2). At the beginning of the experiment, the number of colonies of _E. coli_ were significantly higher (\(p<0.05\)) in treatment Biochar, but significantly lower (\(p<0.05\)) in treatment Clinoptilolite, when compared with treatment Control or Biochar + Clinoptilolite (Table 2). At the end of the experiment, the values the number of colonies of _E. coli_ were not significantly different (\(p>0.05\)) among all treatments and there was no evidence of the presence of _E. coli_ (1.0 colony-forming units (CFU) mL\({}^{-1}\)) (Table 2). Results of this study (Tables 1 and 2) are in line with previous studies [3; 15; 16; 17; 18; 19; 20; 21; 22; 23] who reported that pre-treating animal slurries with biochar could modify the physicochemical properties, like as increasing pH, C/N ratio and cation-exchange capacity, and microbial activities. The explanation is that biochar was a porous carbonaceous material largely containing C jointly with the inorganic components of the biomass utilized, such as alkali and alkaline earth metals [21]. On other hand, the addition of biochar at a rate of 2.5% appear not reduce _E. coli_ during the 85 days of experiment (Table 2), agreeing with [PERSON] et al. [18] who reported a marked decrease in CFU mL\({}^{-1}\) for survival of _E. coli_ by the storage period (90 days) and not by the addition of biochar at a rate of 4.5% to cattle slurry. However, recent studies [24; 25] suggest that the presence of biochar influences the removal of _E. coli_ and minimizes the impact on bacterial viability, which requires further research.